Blood is a body fluid that transports essential elements in the body. About eight percent of the human body weight is blood.
Blood has many functions, the two most important of which, is the transport of things to the tissues and the removal of wastes from the tissues. Blood transports oxygen to all the tissues of the body especially the ones in the brain. Hormones, nutrients like vitamins and minerals, and other body regulating elements are transported through the blood, too.
Blood is composed basically of red blood cells, white blood cells, platelets, and plasma. Nutrients, hormones, and waste products like carbon dioxide are also found in the blood.
The red blood cells called erythrocytes carry oxygen. The white blood cells or leukocytes are the soldier cells that fight infection.
The platelets or thrombocytes are the smallest of the blood cells and are responsible for blood clotting. When a wound bleeds, the platelets release a protein called fibrinogen which becomes fibrin. These turn into strings and weave together to form a clot and thus, prevent more blood from spilling out of the body. In the case of hemophiliacs, whose blood do not have platelets, having a wound can be very fatal.
Plasma is basically water and this supplies the fluids in the cells. It is in the plasma where the nutrients, hormones and other elements are carried.
Blood composition slightly varies from person to person depending on nutrition, general well-being and the over all health of the organs. Various blood tests reveal how healthy or how sick an individual is.