Biology Made Easy - Functions of the Blood

Our blood performs many functions in our body necessary to our survival. The main functions are transport, regulation, and immunity.

Blood transports many different substances throughout the body. It carries oxygen from the lungs to the cells of the body via the red blood cells and hemoglobin. It then carries the carbon dioxide produced by cells back to the lungs to be exhaled. Nutrients from the digestive tract and from storage sites such as the liver and adipose tissue are carried in the blood to cells that need them. The liver stores glycogen, electrolytes and vitamins. The adipose tissue stores lipids. Blood also carries cellular wastes to the liver and kidneys to be detoxified or excreted. Hormones are carried in the bloodstream from their sites of origin to their target cells. Finally, electrolytes and water are carried to cells that need them by the blood.

Blood regulates the pH of the body by controlling the amount of carbonic acid in the bloodstream. Carbonic acid is formed when carbon dioxide dissolves in the blood and reacts with water. In times of intense exercise, the carbonic acid level rises in the blood which causes a person to breathe heavily in an attempt to expel as much CO₂ as possible. If a person cannot exhale the carbon dioxide quickly enough, the pH of the blood drops. This can usually be stopped by buffers such as bicarbonate. This is a good thing because a low pH results in acidosis, and many proteins in the body cannot function properly in a state of acidosis.

Regulation of body temperature is also accomplished by the blood. If you step outside in the cold in winter, your body quickly takes blood away from the surface of your skin and sends it to your core. This keeps your organs warm, which is more important to your survival than your fingers and toes. In hot weather, the opposite occurs. Blood is sent close to the surface of the skin by vasodilation of those surface vessels. Heating the skin causes that heat to be lost to the environment, and helps prevent the internal organs from overheating.

The immune system is a very complex part of the blood, and cannot be gone into full detail here. The immune system includes a non-specific response where phagocytic cells eat and destroy invading cells in the body. There is also a specific response where the body produces antibodies specific for a chemical antigen. These antibodies stay in the blood after exposure to that antigen, so that even years later, a second exposure will trigger a strong attack by the immune system.