Location of the Heart
The center of the circulatory system is the heart, which is the main pumping mechanism. The heart is made of muscle. The heart is shaped something like a cone, with a pointed bottom and a round top. It is hollow so that it can fill up with blood. An adult’s heart is about the size of a large orange and weighs a little less than a pound.
The heart is in the middle of the chest. It fits snugly between the two lungs. It is held in place by the blood vessels that carry the blood to and from its chambers. The heart is tipped somewhat so that there is a little more of it on the left side than on the right. The pointed tip at the bottom of the heart touches the front wall of the chest.

Structure of the Heart

If you looked inside your heart, you would see that a wall of muscle divides it down the middle, into a left half and a right half. The muscular wall is called a septum. The septum is solid so that blood cannot flow back and forth between the left and right halves of the heart. Another wall separates the rounded top part of the heart from the cone-shaped bottom part. So there are actually four chambers (spaces) inside the heart. Each top chamber is called an atrium (plural: atria). The bottom chambers are called ventricles. The atria are often referred to as holding chambers, while the ventricles are called pumping chambers. Thus, each side of the heart forms its own separate system, a right heart and a left heart. Each half consists of an atrium and a ventricle, and blood can flow from the top chamber to the bottom chamber, or ventricle, but not between the two sides.

The Valves
Blood can flow from the atria down into the ventricles because there are openings in the walls that separate them. These openings are called valves because they open in one direction like trapdoors to let the blood pass through. Then they close, so the blood cannot flow backwards into the atria. With this system, blood always flows in only one direction inside the heart. There are also valves at the bottom of the large arteries that carry blood away from the heart: the aorta and the pulmonary artery. These valves keep the blood from flowing backward into the heart once it has been pumped out.

Branching Blood Vessels
The heart is a pump whose walls are made of thick muscle. They can squeeze (contract) to send blood rushing out. The blood does not spill all over the place when it leaves the heart. Instead, it flows smoothly in tubes called blood vessels.

Arteries:

First, the blood flows into tubes called arteriesThe arteries leaving the heart are thick tubes. But the arteries soon branch again and again to form smaller and smaller tubes.
They are not just tubes through which the blood flows. Both arteries and veins have layers of smooth muscle surrounding them. Arteries have a much thicker layer, and many more elastic fibers as well. The largest artery, the aorta leaving the heart, also has cardiac muscle fibers in its walls for the first few inches of its length immediately leaving the heart.
Arteries have to expand to accept the blood being forced into them from the heart, and then squeeze this blood on to the veins when the heart relaxes. Arteries have the property of elasticity, meaning that they can expand to accept a volume of blood, then contract and squeeze back to their original size after the pressure is released.
for Example....A good way to think of them is like a balloon. When you blow into the balloon, it inflates to hold the air. When you release the opening, the balloon squeezes the air back out. It is the elasticity of the arteries that maintains the pressure on the blood when the heart relaxes, and keeps it flowing forward. if the arteries did not have this property, your blood pressure would be more like 120/0, instead of the 120/80 that is more normal. Arteries branch into arterioles as they get smaller. Arterioles eventually become capillaries, which are very thin and branching.




Capillaries:
The smallest blood vessels, called capillaries, form a fine network of tiny vessels throughout the body. Capillaries are really more like a web than a branched tube, having extremely thin walls so that the blood that they carry can come into close contact with the body tissues. The tiny red blood cells can then pass easily through the walls of the capillaries to deliver the oxygen they carry to nearby cells. As the blood flows through the capillaries, it also collects carbon dioxide waste from the body cells. The capillaries containing carbon dioxide return this used blood to the heart through a different series of branching tubes:




Veins

The capillaries join together to form small veins. The veins, in turn, unite with each other to form larger veins until the blood from the body is finally collected into the large veins that empty into the heart.



So the blood vessels of the body carry blood in a circle: moving away from the heart in arteries, traveling to various parts of the body in capillaries, and going back to the heart in veins. The heart is the pump that makes this happen.Veins do not have as many elastic fibers as arteries. Veins do have valves, which keep the blood from pooling and flowing back to the legs under the influence of gravity. When these valves break down, as often happens in older or inactive people, the blood does flow back and pool in the legs. The result is varicose veins, which often appear as large purplish tubes in the lower legs.

The Pulmonary and Systemic Circuits and the Blood Supply to the Heart. (Circulatory system) ( a Repeated Question in Css Exams)

The heart is responsible for pumping the blood to every cell in the body. It is also responsible for pumping blood to the lungs, where the blood gives up carbon dioxide and takes on oxygen. The heart is able to pump blood to both regions efficiently because there are really two separate circulatory circuits with the heart as the common link. Some authors even refer to the heart as two separate hearts--a right heart in the pulmonary circuit and left heart in the systemic circuit.
In the pulmonary circuit, blood leaves the heart through the pulmonary arteries, goes to the lungs, and returns to the heart through the pulmonary veins.
There are four chambers in the heart - two atria and two ventricles. The atria (one is called an atrium) are responsible for receiving blood from the veins leading to the heart. When they contract, they pump blood into the ventricles. However, the atria do not really have to work that hard. Most of the blood in the atria will flow into the ventricles even if the atria fail to contract. It is the ventricles that are the real workhorses, for they must force the blood away from the heart with sufficient power to push the blood all the way back to the heart (this is where the property of contracting with more force when stretched comes into play).



The muscle in the walls of the ventricles is much thicker than the atria. The walls of the heart are really several spirally wrapped muscle layers. This spiral arrangement results in the blood being wrung from the ventricles during contraction.

Between the atria and the ventricles are valves, overlapping layers of tissue that allow blood to flow only in one direction. Valves are also present between the ventricles and the vessels leading from it.
In the systemic circuit, blood leaves the heart through the aorta, goes to all the organs of the body through the systemic arteries, and then returns to the heart through the systemic veins. Thus there are two circuits. Arteries always carry blood away from the heart and veins always carry blood toward the heart. Most of the time, arteries carry oxygenated blood and veins carry deoxygenated blood. There are exceptions. The pulmonary arteries leaving the right ventricle for the lungs carry deoxygenated blood and the pulmonary veins carry oxygenated blood. If you are confused as to which way the blood flows through the heart, try this saying
"When it leaves the right, it comes right back, but when it leaves the left, it's left."

Fig Below: shows the Blood Path......



The blood does not have to travel as far when going from the heart to the lungs as it does from the heart to the toes. It makes sense that the heart would be larger on one side than on the other. When you look at a heart, you see that the right side of the heart is distinctly smaller than the left side, and the left ventricle is the largest of the four chambers.

While you might think the heart would have no problem getting enough oxygen-rich blood, the heart is no different from any other organ. It must have its own source of oxygenated blood. The heart is supplied by its own set of blood vessels. These are the coronary arteries. There are two main ones with two major branches each. They arise from the aorta right after it leaves the heart. The coronary arteries eventually branch into capillary beds that course throughout the heart walls and supply the heart muscle with oxygenated blood. The coronary veins return blood from the heart muscle, but instead of emptying into another larger vein, they empty directly into the right atrium.

Circulation in General:

Composition of Blood –

A General View:
Blood volume is variable, but tends to be about 8% of body weight.
Blood is devided into 2 Parts PLASMA and BLOOD CELLS....

Plasma is 55% of Blood.

AND There are four major types of blood cells:
1)Red blood cells,
2)Platelets,
3)White Blood Cells (Leukocytes) which have sub divisions also:

Each type of blood cell has a specialized function:
Red cells take up oxygen from the lungs and deliver it to the tissues;
Platelets participate in forming blood clots;
White Blood Cells:
-->Lymphocytes are involved with immunity; and
-->Phagocyte


(Now lets move to a bit Detail)...

PLASMA:
The liquid portion of the blood, the plasma,(55% of Blood) is a complex solution containing more than 90 percent water. The water of the plasma is freely exchangeable with that of body cells and other extra cellular fluids and is available to maintain the normal state of hydration of all tissues.
Water, the single largest constituent of the body, is essential to the existence of every living cell. The major solute of plasma is a heterogeneous group of proteins constituting about 7 percent of the plasma by weight. The principle difference between the plasma and the extra cellular fluid of the tissues is the high protein content of the plasma. Plasma protein exerts an osmotic effect by which water tends to move from other extra cellular fluid to the plasma. Fatty substances (lipids) are present in plasma in suspension and in solution. Other plasma constituents include salts, glucose, amino acids, vitamins, hormones, and waste products of metabolism.


Leukocytes (White Blood Cell)
White cells, unlike red cells, are nucleated (have Nucleus) and independently mobile. Highly differentiated for their specialized functions, they do not undergo mitosis (ordinary cell division) in the bloodstream, but some retain the capability of cell division. As a group they are involved in the body's defense mechanisms and reparative activity. The number of leukocytes in normal blood ranges between 4,500 and 11,000 per cubic millimetre. Fluctuations occur during the day; lower values are obtained during rest and higher values during exercise. As living cells, their survival depends on their continuous production of energy. The chemical pathways utilized are more complex than those of the red cells and are similar to those of other tissue cells.
Leukocytes, containing a nucleus and able to produce RNA, can synthesize protein.

Thrombocytes Platelets

Platelets are formed when cytoplasmic fragments of megakaryocytes, which are very large cells in the bone marrow, pinch off into the circulation as they age. The platelet is metabolically more active than the Red blood cell and has a variety of functions. Platelets play an important and not fully understood role in the formation of the blood clot by coagulating to occlude a cut blood vessel and provide a surface on which strands of fibrin form an organized clot, by contracting to pull the fibrin strands together to make the clot firm and permanent, and, perhaps most important, by providing or mediating a series of coagulation (clotting) factors necessary to the formation of the clot. Platelets also store and transport several chemicals, including serotonin, epinephrine, and histamine (the importance of which in this capacity is unknown), and they phagocytose (absorb) foreign bodies, including viruses, as well.


Erythrocytes (Red Blood Cell)
The red cell is enclosed in a thin membrane that is composed of chemically complex lipids, proteins, and carbohydrates in a highly organized structure. Extraordinary distortion of the red cell occurs in its passage through minute blood vessels, many of which have a diameter less than that of the red cell. When the deforming stress is removed, the cell springs back to its original shape. The red cell readily tolerates bending and folding, but, if appreciable stretching of the membrane occurs, the cell is damaged or destroyed. The membrane is freely permeable to water, oxygen, carbon dioxide, glucose, urea, and certain other substances, but it is impermeable to hemoglobin. Within the cell the major cation is potassium; in contrast, in plasma and extra cellular fluids the major cation is predominantly sodium. A pumping mechanism, driven by enzymes within the red cell, maintains its sodium and potassium concentrations.



What is Anemia?

The fraction occupied by the red cells is called the hematocrit. Normally it is approximately 45%. Values much lower than this are a sign of anemia
Anemia is a shortage of
• RBCs and/or
• the amount of hemoglobin in them.
Anemia has many causes. One of the most common is an inadequate intake of iron in the diet.

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What is Blood Pressure?

Blood is carried from the heart to all parts of your body in vessels called arteries. Blood pressure is the force of the blood pushing against the walls of the arteries. Each time the heart beats (about 60-70 times a minute at rest), it pumps out blood into the arteries. Your blood pressure is at its highest when the heart beats, pumping the blood. This is called systolic pressure. When the heart is at rest, between beats, your blood pressure falls. This is the diastolic pressure.

Blood pressure is always given as these two numbers, the systolic and diastolic pressures.

Both are important. Usually they are written one above or before the other, such as 120/80 mmHg. The top number is the systolic and the bottom the diastolic.
When the two measurements are written down, the systolic pressure is the first or top number, and the diastolic pressure is the second or bottom number (for example, 120/80). If your blood pressure is 120/80, you say that it is "120 over 80."

Blood pressure changes during the day. It is lowest as you sleep and rises when you get up. It also can rise when you are excited, nervous, or active.

Still, for most of your waking hours, your blood pressure stays pretty much the same when you are sitting or standing still. That level should be lower than 120/80. When the level stays high, 140/90 or higher, you have high blood pressure. With high blood pressure, the heart works harder, your arteries take a beating, and your chances of a stroke, heart attack, and kidney problems are greater.

What causes it?

In many people with high blood pressure, a single specific cause is not known. This is called essential or primary high blood pressure. Research is continuing to find causes.

In some people, high blood pressure is the result of another medical problem or medication. When the cause is known, this is called secondary high blood pressure.

What is high blood pressure?

A blood pressure of 140/90 or higher is considered high blood pressure. Both numbers are important. If one or both numbers are usually high, you have high blood pressure.

NOTE: If you are being treated for high blood pressure, you still have high blood pressure even if you have repeated readings in the normal range.

There are two levels of high blood pressure: Stage 1 and Stage 2 (see the chart below).

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The ABO grouping and the Rh factor are the most often used to determine blood type.

The physician Karl Lansteiner determined that there were four major blood groups among humans. He designated them as A, B, AB, and O. This same system is used today. It is now a known fact that blood type is based on a type of glycoprotein present in the red blood cells.

Type A blood has A-type glycoproteins,

type B blood has B-type glycoproteins,

type AB blood has both of these glycoproteins, and

type O blood has neither of them.

The A and B glycoproteins function as antigens, and they combine specifically with antibody molecules. When this kind of reaction occurs, the red blood cells agglutinate (join together).

Universal donors:
People who have type O blood are called universal donors. It can be given to anyone without fear of agglutination because it does not contain any antigens that could combine with anti-a or anti-b antibodies

Universal Recipient:
The name universal recipient is given to a person with type AB blood. AB blood does not have anti-a or anti-b antibodies that could combine with any antigens.

Rh factors:

The Rh factors are another group of antigens found on the surface of red blood cells. They are called Rh factors simply because they were first discovered in rhesus monkeys.
About 85% of humans are Rh+, which means they have Rh factors on their red blood cells. The remaining 15% of humans are Rh-, which means that they do not contain the Rh factor. These Rh factors may present a problem when a mother is Rh- and the baby is Rh+.

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What is Clotting -

Unless blood is a free-flowing liquid it will not be able to circulate easily throughout the body's blood vessels. However, in being a liquid it could cause a large variety of problems. If there was an injury that broke a large blood vessel it could lead to a large loss of blood. This problem is resolved by the complex mechanism of clotting. The clots form a temporary barrier to prevent blood loss until the vessel walls have healed.

The Clotting Process-

When a blood vessel is injured, platelets begin to collect near the injury, which forms a barrier known as the platelet plug. When the platelets come in contact with an injured area, they swell up, become sticky, and release certain chemicals.

Blood clotting requires many precise reactions to maintain a certain balance between quick and efficient clot formation. This balance has to be kept exact so that your blood will not clot at the wrong time.

Prothrombin and fribrinogen are two proteins that are produced by the liver that are always present in the plasma of the blood. The injured tissues and platelets release prothrombin activator and calcium ions (Ca2+) to change prothrombin into the enzyme thrombin.

Then the thrombin splits two short amino acid chains from each fibrinogen molecule.
The ends of the fibrinogen then join together, forming threads of fibrin. These fibrin surround the platelet plug in the damaged area of the blood vessel and provide the shape for the clot.

Red blood cells are present within the fibrin which makes the clot appear red. After this the clot stops the bleeding, gets smaller, and hardens. Over time the injury is repaired by the growth of new cells which will replace the cells lost because of the injury. When all the healing has finished an enzyme called plasmin in activated and dissolves the fibrin clot.

Clotting:

Some Clotting Problems -
There are many conditions which can cause the clotting process to be disrupted. People who have the

> hereditary disease haemophilia,
> Lack the essential Factor VIII (Antihaemophilic Globulin, or AHG) of blood clotting.

These people can recieve certain injections which will enable ther blood to clot properly.

> If you don't have enough platelets in the blood or lack vitamin K, this will reduce the ability to clot.

(Note: all the above Questions i took from Past ES Papers)

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"Correct" ! OR "inCorrect" !

Waiting For the Answers!

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Incorrect
Pulmonary artery.........Deoxygenated blood
Pulmonary vein............Oxygenated blood

Great Mr.Green

Pulmonary artery.........carries Deoxygenated blood from heart to Lungs
Pulmonary vein............carries Oxygenated blood from lungs toward the heart

Ye micro-Wave-oven apka hoa

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