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Old Tuesday, September 06, 2011
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Default Anatomy of systems

excretory system


The chemical composition of body fluids is important for the well-being of the cells of the body. The circulatory system is mainly responsible for the physical transport of fluids but not for the composition of those fluids. This function is largely the responsibility of the kidneys.

Although they help with various physiological functions, the kidneys' main roles are the removal of wastes and the maintenance of the body's water balance. The functions of the kidneys can be summarised as follows:

1. Control of the body's water balance. The amount of water in the body must be balanced against the amount of water which we drink and the amount we lose in urine and sweat etc.

2. Regulation of blood pressure via the renin-angiotensin-aldosterone system

3. Regulation of blood electrolyte balance - Na+, Ca2+, K+ etc.

4. Excretion of metabolic wastes such as urea, creatinine and foreign substances such as drugs and the chemicals we ingest with our food

5. Help in the regulation of the body’s acid base balance

6. Regulation of red blood cell production via the hormone erythropoietin

7. Help in the production of vitamin D

As this list indicates, the renal system is very important to the normal functioning of the body.

THE STRUCTURE OF THE RENAL SYSTEM
Urine is produced in the kidneys from water and wastes extracted from the blood. The rest of the urinary system is concerned with the storage and ducting of the urine to the outside of the body - Figure 01.




The kidneys are large, bean shaped organs which lie on the dorsal side of the visceral cavity, roughly level with the waistline. Blood is supplied to the kidneys by the renal arteries which branch off the aorta. The kidneys and are drained by the the renal veins into the inferior vena cava. From the kidneys, urine passes to the urinary bladder via the ureters. Urine is passed to the outside environment via the urethra (this is routed differently in males and females).
http://www.youtube.com/v/iT9S5P8Bsx8


MICROSTRUCTURE OF THE KIDNEY

The kidneys are protected by a tough fibrous coat called the renal capsule. Under the capsule, the arrangement of nephrons and capillaries in the kidney produce the appearance of distinct regions when viewed in longitudinal section. The outer cortex region surrounds darker triangular structures called pyramids which collectively form the medulla. The inner part of the kidney, the renal pelvis, collects the urine draining from the nephron tubules and channels it into the ureter - Figure 02.




MICROSTRUCTURE OF THE KIDNEY

The basic functional unit of the kidney is the nephron. There are over one million nephrons in each human kidney and together they are responsible for the complex water regulation and waste elimination functions of the kidneys. The heads of the nephrons are in the cortical region and the tubular component then descends through the medulla and eventually drains into the renal pelvis - Figure 03.




The key area of interface between the circulatory system and the tubular part of the kidney is the knot of glomerular capillaries in the Bowman's capsule. Those liquid parts of the blood that are able to cross through the filtration membrane of the capillaries pass into the Bowman's capsule and then into the tubular section of the nephron - Figure 04. The filtration membrane only allows water to pass through it and small molecules that will dissolve in water such as waste (urea, creatinine etc.) glucose, amino acids and ions. Large proteins and blood cells are too large to be filtered and remain in the blood.






http://www.youtube.com/v/J61IFsemqio&feature=related


The filtered fluid or filtrate enters the proximal tubule and then into the loop of Henle which is the part of the nephron which dips in and out of the medulla. From the loop of Henle, the filtrate travels through the distal tubule and then into a common collecting duct which passes through the medulla and into the renal pelvis - Figure 05.



PERITUBULAR CAPILLARIES

The nephrons are surrounded by a fine network of capillaries called the peritubular capillaries. These perform an important role in direct secretion, selective reabsorption and the regulation of water (see below).

DIRECT SECRETION

In addition to glomerular filtration, some substances are secreted directly from the adjacent peritubular capillaries into the proximal tubule. These substances include potassium ions and some hormones.

SELECTIVE REABSORPTION

Ultrafiltration is indiscriminate except for size of particle and useful substances are filtered from the blood as well as wastes. This situation is obviously unsatisfactory as the body would soon be depleted of amino acids, glucose and sodium etc. which would need to be replenished from external sources. To resolve this problem, useful substances in the filtrate are reabsorbed back into the peritubular capillaries as the filtrate passes along the tubule, leaving only the wastes which are eliminated in the urine. This process is shown in the animation in Figure 06.



http://www.youtube.com/v/pnRWKoSuFNs&feature=related



WATER REGULATION BY THE KIDNEYS

The water content of the body can vary depending on various factors. Hot weather and physical activity such as exercise make us sweat and so lose body fluids. Drinking tends to be at irregular intervals when socially convenient. This means that sometimes the body has too little water and needs to conserve it and sometimes too much water and needs to get rid of it. Most of the control of water conservation takes place in the distal and collecting tubules of the nephrons under control of anti-diuretic hormone, (ADH), sometimes called vasopressin. This hormone is released by the posterior pituitary under control of the hypothalamus in the mid-brain area. The hypothalamus monitors the water content of the blood. If the blood contains too little water (indicating dehydration) then more ADH is released. If the blood contains too much water (indicating over-hydration) then less ADH is released into the blood stream - Figure 07.


http://www.youtube.com/v/cFWpe6spELA&feature=related





DH released from the pituitary travels in the blood stream to the peritubular capillaries of the nephron. ADH binds to receptors on the distal and collecting tubules of the nephrons which causes water channels to open in the tubule walls. This allows water to diffuse through the tubule walls into the interstitial fluid where it is collected by the peritubular capillaries. The more ADH present, the more water channels are open and the more water is reabsorbed - Figure 08.



ver 99% of the filtrate produced each day can be reabsorbed. The amount of water reabsorbed from the filtrate back into the blood depends on the water situation in the body. When the body is dehydrated, most of the filtrate is reabsorbed but note that even in cases of extreme of water shortage, the kidneys will continue to produce around 500 ml of urine each day in order to perform their excretory function.

THE MICTURION REFLEX

Micturition is another word for urination and in most animals it happens automatically. As the bladder fills with urine, stretch receptors in the wall of the bladder send signals to the parasympathetic nerves to relax the band of smooth muscle that forms the internal urethral sphincter. As the muscle relaxes, the urethra opens and urine is voided to the outside environment.

A second sphincter, the external urethral sphincter is skeletal muscle controlled by motor neurons - Figure 09. These neurons are under conscious control and this means we are able to exercise control over when and where we urinate. This control is a learned response that is absent in the new-born infant.



RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM

The long-term control of blood pressure is via the renin-angiotensin-aldosterone (RAA) system. This system is also one of the body's compensatory mechanisms to a fall in blood pressure. The kidneys release renin into the bloodstream and this converts angiotensinogen to angiotensin I which in turn is converted to angiotensin II by angiotensin converting enzyme in the capillaries of the lungs. Under the influence of Angiotensin II, aldosterone levels increase. This increases blood sodium levels by decreasing the amount of salt excreted by the kidneys. Retaining salt instead of excreting it into urine increases the osmolarity of the blood and so the blood volume. As the volume increases, so does the blood pressure. Angiotensin II is also a potent vasoconstrictor which raises blood pressure by increasing vascular resistance - Figure 10.



ACID BASE BALANCE

The body controls the acidity of the blood very carefully because any deviation from the normal pH of around 7.4 can cause problems - especially with the nervous system. Deviations in pH can occur due to trauma or diseases such as diabetes, pneumonia and acute asthma. The mechanisms that resist and redress pH change are...

1. Minor changes in pH are resisted by plasma proteins acting as buffers in the blood.

2. Adjustment to the rate and depth of breathing. An increase in acidity (decrease in pH) increases the rate and depth of breathing which gets rid of carbon dioxide from the blood and so reduces acidity.

3. The kidneys respond to changes in blood pH by altering the excretion of acidic or basic ions in the urine. If the body becomes more acidic, the kidneys excrete acidic hydrogen ions (H+) and conserve basic bicarbonate ions (HCO3-). If the body becomes more basic, the kidneys excrete basic bicarbonate ions and conserve acidic hydrogen ions.

Together, these three mechanisms maintain tight control over the pH of the body.
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The GI System

The group of organs that break down food and absorb the nutrients used by the body for fuel. The organs in the digestive system, in the order in which food travels through them, are: Mouth
Esophagus
Stomach
Small Intestine
Large Intestine
Rectum
Anus
Mouth
Esophagus
Stomach
Small Intestine
Large Intestine
Rectum
Anus
Parts of food which cannot be broken down, digested, or absorbed are excreted as bowel movements.


http://www.youtube.com/v/Z7xKYNz9AS0


The gastro-intestinal system is essentially a long tube running right through the body, with specialised sections that are capable of digesting material put in at the top end and extracting any useful components from it, then expelling the waste products at the bottom end. The whole system is under hormonal control, with the presence of food in the mouth triggering off a cascade of hormonal actions; when there is food in the stomach, different hormones activate acid secretion, increased gut motility, enzyme release etc. etc.

Nutrients from the GI tract are not processed on-site; they are taken to the liver to be broken down further, stored, or distributed

oesophagus.
Once food has been chewed and mixed with saliva in the mouth, it is swallowed and passes down the oesophagus. The oesophagus has a stratified squamous epithelial lining (SE) which protects the oesophagus from trauma; the submucosa (SM) secretes mucus from mucous glands (MG) which aid the passage of food down the oesophagus. The lumen of the oesophagus is surrounded by layers of muscle (M)- voluntary in the top third, progressing to involuntary in the bottom third- and food is propelled into the stomach by waves of peristalisis.

http://www.youtube.com/v/Q-n_Q0qKXzg&feature=related


The stomach is a 'j'-shaped organ, with two openings- the oesophageal and the duodenal- and four regions- the cardia, fundus, body and pylorus. Each region performs different functions; the fundus collects digestive gases, the body secretes pepsinogen and hydrochloric acid, and the pylorus is responsible for mucus, gastrin and pepsinogen secretion.

The stomach has five major functions;
Temporary food storage
Control the rate at which food enters the duodenum
Acid secretion and antibacterial action
Fluidisation of stomach contents
Preliminary digestion with pepsin, lipases etc

http://www.youtube.com/v/x0Brp0pgBD0&feature=related

The Stomach - Histology

Key:
G- mucosa containing glandular tissue; different areas of the stomach contain different types of cells which secrete compounds to aid digestion. The main types involved are:
parietal cells which secrete hydrochloric acid
chief cells which secrete pepsin
enteroendocrine cells which secrete regulatory hormones.
MM- muscularis mucosae
SM- submucosa
The stomach contains three layers of involuntary smooth muscle which aid digestion by physically breaking up the food particles;
OM- inner oblique muscle
CM- circular muscle
LM- outer longditudional muscle

The Small Intestine (1)

The small intestine is the site where most of the chemical and mechanical digestion is carried out, and where virtually all of the absorption of useful materials is carried out. The whole of the small intestine is lined with an absorptive mucosal type, with certain modifications for each section. The intestine also has a smooth muscle wall with two layers of muscle; rhythmical contractions force products of digestion through the intestine (peristalisis). There are three main sections to the small intestine;
The duodenum forms a 'C' shape around the head of the pancreas. Its main function is to neutralise the acidic gastric contents (called 'chyme') and to initiate further digestion; Brunner's glands in the submucosa secrete an alkaline mucus which neutralises the chyme and protects the surface of the duodenum.
The jejunum
The ileum. The jejunum and the ileum are the greatly coiled parts of the small intestine, and together are about 4-6 metres long; the junction between the two sections is not well-defined. The mucosa of these sections is highly folded (the folds are called plicae), increasing the surface area available for absorption dramatically.



http://www.youtube.com/v/bNMsNHqxszc&feature=related

The pancreas
consists mainly of exocrine glands that secrete enzymes to aid in the digestion of food in the small intestine. the main enzymes produced are lipases, peptidases and amylases for fats, proteins and carbohydrates respectively. These are released into the duodenum via the duodenal ampulla, the same place that bile from the liver drains into.
Pancreatic exocrine secretion is hormonally regulated, and the same hormone that encourages secretion (cholesystokinin) also encourages discharge of the gall bladder's store of bile. As bile is essentially an emulsifying agent, it makes fats water soluble and gives the pancreatic enzymes lots of surface area to work on.
structurally, the pancreas has four sections; head, neck, body and tail; the tail stretches back to just in front of the spleen


http://www.youtube.com/v/PpzfKt-47iA&feature=related


The Large Intestine



By the time digestive products reach the large intestine, almost all of the nutritionally useful products have been removed. The large intestine removes water from the remainder, passing semi-solid faeces into the rectum to be expelled from the body through the anus. The mucosa (M) is arranged into tightly-packed straight tubular glands (G) which consist of cells specialised for water absorption and mucus-secreting goblet cells to aid the passage of faeces. The large intestine also contains areas of lymphoid tissue (L); these can be found in the ileum too (called Peyer's patches), and they provide local immunological protection of potential weak-spots in the body's defences. As the gut is teeming with bacteria, reinforcement of the standard surface defences seems only sensible...

role of liver



http://www.youtube.com/v/aGJCOTiZOew&feature=related
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Old Tuesday, September 13, 2011
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Endocrine System

The endocrine system is made up of glands that produce and secrete hormones. These hormones regulate the body's growth, metabolism (the physical and chemical processes of the body), and sexual development and function. The hormones are released into the bloodstream and may affect one or several organs throughout the body.

Hormones are chemical messengers created by the body. They transfer information from one set of cells to another to coordinate the functions of different parts of the body.

[COLOR="Green"]The major glands of the endocrine system are the hypothalamus, pituitary, thyroid, parathyroids, adrenals, pineal body, and the reproductive organs (ovaries and testes). The pancreas is also a part of this system; it has a role in hormone production as well as in digestion.

[B]he endocrine system in much the same way that a thermostat regulates the temperature in a room. For the hormones that are regulated by the pituitary gland, a signal is sent from the hypothalamus to the pituitary gland in the form of a "releasing hormone," which stimulates the pituitary to secrete a "stimulating hormone" into the circulation. The stimulating hormone then signals the target gland to secrete its hormone. As the level of this hormone rises in the circulation, the hypothalamus and the pituitary gland shut down secretion of the releasing hormone and the stimulating hormone, which in turn slows the secretion by the target gland. This system results in stable blood concentrations of the hormones that are regulated by the pituitary gland.

Hormones Regulated by the Hypothalamic/Pituitary System
Hormone Pituitary Stimulating Hormone Hypothalamic Releasing Hormone
Thyroid hormones T4, T3

Thyroid-stimulating hormone (TSH) Thyrotropin-releasing hormone (TRH)

Cortisol Adrenocorticotropin hormone (ACTH) Corticotropin-releasing factor (CRF)

Estrogen or testosterone
Follicle-stimulating hormone (FSH), luteinizing hormone (LH)
Luteinizing hormone-releasing hormone (LHRH) or gonadotropin-releasing hormone (GnRH)
Insulinlike growth factor-I (IGF-I) Growth hormone Growth hormone-releasing hormone (GHRH)



Adrenal glands
Divided into 2 regions; secrete hormones that influence the body's metabolism, blood chemicals, and body characteristics, as well as influence the part of the nervous system that is involved in the response and defense against stress.

Hypothalamus
Activates and controls the part of the nervous system that controls involuntary body functions, the hormonal system, and many body functions, such as regulating sleep and stimulating appetite.

Ovaries and testicles
Secrete hormones that influence female and male characteristics, respectively.

Pancreas
Secretes a hormone (insulin) that controls the use of glucose by the body.

Parathyroid glands
Secrete a hormone that maintains the calcium level in the blood.

Pineal body
Involved with daily biological cycles.

Pituitary gland
Produces a number of different hormones that influence various other endocrine glands.

Thymus gland

Plays a role in the body's immune system.

Thyroid gland
Produces hormones that stimulate body heat production, bone growth, and the body's metabolism




http://www.youtube.com/v/qswQpP-ZXeI



nervous system sends electrical messages to control and coordinate the body. The endocrine system has a similar job, but uses chemicals to “communicate”. These chemicals are known as hormones. A hormone is a specific messenger molecule synthesized and secreted by a group of specialized cells called an endocrine gland. These glands are ductless, which means that their secretions (hormones) are released directly into the bloodstream and travel to elsewhere in the body to target organs, upon which they act .this is in contrast to our digestive glands, which have ducts for releasing the digestive enzymes.

Pheromones are also communication chemicals, but are used to send signals to other members of the same species. Queen bees, ants, and naked mole rats exert control of their respective colonies via pheromones.


One common use for pheromones is as attractants in mating. Pheromones are widely studied in insects and are the basis for some kinds of Japanese beetle and gypsy moth traps. While pheromones have not been so widely studied in humans, some interesting studies have been done in recent years on pheromonal control of menstrual cycles in women. It has been found that pheromones in male sweat and/or sweat from another “dominant” female will both influence/regulate the cycles of women when smeared on their upper lip, just below the nose. Also, there is evidence that continued reception of a given man’s pheromone(s) by a woman in the weeks just after ovulation/fertilization can significantly increase the chances of successful implantation of the new baby in her uterus. Pheromones are also used for things like territorial markers (urine) and alarm signals.

Each hormone’s shape is specific and can be recognized by the corresponding target cells. The binding sites on the target cells are called hormone receptors. Many hormones come in antagonistic pairs that have opposite effects on the target organs. For example, insulin and glucagon have opposite effects on the liver’s control of blood sugar level. Insulin lowers the blood sugar level by instructing the liver to take glucose out of circulation and store it, while glucagon instructs the liver to release some of its stored supply to raise the blood sugar level. Much hormonal regulation depends on feedback loops to maintain balance and homeostasis.

There are three general classes (groups) of hormones. These are classified by chemical structure, not function.
steroid hormones including prostaglandins which function especially in a variety of female functions (aspirin inhibits synthesis of prostaglandins, some of which cause “cramps”) and the sex hormones all of which are lipids made from cholesterol,
amino acid derivatives (like epinephrine) which are derived from amino acids, especially tyrosine, and
peptide hormones (like insulin) which is the most numerous/diverse group of hormones.

The major human endocrine glands include:
http://www.youtube.com/v/E5NCSWg5E6c&feature=related



the hypothalamus and pituitary gland

http://www.youtube.com/v/iimJsvz_3HY&feature=related


The pituitary gland is called the “master gland” but it is under the control of the hypothalamus. Together, they control many other endocrine functions. They secrete a number of hormones, especially several which are important to the female menstural cycle, pregnancy, birth, and lactation (milk production). These include follicle-stimulating hormone (FSH), which stimulates development and maturation of a follicle in one of a woman’s ovaries, and leutinizing hormone (LH), which causes the bursting of that follicle (= ovulation) and the formation of a corpus luteum from the remains of the follicle.


There are a number of other hypothalamus and pituitary hormones which affect various target organs.


hormone secreted by the posterior pituitary is antidiuretic hormone or ADH. This hormone helps prevent excess water excretion by the kidneys. Ethanol inhibits the release of ADH and can, thus, cause excessive water loss. That’s also part of the reason why a group of college students who go out for pizza and a pitcher of beer need to make frequent trips to the restrooms. Diuretics are chemicals which interfere with the production of or action of ADH so the kidneys secrete more water. Thus diuretics are often prescribed for people with high blood pressure, in an attempt to decrease blood volume.


Another group of hormones that many people have heard of is the endorphins, which belong to the category of chemicals known as opiates and serve to deaden our pain receptors. Endorphins, which are chemically related to morphine, are produced in response to pain. The natural response to rub an injured area, such as a pinched finger, helps to release endorphins in that area. People who exercise a lot and push their bodies “until it hurts” thereby stimulate the production of endorphins. It is thought that some people who constantly over-exercise and push themselves too much may actually be addicted to their own endorphins which that severe exercise regime releases.

the thyroid gland


Thyroid hormones regulate metabolism, therefore body temperature and weight. The thyroid hormones contain iodine, which the thyroid needs in order to manufacture these hormones. If a person lacks iodine in his/her diet, the thyroid cannot make the hormones, causing a deficiency. In response to the body’s feedback loops calling for more thyroid hormones, the thyroid gland then enlarges to attempt to compensate (The body’s plan here is if it’s bigger it can make more, but that doesn’t help if there isn’t enough iodine.). This disorder is called goiter. Dietary sources of iodine include any “ocean foods” because ocean-dwelling organisms tend to accumulate iodine from the seawater, and would include foods like ocean fish (tuna) and seaweeds like kelp. Because of this, people who live near the ocean do not have as much of a problem with goiter as people who live inland and don’t have access to these foods. To help alleviate this problem in our country, our government began a program encouraging salt refiners to add iodine to salt, and encouraging people to choose to consume this iodized salt.
http://www.youtube.com/v/RDfEPMVJq1c&feature=related

the pancreas



Thyroxine secretion is above normal. This causes a raised level of metabolism. Symptoms of over production of thyroxin are bulging eyes, weight loss heat production, nervousness, irritability, and anxiety. This condition is called Grave’s Disease. Corrective measures for Grave’s Disease are:

1. Drugs to suppress thyroid activity

2. Surgically remove part of the gland

3. Use radioactive iodine to destroy some of the gland.


The Parathyroids


There are 4 parathyroid glands. They are located within the thyroid gland. The hormone they produce is called parathormone. This hormone stimulates the release of calcium from the bones. That is why we must continue to include calcium in our diet even when our bones are fully grown.

Adrenal glands



The adrenal glands are located on top of each kidney. They secrete the hormone called adrenaline (also called epinephrine). This hormone prepares the body for stress and is released when we are frightened or feel stress. It does the following:

1. Increases blood flow to the heart, muscles, and brain.

2. Reduces blood flow to the kidneys. This helps reduce blood loss if we are cut. It causes us to get pale.

3. Opens the bronchioles allowing us to get more air.

4. Increases glucose levels in the blood.

5. Increases heartbeat rate.

6. Increase muscular contraction and strength.

7. Increases mental alertness.
This organ has two functions. It serves as a ducte
d gland, secreting digestive enzymes into the small intestine. The pancreas also serves as a ductless gland in that the islets of Langerhans secrete insulin and glucagon to regulate the blood sugar level. The -islet cells secrete glucagon, which tells the liver to take carbohydrate out of storage to raise a low blood sugar level. The -islet cells secrete insulin to tell the liver to take excess glucose out of circulation to lower a blood sugar level that’s too high. If a person’s body does not make enough insulin (and/or there is a reduced response of the target cells in the liver), the blood sugar rises, perhaps out of control, and we say that the person has diabetes mellitus.
http://www.youtube.com/v/BxGR9tAe3f0&feature=related

the adrenal glands





These sit on top of the kidneys. They consist of two parts, the outer cortex and the inner medulla. The medulla secretes epinephrine (= adrenaline) and other similar hormones in response to stressors such as fright, anger, caffeine, or low blood sugar. The cortex secretes corticosteroids such as cortisone. Corticosteroids are well-known as being anti-inflammatory, thus are prescribed for a number of conditions. However, these are powerful regulators that should be used with caution. Medicinal doses are typically higher than what your body would produce naturally, thus the person’s normal feedback loops suppress natural secretion, and it is necessary to gradually taper off the dosage to trigger the adrenal glands to begin producing on their own again. Because the corticosteroids suppress the immune system, their use can lead to increased susceptibility to infections, yet physicians typically prescribe them for people whose immune systems are hard at work trying to fight off some pathogen. For example, back when I was in grad school, I was diagnosed with mono, and the campus doctor prescribed penicillin and cortisone. Since mono is a virus and penicillin only is effective against some bacteria, about all it did was kill off the friendly bacteria in my body, therefore causing me to develop a bad case of thrush. At the same time, the cortisone was supressing my immune system so my body could not as efficiently fight off the mono and the thrush. People with high blood pressure should be leery of taking prescription corticosteroids: they are known to raise blood pressure, thus can cause things like strokes. My mother-in-law had high blood pressure and was being treated with diuretics. Her physician also had her on large doses of cortisone for her arthritis. While he was on vacation, she started having significant back pain and was referred to an orthopedic surgeon. This man decided the back pain was just due to arthritis, and without carefully checking on what dosage she was already taking, prescribed more cortisone. Simultaneously, because of difficulty walking due to her arthritis, she decided to decrease the amount of diuretics she was taking so she didn’t have to make as many “long” trips to the other end of the house. The combination of lowered dose of diuretics and high dose of cortisone raised her blood pressure to the point where a blood vessel in her brain burst, causing a stroke. When the EMTs took her blood pressure, as I recall the systolic was way over 200 mm Hg.

the gonads or sex organs
In addition to producing gametes, the female ovaries and male testes (singular = testis) also secrete hormones. Therefore, these hormones are called sex hormones. The secretion of sex hormones by the gonads is controlled by pituitary gland hormones such as FSH and LH. While both sexes make some of each of the hormones, typically male testes secrete primarily androgens including testosterone. Female ovaries make estrogen and progesterone in varying amounts depending on where in her cycle a woman is. In a pregnant woman, the baby’s placenta also secretes hormones to maintain the pregnancy.

http://www.youtube.com/v/5LjJbgVglyE&feature=related



the pineal gland


This gland is located near the center of the brain in humans, and is stimulated by nerves from the eyes. In some other animals, the pineal gland is closer to the skin and directly stimulated by light (some lizards even have a third eye). The pineal gland secreted melatonin at night when it’s dark, thus secretes more in winter when the nights are longer. Melatonin promotes sleep (makes you feel sleepy). It also affects reproductive functions by depressing the activity of the gonads. Additionally, it affects thyroid and adrenal cortex functions. In some animals, melatonin affects skin pigmentation. Because melatonin production is affected by the amount of light to which a person is exposed, this is tied to circadian rhythm (having an activity cycle of about 24 hours), annual cycles, and biological clock functions. SAD or seasonal affective disorder (syndrome) is a disorder in which too much melatonin is produced, especially during the long nights of winter, causing profound depression, oversleeping, weight gain, tiredness, and sadness. Treatment consists of exposure to bright lights for several hours each day to inhibit melatonin production. It has also been found that melatonin levels drop 75% suddenly just before puberty, suggesting the involvement of melatonin in the regulation of the onset of puberty. Studies have been done on blind girls (with a form of blindness in which no impulses can travel down the optic nerve and reach the brain and pineal gland), which showed that these girls tended to have higher levels of melatonin for a longer time, resulting in a delay in the onset of puberty. While some older people, who don’t make very much melatonin, thus don’t sleep well, might benefit from a melatonin supplement, I’m skeptical of the recent melatonin craze in this country. When so many people apparently are suffering from SAD, I question the wisdom of purposly ingesting more melatonin, especially since the pineal gland is one of the least-studied, least-understood of the endocrine glands.

Local regulators are hormones with target cells nearby or adjacent to the endocrine gland in question. For example, neurotransmitters are secreted in the synapses of our nervous system and their target cells are in the same synapses.
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[B]The respiratory system[/B]
http://www.youtube.com/v/HiT621PrrO0&feature=related


[B]The respiratory system is the anatomical system of an organism that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles. Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood. This exchange process occurs in the alveolar region of the lungs[/B]

http://www.youtube.com/v/fLKOBQ6cZHA&feature=relmfu






The primary function of the respiratory system is to supply the blood with oxygen in order for the blood to deliver oxygen to all parts of the body. The respiratory system does this through breathing. When we breathe, we inhale oxygen and exhale carbon dioxide. This exchange of gases is the respiratory system's means of getting oxygen to the blood.

Respiration is achieved through the mouth, nose, trachea, lungs, and diaphragm. Oxygen enters the respiratory system through the mouth and the nose. The oxygen then passes through the larynx (where speech sounds are produced) and the trachea which is a tube that enters the chest cavity. In the chest cavity, the trachea splits into two smaller tubes called the bronchi. Each bronchus then divides again forming the bronchial tubes. The bronchial tubes lead directly into the lungs where they divide into many smaller tubes which connect to tiny sacs called alveoli. The average adult's lungs contain about 600 million of these spongy, air-filled sacs that are surrounded by capillaries. The inhaled oxygen passes into the alveoli and then diffuses through the capillaries into the arterial blood. Meanwhile, the waste-rich blood from the veins releases its carbon dioxide into the alveoli. The carbon dioxide follows the same path out of the lungs when you exhale.

The diaphragm's job is to help pump the carbon dioxide out of the lungs and pull the oxygen into the lungs. The diaphragm is a sheet of muscles that lies across the bottom of the chest cavity. As the diaphragm contracts and relaxes, breathing takes place. When the diaphragm contracts, oxygen is pulled into the lungs. When the diaphragm relaxes, carbon dioxide is pumped out of the lungs


The Pathway
Air enters the nostrils
passes through the nasopharynx,
the oral pharynx
through the glottis
into the trachea
into the right and left bronchi, which branches and rebranches into
bronchioles, each of which terminates in a cluster of
alveoli


http://www.youtube.com/v/bwXvqSqAgKc



Only in the alveoli does actual gas exchange takes place. There are some 300 million alveoli in two adult lungs. These provide a surface area of some 160 m2 (almost equal to the singles area of a tennis court and 80 times the area of our skin!).
Breathing
In mammals, the diaphragm divides the body cavity into the
abdominal cavity, which contains the viscera (e.g., stomach and intestines) and the
thoracic cavity, which contains the heart and lungs.

The inner surface of the thoracic cavity and the outer surface of the lungs are lined with pleural membranes which adhere to each other. If air is introduced between them, the adhesion is broken and the natural elasticity of the lung causes it to collapse. This can occur from trauma. And it is sometimes induced deliberately to allow the lung to rest. In either case, reinflation occurs as the air is gradually absorbed by the tissues.
Because of this adhesion, any action that increases the volume of the thoracic cavity causes the lungs to expand, drawing air into them.
During inspiration (inhaling),
The external intercostal muscles contract, lifting the ribs up and out.
The diaphragm contracts, drawing it down .
During expiration (exhaling), these processes are reversed and the natural elasticity of the lungs returns them to their normal volume. At rest, we breath 15–18 times a minute exchanging about 500 ml of air.
In more vigorous expiration,
The internal intercostal muscles draw the ribs down and inward
The wall of the abdomen contracts pushing the stomach and liver upward.
Under these conditions, an average adult male can flush his lungs with about 4 liters of air at each breath. This is called the vital capacity. Even with maximum expiration, about 1200 ml of residual air remain.

The table shows what happens to the composition of air when it reaches the alveoli. Some of the oxygen dissolves in the film of moisture covering the epithelium of the alveoli. From here it diffuses into the blood in a nearby capillary. It enters a red blood cell and combines with the hemoglobin therein.


omposition of atmospheric air and expired air in a typical subject.
Note that only a fraction of the oxygen inhaled is taken up by the lungs.
Component Atmospheric Air (%) Expired Air (%)
N2 (plus inert gases) 78.62 74.9
O2 20.85 15.3
CO2 0.03 3.6
H2O 0.5 6.2
100.0% 100.0%
At the same time, some of the carbon dioxide in the blood diffuses into the alveoli from which it can be exhaled.


http://www.youtube.com/v/SWJHSTAWTCk&feature=related


http://www.youtube.com/v/I49XepXy3q8&feature=related



The ease with which oxygen and carbon dioxide can pass between air and blood is clear from this electron micrograph of two alveoli (Air) and an adjacent capillary from the lung of a laboratory mouse. Note the thinness of the epithelial cells (EP) that line the alveoli and capillary (except where the nucleus is located). At the closest point, the surface of the red blood cell is only 0.7 µm away from the air in the alveolus.Central Control of Breathing

The rate of cellular respiration (and hence oxygen consumption and carbon dioxide production) varies with level of activity. Vigorous exercise can increase by 20–25 times the demand of the tissues for oxygen. This is met by increasing the rate and depth of breathing.

It is a rising concentration of carbon dioxide — not a declining concentration of oxygen — that plays the major role in regulating the ventilation of the lungs. Certain cells in the medulla oblongata are very sensitive to a drop in pH. As the CO2 content of the blood rises above normal levels, the pH drops
[CO2 + H2O → HCO3− + H+],
and the medulla oblongata responds by increasing the number and rate of nerve impulses that control the action of the intercostal muscles and diaphragm. This produces an increase in the rate of lung ventilation, which quickly brings the CO2 concentration of the alveolar air, and then of the blood, back to normal levels. Link to a description of experiments that demonstrate this.


However, the carotid body in the carotid arteries does have receptors that respond to a drop in oxygen. Their activation is important in situations (e.g., at high altitude in the unpressurized cabin of an aircraft) where oxygen supply is inadequate but there has been no increase in the production of CO2


http://www.youtube.com/v/SPGRkexI_cs






Oxygen Transport



In adult humans the hemoglobin (Hb) molecule
consists of four polypeptides:
two alpha (α) chains of 141 amino acids and
two beta (β) chains of 146 amino acids

To each of these is attached the prosthetic group heme.
There is one atom of iron at the center of each heme.
One molecule of oxygen can bind to each heme.

The reaction is reversible.

Under the conditions of lower temperature, higher pH, and increased oxygen pressure in the capillaries of the lungs, the reaction proceeds to the right. The purple-red deoxygenated hemoglobin of the venous blood becomes the bright-red oxyhemoglobin of the arterial blood.
Under the conditions of higher temperature, lower pH, and lower oxygen pressure in the tissues, the reverse reaction is promoted and oxyhemoglobin gives up its oxygen.

The pressure of oxygen in the lungs is 90–95 torr; in the interior tissues it is about 40 torr. Therefore, only a portion of the oxygen carried by the red blood cells is normally unloaded in the tissues. However, vigorous activity can lower the oxygen pressure in skeletal muscles below 40 torr, which causes a large increase in the amount of oxygen released. This effect is enhanced by the high concentration of carbon dioxide in the muscles and the resulting lower pH (7.2). The lower carbon dioxide concentration (and hence higher pH) at the lungs promotes the binding of oxygen to hemoglobin and hence the uptake of oxygen.

Temperature changes also influence the binding of oxygen to hemoglobin. In the relative warmth of the interior organs, the curve is shifted to the right (like the curve for pH 7.2), helping to unload oxygen. In the relative coolness of the lungs, the curve is shifted to the left, aiding the uptake of oxygen.Although the oxygen transported by RBCs make possible cellular respiration throughout the body, RBCs lack mitochondria and so cannot perform cellular respiration themselves and must subsist on glycolysis.

Carbon Dioxide Transport
Carbon dioxide (CO2) combines with water forming carbonic acid, which dissociates into a hydrogen ion (H+) and a bicarbonate ions:
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3−

95% of the CO2 generated in the tissues is carried in the red blood cells:
It probably enters (and leaves) the cell by diffusion through the plasma membrane assisted by facilitated diffusion through transmembrane channels in the plasma membrane. (One of the proteins that forms the channel is the D antigen that is the most important factor in the Rh system of blood groups.)
Once inside, about one-half of the CO2 is directly bound to hemoglobin (at a site different from the one that binds oxygen).
The rest is converted — following the equation above — by the enzyme carbonic anhydrase into
bicarbonate ions that diffuse back out into the plasma and
hydrogen ions (H+) that bind to the protein portion of the hemoglobin (thus having no effect on pH).

Only about 5% of the CO2 generated in the tissues dissolves directly in the plasma. (A good thing, too: if all the CO2 we make were carried this way, the pH of the blood would drop from its normal 7.4 to an instantly-fatal 4.5!)
When the red cells reach the lungs, these reactions are reversed and CO2 is released to the air of the alveoli.



http://www.youtube.com/v/WXOBJEXxNEo&feature=related


Local Control of Breathing

The smooth muscle in the walls of the bronchioles is very sensitive to the concentration of carbon dioxide. A rising level of CO2 causes the bronchioles to dilate. This lowers the resistance in the airways and thus increases the flow of air in and out.
Diseases of the Lungs


Pneumonia

Pneumonia is an infection of the alveoli. It can be caused by many kinds of both bacteria (e.g., Streptococcus pneumoniae) and viruses. Tissue fluids accumulate in the alveoli reducing the surface area exposed to air. If enough alveoli are affected, the patient may need supplemental oxygen.

Asthma


In asthma, periodic constriction of the bronchi and bronchioles makes it more difficult to breathe in and, especially, out. Attacks of asthma can be
triggered by airborne irritants such as chemical fumes and cigarette smoke
airborne particles to which the patient is allergic. Link to discussion of allergic asthma.

Emphysema

In this disorder, the delicate walls of the alveoli break down, reducing the gas-exchange area of the lungs. The condition develops slowly and is seldom a direct cause of death. However, the gradual loss of gas-exchange area forces the heart to pump ever-larger volumes of blood to the lungs in order to satisfy the body's needs. The added strain can lead to heart failure.

The immediate cause of emphysema seems to be the release of proteolytic enzymes as part of the inflammatory process that follows irritation of the lungs. Most people avoid this kind of damage during infections, etc. by producing an enzyme inhibitor (a serpin) called alpha-1 antitrypsin. Those rare people who inherit two defective genes for alpha-1 antitrypsin are particularly susceptible to developing emphysema.

Chronic Bronchitis

Any irritant reaching the bronchi and bronchioles will stimulate an increased secretion of mucus. In chronic bronchitis the air passages become clogged with mucus, and this leads to a persistent cough. Chronic bronchitis is usually associated with cigarette smoking.


Chronic Obstructive Pulmonary Disease (COPD)

Irritation of the lungs can lead to asthma, emphysema, and chronic bronchitis. And, in fact, many people develop two or three of these together. This constellation is known as chronic obstructive pulmonary disease (COPD).
Among the causes of COPD are
cigarette smoke (often)
cystic fibrosis (rare)

Cystic fibrosis is a genetic disorder caused by inheriting two defective genes for the cystic fibrosis transmembrane conductance regulator (CFTR), a transmembrane protein needed for the transport of Cl− and HCO3− ions through the plasma membrane of epithelial cells. Defective ion transport in the lung reduces the water content of the fluid in the lungs making it more viscous and difficult for the ciliated cells to move it up out of the lungs. Precisely how defective CFTR function produces this effect is still under investigation. In any case, the accumulation of mucus plugs the airways and provides a fertile breeding ground for pathogenic fungi and bacteria. All of this damages the airways — interfering with breathing and causing a persistent cough. Cystic fibrosis is the most common inherited disease in the U.S. white population. Some mutations that cause cystic fibrosis.

Lung Cancer

Lung cancer is the most common cancer and the most common cause of cancer deaths in U.S. males. Although more women develop breast cancer than lung cancer, since 1987 U.S. women have been dying in larger numbers from lung cancer than from breast cancer. Link to lung cancer data.


Lung cancer, like all cancer, is an uncontrolled proliferation of cells. There are several forms of lung cancer, but the most common (and most rapidly increasing) types are those involving the epithelial cells lining the bronchi and bronchioles.

Ordinarily, the lining of these airways consists of two layers of cells. Chronic exposure to irritants
causes the number of layers to increase. This is especially apt to happen at forks where the bronchioles branch.
The ciliated and mucus-secreting cells disappear and are replaced by a disorganized mass of cells with abnormal nuclei.
If the process continues, the growing mass penetrates the underlying basement membrane. Link to illustrations of the cellular changes in developing lung cancer.

At this point, malignant cells can break away and be carried in lymph and blood to other parts of the body where they may lodge and continue to proliferate.
It is this metastasis of the primary tumor that eventually kills the patient.
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Default Cardiovascular System

Cardiovascular System




System of vessels that convey blood to and from tissues throughout the body, bringing nutrients and oxygen and removing wastes and carbon dioxide. It is essentially a long, closed tube through which blood moves in a double circuit — one through the lungs (pulmonary circulation) and one through the rest of the body (systemic circulation). The heart pumps blood through the arteries, which branch into smaller arterioles, which feed into microscopic capillaries (see artery; capillary). These converge to form small venules, which join to become larger veins, generally following the same path as the arteries back to the heart








http://www.youtube.com/v/r_RQMdqccqc&feature=related













The cardiovascular/circulatory system transports food, hormones, metabolic wastes, and gases (oxygen, carbon dioxide) to and from cells. Components of the circulatory system include:
  • blood: consisting of liquid plasma and cells
  • blood vessels (vascular system): the "channels" (arteries, veins, capillaries) which carry blood to/from all tissues. (Arteries carry blood away from the heart. Veins return blood to the heart. Capillaries are thin-walled blood vessels in which gas/ nutrient/ waste exchange occurs.)
  • heart: a muscular pump to move the blood
There are two circulatory "circuits": Pulmonary circulation, involving the "right heart," delivers blood to and from the lungs. The pulmonary artery carries oxygen-poor blood from the "right heart" to the lungs, where oxygenation and carbon-dioxide removal occur. Pulmonary veins carry oxygen-rich blood from tbe lungs back to the "left heart." Systemic circulation, driven by the "left heart," carries blood to the rest of the body. Food products enter the sytem from the digestive organs into the portal vein. Waste products are removed by the liver and kidneys. All systems ultimately return to the "right heart" via the inferior and superior vena cavae.
A specialized component of the circulatory system is the lymphatic system, consisting of a moving fluid (lymph/interstitial fluid); vessels (lymphatics); lymph nodes, and organs (bone marrow, liver, spleen, thymus). Through the flow of blood in and out of arteries, and into the veins, and through the lymph nodes and into the lymph, the body is able to eliminate the products of cellular breakdown and bacterial invasion.











Blood Components
http://www.youtube.com/v/LWtXthfG9_M&feature=relmfu








Heart Anatomy




Coronary Arteries

Because the heart is composed primarily of cardiac muscle tissue that continuously contracts and relaxes, it must have a constant supply of oxygen and nutrients. The coronary arteries are the network of blood vessels that carry oxygen- and nutrient-rich blood to the cardiac muscle tissue.
The blood leaving the left ventricle exits through the aorta, the body’s main artery. Two coronary arteries, referred to as the "left" and "right" coronary arteries, emerge from the beginning of the aorta, near the top of the heart.
The initial segment of the left coronary artery is called the left main coronary. This blood vessel is approximately the width of a soda straw and is less than an inch long. It branches into two slightly smaller arteries: the left anterior descending coronary artery and the left circumflex coronary artery. The left anterior descending coronary artery is embedded in the surface of the front side of the heart. The left circumflex coronary artery circles around the left side of the heart and is embedded in the surface of the back of the heart.
Just like branches on a tree, the coronary arteries branch into progressively smaller vessels. The larger vessels travel along the surface of the heart; however, the smaller branches penetrate the heart muscle. The smallest branches, called capillaries, are so narrow that the red blood cells must travel in single file. In the capillaries, the red blood cells provide oxygen and nutrients to the cardiac muscle tissue and bond with carbon dioxide and other metabolic waste products, taking them away from the heart for disposal through the lungs, kidneys and liver.
When cholesterol plaque accumulates to the point of blocking the flow of blood through a coronary artery, the cardiac muscle tissue fed by the coronary artery beyond the point of the blockage is deprived of oxygen and nutrients. This area of cardiac muscle tissue ceases to function properly. The condition when a coronary artery becomes blocked causing damage to the cardiac muscle tissue it serves is called a myocardial infarction or heart attack.
Superior Vena Cava





The superior vena cava is one of the two main veins bringing de-oxygenated blood from the body to the heart. Veins from the head and upper body feed into the superior vena cava, which empties into the right atrium of the heart.
Inferior Vena Cava

The inferior vena cava is one of the two main veins bringing de-oxygenated blood from the body to the heart. Veins from the legs and lower torso feed into the inferior vena cava, which empties into the right atrium of the heart.
Aorta

The aorta is the largest single blood vessel in the body. It is approximately the diameter of your thumb. This vessel carries oxygen-rich blood from the left ventricle to the various parts of the body.


Pulmonary Artery

The pulmonary artery is the vessel transporting de-oxygenated blood from the right ventricle to the lungs. A common misconception is that all arteries carry oxygen-rich blood. It is more appropriate to classify arteries as vessels carrying blood away from the heart.

Pulmonary Vein

The pulmonary vein is the vessel transporting oxygen-rich blood from the lungs to the left atrium. A common misconception is that all veins carry de-oxygenated blood. It is more appropriate to classify veins as vessels carrying blood to the heart.

Right Atrium

The right atrium receives de-oxygenated blood from the body through the superior vena cava (head and upper body) and inferior vena cava (legs and lower torso). The sinoatrial node sends an impulse that causes the cardiac muscle tissue of the atrium to contract in a coordinated, wave-like manner. The tricuspid valve, which separates the right atrium from the right ventricle, opens to allow the de-oxygenated blood collected in the right atrium to flow into the right ventricle.
Right Ventricle

The right ventricle receives de-oxygenated blood as the right atrium contracts. The pulmonary valve leading into the pulmonary artery is closed, allowing the ventricle to fill with blood. Once the ventricles are full, they contract. As the right ventricle contracts, the tricuspid valve closes and the pulmonary valve opens. The closure of the tricuspid valve prevents blood from backing into the right atrium and the opening of the pulmonary valve allows the blood to flow into the pulmonary artery toward the lungs.

Left Atrium

The left atrium receives oxygenated blood from the lungs through the pulmonary vein. As the contraction triggered by the sinoatrial node progresses through the atria, the blood passes through the mitral valve into the left ventricle.
Left Ventricle

The left ventricle receives oxygenated blood as the left atrium contracts. The blood passes through the mitral valve into the left ventricle. The aortic valve leading into the aorta is closed, allowing the ventricle to fill with blood. Once the ventricles are full, they contract. As the left ventricle contracts, the mitral valve closes and the aortic valve opens. The closure of the mitral valve prevents blood from backing into the left atrium and the opening of the aortic valve allows the blood to flow into the aorta and flow throughout the body.

Papillary Muscles

The papillary muscles attach to the lower portion of the interior wall of the ventricles. They connect to the chordae tendineae, which attach to the tricuspid valve in the right ventricle and the mitral valve in the left ventricle. The contraction of the papillary muscles closes these valves. When the papillary muscles relax, the valves open.

Chordae Tendineae

The chordae tendineae are tendons linking the papillary muscles to the tricuspid valve in the right ventricle and the mitral valve in the left ventricle. As the papillary muscles contract and relax, the chordae tendineae transmit the resulting increase and decrease in tension to the respective valves, causing them to open and close. The chordae tendineae are string-like in appearance and are sometimes referred to as "heart strings."

Tricuspid Valve

The tricuspid valve separates the right atrium from the right ventricle. It opens to allow the de-oxygenated blood collected in the right atrium to flow into the right ventricle. It closes as the right ventricle contracts, preventing blood from returning to the right atrium; thereby, forcing it to exit through the pulmonary valve into the pulmonary artery.

Mitral Value

The mitral valve separates the left atrium from the left ventricle. It opens to allow the oxygenated blood collected in the left atrium to flow into the left ventricle. It closes as the left ventricle contracts, preventing blood from returning to the left atrium; thereby, forcing it to exit through the aortic valve into the aorta.
Pulmonary Valve

The pulmonary valve separates the right ventricle from the pulmonary artery. As the ventricles contract, it opens to allow the de-oxygenated blood collected in the right ventricle to flow to the lungs. It closes as the ventricles relax, preventing blood from returning to the heart.
Aortic Valve

The aortic valve separates the left ventricle from the aorta. As the ventricles contract, it opens to allow the oxygenated blood collected in the left ventricle to flow throughout the body. It closes as the ventricles relax, preventing blood from returning to the heart.



This cross section of the heart shows the right ventricle, tricuspid valve, left ventricle, bicuspid (mitral) valve, left atrium, right atrium, superior vena cava, inferior vena cava, aorta, aortic valve, papillary muscle, chordae tendineae, and trabeculae carneae.

The heart ventricular walls consist of three layers: the 1.epicardium, the 2.myocardium (cardiac muscle), and the 3.endocardium.

The muscular wall separating the two ventricles is the interventricular septum



Capillaries
The arterioles branch into the microscopic capillaries, or capillary beds, which lie bathed in interstitial fluid, or lymph, produced by the lymphatic system. Capillaries are the points of exchange between the blood and surrounding tissues. Materials cross in and out of the capillaries by passing through or between the cells that line the capillary. The extensive network of capillaries is estimated at between 50,000 and 60,000 miles long.1
Veins
Blood leaving the capillary beds flows into a series of progressively larger vessels, called venules, which in turn unite to form veins. Veins are responsible for returning blood to the heart after the blood and the body cells exchange gases, nutrients, and wastes. Pressure in veins is low, so veins depend on nearby muscular contractions to move blood along. Veins have valves that prevent back-flow of blood.
Blood in veins is oxygen-poor, with the exception of the pulmonary veins, which carry oxygenated blood from the lungs back to the heart. The major veins, like their companion arteries, often take the name of the organ served. The exceptions are the superior vena cava and the inferior vena cava, which collect body from all parts of the body (except from the lungs) and channel it back to the heart.


Red blood cells .and heart function
http://www.youtube.com/v/fLKOBQ6cZHA&feature=relmfu


http://www.youtube.com/v/QhiVnFvshZg&feature=relmfu




Blood Pressure and Heart Rate
The heart beats or contracts around 70 times per minute.1 The human heart will undergo over 3 billion contraction/cardiac cycles during a normal lifetime.
One heartbeat, or cardiac cycle, includes atrial contraction and relaxation, ventricular contraction and relaxation, and a short pause. Atria contract while ventricles relax, and vice versa. Heart valves open and close to limit flow to a single direction. The sound of the heart contracting and the valves opening and closing produces a characteristic "lub-dub" sound.
The cardiac cycle consists of two parts: systole (contraction of the heart muscle in the ventricles) and diastole (relaxation of the ventricular heart muscles). When the ventricles contract, they force the blood from their chambers into the arteries leaving the heart. The left ventricle empties into the aorta (systemic circuit) and the right ventricle into the pulmonary artery (pulmonary circuit). The increased pressure on the arteries due to the contraction of the ventricles (heart pumping) is called systolic pressure.
When the ventricles relax, blood flows in from the atria. The decreased pressure due to the relaxation of the ventricles (heart resting) is called diastolic pressure.
Blood pressure is measured in mm of mercury, with the systole in ratio to the diastole. Healthy young adults should have a ventricular systole of 120mm, and 80mm at ventricular diastole, or 120/80.
Receptors in the arteries and atria sense systemic pressure. Nerve messages from these sensors communicate conditions to the medulla in the brain. Signals from the medulla regulate blood pressure.
Electrocardiography (ECG, EKG)
An electrocardiogram measures changes in electrical potential across the heart and detects contraction pulses that pass over the surface of the heart. There are three slow, negative changes, known as P, R, and T. Positive deflections are the Q and S waves. The P wave represents atrial contraction ("the lub"), the T wave the ventricular contraction ("the dub").
The Lymphatic System
The lymphatic system functions 1) to absorb excess fluid, thus preventing tissues from swelling; 2) to defend the body against microorganisms and harmful foreign particles; and 3) to facilitate the absorption of fat (in the villi of the small intestine).

Capillaries release excess water and plasma into intracellular spaces, where they mix with lymph, or interstitial fluid. "Lymph" is a milky body fluid that also contains proteins, fats, and a type of white blood cells, called "lymphocytes," which are the body's first-line defense in the immune system.

Lymph flows from small lymph capillaries into lymph vessels that are similar to veins in having valves that prevent backflow. Contraction of skeletal muscle causes movement of the lymph fluid through valves. Lymph vessels connect to lymph nodes, lymph organs (bone marrow, liver, spleen, thymus), or to the cardiovascular system.
  • Lymph nodes are small irregularly shaped masses through which lymph vessels flow. Clusters of nodes occur in the armpits, groin, and neck. All lymph nodes have the primary function (along with bone marrow) of producing lymphocytes.
  • The spleen filters, or purifies, the blood and lymph flowing through it.
  • The thymus secretes a hormone, thymosin, that produces T-cells, a form of lymphocyte.
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The Central Nervous System is arguably the most important part of the body because of the way it controls the biological processes of our body and all conscious thought. Due to their importance, they are safely encased within bones, namely the cranium protecting the brain and the spine protecting the spinal cord
Brain Divisions

There are three main components of the brain, namely the brainstem, cerebellum and the forebrain. These are elaborated upon below
  • The Brainstem - The brainstem is the connection between the rest of the brain and the rest of the central nervous system. This part of the brain was the first to be found in the evolutionary chain, though has developed over time and via evolution to develop into the two other components. It is primarily concerned with life support and basic functions such as movement, thus meaning that more advanced processes are left to the more evolved areas of the brain, as explained below.
  • The Cerebellum - Consisting of two hemispheres, the cerebellum is primarily concerned with movement and works in partnership with the brainstem area of the brain and focuses on the well being and functionality of muscles. The structure can be found below the occipital lobe and adjacent to the brainstem
  • The Forebrain - The forebrain lies above the brainstem and cerebellum and is the most advanced in evolutionary terms. Due to its complexity, more info is divulged about this part of the brain below
The Forebrain

The forebrain has many activities that it is responsible for and is divided into many component parts. The below list elaborates on the localised areas of the forebrain and their functions.
  • The Hypothalamus - A section of the brain found next to the thalamus that is involved in many regulatory functions such as osmoregulation and thermoregulation. The hypothalamus has a degree of control over the pituitary gland, another part of the brain situated next to it, and also controls sleeping patterns, eating and drinking and speech. The hypothalamus is also responsible for the secretion of ADH (Anti-Diuretic Hormone) via its neurosecretory cells
  • The Cerebrum - The cerebrum is the largest part of the human brain, and the part responsible for intelligence and creativity, and also involved in memory. The 'grey matter' of the cerebrum is the cerebral cortex, the centre that receives information from the thalamus and all the other lower centres in the brain.
  • The Cerebral Cortex - Part of the cerebrum, this part of the brain deals with almost all of the higher functions of an intelligent being. It is this part of brain that deals with the masses of information incoming from the periphery nervous system, furiously instructing the brain of what is going on inside its body and the external environment. It is this part that translates our nervous impulses into understandable quantifiable feelings and thoughts. So important is the cerebral cortex that it is sub-divided into 4 parts, explained below
  1. Frontal Lobe - Found at the front of the head, near the temples and forehead, the frontal lobe is essential to many of the advanced functions of an evolved brain. It deals with voluntary muscle movements and deals with more intricate matters such as thought and speech
  2. Parietal Lobe - Situated behind the frontal lobe, this section deals with spatial awareness in the external environment and acts as a receptor area to deal with signals associated with tough.
  3. Temporal Lobe - The temporal lobes are situated in parallel with the ears, they serve the ears by interpreting audio signals received from the auditory canal
  4. Occipital Lobe - This is the smallest of the four lobe components of the cerebrum, and is responsible in interpreting nerve signals from the eye at the back of the brain
The above components of the brain work in tandem in a healthy brain. However, in some cases the brain can be injured in some way, causing brain damage. The next page looks at how brain damage can affect the way we operate.

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THE NERVOUS SYSTEM

The system of cells, tissues, and organs that regulates the body's responses to internal and external stimuli. In vertebrates it consists of the brain, spinal cord, nerves, ganglia, and parts of the receptor and effector organs.





Cerebrospinal Fluid Circulation
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THE NORMAL CSF The cerebrospinal fluid (CSF) is produced from arterial blood by the choroid plexuses of the lateral and fourth ventricles by a combined process of diffusion, pinocytosis and active transfer. A small amount is also produced by ependymal cells. The choroid plexus consists of tufts of capillaries with thin fenestrated endothelial cells. These are covered by modified ependymal cells with bulbous microvilli. The total volume of CSF in the adult ranges from140 to 270 ml. The volume of the ventricles is about 25 ml. CSF is produced at a rate of 0.2 - 0.7 ml per minute or 600-700 ml per day. The circulation of CSF is aided by the pulsations of the choroid plexus and by the motion of the cilia of ependymal cells. CSF is absorbed across the arachnoid villi into the venous circulation and a significant amount probably also drains into lymphatic vessels around the cranial cavity and spinal canal. The arachnoid villi act as one-way valves between the subarachnoid space and the dural sinuses. The rate of absorption correlates with the CSF pressure. CSF acts as a cushion that protects the brain from shocks and supports the venous sinuses (primarily the superior sagittal sinus, opening when CSF pressure exceeds venous pressure). It also plays an important role in the homeostasis and metabolism of the central nervous system.CSF from the lumbar region contains 15 to 45 mg/dl protein (lower in childen) and 50-80 mg/dl glucose (two-thirds of blood glucose). Protein concentration in cisternal and ventricular CSF is lower. Normal CSF contains 0-5 mononuclear cells. The CSF pressure, measured at lumbar puncture (LP), is 100-180 mm of H2O (8-15 mm Hg) with the patient lying on the side and 200-300 mm with the patient sitting up.

The Conscious & Unconscious Nervous System
- Human Neurology

The Central Nervous System is arguably the most important part of the body because of the way it controls the biological processes of our body and all conscious thought. Due to their importance, they are safely encased within bones, namely the cranium protecting the brain and the spine protecting the spinal cord
Brain Divisions

There are three main components of the brain, namely the brainstem, cerebellum and the forebrain. These are elaborated upon below
  • The Brainstem - The brainstem is the connection between the rest of the brain and the rest of the central nervous system. This part of the brain was the first to be found in the evolutionary chain, though has developed over time and via evolution to develop into the two other components. It is primarily concerned with life support and basic functions such as movement, thus meaning that more advanced processes are left to the more evolved areas of the brain, as explained below.
  • The Cerebellum - Consisting of two hemispheres, the cerebellum is primarily concerned with movement and works in partnership with the brainstem area of the brain and focuses on the well being and functionality of muscles. The structure can be found below the occipital lobe and adjacent to the brainstem
  • The Forebrain - The forebrain lies above the brainstem and cerebellum and is the most advanced in evolutionary terms. Due to its complexity, more info is divulged about this part of the brain below
The Forebrain

The forebrain has many activities that it is responsible for and is divided into many component parts. The below list elaborates on the localised areas of the forebrain and their functions.
  • The Hypothalamus - A section of the brain found next to the thalamus that is involved in many regulatory functions such as osmoregulation and thermoregulation. The hypothalamus has a degree of control over the pituitary gland, another part of the brain situated next to it, and also controls sleeping patterns, eating and drinking and speech. The hypothalamus is also responsible for the secretion of ADH (Anti-Diuretic Hormone) via its neurosecretory cells
  • The Cerebrum - The cerebrum is the largest part of the human brain, and the part responsible for intelligence and creativity, and also involved in memory. The 'grey matter' of the cerebrum is the cerebral cortex, the centre that receives information from the thalamus and all the other lower centres in the brain.
  • The Cerebral Cortex - Part of the cerebrum, this part of the brain deals with almost all of the higher functions of an intelligent being. It is this part of brain that deals with the masses of information incoming from the periphery nervous system, furiously instructing the brain of what is going on inside its body and the external environment. It is this part that translates our nervous impulses into understandable quantifiable feelings and thoughts. So important is the cerebral cortex that it is sub-divided into 4 parts, explained below
  1. Frontal Lobe - Found at the front of the head, near the temples and forehead, the frontal lobe is essential to many of the advanced functions of an evolved brain. It deals with voluntary muscle movements and deals with more intricate matters such as thought and speech
  2. Parietal Lobe - Situated behind the frontal lobe, this section deals with spatial awareness in the external environment and acts as a receptor area to deal with signals associated with tough.
  3. Temporal Lobe - The temporal lobes are situated in parallel with the ears, they serve the ears by interpreting audio signals received from the auditory canal
  4. Occipital Lobe - This is the smallest of the four lobe components of the cerebrum, and is responsible in interpreting nerve signals from the eye at the back of the brain
The above components of the brain work in tandem in a healthy brain. However, in some cases the brain can be injured in some way, causing brain damage. The next page looks at how brain damage can affect the way we operate .





Tutorials » Human Neurology » The Conscious & Unconscious Nervous System
The Conscious & Unconscious Nervous System - Human Neurology



The Central Nervous System is arguably the most important part of the body because of the way it controls the biological processes of our body and all conscious thought. Due to their importance, they are safely encased within bones, namely the cranium protecting the brain and the spine protecting the spinal cord
Brain Divisions

There are three main components of the brain, namely the brainstem, cerebellum and the forebrain. These are elaborated upon below
  • The Brainstem - The brainstem is the connection between the rest of the brain and the rest of the central nervous system. This part of the brain was the first to be found in the evolutionary chain, though has developed over time and via evolution to develop into the two other components. It is primarily concerned with life support and basic functions such as movement, thus meaning that more advanced processes are left to the more evolved areas of the brain, as explained below.
  • The Cerebellum - Consisting of two hemispheres, the cerebellum is primarily concerned with movement and works in partnership with the brainstem area of the brain and focuses on the well being and functionality of muscles. The structure can be found below the occipital lobe and adjacent to the brainstem
  • The Forebrain - The forebrain lies above the brainstem and cerebellum and is the most advanced in evolutionary terms. Due to its complexity, more info is divulged about this part of the brain below
The Forebrain

The forebrain has many activities that it is responsible for and is divided into many component parts. The below list elaborates on the localised areas of the forebrain and their functions.
  • The Hypothalamus - A section of the brain found next to the thalamus that is involved in many regulatory functions such as osmoregulation and thermoregulation. The hypothalamus has a degree of control over the pituitary gland, another part of the brain situated next to it, and also controls sleeping patterns, eating and drinking and speech. The hypothalamus is also responsible for the secretion of ADH (Anti-Diuretic Hormone) via its neurosecretory cells
  • The Cerebrum - The cerebrum is the largest part of the human brain, and the part responsible for intelligence and creativity, and also involved in memory. The 'grey matter' of the cerebrum is the cerebral cortex, the centre that receives information from the thalamus and all the other lower centres in the brain.
  • The Cerebral Cortex - Part of the cerebrum, this part of the brain deals with almost all of the higher functions of an intelligent being. It is this part of brain that deals with the masses of information incoming from the periphery nervous system, furiously instructing the brain of what is going on inside its body and the external environment. It is this part that translates our nervous impulses into understandable quantifiable feelings and thoughts. So important is the cerebral cortex that it is sub-divided into 4 parts, explained below
  1. Frontal Lobe - Found at the front of the head, near the temples and forehead, the frontal lobe is essential to many of the advanced functions of an evolved brain. It deals with voluntary muscle movements and deals with more intricate matters such as thought and speech
  2. Parietal Lobe - Situated behind the frontal lobe, this section deals with spatial awareness in the external environment and acts as a receptor area to deal with signals associated with tough.
  3. Temporal Lobe - The temporal lobes are situated in parallel with the ears, they serve the ears by interpreting audio signals received from the auditory canal
  4. Occipital Lobe - This is the smallest of the four lobe components of the cerebrum, and is responsible in interpreting nerve signals from the eye at the back of the brain
The above components of the brain work in tandem in a healthy brain. However, in some cases the brain can be injured in some way, causing brain damage. The next page looks at how brain damage can affect the way we operate.





Tutorials » Human Neurology » The Conscious & Unconscious Nervous System
The Conscious & Unconscious Nervous System - Human Neurology



The Central Nervous System is arguably the most important part of the body because of the way it controls the biological processes of our body and all conscious thought. Due to their importance, they are safely encased within bones, namely the cranium protecting the brain and the spine protecting the spinal cord
Brain Divisions

There are three main components of the brain, namely the brainstem, cerebellum and the forebrain. These are elaborated upon below
  • The Brainstem - The brainstem is the connection between the rest of the brain and the rest of the central nervous system. This part of the brain was the first to be found in the evolutionary chain, though has developed over time and via evolution to develop into the two other components. It is primarily concerned with life support and basic functions such as movement, thus meaning that more advanced processes are left to the more evolved areas of the brain, as explained below.
  • The Cerebellum - Consisting of two hemispheres, the cerebellum is primarily concerned with movement and works in partnership with the brainstem area of the brain and focuses on the well being and functionality of muscles. The structure can be found below the occipital lobe and adjacent to the brainstem
  • The Forebrain - The forebrain lies above the brainstem and cerebellum and is the most advanced in evolutionary terms. Due to its complexity, more info is divulged about this part of the brain below
The Forebrain

The forebrain has many activities that it is responsible for and is divided into many component parts. The below list elaborates on the localised areas of the forebrain and their functions.
  • The Hypothalamus - A section of the brain found next to the thalamus that is involved in many regulatory functions such as osmoregulation and thermoregulation. The hypothalamus has a degree of control over the pituitary gland, another part of the brain situated next to it, and also controls sleeping patterns, eating and drinking and speech. The hypothalamus is also responsible for the secretion of ADH (Anti-Diuretic Hormone) via its neurosecretory cells
  • The Cerebrum - The cerebrum is the largest part of the human brain, and the part responsible for intelligence and creativity, and also involved in memory. The 'grey matter' of the cerebrum is the cerebral cortex, the centre that receives information from the thalamus and all the other lower centres in the brain.
  • The Cerebral Cortex - Part of the cerebrum, this part of the brain deals with almost all of the higher functions of an intelligent being. It is this part of brain that deals with the masses of information incoming from the periphery nervous system, furiously instructing the brain of what is going on inside its body and the external environment. It is this part that translates our nervous impulses into understandable quantifiable feelings and thoughts. So important is the cerebral cortex that it is sub-divided into 4 parts, explained below
  1. Frontal Lobe - Found at the front of the head, near the temples and forehead, the frontal lobe is essential to many of the advanced functions of an evolved brain. It deals with voluntary muscle movements and deals with more intricate matters such as thought and speech
  2. Parietal Lobe - Situated behind the frontal lobe, this section deals with spatial awareness in the external environment and acts as a receptor area to deal with signals associated with tough.
  3. Temporal Lobe - The temporal lobes are situated in parallel with the ears, they serve the ears by interpreting audio signals received from the auditory canal
  4. Occipital Lobe - This is the smallest of the four lobe components of the cerebrum, and is responsible in interpreting nerve signals from the eye at the back of the brain
The above components of the brain work in tandem in a healthy brain. However, in some cases the brain can be injured in some way, causing brain damage. The next page looks at how brain damage can affect the way we operate.





Tutorials » Human Neurology » The Conscious & Unconscious Nervous System
The Conscious & Unconscious Nervous System - Human Neurology



The Central Nervous System is arguably the most important part of the body because of the way it controls the biological processes of our body and all conscious thought. Due to their importance, they are safely encased within bones, namely the cranium protecting the brain and the spine protecting the spinal cord
Brain Divisions

There are three main components of the brain, namely the brainstem, cerebellum and the forebrain. These are elaborated upon below
  • The Brainstem - The brainstem is the connection between the rest of the brain and the rest of the central nervous system. This part of the brain was the first to be found in the evolutionary chain, though has developed over time and via evolution to develop into the two other components. It is primarily concerned with life support and basic functions such as movement, thus meaning that more advanced processes are left to the more evolved areas of the brain, as explained below.
  • The Cerebellum - Consisting of two hemispheres, the cerebellum is primarily concerned with movement and works in partnership with the brainstem area of the brain and focuses on the well being and functionality of muscles. The structure can be found below the occipital lobe and adjacent to the brainstem
  • The Forebrain - The forebrain lies above the brainstem and cerebellum and is the most advanced in evolutionary terms. Due to its complexity, more info is divulged about this part of the brain below
The Forebrain

The forebrain has many activities that it is responsible for and is divided into many component parts. The below list elaborates on the localised areas of the forebrain and their functions.
  • The Hypothalamus - A section of the brain found next to the thalamus that is involved in many regulatory functions such as osmoregulation and thermoregulation. The hypothalamus has a degree of control over the pituitary gland, another part of the brain situated next to it, and also controls sleeping patterns, eating and drinking and speech. The hypothalamus is also responsible for the secretion of ADH (Anti-Diuretic Hormone) via its neurosecretory cells
  • The Cerebrum - The cerebrum is the largest part of the human brain, and the part responsible for intelligence and creativity, and also involved in memory. The 'grey matter' of the cerebrum is the cerebral cortex, the centre that receives information from the thalamus and all the other lower centres in the brain.
  • The Cerebral Cortex - Part of the cerebrum, this part of the brain deals with almost all of the higher functions of an intelligent being. It is this part of brain that deals with the masses of information incoming from the periphery nervous system, furiously instructing the brain of what is going on inside its body and the external environment. It is this part that translates our nervous impulses into understandable quantifiable feelings and thoughts. So important is the cerebral cortex that it is sub-divided into 4 parts, explained below
  1. Frontal Lobe - Found at the front of the head, near the temples and forehead, the frontal lobe is essential to many of the advanced functions of an evolved brain. It deals with voluntary muscle movements and deals with more intricate matters such as thought and speech
  2. Parietal Lobe - Situated behind the frontal lobe, this section deals with spatial awareness in the external environment and acts as a receptor area to deal with signals associated with tough.
  3. Temporal Lobe - The temporal lobes are situated in parallel with the ears, they serve the ears by interpreting audio signals received from the auditory canal
  4. Occipital Lobe - This is the smallest of the four lobe components of the cerebrum, and is responsible in interpreting nerve signals from the eye at the back of the brain
The above components of the brain work in tandem in a healthy brain. However, in some cases the brain can be injured in some way, causing brain damage. The next page looks at how brain damage can affect the way we operate.



Myelin Sheath

Myelin is a substance that forms the myelin sheath associated with nerve cells. This sheath is a layer of phospholipids that increases the conductivity of the electrical messages that are sent through the cell. Diseases such as multiple sclerosis are a result in a lack of this myelin sheath, with the resultant effect being that the conductivity of signals is much slower severely decreasing the effectiveness of the nervous system in sufferers.
In total, there are 43 main nerves that branch of the CNS to the peripheral nervous system (the peripheral system is the nervous system outside the CNS. These are the efferent neurones that carry signals away from the CNS to the peripheral system.
Somatic Nervous System

These efferent fibres are divided into the somatic nervous system and the autonomic nervous system. The somatic fibres are responsible for the voluntary movement of our body, i.e. movement that you consciously thought about doing.
The Autonomic Nervous System

The autonomic nervous system incorporates all the impulses that are done involuntarily, and are usually associated with essential functions such as breathing, heartbeat etc. However this type of system can further be broken down into the sympathetic and parasympathetic systems which keep one another in check in a form of negative feedback such as the release of insulin and glucagon in sugar control of the blood.

Causes of Brain Damage

The brain is a highly specialised tissue, far more complex than today's 21st century supercomputers. Due to this magnificent complexity, even the slightest damage can have extreme consequences
The brain can be damaged in a variety of ways, and depending on the areas damaged and the severity of the damage, it can prove relatively harmless to fatal. Some causes of brain damage are below
  • Genetics - A dysfunctional hereditary gene could have been passed on to the offspring which prevented the full development of a healthy brain
  • Blow - A sufficient blow to the head can supercede the skulls defences (particularly at the temple) and can therefore allow structural damage to occur.
  • Lack of Blood - Lack of blood to the brain can cause severe problems for the cells associated with the brain. A human can survive for four minutes without oxygen before the brain damage becomes so severe there is no realistic chance of survival. A stroke is an event where there is a blood shortage to the brain, which is caused by a blood clot
  • Tumours - Cancer has been a major non-infectious disease more recognised over the last decade, and more cases of brain tumours are detected nowadays due to more sophisticated techniques. The continued growth of these cancerous cells puts pressure on the brain, which can cause a blood clot or directly cause brain damage due to the pressure of the tumour pressing against it.
Types of Brain Damage
  • Aphasia - A type of brain damage affecting communication capabilities in the organism. This can range from the inability to construct a sentence either in voice or on paper, to the inability to recognise speech itself. This sort of damage focuses on the frontal lobe area of the brain
  • Visual Neglect - This is where the information collated on one half of the brain is rejected and therefore the sufferer can only operate with one eye, because the part of the brain receiving visual information from the other eye is not functioning properly. In some cases, sufferers may only be able to paint half a painting or eat one half of a plate of food as they are unaware of the information about the other half of the environment.
  • Amnesia - Or retrograde amnesia, this sort of damage affects the memory, caused by degeneration / damage in the frontal lobe. Sufferers have memory blanks when relating to past experiences in their life
  • Agnosia - This unusual sort of brain damage is where sufferers still have the complete ability to see around them (unlike visual neglect), though cannot relate their surroundings in a quantifiable way, i.e. they fail to recognise a familiar surrounding, person or object, due to a malfunction in recalling past events involving the surrounding, person or object .
The Human Body: Nervous System


The Human Nervous System
- Human Neurology

The nervous system is essentially a biological information highway, and is responsible for controlling all the biological processes and movement in the body, and can also receive information and interpret it via electrical signals which are used in this nervous system
It consists of the Central Nervous System (CNS), essentially the processing area and the Peripheral Nervous System which detects and sends electrical impulses that are used in the nervous system
The Central Nervous System (CNS)

The Central Nervous System is effectively the centre of the nervous system, the part of it that processes the information received from the peripheral nervous system. The CNS consists of the brain and spinal cord. It is responsible for receiving and interpreting signals from the peripheral nervous system and also sends out signals to it, either consciously or unconsciously. This information highway called the nervous system consists of many nerve cells, also known as neurones, as seen below.
The Nerve Cell


Each neurone consists of a nucleus situated in the cell body, where outgrowths called processes originate from. The main one of these processes is the axon, which is responsible for carrying outgoing messages from the cell. This axon can originate from the CNS and extend all the way to the body's extremities, effectively providing a highway for messages to go to and from the CNS to these body extremities.
Dendrites are smaller secondary processes that grow from the cell body and axon. On the end of these dendrites lie the axon terminals, which 'plug' into a cell where the electrical signal from a nerve cell to the target cell can be made. This 'plug' (the axon terminal) connects into a receptor on the target cell and can transmit information between cells.




neuron
also known as a neurone or nerve cell) is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous system, which includes the brain, spinal cord, and peripheral ganglia. A number of specialized types of neurons exist: sensory neurons respond to touch, sound, light and numerous other stimuli affecting cells of the sensory organs that then send signals to the spinal cord and brain. Motor neurons receive signals from the brain and spinal cord, cause muscle contractions, and affect glands. Interneurons connect neurons to other neurons within the same region of the brain or spinal cord.
A typical neuron possesses a cell body (often called the soma), dendrites, and an axon. Dendrites are thin structures that arise from the cell body, often extending for hundreds of micrometres and branching multiple times, giving rise to a complex "dendritic tree". An axon is a special cellular extension that arises from the cell body at a site called the axon hillock and travels for a distance, as far as 1 m in humans or even more in other species. The cell body of a neuron frequently gives rise to multiple dendrites, but never to more than one axon, although the axon may branch hundreds of times before it terminates. At the majority of synapses, signals are sent from the axon of one neuron to a dendrite of another. There are, however, many exceptions to these rules: neurons that lack dendrites, neurons that have no axon, synapses that connect an axon to another axon or a dendrite to another dendrite, etc.
All neurons are electrically excitable, maintaining voltage gradients across their membranes by means of metabolically driven ion pumps, which combine with ion channels embedded in the membrane to generate intracellular-versus-extracellular concentration differences of ions such as sodium, potassium, chloride, and calcium. Changes in the cross-membrane voltage can alter the function of voltage-dependent ion channels. If the voltage changes by a large enough amount, an all-or-none electrochemical pulse called an action potential is generated, which travels rapidly along the cell's axon, and activates synaptic connections with other cells when it arrives.


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How the Body Works : The Regions of the Brain

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The Reflex Arc[back to top]

The three types of neurones are arranged in circuits and networks, the simplest of which is the reflex arc.
In a simple reflex arc, such as the knee jerk, a stimulus is detected by a receptor cell, which synapses with a sensory neurone. The sensory neurone carries the impulse from site of the stimulus to the central nervous system (the brain or spinal cord), where it synapses with an interneurone. The interneurone synapses with a motor neurone, which carries the nerve impulse out to an effector, such as a muscle, which responds by contracting.
Reflex arc can also be represented by a simple flow diagram:
Organisation Of The Human Nervous System
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The human nervous system is far more complex than a simple reflex arc, although the same stages still apply. The organisation of the human nervous system is shown in this diagram:
It is easy to forget that much of the human nervous system is concerned with routine, involuntary jobs, such as homeostasis, digestion, posture, breathing, etc. This is the job of the autonomic nervous system, and its motor functions are split into two divisions, with anatomically distinct neurones. Most body organs are innervated by two separate sets of motor neurones; one from the sympathetic system and one from the parasympathetic system. These neurones have opposite (or antagonistic) effects. In general the sympathetic system stimulates the “fight or flight” responses to threatening situations, while the parasympathetic system relaxes the body. The details are listed in this table:
OrganSympathetic SystemParasympathetic System
Eye
Tear glands
Salivary glands
Lungs
Heart
Gut
Liver
Bladder
Dilates pupil
No effect
Inhibits saliva production
Dilates bronchi
Speeds up heart rate
Inhibits peristalsis
Stimulates glucose production
Inhibits urination
Constricts pupil
Stimulates tear secretion
Stimulates saliva production
Constricts bronchi
Slows down heart rate
Stimulates peristalsis
Stimulates bile production
Stimulates urination


Spinal Cord Anatomy and Innervation

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The human spinal cord consists of nerves that connect the brain to nerves in the body. It is a superhighway for messages between the brain and the rest of the body. The spinal cord is surrounded for most of its length by the bones (vertebrae) that form the spine.
* * *
The human spinal cord, part of the central nervous system, is generally around 17 inches long, and extends from the brain to the lower back.
Your spine is protected by the vertebral column (also known as the spinal column or backbone).
The human spinal column is made up of 33 bones - 7 vertebrae in the cervical region, 12 in the thoracic region, 5 in the lumbar region, 5 in the sacral region and 4 in the coccygeal region.The outer layer of the human spinal cord consists of white matter, i.e., myelin-sheathed nerve fibers.

These are bundled into specialized tracts that conduct impulses triggered by pressure, pain, heat, and other sensory stimuli or conduct motor impulses activating muscles and glands. The inner layer, or gray matter, is mainly composed of nerve cell bodies. Within the gray matter, running the length of the cord and extending into the brain, lies the central canal through which the cerebrospinal fluid circulates.A spinal cord injury (SCI) can occur anywhere along the spinal cord. It is the result of damage to cells in the spinal cord and causes a loss of communication between the brain and the parts of the body below the injury.Complete and Incomplete Spinal cord injuries (SCI)

Complete Spinal Cord Injury: Generally persons with a complete spinal cord injury suffer a loss of sensation and motor ability caused by bruising, loss of blood to the spinal cord, or pressure on the spinal cord; cut and severed spinal cords are rare. Generally, complete spinal cord injuries result in total loss of sensation and movement below the site of the injury.
Incomplete Spinal Cord Injury: An incomplete spinal cord injury does not result in complete loss of movement and sensation below the injury site. These injuries are usually classified as:
a) Anterior cord syndrome: Damage to the front of the spinal cord, affecting pain, temperature and touch sensation, but leaving some pressure and joint sensation. Often motor function is unaffected.
b) Central Cord Syndrome: Form of incomplete spinal cord injury in which some of the signals from the brain to the body are not received, characterized by impairment in the arms and hands and, to a lesser extent, in the legs. Sensory loss below the site of the spinal injury and loss of bladder control may also occur. This syndrome, usually the result of trauma, is associated with damage to the large nerve fibers that carry information directly from the cerebral cortex to the spinal cord. These nerves are particularly important for hand and arm function. Symptoms may include paralysis and/or loss of fine control of movements in the arms and hands, with relatively less impairment of leg movements. The brain's ability to send and receive signals to and from parts of the body below the site of trauma is affected but not entirely blocked.
c) Brown-Sequard syndrome: Injury to the lateral half of the spinal cord. The condition is characterized by the following clinical features found below the level of the lesion - contralateral hemisensory anesthesia to pain and temperature, ipsilateral loss of propioception, and ipsilateral motor paralysis. Tactile sensation is generally spared.
d) Spinal contusions: The most common type of spinal cord injury. The spinal cord is bruised but not severed. Inflammation and bleeding occurs near the injury as a result of the injury.
e) Injuries to individual nerve cells: Loss of sensory and motor functions in the area of the body to which the injured nerve root corresponds.

The spine is surrounded by many muscles and ligaments to give it strengthCervical (neck) injuries (C1 - C8)

C1 or atlas: The Atlas is the topmost vertebra, and along with C2, forms the joint connecting the skull and spine. Its chief peculiarity is that it has no body, and this is due to the fact that the body of the atlas has fused with that of the next vertebra.
C2 or axis: Forms the pivot upon which C1 rotates. The most distinctive characteristic of this bone is the strong odontoid process (dens) which rises perpendicularly from the upper surface of the body. The body is deeper in front than behind, and prolonged downward anteriorly so as to overlap the upper and front part of the third vertebra.
Injuries to C-1 and C-2 can result in a loss of many involuntary functions including the ability to breathe, necessitating breathing aids such as ventilators or diaphragmatic pacemakers.
C4 (cervical vertebra): The fourth cervical (neck) vertebra from the top. Injuries above the C-4 level may require a ventilator for the person to breathe properly.
C5 5th cervical vertabrae down from the base of the skull, found in the neck. C5 injuries often maintain shoulder and biceps control, but have no control at the wrist or hand.
C6 (cervical vertebra): The sixth cervical (neck) vertebra from the top. The next-to-last of the seven cervical vertebrae. An injury to the spinal cord between C6 and C7 vertebrae is called a C6-7 injury. These injuries generally allow wrist control, but no hand function.
C7 or vertebra prominens: The most distinctive characteristic of this vertebra is the existence of a long and prominent spinous process, hence the name vertebra prominens. In some subjects, the seventh cervical vertebra is associated with an abnormal pair of ribs, known as cervical ribs. These ribs are usually small, but may occasionally compress blood vessels (such as the subclavian artery) or nerves in the brachial plexus, causing unpleasant symptoms. C-7 and T-1 can straighten their arms but still may have dexterity problems with the hand and fingers. Injuries at the thoracic level and below result in paraplegia, with the hands not affected.
C8 Although there are seven cervical vertebrae (C1-C7), there are eight cervical nerves (C1-C8). All nerves except C8 emerge above their corresponding vertebrae, while the C8 nerve emerges below the C7 vertebra. In other words C8 is a nerve root not a vertebrae.
Thoracic Vertebrae (T1- T12)

Human vertebra pictureThe thoracic vertebrae increase in size from T1 through T12 and represent the 12 thoracic vertebrae. The thoracic vertebrae are situated between the cervical (neck) vertebrae and the lumbar vertebrae. These thoracic vertebrae provide attachment for the ribs and make up part of the back of the thorax or chest.

Damage or SCI's above the T1 vertebra affects the arms and the legs. Injuries below the T1 vertebra affect the legs and trunk below the injury, but usually do not affect the arms and hands. Paralysis of the legs is called paraplegia. Paralysis of the arms and legs is called quadriplegia.
T-1 to T-8 most often control of the hands, but poor trunk control as the result of lack of abdominal muscle control.
T-9 to T-12 allow good trunk control and abdominal muscle control. Lumbar and Sacral injuries yield decreasing control of the hip flexors and legs. Individuals with SCI also experience other changes. For example, they may experience dysfunction of the bowel and bladder.
Lumbar Vertebrae (L1- L5)
The lumbar vertebrae graduate in size from L1 through L5. These vertebrae bear much of the body's weight and related biomechanical stress.
The lumbar vertebrae are the largest segments of the movable part of the vertebral column, and are characterized by the absence of the foramen transversarium within the transverse process, and by the absence of facets on the sides of the body.
Some individuals have four lumbar vertebrae, while others have six. Lumbar disorders that normally affect L5 will affect L4 or L6 in these individuals.
L1 The first lumbar vertebra is at the level as the ninth rib. This level is also called the important transpyloric plane, since the pylorus of the stomach is at this level.
L3 - L5 A lot of motion in the back is divided between these five motion segments with segments L3 - L4 and L4 - L5 taking most of the stress. L3 - L4 and L4 - L5 segments are most likely to breakdown from wear and tear causing such conditions as Osteoarthritis.
L4 - L5 and L5 - S1 are the most likely to herniate (herniated disc, bulging disk, compressed disk, herniated intervertebral disk, herniated nucleus pulposus, prolapsed disk, ruptured disk, slipped disk). The effects of this can cause pain and numbness that can radiate through the leg and extend down to the feet (sciatica).
L5 The fifth lumbar vertebra is the most common site of spondylolysis and spondylolisthesis.
Sacral Spine (s1 - S5)
The Sacrum is located behind the pelvis. Five bones (abbreviated S1 through S5) fused into a triangular shape, form the sacrum. The sacrum fits between the two hipbones connecting the spine to the pelvis located just below the lumbar vertebrae.
It consists of four or five sacral vertebrae in a child, which become fused into a single bone after age 26. The sacrum forms the back wall of the pelvic girdle and moves with it.
The first three vertebrae in the sacral have transverse processes which come together to form wide lateral wings called alae. These alae articulate with the blades of the pelvis (ilium).
As part of the pelvic girdle, the sacrum forms the back wall of the pelvis and also forms joints at the hip bone called the sacroiliac joints. The sacrum contains a series of four openings on each side through which the sacral nerves and blood vessels run. The sacral canal runs down the center of the sacrum and represents the end of the vertebral canal.
Back pain or leg pain (sciatica) can typically arise due to injury where the lumbar spine and sacral region connect (at L5 - S1) because this section of the spine is subjected to a large amount of stress and twisting.
People with rheumatoid arthritis or osteoporosis are inclined to develop stress fractures and fatigue fractures in the sacrum.
The sacrum is shaped diferent in males and females. In females the sacrum is shorter and wider than in males.
The bottom of the spinal column is called the coccyx or tailbone. It consists of 3-5 bones that are fused together in an adult. Many muscles connect to the coccyx.
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Default Scientists Discovered Genetic Factors in Frogs that Make it Immune to the Fungal Dise

Scientists Discovered Genetic Factors in Frogs that Make it Immune to the Fungal Disease

Scientists discovered genetic factors that make frog immune to the fungal disease chytridiomycosis. This could improve captive breeding schemes. Chytridiomycosis is slowly spreading across the world and has already sent a number of species extinct. Chytridiomycosis kills by damaging the skin of the living being, which eventually results into cardiac arrest.

Frogs and other amphibians that had no resistance succumbed quickly. For their experiment, Scientists collected lowland leopard frogs (Lithobates yavapaiensis) from five places in Arizona.

In the lab, they infected the animals with the chytrid fungus (Batratochytrium dendrobatidis, or Bd). All the frogs collected from three of the locations died. However, the frogs from the other two locations survived and fought off the infection completely.

The researchers traced the difference back to regions of DNA that form part of the immune system called the Major Histocompatibility Complex (MHC).

It is likely that the two populations whose members survived infection in the lab are the ones that had been most strongly exposed to the fungus in the wild since it was detected in Arizona in the 1970s.

Scientists Discovered Genetic Factors in Frogs that Make it Immune to the Fungal Disease
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ANATOMY OF A FROG


Study Guide





Frogs are amphibians, living both on land and in water. Their anatomy is very unique. Their bodies are similar to humans in that they have skin, bones, muscles, and organs. The body of a frog can be divided into a head, a short neck, and a trunk. The head contains the brain, mouth, eyes, ears and nose. The frog's head movement is limited due to the short, almost rigid neck. The trunk of a frog forms walls for a single body cavity known as the coelom. The coelom holds all of the frog's internal organs. Frogs have the same kinds of organs as humans and the same organ systems. For example, frogs have a long, sticky tongue which they use to capture food. They also have teeth, which unfortunately are very weak and rather useless. Humans have tongues and teeth as well (and a mouth of course).







If you closely examine the head of a frog, you will find the following: eye sockets, eyes, mouth, tongue, vomerine teeth, maxillary teeth, gullet teeth, external nostrils, internal nostrils, the glottis opening, eustachian tube openings, the tympanic membranes and the esophagus. The eyes, the mouth and the nostrils are all examples of a frog's external structures. In addition, a frog's external structures also include the webbed feet and the cloaca opening. The tympanic membranes or eardrums are exposed, but a frog does not have external ears. The internal structures of a frog include: the heart, the lungs, the kidneys, the stomach, the liver, the small intestine, the large intestine, the spleen, the pancreas, the gall bladder, the urinary bladder, the cloaca, the ureter, the oviducts, the testes, the ovaries and fat bodies. Again, the frog has organs that are similar to those of humans. For example, a frog has a brain, kidneys, lungs, eyes, a stomach, intestines and a heart. The one major difference between the anatomy of a frog and that of humans is that the anatomy of a frog is simpler than the anatomy of a man. Frogs don't have ribs or a diaphragm. Humans have both and a diaphragm (thoracic diaphragm) plays an important function in breathing and respiration. Breathing takes oxygen in and carbon dioxide out of the body. Respiration is the process by which our cells are provided with oxygen for metabolism and carbon dioxide, which is produced as a waste gas, is removed.








A frog uses its tongue for grabbing prey. The vomarine and maxillary teeth are used for holding the prey. The internal nostrils are used by the frog for breathing. The tympanic membrane is the eardrum. It is located behind the frog's eyes. The eustachian tubes equalize the pressure in the frog's inner ear. The glottis is a tube, which leads to the lungs, while the esophagus is a tube which leads to the frog's stomach. The stomach helps the frog break down food and the liver also helps with digestion (it makes bile). Bile (also known as gall) is a fluid secreted by hepatocytes from the liver of most vertebrates (humans and frogs are vertebrates). Hepatocytes are cells present in the liver, and they initiate the formation and secretion of bile. In many species, bile is stored in the gall bladder between meals. When eating, the bile is discharged into the duodenum. Bile, therefore helps with digestion. The duodenum, which is the first and shortest part of the small intestine, is responsible for the breakdown of food in the small intestine. Most chemical digestion takes place in the duodenum. The small intestine absorbs nutrients from food. The large intestine absorbs water. It also collects waste. You can also think of the cloaca as storing waste, as this part of the frog collects eggs, sperm, urine and feces. The cloaca (opening) is also where sperm, eggs, urine, and feces exit the frog's body. The spleen stores blood, while the kidneys filter the blood. The ureters carry urine from the kidneys to the bladder. The (urinary) bladder stores urine. The testes make sperm, while the ovaries makes eggs and the eggs travel through the oviducts.











A frog's skin is always moist. It is made up of two layers, an outer epidermis and an inner dermis. In addition to protecting the frog, the skin also helps the frog breathe. A frog will take in oxygen from the water through their skin. The oxygen in the water passes through their skin and goes directly to their blood. Frogs also have a pair of lungs which allows them to breathe when on land. A frog has very few bones. They make up the skeleton of the frog. The skull (head bone) is large and flat. The legs are long for jumping. In addition to being specialized for jumping, the bones in their upper and hind legs are also specialized for leaping. The muscles move the skeleton of the frog. The muscles help the frog jump and swim.Frogs have other systems similar to humans that are a part of their bodies. For example, a



frog has a nervous system (all of the nerves and the spine), a circulatory system (the heart and blood going through the body) and a digestive system (the food going through the mouth to the intestines). The heart (which is part of the circulatory system) is three-chambered. There are two atria and one ventricle. There is a valve within the frog's heart known as the spiral valve. It directs the flow of blood to prevent oxygenated and de-oxygenated blood from mixing. A frog's sense of hearing (which is part of the nervous system) is highly developed. Frogs can detect high-pitched sounds with their ears. In addition to breathing oxygen through their skin when in water, frogs can also detect low-pitched sounds through their skin. Another highly developed system is a frog's sense of sight and smell (which again are both part of the nervous system). Frogs detect predators and prey using their large eyes. Their eyes however have poorly developed eyelids, which do not close. In order to close its eye, a frog has to draw the eye into its socket. There is a third eyelid, known as the nictitating membrane. It can be drawn over the pulled in eye (eyeball). Frogs also use their sense of smell to detect chemical signals. These signals help them to identify potential food
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short answers about reproductive systems




Question: What are the main parts of the human male reproductive system?



Answer: The human male reproductive system comprises of the following:
1) a pair of testes, organs that produce the male gametes, sperms
2) a network of tubules and tubes for passage of the sperms called the duct system
3) associated glands
4) a mating organ called the penis




Question: Name the constituents of the duct system of the male reproductive part.


Answer: Vasa efferentia, epididymis, vas deferens, ejaculatory tube and the urethra are the constituents of the duct system of the male reproductive system.




Question: Which are the various glands associated with the male reproductive system?


Answer: The various glands associated with the male reproductive system are seminal vesicles, prostate glands and Cowper's glands.




Question: Write short notes on seminal vesicles.


Answer: Seminal vesicles A pair of seminal vesicles are glands that are present behind the urinary bladder. Each sperm duct has the seminal vesicle of its side secreting a fluid into the common ejaculatory duct. This fluid along with the sperms is called the semen, a milky fluid.


Question: What are the functions of prostate and Cowper's glands?

Answer: Prostate gland makes the semen alkaline with its secretions and Cowper's glands secretes lubricating fluid into the urethral tube.


Question: What are the different parts of the female reproductive system?



Answer: The female reproductive system consists of a pair of ovaries, a pair of oviducts, uterus, vagina and vulva.




Question: What are the functions of the female reproductive system?
Answer: The main functions of the female reproductive system are:
1) to produce eggs
2) receive the sperms
3) provide the site for fertilization
4) implantation of the growing embryo and development of the foetus
5) production of hormones that control the various stages of ovulation and maintenance of pregnancy.
Question 48



Question: What is the function of the fallopian tubes?
Answer: The fallopian tubes transport the eggs from the ovary to the uterus and also serve as the site for fertilization of the egg by sperm.
Question 49



Question: Write short notes on uterus.
Answer: Uterus is a pear-shaped structure, broader on the upper end and narrower on the lower end. The upper end is called the body of the uterus and the lower end is called the cervix. At the upper end, it receives the oviducts of either side whereas the lower end the cervix opens into the vaginal canal that opens to the outside.

The uterine wall has three layers. They are the innermost endometrium made up of several glands and blood vessels, the middle myometrium made of smooth muscles and the outer perimetrium made of connective tissue. The inner surface of the uterus provides a site for the implantation of the embryo. The uterine wall plays an important role during childbirth. Cervix is made of sphincter muscle that controls the opening and closing of the uterus.




Question: What is onset of puberty in females?
]

Answer: At about the age of 10 to 13 years, the ovaries of females are stimulated by the follicle stimulating hormone (FSH) of the pituitary. This is called the onset of puberty and is accompanied by release of hormones oestrogen and progesterone.
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Immune System

http://www.youtube.com/v/oqI4skjr6lQ&feature=relmfu


http://www.youtube.com/v/Z36dUduOk1Y&feature=relmfu



Introduction
The human immune system is a truly amazing constellation of responses to attacks from outside the body. It has many facets, a number of which can change to optimize the response to these unwanted intrusions. The system is remarkably effective, most of the time. This note will give you a brief outline of some of the processes involved.
An antigenis any substance that elicits an immune response, from a virus to a sliver.
The immune system has a series of dual natures, the most important of which is self/non-self recognition. The others are: general/specific, natural/adaptive = innate/acquired, cell-mediated/humoral, active/passive, primary/secondary. Parts of the immune system are antigen-specific(they recognize and act against particular antigens), systemic (not confined to the initial infection site, but work throughout the body), and have memory (recognize and mount an even stronger attack to the same antigen the next time).
Self/non-self recognition is achieved by having every cell display a marker based on the major histocompatibility complex (MHC). Any cell not displaying this marker is treated as non-self and attacked. The process is so effective that undigested proteins are treated as antigens.
Sometimes the process breaks down and the immune system attacks self-cells. This is the case of autoimmune diseases like multiple sclerosis, systemic lupus erythematosus, and some forms of arthritis and diabetes. There are cases where the immune response to innocuous substances is inappropriate. This is the case of allergies and the simple substance that elicits the response is called an allergen.



Fluid Systems of the Body
There are two main fluid systems in the body: blood and lymph. The blood and lymph systems are intertwined throughout the body and they are responsible for transporting the agents of the immune system.



The Blood System
The 5 liters of blood of a 70 kg (154 lb) person constitute about 7% of the body's total weight. The blood flows from the heart into arteries, then to capillaries, and returns to the heart through veins.
Blood is composed of 52–62% liquid plasma and 38–48% cells. The plasma is mostly water (91.5%) and acts as a solvent for transporting other materials (7% protein [consisting of albumins (54%), globulins (38%), fibrinogen (7%), and assorted other stuff (1%)] and 1.5% other stuff). Blood is slightly alkaline (pH = 7.40 ± .05) and a tad heavier than water (density = 1.057 ± .009).
All blood cells are manufactured by stem cells, which live mainly in the bone marrow, via a process called hematopoiesis. The stem cells produce hemocytoblasts that differentiate into the precursors for all the different types of blood cells. Hemocytoblasts mature into three types of blood cells: erythrocytes (red blood cells or RBCs),





leukocytes (white blood cells or WBCs), and thrombocytes (platelets).
The leukocytes are further subdivided into granulocytes (containing large granules in the cytoplasm) and agranulocytes (without granules). The granulocytes consist of neutrophils (55–70%), eosinophils (1–3%), and basophils (0.5–1.0%). The agranulocytes are lymphocytes (consisting of B cells and T cells) and monocytes. Lymphocytes circulate in the blood and lymph systems, and make their home in the lymphoid organs.
All of the major cells in the blood system are illustrated below.


There are 5000–10,000 WBCs per mm3 and they live 5-9 days. About 2,400,000 RBCs are produced each second and each lives for about 120 days (They migrate to the spleen to die. Once there, that organ scavenges usable proteins from their carcasses). A healthy male has about 5 million RBCs per mm3, whereas females have a bit fewer than 5 million.

Normal Adult Blood Cell Counts


Red Blood Cells


5.0*106/mm3



Platelets


2.5*105/mm3



Leukocytes


7.3*103/mm3




Neutrophil



50-70%



Lymphocyte



20-40%



Monocyte



1-6%



Eosinophil



1-3%



Basophil



<1%



The goo on RBCs is responsible for the usual ABO blood grouping, among other things. The grouping is characterized by the presence or absence of A and/or B antigens on the surface of the RBCs. Blood type AB means both antigens are present and type O means both antigens are absent. Type A blood has A antigens and type B blood has B antigens.
Some of the blood, but not red blood cells (RBCs), is pushed through the capillaries into the interstitial fluid.



The Lymph System
Lymph is an alkaline (pH > 7.0) fluid that is usually clear, transparent, and colorless. It flows in the lymphatic vessels and bathes tissues and organs in its protective covering. There are no RBCs in lymph and it has a lower protein content than blood. Like blood, it is slightly heavier than water (density = 1.019 ± .003).
The lymph flows from the interstitial fluid through lymphatic vessels up to either the thoracic duct or right lymph duct, which terminate in the subclavian veins, where lymph is mixed into the blood. (The right lymph duct drains the right sides of the thorax, neck, and head, whereas the thoracic duct drains the rest of the body.) Lymph carries lipids and lipid-soluble vitamins absorbed from the gastrointestinal (GI) tract. Since there is no active pump in the lymph system, there is no back-pressure produced. The lymphatic vessels, like veins, have one-way valves that prevent backflow. Additionally, along these vessels there are small bean-shaped lymph nodes that serve as filters of the lymphatic fluid. It is in the lymph nodes where antigen is usually presented to the immune system.
The human lymphoid system has the following:
· primary organs: bone marrow (in the hollow center of bones) and the thymus gland (located behind the breastbone above the heart), and
· secondary organs at or near possible portals of entry for pathogens: adenoids, tonsils, spleen (located at the upper left of the abdomen), lymph nodes (along the lymphatic vessels with concentrations in the neck, armpits, abdomen, and groin), Peyer's patches (within the intestines), and the appendix.




Innate Immunity
The innate immunity system is what we are born with and it is nonspecific; all antigens are attacked pretty much equally. It is genetically based and we pass it on to our offspring.



Surface Barriers or Mucosal Immunity
  1. The first and, arguably, most important barrier is the skin. The skin cannot be penetrated by most organisms unless it already has an opening, such as a nick, scratch, or cut. Mechanically, pathogens are expelled from the lungs by ciliary action as the tiny hairs move in an upward motion; coughing and sneezing abruptly eject both living and nonliving things from the respiratory system; the flushing action of tears, saliva, and urine also force out pathogens, as does the sloughing off of skin. Sticky mucus in respiratory and gastrointestinal tracts traps many microorganisms. Acid pH (< 7.0) of skin secretions inhibits bacterial growth. Hair follicles secrete sebum that contains lactic acid and fatty acids both of which inhibit the growth of some pathogenic bacteria and fungi. Areas of the skin not covered with hair, such as the palms and soles of the feet, are most susceptible to fungal infections. Think athlete's foot. Saliva, tears, nasal secretions, and perspiration contain lysozyme, an enzyme that destroys Gram positive bacterial cell walls causing cell lysis. Vaginal secretions are also slightly acidic (after the onset of menses). Spermine and zinc in semen destroy some pathogens. Lactoperoxidase is a powerful enzyme found in mother's milk.
  2. The stomach is a formidable obstacle insofar as its mucosa secrete hydrochloric acid (0.9 < pH < 3.0, very acidic) and protein-digesting enzymes that kill many pathogens. The stomach can even destroy drugs and other chemicals.
Normal flora are the microbes, mostly bacteria, that live in and on the body with, usually, no harmful effects to us. We have about 1013 cells in our bodies and 1014 bacteria, most of which live in the large intestine. There are 103–104 microbes per cm2 on the skin (Staphylococcus aureus, Staph. epidermidis, diphtheroids, streptococci, Candida, etc.). Various bacteria live in the nose and mouth. Lactobacilli live in the stomach and small intestine. The upper intestine has about 104 bacteria per gram; the large bowel has 1011 per gram, of which 95–99% are anaerobes (An anaerobe is a microorganism that can live without oxygen, while an aerobe requires oxygen.) or bacteroides. The urogenitary tract is lightly colonized by various bacteria and diphtheroids. After puberty, the vagina is colonized by Lactobacillus aerophilus that ferment glycogen to maintain an acid pH.
Normal flora fill almost all of the available ecological niches in the body and produce bacteriocidins, defensins, cationic proteins, and lactoferrin all of which work to destroy other bacteria that compete for their niche in the body.
The resident bacteria can become problematic when they invade spaces in which they were not meant to be. As examples: (a) staphylococcus living on the skin can gain entry to the body through small cuts/nicks. (b) Some antibiotics, in particular clindamycin, kill some of the bacteria in our intestinal tract. This causes an overgrowth of Clostridium difficile, which results in pseudomembranous colitis, a rather painful condition wherein the inner lining of the intestine cracks and bleeds.
A phagocyte is a cell that attracts (by chemotaxis), adheres to, engulfs, and ingests foreign bodies. Promonocytes are made in the bone marrow, after which they are released into the blood and called circulating monocytes, which eventually mature into macrophages(meaning "big eaters", see below).



Some macrophages are concentrated in the lungs, liver (Kupffer cells), lining of the lymph nodes and spleen, brain microglia, kidney mesoangial cells, synovial A cells, and osteoclasts. They are long-lived, depend on mitochondria for energy, and are best at attacking dead cells and pathogens capable of living within cells. Once a macrophage phagocytizes a cell, it places some of its proteins, called epitopes, on its surface—much like a fighter plane displaying its hits. These surface markers serve as an alarm to other immune cells that then infer the form of the invader. All cells that do this are called antigen presenting cells (APCs).


The non-fixed or wandering macrophages roam the blood vessels and can even leave them to go to an infection site where they destroy dead tissue and pathogens. Emigration by squeezing through the capillary walls to the tissue is called diapedesis or extravasation. The presence of histamines at the infection site attract the cells to their source.


Natural killer cells move in the blood and lymph to lyse (cause to burst) cancer cells and virus-infected body cells. They are large granular lymphocytes that attach to the glycoproteins on the surfaces of infected cells and kill them.
Polymorphonuclear neutrophils, also called polys for short, are phagocytes that have no mitochondria and get their energy from stored glycogen. They are nondividing, short-lived (half-life of 6–8 hours, 1–4 day lifespan), and have a segmented nucleus. [The picture below shows the neutrophil phagocytizing bacteria, in yellow.] They constitute 50–75% of all leukocytes. The neutrophils provide the major defense against pyogenic (pus-forming) bacteria and are the first on the scene to fight infection. They are followed by the wandering macrophages about three to four hours later.



The complement system is a major triggered enzyme plasma system. It coats microbes with molecules that make them more susceptible to engulfment by phagocytes. Vascular permeability mediators increase the permeability of the capillaries to allow more plasma and complement fluid to flow to the site of infection. They also encourage polys to adhere to the walls of capillaries (margination) from which they can squeeze through in a matter of minutes to arrive at a damaged area. Once phagocytes do their job, they die and their "corpses," pockets of damaged tissue, and fluid form pus.


Eosinophils are attracted to cells coated with complement C3B, where they release major basic protein (MBP), cationic protein, perforins, and oxygen metabolites, all of which work together to burn holes in cells and helminths (worms). About 13% of the WBCs are eosinophils. Their lifespan is about 8–12 days. Neutrophils, eosinophils, and macrophages are all phagocytes.
Dendritic cells are covered with a maze of membranous processes that look like nerve cell dendrites. Most of them are highly efficient antigen presenting cells. There are four basic types: Langerhans cells, interstitial dendritic cells, interdigitating dendritic cells, and circulating dendritic cells. Our major concern will be Langerhans cells, which are found in the epidermis and mucous membranes, especially in the anal, vaginal, and oral cavities. These cells make a point of attracting antigen and efficiently presenting it to T helper cells for their activation. [This accounts, in part, for the transmission of HIV via sexual contact.]


Each of the cells in the innate immune system bind to antigen using pattern-recognition receptors. These receptors are encoded in the germ line of each person. This immunity is passed from generation to generation. Over the course of human development these receptors for pathogen-associated molecular patterns have evolved via natural selection to be specific to certain characteristics of broad classes of infectious organisms. There are several hundred of these receptors and they recognize patterns of bacterial lipopolysaccharide, peptidoglycan, bacterial DNA, dsRNA, and other substances. Clearly, they are set to target both Gram-negative and Gram-positive bacteria.


Adaptive or Acquired Immunity
Lymphocytes come in two major types: B cells and T cells. The peripheral blood contains 20–50% of circulating lymphocytes; the rest move in the lymph system. Roughly 80% of them are T cells, 15% B cells and remainder are null or undifferentiated cells. Lymphocytes constitute 20–40% of the body's WBCs. Their total mass is about the same as that of the brain or liver. (Heavy stuff!)
B cells are produced in the stem cells of the bone marrow; they produce antibody and oversee humoral immunity. T cells are nonantibody-producing lymphocytes which are also produced in the bone marrow but sensitized in the thymus and constitute the basis of cell-mediated immunity. The production of these cells is diagrammed below.
Parts of the immune system are changeable and can adapt to better attack the invading antigen. There are two fundamental adaptive mechanisms: cell-mediated immunity and humoral immunity.



Cell-mediated immunity
Macrophages engulf antigens, process them internally, then display parts of them on their surface together with some of their own proteins. This sensitizes the T cells to recognize these antigens. All cells are coated with various substances. CD stands for cluster of differentiation and there are more than one hundred and sixty clusters, each of which is a different chemical molecule that coats the surface. CD8+ is read "CD8 positive." Every T and B cell has about 105 = 100,000molecules on its surface. B cells are coated with CD21, CD35, CD40, and CD45 in addition to other non-CD molecules. T cells have CD2, CD3, CD4, CD28, CD45R, and other non-CD molecules on their surfaces.
The large number of molecules on the surfaces of lymphocytes allows huge variability in the forms of the receptors. They are produced with random configurations on their surfaces. There are some 1018 different structurally different receptors. Essentially, an antigen may find a near-perfect fit with a very small number of lymphocytes, perhaps as few as one.
T cells are primed in the thymus, where they undergo two selection processes. The first positive selection process weeds out only those T cells with the correct set of receptors that can recognize the MHC molecules responsible for self-recognition. Then a negative selection process begins whereby T cells that can recognize MHC molecules complexed with foreign peptides are allowed to pass out of the thymus.
Cytotoxic or killer T cells (CD8+) do their work by releasing lymphotoxins, which cause cell lysis. Helper T cells (CD4+) serve as managers, directing the immune response. They secrete chemicals called lymphokines that stimulate cytotoxic T cells and B cells to grow and divide, attract neutrophils, and enhance the ability of macrophages to engulf and destroy microbes. Suppressor T cells inhibit the production of cytotoxic T cells once they are unneeded, lest they cause more damage than necessary. Memory T cells are programmed to recognize and respond to a pathogen once it has invaded and been repelled.


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Humoral immunity
An immunocompetent but as yet immature B-lymphocyte is stimulated to maturity when an antigen binds to its surface receptors and there is a T helper cell nearby (to release a cytokine). This sensitizes or primes the B cell and it undergoes clonal selection, which means it reproduces asexually by mitosis. Most of the family of clones become plasma cells. These cells, after an initial lag, produce highly specific antibodies at a rate of as many as 2000 molecules per second for four to five days. The other B cells become long-lived memory cells.
Antibodies, also called immunoglobulins or Igs [with molecular weights of 150–900 Md], constitute the gamma globulin part of the blood proteins. They are soluble proteins secreted by the plasma offspring (clones) of primed B cells. The antibodies inactivate antigens by, (a) complement fixation (proteins attach to antigen surface and cause holes to form, i.e., cell lysis), (b) neutralization (binding to specific sites to prevent attachment—this is the same as taking their parking space), (c) agglutination (clumping), (d) precipitation (forcing insolubility and settling out of solution), and other more arcane methods.
Constituents of gamma globulin are: IgG-76%, IgA-15%, IgM-8%, IgD-1%, and IgE-0.002% (responsible for autoimmune responses, such as allergies and diseases like arthritis, multiple sclerosis, and systemic lupus erythematosus). IgG is the only antibody that can cross the placental barrier to the fetus and it is responsible for the 3 to 6 month immune protection of newborns that is conferred by the mother.


I


gM is the dominant antibody produced in primary immune responses, while IgG dominates in secondary immune responses. IgM is physically much larger than the
other immunoglobulins.


Notice the many degrees of flexibility of the antibody molecule. This freedom of movement allows it to more easily conform to the nooks and crannies on an antigen. The upper part or Fab (antigen binding) portion of the antibody molecule (physically and not necessarily chemically) attaches to specific proteins [called epitopes] on the antigen. Thus antibody recognizes the epitope and not the entire antigen. The Fc region is crystallizable and is responsible for effector functions, i.e., the end to which immune cells can attach.
Lest you think that these are the only forms of antibody produced, you should realize that the B cells can produce as many as 1014 conformationally different forms.
The process by which T cells and B cells interact with antigens is summarized in the diagram below.



I


n the ABO blood typing system, when an A antigen is present (in a person of blood type A), the body produces an anti-B antibody, and similarly for a B antigen. The blood of someone of type AB, has both antigens, hence has neither antibody. Thus that person can be transfused with any type of blood, since there is no antibody to attack foreign blood antigens. A person of blood type O has neither antigen but both antibodies and cannot receive AB, A, or B type blood, but they can donate blood for use by anybody. If someone with blood type A received blood of type B, the body's anti-B antibodies would attack the new blood cells and death would be imminent.
All of these of these mechanisms hinge on the attachment of antigen and cell receptors. Since there are many, many receptor shapes available, WBCs seek to optimize the degree of confluence between the two receptors. The number of these "best fit" receptors may be quite small, even as few as a single cell. This attests to the specificity of the interaction. Nevertheless, cells can bind to receptors whose fit is less than optimal when required. This is referred to as cross-reactivity. Cross-reactivity has its limits. There are many receptors to which virions cannot possibly bind. Very few viruses can bind to skin cells. The design of immunizing vaccines hinges on the specificity and cross-reactivity of these bonds. The more specific the bond, the more effective and long-lived the vaccine. The smallpox vaccine, which is made from the vaccinia virus that causes cowpox, is a very good match for the smallpox receptors. Hence, that vaccine is 100% effective and provides immunity for about 20 years. Vaccines for cholera have a relatively poor fit so they do not protect against all forms of the disease and protect for less than a year.
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