b. The lymph nodes, or glands, are small oval or bean-shaped bodies, varying
from a pinhead to a lima bean in size. They are distributed along the course of the
lymph vessels, sometimes singly, but usually in groups or clusters. These are
sometimes superficial, and are sometimes deep nodes in close contact with arteries and
veins. Lymph nodes are especially numerous in the neck (cervical), the armpit
(axillary), the groin (inguinal), and in the thorax and abdomen. Lymph vessels enter
these nodes, and a larger trunk leaves the nodes. The nodes provide a tortuous maze
containing lymphocytes that defend the body against invasion of bacteria. Eventually,
vessels from the nodes carry lymph to the thoracic duct (where lymph from the left and
lower portions of the body enters the bloodstream at the junction of the left subclavian
vein and the left internal jugular vein) or the right lymphatic duct (where lymph from the
upper right portion of the body enters the bloodstream at the junction of the right
subclavian vein and the right internal jugular vein). Valves prevent any backflow. The
distribution of the principal lymph nodes and their vessels is shown in figure 3-22.
3-37. THE SPLEEN
The spleen is the largest collection of lymphoid tissue in the body. It is a large,
gland-like, but ductless, organ directly beneath the diaphragm behind and to the left of
the stomach. The spleen is an elongated ovoid body, more or less bean-shaped, and is
enclosed in a capsule of connective and muscular tissue. Its main functions are to store
and cleanse blood to destroy old red blood cells and, in the fetus, to produce new red
blood cells.
It also produces lymphocytes. The spleen may be visualized
radiographically both with and without contrast media.
3-38. BLOOD
a. The blood is a red fluid, (bright red in the arteries and dark red in the veins)
containing erythrocytes (red blood cells-(RBC)), leukocytes (white blood cells-(WBC)),
platelets, and plasma. The red cell count in the normal male is from 5 to 6 million per
cubic millimeter and in the normal female from 4.5 to 5.5 million per cubic millimeter.
These cells give the blood its red color. The number of white cells is approximately
7,000 to 9,000 per cubic millimeter in the normal adult. The average number of
platelets is about 300,000 per cubic millimeter of blood. Their chief function is
concerned with the clotting of blood. The plasma is the fluid portion of the circulating
blood. It is composed of serum (the fluid containing the nourishing elements of the
blood) and fibrinogen, which is a substance that aids in the clotting of the blood.
b. The functions of the blood are to carry nutritive material and oxygen to the
tissues of the body, to remove the waste products of the tissues, to protect the body
against bacterial invasion, and to maintain proper temperature and moisture content in
the body.
MD0956
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