Circulatory system

From ArticleWorld

The circulatory system is the anatomic and physiologic body system involved in the transport of oxygen and nutrients throughout the body and in the removal of waste products of metabolism to the lungs, to the kidneys and to the liver and digestive system. In lower animals, the circulatory system is “open”, meaning that blood is pumped to the other body systems and then flows back into the heart passively. Open systems have no veins or capillaries.

Anatomy and Physiology

In humans and in higher animal systems, the circulatory system is considered to be “closed” so that the blood stays within the body and continually travels in a loop-like fashion throughout the body.

The heart is the primary pump in the circulatory system. It is a strong muscular structure with two-four separate chambers that keep the oxygen-rich blood from the oxygen-poor blood. The heart, in humans, pumps the oxygen-rich blood into a large artery called the aorta. The each chamber in the heart has a one-way valve that prevents blood from backing up.

The blood then travels to smaller and smaller arteries until they reach a size small enough to be called arterioles (small arteries). Arteries have thick, muscular walls that help continue the blood flow throughout the arterial part of the circulatory system.

The arterioles take the blood into even tinier blood vessels called capillaries, which have very thin walls that allow the transfer of oxygen, nutrients, carbon dioxide and by-products of metabolism between the cells of the body and the blood in the capillaries.

Now that much of the oxygen has been delivered and waste products and carbon dioxide have been picked up, the blood travels through venules (small veins) and into the venous part of the circulatory system. The waste products can be dropped off in the kidneys or the liver before reaching the vessels that lead to the heart.

The two biggest veins in the circulatory system are the superior vena cava and the inferior vena cava. These veins dump the blood into the right atrium (in hearts with four chambers) which, in turn, passes it onto the right ventricle.

The blood leaves the heart via the pumping action of the heart muscle and travels by means of the pulmonary artery to the lungs. Once again, the blood is separated out into tiny segments of capillaries that form lattice-like areas that surround the small air sacs inside the lung. This is where the lungs exchange the carbon dioxide in the blood for fresh oxygen from the air in the air sacs.

The blood, now rich in oxygen, leaves the lungs via the pulmonary vein and empties into the left atrium. Finally, the oxygen-rich blood in the right atrium passes into the left ventricle where the entire process begins again.