Blood

What is the function of each component in blood?

You might think that the most important function of blood is to serve as the body's transportation system. But the various components of blood also help regulate body temperature, fight infections, and produce clots that help minimize the loss of body fluids from wounds.

Plasma The human body contains 4 to 6 liters of blood. About 55 percent of total blood volume is a straw-colored fluid called plasma. Plasma is about 90 percent water and 10 percent dissolved gases, salts, nutrients, enzymes, hormones, waste products, plasma proteins, cholesterol, and other important compounds.

The water in plasma helps to control body temperature. Plasma proteins consist of three types—albumin, globulins, and fibrinogen. Albumin and globulins transport substances such as fatty acids, hormones, and vitamins. Albumin also plays an important role in regulating osmotic pressure and blood volume. Some globulins fight viral and bacterial infections. Fibrinogen is necessary for blood to clot.

Red Blood Cells The most numerous cells in blood are red blood cells, or erythrocytes (eh RITH roh syts). The main function of red blood cells is to transport oxygen. They get their crimson color from the iron in hemoglobin, a protein that binds oxygen in the lungs and releases it in capillary networks throughout the body. Then red blood cells transport some carbon dioxide to the lungs.

Red blood cells are disks that are thinner in their center than along their edges. They are produced by cells in red bone marrow. As red blood cells mature and fill with hemoglobin, their nuclei and other organelles are forced out. Red blood cells circulate for an average of 120 days before they are destroyed in the liver and spleen.

FIGURE 33–8 Blood Cells The micrograph shows red blood cells (red disks), white blood cells (gold orbs), and platelets (pink fragments) (SEM 1866X).