Cardiovascular from Cyber-Anatomy Web site and Think Quest
The cardiovascular system is a
complex system with one central organ:
the heart. The heart is the body’s
pacemaker. It pumps oxygen-rich blood
to the different parts of the body. The
blood’s journey through the body is an
extensive trip through highways of
veins, arteries, and other branches.
The heart is somewhat centrally
located. Two thirds of the heart is on the
left side of the sternum. It is the size of
your fist, weighing in at a whopping
pound and a half. Although it appears
small, its importance cannot be
understated.
The heart is divided into four chambers: the left and right
atria, and the left and right ventricle. The atria are on the upper
half of the heart, and the ventricles make up the lower portion.
The object of the blood is to circulate oxygen for the growth
and development of cells. The blood is composed of red and
white blood cells, platelets, lymph, plasma, and water. The red
blood cells carry the oxygen. The white blood cells are part of
the immune system. Platelets are used when blood clots, to stop
the bleeding. Lymph is the interstitial fluid in the blood, also
part of the immune system. Plasma is the remaining portion of
the blood, the water in which the blood cells are suspended.
Blood enters the heart in the left atrium, from the superior
and inferior vena cava. The superior vena cava is the vein that
collects the blood returning from the upper body, and the
inferior vena cava returns blood from the lower body. The
deoxygenated blood of these two veins enters the heart in the
right atrium and is pumped to the right ventricle. Then the
blood travels out of the heart and enters the pulmonary artery.
This artery carries the blood to the lungs to get oxygen.
Once the blood reaches the lungs, carbon dioxide already in
the blood is diffused into the lungs. Carbon dioxide is a cell’s
waste product after using oxygen. This is where the circulatory
system and the respiratory system intertwine.
The oxygen in the lungs is diffused through the alveoli sacs and then through the wall of the lungs
into the bloodstream. The blood carries the oxygen to the various cells in the body. To get the oxygen
to the actual cells, the arteries branch off into smaller arterioles. These even branch off to capillaries,
the smallest of blood vessels. Their walls are extremely thin and elastic. In these vessels, the red
blood cells must travel single file to pass through. The oxygen diffuses across the capillary wall. It
then travels to a nearby cell and enters through the cell membrane.
The carbon dioxide that leaves the cell to allow room for the oxygen makes its way to the
bloodstream. Once it reaches the capillaries, it has entered the bloodstream. The capillaries then fork
into venules, which then fork into veins. The veins carry the carbon dioxide in the blood back to the
heart. This completes the cycle of the circulatory system.