Useful information on the functions and composition of blood

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Composition of Blood

Blood is a liquid tissue that circulates in a closed system of blood vessels. Total volume of blood in human body is 5.4 liters. In man, it may be 85 ml/kg body weight. The specific gravity of blood varies between 1.05-1.06. The viscosity of blood is 4.5 times that of water. Blood is alkaline (pH 7.4). Blood consists of (i) solid elements which include red blood corpuscles (RBC), white blood corpuscles (WBC), and blood platelets, (ii) liquid element, and the plasma.

Plasma:

If we take 100 milliliters of blood and keep it in a tube for a few hours, the corpuscles would settle down towards the lower side and a straw-coloured liquid would rise to the top. The corpuscles comprise 45% of the volume and plasma 55.

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If we take only plasma part of the blood and try to find out what substances are dissolved in it, we will be struck by the variety of molecules. But plasma contains 92 % water. If one of the proteins, fibrinogen, is removed from the plasma, it is no longer called plasma. It is called the serum.

Blood corpuscles:

Blood corpuscles are of three types;

Red blood Corpuscles (RBC):

There are 5 x 10×6 RBC per cubic mm of blood in man. Each corpuscle is biconcave. It is full of haemoglobin molecules which are red. One haemoglobin molecule picks up four molecules of oxygen from the lungs and off-loads them into the tissues, after off-loading oxygen; they pick up carbon dioxide and off-load it in the lungs. In the RBC of mammal we do not find nucleus.

White blood Corpuscles (WBC):

These are also called leucocytes. Some of the leucocytes have granules in their cytoplasm and, therefore, they are termed granulocytes. These granulocytes eat bacteria and dust particles, etc, that happen to be present in the blood. When bacteria are engulfed, our blood gets rid of them the leucocytes which do not have granules in their cytoplasm are called a granulocytes. One of the kinds of granulocytes is lymphocyte, which manufactures a characteristic protein molecule called antibody. Antibodies may be compared to the gloves which fit into the foreign particles (such as viruses) that invade our body.

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These foreign particles are termed antigens. When we are inoculated with vaccines, we actually let the foreign particles enter our body so that lymphocytes may recognize them and start tailoring antibodies in huge numbers. When these antibodies circulate in the blood, we remain protected from the disease. In other words, we remain immune from the disease, whose vaccine has been inoculated.

Blood platelets:

there is third kind of corpuscle in the blood called blood platelet. It is smaller than those of RBC and WBC. Blood platelets are produced by cells called megakaryocytic which have giant nuclei. Blood platelets release enzyme when there is injury. This enzyme sets a chain reaction which ultimately converts a protein, fibrinogen, into fibrin. The latter precipitates to form clot. The whole process is called clotting of blood or coagulation of blood.

Functions of Blood

1. Regulation of water content of cells

Blood regulates water content of the cells. When the water content in cells increases blood takes up the excess amount of cellular water. Blood provides water to cells when they need it.

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2. Liberation of Energy

Blood helps in the liberation of energy from food in the sense that it supplies oxygen through hemoglobin. Oxygen is needed for cell respiration.

3. Distribution of food

Digested food which is absorbed in the small intestine comes to the blood capillarity. From here it has to be distributed to all parts of the body. It is a task performed by the blood.

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4. Regulation of body temperature

Body temperature resulting from the excess respiration of a particular tissue is equalized by circulation of blood.

5. Transport of chemical substances

Hormones are released in the blood by the ductless glands. Hormones are circulated and taken to the target organs by blood. Drugs and poison introduced into the body also get circulated.

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6. Defense against infection

When bacteria and other foreign matter enter the blood, they are engulfed by leucocytes. This process of cell eating is called phagocytosis. One type of leucocytes, the lymphocyte, manufactures antibodies against specific against specific foreign matter (bacteria, viruses) so as to confer immunity against the disease caused by the foreign matter.

7. Disposal of cell debris

In the body some cells are in the process of breakdown. Cell debris produced as a result thereof is removed by leucocytes.

8. Maintenance of body ph

In the red blood corpuscle, some carbon dioxide is combined with water to form carbonic acid, which dissociates into H and HCO. These ions along with a number of other ions present in the plasma help maintain the ionic balance and keep the body from fluctuations in H and of ions.

9. Clotting of blood

Clotting of blood is needed to prevent excess bleeding. Blood platelets and some plasma proteins help in the formation of clot.

10. Wound healing

Blood helps in rapid healing of wound.

11. Help in excretion

Adequate blood and blood pressure is essential for kidney to perform its function of excretion.

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