The four main components of the blood are plasma, white blood cells (WBCs), red blood cells (RBCs), and platelets.

More details, including the functions of these components of the blood, are presented here.

1) Plasma: It is the liquid portion of the blood and consists of water (mostly), sugar, fats, proteins, salts, and so on. Blood cells are suspended in the plasma. About 55% of our blood is made up of plasma. The main function of the plasma is to transport the blood cells throughout our body along with substances such as antibodies, hormones, and nutrients.

2) White Blood Cells: WBCs, also known as leukocytes, help the body fight against infection. These cells protect us against mutated cells, help the healing of wounds by ingesting dead cells, and fight against foreign bodies such as allergens. These are fewer in number as compared to the red blood cells and constitute less than 1% of the human blood. The two major types of WBCs include lymphocytes and neutrophils.

3) Red Blood Cells: RBCs, also known as erythrocytes, account for 40–45% of the blood volume. Their main function is to carry oxygen from the lungs to the body tissues. These also carry the carbon dioxide molecules (as a waste product) from the body tissues back to the lungs. Hemoglobin, a special protein, is present in the RBCs and it is this protein that provides the red color of these cells.

4) Platelets: Also known as thrombocytes, they are actually small cell fragments. Their main function is blood clotting. Platelets gather at the site of an injury and form a plug in the injured vessel to stop the bleeding.

Hope this helps.