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Old Thursday, October 27, 2005
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Default Bio part-Everyday Science

The cell,
Chromosomes,
Genes,
Nucleic acids.

The building blocks—Proteins.
Harmones and other nutrients.
Concept of balanced diet.
Metabolism.

a brief survey of plant and animal kingdom to pinpoint similarities and diversities in nature.


The Human body—a brief account of human Physiology ,Human behaviour.

(digestive system, skeletal system,respiratory system, excretory system,circulatory sysyetm,nervous system, human teeth, kidneys,heart,eye,
skin,ear, liver,pancreas)
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THE CELL:

The basic structural and functional unit of all organisms is called cell.
The cell is one of the most basic units of life. There are millions of different types of cells. There are cells that are organisms onto themselves, such as microscopic amoeba and bacteria cells. And there are cells that only function when part of a larger organism, such as the cells that make up our body. The cell is the smallest unit of life in our bodies. In the body, there are brain cells, skin cells, liver cells, stomach cells, and etc. All of these cells have unique functions and features. And all have some recognizable similarities.

SIMILARITIES:
All cells have a 'skin', called the plasma membrane, protecting it from the outside environment. The cell membrane regulates the movement of water, nutrients and wastes into and out of the cell. Inside of the cell membrane are the working parts of the cell. At the center of the cell is the cell nucleus. The cell nucleus contains the cell's DNA, the genetic code that coordinates protein synthesis. In addition to the nucleus, there are many organelles inside of the cell - small structures that help carry out the day-to-day operations of the cell. One important cellular organelle is the ribosome. Ribosomes participate in protein synthesis. The transcription phase of protein synthesis takes places in the cell nucleus. After this step is complete, the RNA leaves the nucleus and travels to the cell's ribosomes, where translation occurs. Another important cellular organelle is the mitochondria. Mitochondria are often referred to as the power houses of the cell because many of the reactions that produce energy take place in mitochondria. Also important in the life of a cell are the lysosomes. Lysosomes are organelles that contain enzymes that aid in the digestion of nutrient molecules and other materials.

TYPES:
There are many different types of cells. One major difference in cells occurs between PLANT CELLS and ANIMAL CELLS.
While both plant and animal cells contain the structures discussed above, plant cells have some additional specialized structures. Many animals have skeletons to give their body structure and support. Plants do not have a skeleton for support and yet plants don't just flop over in a big spongy mess. This is because of a unique cellular structure called the CELL WALL.

The cell wall is a rigid structure outside of the cell membrane composed mainly of the polysaccharide cellulose. The cell wall gives the plant cell a defined shape which helps support individual parts of plants. In addition to the cell wall, plant cells contain an organelle called the CHLOROPLAST. The chloroplast allow plants to harvest energy from sunlight. Specialized pigments in the chloroplast (including the common green pigment chlorophyll) absorb sunlight and use this energy to complete the chemical reaction.


CHROMOSOMES:

A threadlike body in the cell nucleus that carries the genes in a linear order are called chromosomes.
Chromosomes are composed of depxyribonucleic acids (DNA) and are blue prints in the cell structure in the form of genetic code.
Chromosomes appear thickened rod when a cell is dividing but in the phase between the divisions the DNA is distributed throughout teh nucleoplasm and only fine threads of chromatin can be seen.These threads thicken again prior to cell division.

GENES:

The fundamental unit of heredity formed as a sequence of basis in a DNA chain .
Genes determine all the functional and structural chracters of an individual like eye colour,intelligence ,temperament etc.
The genes transfer from one living organism to another through the process of reproduction.Genes are very stable which gurantee the similarity of the offsprings generation after generation.The accurate structure of the proteins and enzymes in the body is also determined by genes.

NUCLEIC ACIDS:

By definition, nucleic acids are biomolecules that store genetic information in cells or that transfer this information from old cells to new cells. There are two groups of nucleic acids: DeoxyRiboNucleic Acid and RiboNucleic Acid, DNA and RNA, respectively. DNA codes for the functioning of the cell and RNA is the "worker" that helps get the DNA message out to the rest of the cell. DNA is located mainly in the nucleus of the cell .RNA is primarily in the cytosol of the cell. DNA is double stranded and RNA is single stranded. BOTH are "codes" for the cell and , hence, the body's activities at the cellular level.
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THE BUILDING BLOCKS PROTEINS:

Amino acids are the "building blocks", as they are popularly called, that make up proteins. Protein could not exist without the proper combination of amino acids. To understand how vital amino acids are, it is essential to understand how important proteins are to life. It is protein that provides the structure for all living things. Each organism from the largest animal to the tiniest microbe is composed of protein. It is protein that participates in the vital chemical processes that enable us to sustain life.

In the human body, protein substances make up the muscles, ligaments, tendons, organs, glands, nails, hair, and body fluids (except for bile and urine). Proteins are essential for the growth of bones. Enzymes, hormones, and genes are also comprised of various proteins. Next to water, protein makes up the greatest portion of our body weight. Consequently, it is easy to see why meeting our body's protein requirements is so important to good health.

In order for a protein to be complete, it must contain all of its particular amino acids. Amino acids may be linked together almost indefinitely to form more than 50,000 different proteins and 20,000 known enzymes. Because each type of protein is composed of different amino acids, each being tailored for a specific need, they are not interchangeable. Amino acids contain about 16 percent nitrogen. This distinguishes them from carbohydrates and fats in the body.

The central nervous system cannot function without amino acids, which act as neurotransmitters or as precursers to the neurotransmitters. They are necessary in order for the brain to receive and send massages. Unless all of the amino acids are present together, almost anything can go wrong with the transmission of the message.

In addition to their other vital functions, amino acids enable vitamins and minerals to perform their jobs properly. Even if the vitamins and minerals are absorbed and assimilated rapidly, they will not be effective unless amino acids are present.


CONCEPT OF BALANCED DIET:

A diet that contains adequate amounts of all the necessary nutrients required for healthy growth and activity comes under the category of balanced diet.

A balanced diet is essential for a healthy person.. Deficiencies in particular elements can lead to a decline in health, and exhibit symptoms that are not desirable at all. The following information looks at some of these deficiencies and why they happen

VITAMIN A
Vitamin A is essential for night vision and improves effectiveness of the immune system. It can be found in many dairy products, and especially in carrots.

VITAMIN B12:
This vitamin is essential in the formation of red blood cells and lack of this may cause anaemia.

VITAMIN C
Scurvy is caused by a lack of vitamin C in the diet. Vitamin C is essential in the formation of red blood cells, antibodies and a healthy circulatory system. Symptoms of scurvy include bleeding gums and dizziness caused by the deficient blood supply.

VITAMIN D
Essential part of the diet required in the absorption of minerals in food, where a lack of vitamin D in the diet leads to a condition called rickets, where softening of the bones cause them to bend from the lack of calcium. Humans have the ability to synthesise vitamin D from sunlight

VITAMIN E
Important in preventing the oxidation of fatty acids in cells, and is commonly found in cereals and green vegetables

VITAMIN K
Vitamin K is important for the blood clotting process and can be synthesised in the human gut, and found in green vegetables.

Alongside the numerous vitamins that are required as part of a healthy diet, we must also eat food containing a variety of other materials to ensure the day to day running of our body.
These building materials are essential to the daily maintenance and growth of a human body, as each are required in the various biological processes that allow us to survive and fight off infection.

CARBOHYDRATES:

Carbohydrates are a major source of energy, and contain all the necessary building materials to create glucose, a compound that is used in numerous areas across animals and plants. Glucose itself can be found abundantly in sweet fruits, as can fructose, and is the body\'s method of delivering energy to cells across our body

Complex sugars, deemed dissacharides due to their more complex molecular structure, consist of monosaccharides - the fundamental unit of a carbohydrate. Glucose and fructose are examples of monosaccharides.

Important carbohydrates are mentioned below:

* Lactose - A dissacharide carbohydrate found in milk that is a compound of glucose and galactose.

* Maltose - A dissacharide that is found abundantly in germinating grain, as they have a large reserve of starch which can be broken down by the enzyme amylase.

* Sucrose - Found in sugar cane, sucrose can be broken down by the enzyme sucrase into fructose and glucose.

* Glycogen - The body\'s preferred storage form of glucose, which can be broken down by glucagon. More information can be seen in the blood / sugar homeostatis tutorial surrounding the relationship between glycogen and glucose.

* Deoxyribose - A pentose sugar that forms the very genetic material responsible for the creation of all proteins in the body, DNA.

* Ribose - A pentose sugar.
* Cellulose - Is a compound of 4 glucose molecules that are present in the cell walls of plants, and is the most abundant biological material on Earth, due to its tensile nature in acting as a barrier to the outside environment. Cellulose is a type of fibre, which is required in our diet to help digestion.

All in all these malleable compounds that are carbohydrates form an essential part of our diet, with dissacharides and complex carbohydrates acting as building blocks themselves while also being capable of being broken down into a more simple monosaccharide.

FATS:

Fats are an important part of a healthy balanced diet, and also act as a means of insulation in our bodies when it is stored under the skin as stored energy, due to them containing twice as much potential energy as carbon. Fats can be broken down into 5 different categories:

* Triglyceride - These are formed by glycerol and a set of 3 fatty acids, which together form a triglyceride.

* Phospholipid - These consist of a glycerol and phosphate molecule and two fatty acids, which form the cell membrane of cells and responsible for transferring other fats around the body.

* Wax - Consisting of alcohols and fatty acid molecules, these types of fat have waterproof qualities and is rimportant consitutent in many species lives.

* Glycolipid - Any type of fat that also contains a carbohydrate
* Steroid - Cholesterol and cortisone are examples of steroid types of fat.

Fats are an important part of a healthy human diet, due to the compounds they contain as well as their potential energy that is stored in our body's.

MINERALS:


Various mineral in the Earth's crust are required for a healthy balanced diet. These inorganic compounds have various roles in functions of the human body as well as many other species minerals needed by plants,. A summary of the main minerals involved in a balanced diet are outlined below:

* Iron - Iron is an essential consitutent of haemoglobin, the molecule responsible for transporting oxygen in the bloodstream, and is also a part of cytochrome (an area important in cell respiration) thus is an important mineral to have in our diet.

* Calcium - Calcium is required for strong bones and teeth, and also for muscle contraction. Calcium can be found in rich supply in various dairy products such as cheese and milk.

* Sodium - Sodium, known more commonly as salt, is required by nerve cells and is also used to produce hydrochloric acid for digestion, which is capable of killing off infections entering the mouth and nose due to its acidic nature.

* Iodine - Iodine is used to create thyroxine, a hormone that is partly responsible for controlling metabolic rate in the body.

PROTEINS:

It is essential that our diet contains protein to achieve a healthy balanced diet. They are the building blocks of enzymes, hormones and antibodies, all of which are essential in many biological processes.
Proteins consist of amino acids, some of these amino acids are deemed essential amino acids as they cannot be synthesized from other materials and thus must be part of the diet.
Protein is abundant in dairy products, soy beans, meat and cereal; which are all constituents of a healthy balanced diet.


METABOLISM:

Definition of Metabolism

The Scientific Definition All chemical reactions within organisms that enable them to maintain life. It includes all physical and chemical processes within the body related to body functions. Processes of energy generation and use; including nutrition, digestion, absorption, elimination, respiration, circulation, and temperature regulation. The two main categories of metabolism are catabolism and anabolism. Catabolism is any metabolic process whereby cells break down complex substances into simpler, smaller ones, while Anabolism refers to any metabolic process whereby cells build complex substances from simpler, smaller units. Anabolic reactions usually require energy. The energy of catabolic reactions is used to drive anabolic reactions.

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HUMAN PHYSIOLOGY:

--DIGESTIVE SYSTEM:

The digestive system includes the digestive tract and its accessory organs, which process food into molecules that can be absorbed and utilized by the cells of the body. Food is broken down, bit by bit, until the molecules are
small enough to be absorbed and the waste products are eliminated. The digestive tract, also called the alimentary canal or gastrointestinal tract, consists of a long continuous tube that extends from the mouth to the anus. It includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. The tongue and teeth are accessory structures located in the mouth. The salivary glands, liver, gallbladder, and

pancreas are major accessory organs that have a role in digestion. These organs secrete fluids into the digestive tract.

Food undergoes three types of processes in the body:

o Digestion
o Absorption
o Elimination

Digestion and absorption occur in the digestive tract. After the nutrients are absorbed, they are available to all cells in the body and are utilized by the body cells in metabolism.

The digestive system prepares nutrients for utilization by body cells through six activities, or functions.

Ingestion

The first activity of the digestive system is to take in food through the mouth. This process, called ingestion, has to take place before anything else can happen.

Mechanical Digestion


The large pieces of food that are ingested have to be broken into smaller particles that can be acted upon by various enzymes. This is mechanical digestion, which begins in the mouth with chewing or mastication and continues with churning and mixing actions in the stomach.

Chemical Digestion

The complex molecules of carbohydrates, proteins, and fats are transformed by chemical digestion into smaller molecules that can be absorbed and utilized by the cells. Chemical digestion, through a process called hydrolysis, uses water and digestive enzymes to break down the complex molecules. Digestive enzymes speed up the hydrolysis process, which is otherwise very slow.

Movements

After ingestion and mastication, the food particles move from the mouth into the pharynx, then into the esophagus. This movement is deglutition, or swallowing. Mixing movements occur in the stomach as a result of smooth muscle contraction. These repetitive contractions usually occur in small segments of the digestive tract and mix the food particles with enzymes and other fluids. The movements that propel the food particles through the digestive tract are called peristalsis. These are rhythmic waves of contractions that move the food particles through the various regions in which mechanical and chemical digestion takes place.

Absorption

The simple molecules that result from chemical digestion pass through cell membranes of the lining in the small intestine into the blood or lymph capillaries. This process is called absorption.

Elimination
The food molecules that cannot be digested or absorbed need to be eliminated from the body. The removal of indigestible wastes is defecation or elimination.


--SKELETAL SYSTEM:

The Skeletal System serves many important functions; it provides the shape and form for our bodies in addition to supporting, protecting, allowing bodily movement, producing blood for the body, and storing minerals.

Functions

Its 206 bones form a rigid framework to which the softer tissues and organs of the body are attached.

Vital organs are protected by the skeletal system. The brain is protected by the surrounding skull as the heart and lungs are encased by the sternum and rib cage.

Bodily movement is carried out by the interaction of the muscular and skeletal systems. For this reason, they are often grouped together as the musculo-skeletal system. Muscles are connected to bones by tendons. Bones are connected to each other by ligaments. Where bones meet one another is typically called a joint. Muscles which cause movement of a joint are connected to two different bones and contract to pull them together. An example would be the contraction of the biceps and a relaxation of the triceps. This produces a bend at the elbow. The contraction of the triceps and relaxation of the biceps produces the effect of straightening the arm.

Blood cells are produced by the marrow located in some bones. An average of 2.6 million red blood cells are produced each second by the bone marrow to replace those worn out and destroyed by the liver.

Bones serve as a storage area for minerals such as calcium and phosphorus. When an excess is present in the blood, buildup will occur within the bones. When the supply of these minerals within the blood is low, it will be withdrawn from the bones to replenish the supply.

Divisions of the Skeleton

The human skeleton is divided into two distinct parts:

The axial skeleton consists of bones that form the axis of the body and support and protect the organs of the head, neck, and trunk.

The Skull
The Sternum
The Ribs
The Vertebral Column

The appendicular skeleton is composed of bones that anchor the appendages to the axial skeleton.

The Upper Extremities
The Lower Extremities
The Shoulder Girdle
The Pelvic Girdle

Types of Bone

The bones of the body fall into four general categories: long bones, short bones, flat bones, and irregular bones. Long bones are longer than they are wide and work as levers. The bones of the upper and lower extremities (ex. humerus, tibia, femur, ulna, metacarpals, etc.) are of this type. Short bones are short, cube-shaped, and found in the wrists and ankles. Flat bones have broad surfaces for protection of organs and attachment of muscles (ex. ribs, cranial bones, bones of shoulder girdle). Irregular bones are all others that do not fall into the previous categories. They have varied shapes, sizes, and surfaces features and include the bones of the vertebrae and a few in the skull.

Bone Composition

Bones are composed of tissue that may take one of two forms. Compact, or dense bone, and spongy, or cancellous, bone. Most bones contain both types. Compact bone is dense, hard, and forms the protective exterior portion of all bones. Spongy bone is inside the compact bone and is very porous (full of tiny holes). Spongy bone occurs in most bones. The bone tissue is composed of several types of bone cells embedded in a web of inorganic salts (mostly calcium and phosphorus) to give the bone strength, and collagenous fibers and ground substance to give the bone flexibility


--RESPIRATORY SYSTEM:

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.
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EXCRETORY SYSTEM:

The job of the excretory system is to remove various produced by the body. The removal is known as excreation. It is important for the body to remove these various waste, also known as toxic, because toxic build up can lead to servere death.

About sixty percent of our body contains water. A portion of the water is in the tissues and cells. The water contains salt. the salt needs to be kept at the right concentrations. If there is little salt the body feeds it more, if there is too much salt the body gets rid of the salt not needed. This is the task of the two Kidneys.

The liver acts as a filter for the blood. It cleans out toxic waste and acid in the blood.

The skin plays a major role in excreation. It helps the body get rid of excess water, salts, and waste such as urea.

KIDNEYS:
Sixty percent of the human body wight is water, over half of which is inside the body cells and tissues. The rest of the water bathes all the body's cells. This water contains salt. The amount of salt in the watery blood tissue, is very important. Too much or too little salt can lead to servere problems, therefore, the salt in the body's water has to be kept at exactly the same concentrations. That task is the job of the Kidneys.

Each bean shaped kidney is divided into inner and an outer section. The outer section contains millions of chemical filtering factors called nephrons.

Blood is carried by the arteries into the inner section of the kidneys. When the blood gets into the kidneys, the blood travels into smaller and smaller arteries. Eventually, it enters a cluster of capillaries. Various substance in the blood, including water, salts, digested food particles, and other materials are filtered out of the blood here. A nitrogen waste, known as urea, is also filtered out of the blood. Then these substances pass into a cup-shaped part of the nephron called the capsule. The capsule leads to a set of tiny tubes in the nephron.

As the filtered material moves through pipe like passages in the nephron, much of the water and digested food that was filtered out of the blood is reabsorbed into the blood stream. This liquid that is left after reabsorption is called urine.

In the inner section of the kidney the, the urine passes through a cone shaped area into a funnel shaped area. This area is connected to a tube called the ureter, which conducts the urine to the urinary bladder. The urinary bladder is a sac of tissue that has the ability to expand as it fills with urine. Eventually, the urine passes out of the body through a tube at the bottom of the bladder called the urethra.

--CIRCULATORY SYSTEM:

A typical person has around 4-5 litres of blood. The blood is the transport system by which oxygen and nutrients reach the body's cells, and waste materials are carried away. In addition, blood carries substances called hormones, which control body processes, and antibodies to fight invading germs. The heart, a muscular organ, positioned behind the ribcage and between the lungs, is the pump that keeps this transport system moving.
Our heart is about the size of our clenched fist. It has thick muscular walls and is divided into two pumps. Each pump has two chambers. The upper, smaller, thin-walled atrium receives blood coming in from the veins. The blood flows through a one-way valve, which makes sure it always moves in the correct direction, into the larger, lower chamber called the ventricle. It has thick strong walls that contract to squeeze blood through another valve, out into the arteries.

Two-part Circulation

The body's circulation has two parts, with the heart acting as a double pump. Blood from the right side pump is dark red (bluish) and low in oxygen. It travels along pulmonary arteries to the lungs where it receives fresh supplies of oxygen and becomes bright red. It flows along pulmonary veins back to the heart's left side pump.

Blood leaves the left side of the heart and travels through arteries which gradually divide into capillaries. In the capillaries, food and oxygen are released to the body cells, and carbon dioxide and other waste products are returned to the bloodstream.The blood then travels in veins back to the right side of the heart, and the whole process begins again.

--NERVOUS SYSTEM:

Communication is vital to the survival of living organisms.To interact with their environment, multicellular organisms have developed a communication system at the Cellular Level..Specialized Cells (Neurons) allow Messages to be carried from one cell to another so that communication among all body parts is smooth and efficient. In HUMANS, these Cells called NEURONS make up the Nervous System.
The Nervous System CONTROLS and COORDINATES ALL ESSENTIAL FUNCTIONS of the Human Body. The Nervous System RECEIVES and RELAYS information about activities within the body and Monitors and Responds to INTERNAL and EXTERNAL CHANGES.
The Nervous System has FOUR FUNCTIONS that enable the body to respond quickly. The Nervous System:

A. Gathers information both from the outside world and from inside the body. SENSORY FUNCTION

B. Transmits the information to the processing area of the brain and spinal cord.

C. Processes the information to determine the best response. INTEGRATIVE FUNCTION

D. Sends information to muscles, glands, and organs (effectors) so they can respond correctly. Muscular contraction or glandular secretions. MOTOR FUNCTION The Nervous System has TWO Major Divisions.

A. The Central Nervous System (CNS) consist of the Brain and the Spinal Cord. The Spinal Cord carries messages from the body to the Brain, where they are analyzed and interpreted. Response Messages are then passed from the Brain through the Spinal Cord and to the rest of the Body.

B. The Peripheral Nervous System (PNS) consists of the neurons NOT Included in the Brain and Spinal Cord. Some Peripheral Neurons Collect Information from the Body and Transmit it TOWARD the CNS. These are called AFFERENT NEURONS. Other Peripheral Neurons Transmit Information AWAY from the CNS. These are called EFFERENT NEURONS.

The Functioning Nervous System is an enormous network of "one-way streets".

THE NEURON

The CELLS that Carry Messages Throughout the Nervous System are called NEURONS.
The Neuron is the Basic Functional Unit of the Nervous System.
Whatever their specific function, all neurons have the same physical parts: The Cell Body, Dendrites and One Axon.
Messages take the form of ELECTRICAL SIGNALS, and are known as IMPULSES. A Neuron carries impulses in only ONE direction.

Neurons can be classified into THREE TYPES:

A. SENSORY (RECEPTOR) NEURONS (AFFERENT) - Carry impulses from the SENSE ORGANS (RECEPTORS) to the Brain and Spinal Cord. Receptors detect external or internal changes and send the information to the Central Nervous System in the form of impulses by way of the Afferent Neurons.

B. MOTOR NEURONS (EFFERENT) - Carry impulses from the Brain and Spinal Cord to MUSCLES or GLANDS. Muscles and Glands are Two Types of Effectors. In response to impulses, Muscles Contract and Glands Secrete.

C. INTERNEURONS - Connect Sensory and Motor neurons and carry impulses between them. They are found entirely within the Central Nervous System.


--KIDNEYS:

The structure of the Kidney is as follows:

RENAL VEIN:

This has a large diameter and a thin wall. It carries blood away from the kidney and back to the right hand side of the heart. Blood in the kidney has had all its urea removed. Urea is produced by your liver to get rid of excess amino-acids.

Blood in the renal vein also has exactly the right amount of water and salts. This is because the kidney gets rid of excess water and salts. The kidney is controlled by the brain. A hormone in our blood called Anti-Diuretic Hormone (ADH for short) is used to control exactly how much water is excreted.


RENAL ARTERY:

This blood vessel supplies blood to the kidney from the left hand side of the heart. This blood must contain glucose and oxygen because the kidney has to work hard producing urine. Blood in the renal artery must have sufficient pressure or the kidney will not be able to filter the blood.

Blood supplied to the kidney contains a toxic product called urea which must be removed from the blood. It may have too much salt and too much water. The kidney removes these excess materials; that is its function.


PELVIS:
This is the region of the kidney where urine collects. If you are very unlucky, you may develop kidney stones. Sometimes the salts in the urine crystallise in the pelvis and form a solid mass which prevents urine from draining out of the medulla of the kidney.

MEDULLA:

The medulla is the inside part of the kidney. , it is a very dark red colour. This is where the amount of salt and water in urine is controlled.

CORTEX:

The cortex is the outer part of the kidney. This is where blood is filtered. We call this process "ultra-filtration" or "high pressure filtration" because it only works if the blood entering the kidney in the renal artery is at high pressure.

Billions of glomeruli are found in the cortex. A glomerulus is a tiny ball of capillaries. Each glomerulus is surrounded by a "Bowman's Capsule". Glomeruli leak. Things like red blood cells, white blood cells, platelets and fibrinogen stay in the blood vessels. Most of the plasma leaks out into the Bowman's capsules. This is about 160 litres of liquid every 24 hours.

Most of this liquid, which we call "ultra-filtrate" is re-absorbed in the medulla and put back into the blood.

Last edited by Amoeba; Thursday, October 27, 2005 at 05:07 PM.
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HEART:

The heart is one of the most important organs in the entire human body. It is really nothing more than a pump, composed of muscle which pumps blood throughout the body, beating approximately 72 times per minute of our lives. The heart pumps the blood, which carries all the vital materials which help our bodies function and removes the waste products that we do not need. For example, the brain requires oxygen and glucose, which, if not received continuously, will cause it to loose consciousness. Muscles need oxygen, glucose and amino acids, as well as the proper ratio of sodium, calcium and potassium salts in order to contract normally. The glands need sufficient supplies of raw materials from which to manufacture the specific secretions. If the heart ever ceases to pump blood the body begins to shut down and after a very short period of time will die The heart is essentially a muscle(a little larger than the fist). Like any other muscle in the human body, it contracts and expands. Unlike skeletal muscles, however, the heart works on the "All -or-Nothing Law". That is, each time the heart contracts it does so with all its force. In skeletal muscles, the principle of "gradation" is present. The pumping of the heart is called the Cardiac Cycle, which occurs about 72 times per minute. This means that each cycle lasts about eight-tenths of a second. During this cycle the entire heart actually rests for about four-tenths of a second.

STRUCTURE OF HEART:

The walls of the heart are made up of three layers, while the cavity is divided into four parts. There are two upper chambers, called the right and left atria, and two lower chambers, called the right and left ventricles. The Right Atrium, as it is called, receives blood from the upper and lower body through the superior vena cava and the inferior vena cava, respectively, and from the heart muscle itself through the coronary sinus. The right atrium is the larger of the two atria, having very thin walls. The right atrium opens into the right ventricle through the right atrioventicular valve(tricuspid), which only allows the blood to flow from the atria into the ventricle, but not in the reverse direction. The right ventricle pumps the blood to the lungs to be reoxygenated. The left atrium receives blood from the lungs via the four pulmonary veins. It is smaller than the right atrium, but has thicker walls. The valve between the left atrium and the left ventricle, the left atrioventicular valve(bicuspid), is smaller than the tricuspid. It opens into the left ventricle and again is a one way valve. The left ventricle pumps the blood throughout the body. It is the Aorta, the largest artery in the body, which originates from the left ventricle.

FUNCTION OF HEART:

The Heart works as a pump moving blood around in our bodies to nourish every cell. Used blood, that is blood that has already been to the cells and has given up its nutrients to them, is drawn from the body by the right half of the heart, and then sent to the lungs to be reoxygenated. Blood that has been reoxygenated by the lungs is drawn into the left side of the heart and then pumped into the blood stream. It is the atria that draw the blood from the lungs and body, and the ventricles that pump it to the lungs and body. The output of each ventricle per beat is about 70 ml, or about 2 tablespoons. In a trained athlete this amount is about double. With the average heart rate of 72 beats per minute the heart will pump about 5 litres per ventricle, or about 10 litres total per minute. This is called the cardiac output.
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Old Thursday, October 27, 2005
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HUMAN EYE:

Sight is an amazing process made possible by many parts of the eye working together. Light enters the eye and is bent or refracted by the cornea (the window of the eye) through the pupil (the opening in the iris). This light passes through the lens (located behind the pupil). This completes refraction by fine tuning the focused light onto the retina. The retina changes the light (energy) into electric impulses that are carried through the optic nerve to the vision center (occipital cortex) of the brain where the image is interpreted. A summary of the eye's structures and their functions follows:

THE CORNEA:

The cornea is the "window" of the eye (like a watch crystal). It is the clear part of the eye, through which the colored part of the eye is seen. It is the main source of refraction. The cornea is made up of five layers of strong clear tissue. The first layer (epithelium) is made up of rapidly-replaced cells that allow for fast healing (24-48 hrs) of surface injuries. The last four layers add rigidity, provide a barrier against infection and keep the cornea clear.

THE SCLERA:

The outer "white part" of an eye is the sclera. This tough structure is the outer wall of the eye that gives protection to the delicate inner structures.

THE CHOROID:

This structure, between the sclera and the retina, is made up of blood vessels that provide nourishment to the eye.

THE IRIS:

This colored part of the eye has very fine muscles to control the size of the pupil.

THE PUPIL:

The pupil is the black-appearing spot in the center of the iris. Its size changes since its function is to control the amount of light reaching the retina. In the dark, it expands allowing more light to enter. It contracts in bright light to keep out excess light.

THE LENS:

This controls 1/3 of the refraction of light that enters the eye (the cornea, the other 2/3). Located just behind the pupil it allows for changing of focus from distance to near objects by altering its shape. This changing focus is called accommodation. As a person ages the lens hardens and accommodation becomes more difficult.

THE ZONULES:

These "threads" attach the lens to the ciliary muscle and help the lens to change its curvature during accomodation.

THE CILIARY BODY

This contains two main structures. The first is a muscle that contracts and expands to control the curvature of the lens during accommodation. The second is a gland that secretes aqueous humor.


THE AQUEOUS HUMOUR:

This fluid is produced by the ciliary body and circulates in the front part of the eye. It provides nourishment to the front parts of the eye and maintains the eye pressure.


THE RETINA:
This membrane lines the inside wall of the eye. It contains photoreceptors (rods and cones) that change light into sight by converting light into electrical impulses. These electrical messages are sent from the retina to the brain and interpreted as images.

THE MACULA:
This tiny part of the retina is the central focusing spott. It is responsible for seeing details (such as reading) and also for color vision.

THE OPTIC NERVE:

This nerve is the pathway that the light rays take from the retina to the processing center of the brain. It actually is made of about a million tiny nerves bundled together.

THE OPTIC DISC
Tthis area is not sensitive to light and it is often referred to as the "blind spot". It is where the retina meets the optic nerve.

THE VIRTEROUS GEL:
This clear gel fills the central core of the eye. It helps to maintain a spherical shape to the eye.

--THE SKIN:

From the biological point of view, skin can be described as a layered structure,Skin is the largest organ in our body and is essential for survival. Functionally, it maintains a rich and reactive blood supply that provides our body essential nutrients while controlling body temperature. Externally, skin often defines our emotional wellbeing through appearance.

LAYERS OF SKIN:
Our skin is made up of two layers - the epidermis outer layer and the underlying dermis. The epidermis protects against infection and dehydration. The dermis is responsible for the elasticity of our skin, which is vital to unimpaired body movement.

EPIDERMIS:

The epidermis is the outermost layer of skin. While only 0.1 mm thick, it has five layers, but contains no blood vessels. Your body reproduces a new epidermis layer approximately every 30 days. When damaged, the epidermis is capable of healing itself, usually without scarring.

DERMIS:
The dermis is the sensitive, vascular, inner layer of skin below the epidermis. It supports the epidermis with a necessary blood supply through a network of connective tissues. The dermis provides your skin with strength and elasticity. When injured or damaged, the dermis does not regenerate. When completely destroyed, our skin may heal itself by scar formation.

SUBCUTANEOUS TISSUE:
Subcutaneous tissue or fat lies beneath the dermis and protects bone, tendon, muscle and other tissues.

Last edited by Amoeba; Thursday, October 27, 2005 at 05:08 PM.
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--HUMAN EAR:

The ear consists of three basic parts - the outer ear, the middle ear, and the inner ear. Each part of the ear serves a specific purpose in the task of detecting and interpreting sound. The outer ear serves to collect and channel sound to the middle ear. The middle ear serves to transform the energy of a sound wave into the internal vibrations of the bone structure of the middle ear and ultimately transform these vibrations into a compressional wave in the inner ear. The inner ear serves to transform the energy of a compressional wave within the inner ear fluid into nerve impulses which can be transmitted to the brain.

THE OUTER EAR:

The outer ear consists of an ear flap and an approximately 2-cm long ear canal. The ear flap provides protection for the middle ear in order to prevent damage to the eardrum. The outer ear also channels sound waves which reach the ear through the ear canal to the eardrum of the middle ear. Because of the length of the ear canal, it is capable of amplifying sounds with frequencies of approximately 3000 Hz. As sound travels through the outer ear, the sound is still in the form of a pressure wave, with an alternating pattern of high and low pressure regions. It is not until the sound reaches the eardrum at the interface of the outer and the middle ear that the energy of the mechanical wave becomes converted into vibrations of the inner bone structure of the ear.

THE MIDDLE EAR:

The middle ear is an air-filled cavity which consists of an eardrum and three tiny, interconnected bones - the hammer, anvil, and stirrup. The eardrum is a very durable and tightly stretched membrane which vibrates as the incoming pressure waves reach it. As shown at the right, a compression forces the eardrum inward and a rarefaction forces the eardrum outward, thus vibrating the eardrum at the same frequency of the sound wave. Being connected to the hammer, the movements of the eardrum will set the hammer, anvil, and stirrup into motion at the same frequency of the sound wave. The stirrup is connected to the inner ear; and thus the vibrations of the stirrup are transmitted to the fluid of the middle ear and create a compression wave within the fluid. The three tiny bones of the middle ear act as levers to amplify the vibrations of the sound wave. Due to a mechanical advantage, the displacements of the stirrup are greater than that of the hammer. Furthermore, since the pressure wave striking the large area of the eardrum is concentrated into the smaller area of the stirrup, the force of the vibrating stirrup is nearly 15 times larger than that of the eardrum. This feature enhances our ability of hear the faintest of sounds. The middle ear is an air-filled cavity which is connected by the Eustachian tube to the mouth. This connection allows for the equalization of pressure within the air-filled cavities of the ear. When this tube becomes clogged during a cold, the ear cavity is unable to equalize its pressure; this will often lead to earaches and other pains.

THE INNER EAR:

The inner ear consists of a cochlea, the semicircular canals, and the auditory nerve. The cochlea and the semicircular canals are filled with a water-like fluid. The fluid and nerve cells of the semicircular canals provide no roll in the task of hearing; they merely serve as accelerometers for detecting accelerated movements and assisting in the task of maintaining balance. The cochlea is a snail-shaped organ which would stretch to approximately 3 cm. In addition to being filled with fluid, the inner surface of the cochlea is lined with over 20 000 hair-like nerve cells which perform one of the most critical roles in our ability to hear. These nerve cells have a differ in length by minuscule amounts; they also have different degrees of resiliency to the fluid which passes over them. As a compressional wave moves from the interface between the hammer of the middle ear and the oval window of the inner ear through the cochlea, the small hair-like nerve cells will be set in motion. Each hair cell has a natural sensitivity to a particular frequency of vibration. When the frequency of the compressional wave matches the natural frequency of the nerve cell, that nerve cell will resonate with a larger amplitude of vibration. This increased vibrational amplitude induces the cell to release an electrical impulse which passes along the auditory nerve towards the brain. In a process which is not clearly understood, the brain is capable of interpreting the qualities of the sound upon reception of these electric nerve impulses.


-- LIVER:

The liver is the largest glandular organ of the body. It weighs about 3 lb (1.36 kg). It is reddish brown in color and is divided into four lobes of unequal size and shape. The liver lies on the right side of the abdominal cavity beneath the diaphragm. Blood is carried to the liver via two large vessels called the hepatic artery and the portal vein. The heptic artery carries oxygen-rich blood from the aorta (a major vessel in the heart). The portal vein carries blood containing digested food from the small intestine. These blood vessels subdivide in the liver repeatedly, terminating in very small capillaries. Each capillary leads to a lobule. Liver tissue is composed of thousands of lobules, and each lobule is made up of hepatic cells, the basic metabolic cells of the liver.


MAJOR FUNCTION:


The liver has many functions. Some of the functions are: to produce substances that break down fats, convert glucose to glycogen, produce urea (the main substance of urine), make certain amino acids (the building blocks of proteins), filter harmful substances from the blood (such as alcohol), storage of vitamins and minerals (vitamins A, D, K and B12) and maintain a proper level or glucose in the blood. The liver is also responsible for producing cholesterol. It produces about 80% of the cholesterol in our body.

--PANCREAS:

The pancreas is a glandular organ that secretes digestive enzymes (internal secretions) and hormones (external secretions). In humans, the pancreas is a yellowish organ about 7 inches (17.8 cm) long and 1.5 inches. (3.8 cm) wide.
The pancreas lies beneath the stomach and is connected to the small intestine at the duodenum .

The pancreas contains enzyme producing cells that secrete two hormones. The two hormones are insulin and glucagon. Insulin and glucagon are secreted directly into the bloodstream, and together, they regulate the level of glucose in the blood. Insulin lowers the blood sugar level and increases the amount of glycogen (stored carbohydrate) in the liver. Glucagon slowly increases the blood sugar level if it falls too low. If the insulin secreting cells do not work properly, diabetes occurs.

The pancreas produces the body's most important enzymes. The enzymes are designed to digest foods and break down starches.

The pancreas also helps neutralize chyme and helps break down proteins, fats and starch. Chyme is a thick semifluid mass of partly digested food that is passed from the stomach to the duodenum. If the pancreas is not working properly to neutralize chyme and break down proteins, fats and starch, starvation may occur.
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