The formed elements found in the blood are as follows:
(1) Erythrocytes- These are the most abundant cells (red blood cells) and they contain the red pigment called haemoglobin that imparts a red colour to these cells. Erythrocytes carry oxygen to all parts of the body. These 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 millimetre of blood.
(2) Leukocytes- These are colourless cells that do not contain haemoglobin. 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- These 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.