Blood Cells

Blood Tissue and its Functions

Blood is a vital tissue of the body. It is a type of connective tissue. Blood has four basic components: white blood cells, red blood cells, plasma, and platelets. Blood performs various functions like transport of oxygen to the lungs and tissues, blood clot formation to prevent blood loss in case of injury. It also regulates body temperature, carries antibodies to fight and prevent infection and brings waste products to the kidneys and liver for filtration and cleaning of blood.

The blood that runs through our arteries, veins, and capillaries is a mixture of about 45% blood cells and 55% plasma. An average adult human has about 5 liters of blood in his body. Blood adapts to your needs through the circulatory system. When we are doing a strenuous activity like running or exercising, our heart pumps faster to send more blood and hence more oxygen to the muscles. When our body is attacked by an infection, the blood transports the antibodies to the site of infection, where they fight with those invaders.

Components of the Blood


Plasma is the liquid part of the blood. It is a mixture of water, salts, proteins, fats and sugars. The plasma performs the function of transporting blood cells to the body. It also carries nutrients, antibodies, hormones, waste materials, clotting proteins and the proteins which are responsible for maintaining fluid balance in the body.

Red Blood Cells (Erythrocytes)

Red blood cells are also called as RBCs or erythrocytes. They are known for their bright red color and are the most abundant cells in the blood. RBCs account for bout 40-45% of the total volume of blood. The immature RBCs does contain a nucleus but mature ones do not. They can live up to 120 days. Their main function is to transport oxygen to the body. The shape of RBCs is like a doughnut, a biconcave disk which is flattened from the center.

The RBCs possess a special protein called hemoglobin. The hemoglobin carries and transports oxygen from the lungs to the body and takes carbon dioxide from the body and returns it to the lungs where it is exhaled. Hematocrit is a term used for the total volume of RBCs is the blood and is used to measure RBC levels in the blood.

White Blood Cells (Leukocytes)

White blood cells are also known as WBCs and leukocytes. Their main function is to protect the body from infection. They are much less in number than RBCs and account for about 1% of the total blood volume. Their lifetime is few hours to few days however, some can live for many years. There are different types of leukocytes which are classified into two categories:

Granulocytes contain granules and are of three types, eosinophils, neutrophils, and basophils

Agranulocytes contain granules and are of two types, lymphocytes, and monocytes.

Platelets (Thrombocytes)

Platelets or thrombocytes are not cells actually but are small cell fragments. Platelets gather at the site of injury and help the blood clot. They stick to the lining of the injured blood vessel which results in the formation of the fibrin clot. Fibrin also promotes the healing process by providing a platform upon which new tissue forms.

Where are the Blood Cells formed?

Blood cells are formed in the bone marrow and develop from hematopoietic stem cells.They develop through the highly regulated process of hematopoiesis. These stem cells can transform into white blood cells, red blood cells, and platelets.

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