The component elements in the blood are:

(1) Erythrocytes:

They are the most abundant cells and contain the red pigment called hemoglobin. They carry oxygen to all parts of the body. Red blood cells are produced continuously in some parts of the body such as the marrow of long bones, ribs, etc. There are about 4 – 6 million RBCs per cubic millimeter of blood.

(2) Leukocytes

Leucocytes are colorless cells. These cells do not contain hemoglobin. They are the largest cells of the body and are divided into two main categories.

(a) Granulocytes

These leucocytes have granules in their cytoplasm and include neutrophils, eosinophils, and basophils. Neutrophils are phagocytic cells that protect the body against various infecting agents. Eosinophils are associated with allergic reactions, while basophils are involved in inflammatory responses.

(b) Agranulocytes

Lymphocytes and monocytes are agranulocytes. Lymphocytes generate immune responses against infecting agents, while monocytes are phagocytic in nature.

(3) Platelets

Platelets are small irregular bodies present in the blood. They contain essential chemicals that help in clotting. The main function of platelets is to promote clotting.