Types of Cells

The tissue blood provides an amazingly wide array of life-supporting functions in the human body. It delivers oxygen, hormones, nutrients and minerals to body cells and picks up cellular waste products. It prevents blood loss by healing wounds. Finally, blood acts as the primary carrier of immunity. Vital organs not only depend on blood for health, but most are involved in the continuous processing of blood. For example, the heart pumps enormous amounts of blood throughout the body, the kidneys filter out impurities, the liver produces most of the proteins found in blood and the lungs function in the exchange of oxygen and carbon dixoide between blood and tissues and the external environment.

Each kind of blood cell - red, white and platelet - has its own function. The white blood cells, or leukocytes, are part of the immune system, which provides protection against micro-organisms and foreign matter. The red blood cells, also called erythrocytes, transport oxygen from the lungs to the cells. Platelets, or thrombocytes, are essential in preventing blood loss through platelet plug formation at the site of vascular injury. Once a platelet plug forms, a fibrin clot then forms and stabilizes the plug. All of these blood cells are suspended in the liquid medium of blood, called plasma.

Blood is a transportation system, with the vessels of the circulatory system functioning as roadways. As blood circulates throughout the body, it transports oxygen from the lungs to all body cells. Nutrients are absorbed from the intestine and distributed to the cels by blood. And waste products of cellular metabolism are removed by the blood and delivered to organs such as the lungs, kidneys and skin for excretion.