They secrete a yellow, waxy substance called
cerumen that protects the eardrum.
The circulatory system, also called the
VASCULAR SYSTEM, consists of the heart,
blood vessels, and lymphatic system. It is the
primary fuel supplier of the body. The transpor-
tation media is the blood. This system is a closed
circuit. At no place does it have access to other
tissues of the body except at the capillaries.
OSMOSIS, the transfer of fluids through the
plasma membrane from an area of lower concen-
tration of particles to an area of higher concen-
tration, is the method of feeding body tissues and
eliminating waste materials. This occurs in the
capillaries, the smallest of the blood vessels.
Blood is fluid tissue composed of formed
elements (cells) suspended in plasma. It is pumped
by the heart through miles of arteries, capillaries,
and veins to all parts of the body. Total blood
volume of the average adult is 5 to 6 liters.
PLASMA is the liquid part of blood; the
whole blood minus cells. Plasma constitutes 50
to 60 percent of whole blood. It is a clear, slightly
alkaline, straw-colored liquid consisting of about
92 percent water. The remainder is made up
mainly of proteins. One of these, fibrinogen, con-
tributes to coagulation.
BLOOD SERUM is a clear, pale yellow liquid.
It is the liquid portion of blood after coagulation.
Plasma and serum differ in that plasma is whole
blood minus the cells, and serum is plasma minus
the clotting elements.
Red blood cells (RBCs), or ERYTHRO-
CYTES, are small, biconcave, nonnucleated
disks, formed in the red bone marrow. Blood of
the average man contains 5 million red cells per
cubic millimeter. Women have fewer red cells, 4.5
million per cubic millimeter. Emotional stress,
strenuous exercise, high altitudes, and some dis-
eases may cause an increase in the number of
During the development of the red blood cell,
a substance called hemoglobin is combined with
it. HEMOGLOBIN is the key of the red cells
ability to carry oxygen and carbon dioxide.
Thus the main function of erythrocytes is the
transportation of respiratory gases. The red cells
deliver oxygen to the body tissues, holding some
oxygen in reserve for an emergency. Carbon diox-
ide is picked up by the same cells and discharged
via the lungs.
The color of the red blood cell is determined
by the hemoglobin content. Bright red, or arterial,
blood is due to the combination of oxygen and
hemoglobin. Dark red, or venous, blood is the
result of hemoglobin combining with carbon
A red blood cell will live only about 100 to
120 days in the body. There are several reasons
for its short life span. This delicate cell has to
withstand constant knocking around as it is
pumped into the arteries by the heart. It travels
through blood vessels at high speed, bumps into
other cells, bounces off the walls of arteries and
veins, and squeezes through narrow passages. It
must adjust to continual pressure changes.
Fragments of red blood cells are found in the
spleen and other body tissues. The spleen is the
graveyard where old, worn out cells are re-
moved from the blood stream.
White blood cells (WBCs), or LEUKO-
CYTES, are almost colorless, nucleated cells
originating in the bone marrow and in certain lyrn-
phoid tissues of the body. There is only one white
cell to every 600 red cells. Normal WBC count
is 6,000 to 8,000 per cubic millimeter, although
the number of white cells maybe 15,000 to 20,000
or higher during infection.
Leukocytes are important for the protection
of the body against disease. Their AMEBOID
movement permits them to leave the blood stream
through the capillary wall and to attack
pathogenic bacteria. They can travel anywhere in
the body and are often named the wandering
cells. They protect the body tissues by engulf-
ing disease-bearing bacteria and foreign matter,
a process called phagocytosis. When white cells
are undermanned, more are produced, causing an
increase in their number and a condition known
as leukocytosis. Another way they protect the
body from disease is by the production of
bacteriolysins that dissolve the foreign bacteria.
The secondary function of WBCS is to aid in
Blood platelets, or THROMBOCYTES, are
round bodies in the blood that contain no nucleus,
only cytoplasm. They are smaller than red blood
cells and average about 250,000 per cubic
millimeter of blood. They play an important role
in the process of blood coagulation, clumping
together in the presence of jagged, torn tissue.