1-2

[Previous] [Next]

1-2. PROPERTIES AND FUNCTIONS OF THE BLOOD

a. Amount. Blood accounts for 7 to 9 percent of the body weight. A person weighing 150 pounds will have about 4 to 6 liters of blood. The actual amount of blood in each person's body is affected by several factors, such as body size and age. The older the person, the less blood in his body. A big person has more blood than a small person and, all else being equal, a male has more blood than a female.

b. Functions. Blood is constantly in motion. Asleep or awake, the blood flows in a circulation system at almost the same rate. This process begins before we are born and does not stop until after death. Blood flows in virtually a closed system to all tissues of the body. It brings oxygen and nutritive substances to the

capillaries (smallest blood vessels) and removes metabolic waste products and carbon dioxide, which are then eliminated from the body by the excretory organs. The blood coordinates activities of various organs by carrying chemical regulators called hormones. See paragraph 2-14 for a discussion of hormones. Blood regulates body temperature and protects the body against disease. Blood maintains acid-base equilibrium of the body (about pH 7.35 in the veins and about pH 7.39 in the arteries). See paragraph 2-6 for a discussion of acid-base balance.

c. Major Components. Blood has a liquid portion and a solid portion. The liquid portion is called plasma, which is about 55 percent of the blood's volume. The solid portion (red cells, white cells, and other vital factors) makes up the remaining 45 percent.

[Previous] [Next]