They constitute 45% by volume of the blood. These include red blood cells, white blood cells and platelets.
a) RED BLOOD CELLS: These are called erythrocytes (eurothos, red).
Number: A cubic millimeter contains 5 to 5.5 millions in males and 4 to 4.5 millions in females.
Shape: The erythrocyte is a disk slightly concave on both sides i.e. biconcave. This shape has two advantages (i) it provides a large surface for gas diffusion. (ii) The biconcave shave allows the RBCs to move easily the narrowest blood capillaries without getting trapped.
Structure: RBCs when formed have nucleus, but it is lost before they enter the blood. 95% of the cytoplasm of red blood cells is the hemoglobin. It is an iron containing pigmented compound. It gives red color to the blood.
Formation: In the embryonic stages they are formed in the yolk sac, liver or spleen. After birth they are formed in the bones. In the adult RBCs are formed in marrow of certain short bones such as ribs, sternum (breast bone) spongy bones, vertebrae and end of long bones.
Average Life: An erythrocyte exists for about 120 days in the blood stream before it finally fragments. About 2-10 million red blood cells are formed and destroyed every second in normal person. The fragments of RBCs are engulfed by scavenger cells called macrophages in the liver, bone marrow and spleen. The iron from the hemoglobin is retained and used again. The rest of haeme is converted in liver to bilirubin a bile pigment, which is excreted in the faeces.
Function: RBCs carry oxygen to all cells of the body. RBCs also help in transport of CO2.
a) WHITE BLOOD CELLS: These cells are called leucocytes (leukos, colorless). These are not white in color. These are colorless. In WBCs hemoglobin is absent i.e. these are not red in color. So these cells are called white blood cells. Their number is 7-8 thousand per cubic ml, and life span is 3-4 days.
Structure: WBCs are classified into two main groups. (i) Agranular (ii) Granular.
(i) Agranular: In these cells the cytoplasm is clear having one nucleus. These cells originate in bone marrow and migrate and also produced in large numbers in the lymph nodes. Examples: (i) Lymphocytes (ii) Monocytes.
(ii) Granular: These are also called polymorph. Nucleus is highly variable in shape. (Poly = many, morph = shape). Nucleus has lobes. Cytoplasm contains fine granules. These originate in bone marrow. Examples: i) eosinophils ii) neutrophils iii) basophils.
Functions: different leucocytes have different functions. Their main function is to protect the body against the invading micro-organisms.
Agranular Leucocytes:
i) Lymphocytes: These are in Lymph Nodes. Lymphocytes produce and carry antibodies and are part of immune system.
ii) Monocytes: These are highly mobile and phagocytic. Monocytes ingest bacteria, other foreign matter and dead cells at the damaged tissue region.
Granular Leucocytes:
i) Eosinophils: Have large granules that stain bright red with eosin, (an acidic dye). Eosinophils are phagocytic and are involved in the control of the allergic reaction. So their number may rise greatly during an allergic reaction.
ii) Neutrophils: These are mobile; many can squeeze between the cells of capillary walls and move like amoeba, forming pseudopodia. Neutrophils are phagocytic cells.
iii) Basophils: Exhibit deep blue granules when stained with basic dyes. These are phagocytic and contain anti clotting chemical heparin that are important in blood clotting. Basophils contain large amount of histamine which these release in injured tissues and in allergic response.
Pus: the leucocytes die when these fight bacteria. The dead leucocytes accumulate at the infected wound. This accumulation of dead leucocytes is called pus.
3) Platelets: Certain large cells within bone marrow called megakaryocytes regularly pinch off bits of their cytoplasm. These cell fragments are called platelets. Thus a platelet is not a whole cell but a fragment of cytoplasm enclosed by a membrane. These contain no nuclei.
Function of Platelets: They play an important role in controlling blood clotting. When a blood vessel is cut, it constricts, reducing loss of blood. Platelets stick to the rough cut edges of the vessel, physically patching the break in the wall. Prothrombin, a plasma protein manufactured in the liver requires vitamin K for its production. In the presence of clotting factors, calcium ions and compounds released from platelets Prothrombin is converted to thrombin. Then thrombin catalyzes the conversion of the soluble plasma protein fibrinogen to an insoluble protein fibrin. Once formed fibrin polymerizes producing long threads that stick to the webbing of the clot. These thread trap blood cells and platelets which help to strengthen the clot.
0 comments:
Post a Comment