Blood Cells and Cell like Bodies

Blood is composed of various cellular elements that make up 45% of its volume. These components include red blood cells (erythrocytes), white blood cells (leucocytes), and platelets.

 

Red Blood Cells (Erythrocytes)

Structure: Erythrocytes, also known as red blood cells, are disk-shaped cells that are slightly concave on both sides, giving them a biconcave shape. This unique shape allows for a large surface area for gas diffusion and enables the cells to move easily through narrow blood capillaries without getting trapped.

Formation: Erythrocytes are formed in the embryonic stages in the yolk sac, liver, or spleen. After birth, they are formed in the bones, specifically in the marrow of certain short bones such as ribs, sternum, spongy bones, vertebrae, and the ends of long bones.

Life Span: An erythrocyte exists in the bloodstream for about 120 days before it finally fragments. Approximately 2-10 million red blood cells are formed and destroyed every second in a normal person. The fragments of erythrocytes are engulfed by scavenger cells called macrophages in the liver, bone marrow, and spleen. The iron from the hemoglobin is retained and used again, while the rest of the haeme is converted in the liver to bilirubin, a bile pigment, which is excreted in the feces.

Function: The main function of erythrocytes is to carry oxygen to all cells of the body. They also play a role in the transport of carbon dioxide.

 

White Blood Cells (Leucocytes)

Structure: White blood cells, also known as leucocytes, are colorless cells that lack hemoglobin, giving them a white appearance. They are classified into two main groups: agranular and granular.

Agranular Leucocytes: Agranular leucocytes have a clear cytoplasm with one nucleus. They are produced in large numbers in the lymph nodes and originate in the bone marrow. Examples of agranular leucocytes include lymphocytes, which produce and carry antibodies as part of the immune system, and monocytes, which are highly mobile and phagocytic, ingesting bacteria and other foreign matter at the site of tissue damage.

Granular Leucocytes: Granular leucocytes, also known as polymorphs, have a highly variable-shaped nucleus with lobes and contain fine granules in the cytoplasm. They originate in the bone marrow and examples include eosinophils, neutrophils, and basophils.

Functions: White blood cells have different functions depending on the type. They mainly protect the body against invading microorganisms.

 

Platelets

Structure: Platelets are not whole cells, but rather fragments of cytoplasm enclosed by a membrane. They are produced from large cells called megakaryocytes in the bone marrow.

Function: Platelets play a crucial role in blood clotting. When a blood vessel is cut, platelets stick to the rough cut edges of the vessel, physically patching the break in the wall. This, along with other clotting factors, calcium ions, and compounds released from platelets, leads to the conversion of soluble plasma protein fibrinogen to insoluble fibrin. Fibrin forms long threads that trap blood cells and platelets, strengthening the clot and preventing further blood loss.