In the seventeenth century, William
Harvey demonstrated that the cardiovascular system is a closed loop containing
blood which is pumped by the heart. As seen in the picture, the loop consists
of two pumps, the left
heart and the right
heart, along with two vascular systems, pulmonary circulation and systemic
circulation. These components form a series, meaning that blood flows through
them in sequence. The sequence is as follows:
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1. Blood flows through the lungs by way of pulmonary circulation.
2. Oxygen is added, and carbon dioxide is removed. 3. The oxygenated blood flows to all the cells of the body
by way of systemic circulation. 4. The cells remove the oxygen and add carbon dioxide to it. 5. The blood flows back to the lungs, and the process repeats
itself. |
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Arteries
carry blood from the heart, and they make up the arterial system. Veins
carry blood back to the heart, and they make up the venous system. Just remember:
arteries = away , veins = toward. Systemic circulation begins with the largest artery,
the aorta,
which receives all the blood the heart pumps out. The aorta branches into many
smaller arteries. The arteries take the blood to the organs. Upon entering an
organ, an artery branches into smaller arteries, which branch into even smaller
ones called arterioles. The arterioles branch into capillaries,
completing the tree of blood vessels. From the capillaries, the blood can reach
the cells of the organ. The blood is then carried back to the heart by way of
the venous system. Similar to the arterial system, the venous system contains
small vessels, venules, which branch together to make veins. In the upper section
of the body, the blood flows from the veins into the superior
vena cava. In the lower section of the body, the blood flows from the veins
into the inferior
vena cava. These two vessels unite to return the blood to the right heart.
This completes systemic circulation.
Need a more in depth look at blood vessels?
Pulmonary Circulation
Pulmonary circulation works in very much the same way as systemic circulation. Blood exits the right heart through the pulmonary trunk, which branches into pulmonary arteries. Blood enters the lungs through the pulmonary arteries, and pulmonary capillaries provide for the exchange of carbon dioxide and oxygen. Once the blood is oxygenated, it flows to the left heart through progressively larger venules and veins until it reaches the pulmonary veins. The pulmonary veins are responsible for returning the blood to the left heart. This concludes pulmonary circulation.
