b. The lymphatic system is a drainage-type circulatory system involved with the
clear fluid known as lymph.
c. There are other minor circulatory systems in the human body, such as the
one involved with cerebrospinal fluid.
Section II. THE HUMAN CARDIOVASCULAR SYSTEM
The human cardiovascular system is a collection of interacting structures
designed to supply oxygen and nutrients to living cells and to remove carbon dioxide
and other wastes. Its major components are the:
a. Blood. Blood is the vehicle for oxygen, nutrients, and wastes.
b. Blood Vessels. Blood vessels are the conduits, or channels, through which
the blood is moved.
c. Heart. The heart is the pump which provides the primary motive force.
d. Capillaries. The capillaries, minute (very small) vessels, provide exchange
areas. For example, in the capillaries of the lungs, oxygen is added and carbon dioxide
is removed from the blood.
Blood is the vehicle for the human cardiovascular system. Its major subdivisions
are the plasma, a fluid containing proteins, and the formed elements, including red
blood cells, white blood cells, and platelets.
(1) Plasma makes up about 55 percent of the total blood volume. It is mainly
composed of water. A variety of materials are dissolved in plasma. Among the most
important of these are proteins.
(2) After the blood clots, the clear fluid remaining is called serum. Serum
does not contain the proteins used for clotting. Otherwise, it is very similar to plasma.
b. Formed Elements. The formed elements make up about 45 percent of the
total blood volume. The formed elements are cellular in nature. While the red blood
cells (RBCs) and white blood cells (WBCs) are cells, the platelets are only fragments of