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The “Plumbing” (Circulatory) System
editor
May 7, 2025
3:59 am
The circulatory system is the network of blood vessels that circulate blood to and from the heart and lungs. With each beat, the heart pumps blood into the vessels and through the body, bringing oxygen and other nutrients necessary to the life of the cells. As the blood gives off oxygen and nutrients, it also removes waste products, toxins and other harmful substances. The circulatory system works with many other systems. It plays an especially important role in:
The Respiratory System. Blood circulates through the lungs where it exchanges carbon dioxide and oxygen. The Digestive System. Blood circulating through the intestines absorbs nutrients from food that was eaten and digested. The Excretory System. The blood transports waste products to be filtered and excreted from the body. Temperature Control. As the blood flows, heat moves back and forth between the blood and the cells. This constant exchange of heat keeps all the body parts at the same temperature.

The Blood Vessels
There are three types of vessels that aid in the transport of blood, and in keeping it in constant circulation from the heart to the body, and back to the heart:

Arteries Capillaries Veins

The blood vessels are more than simple tubes through which blood flows. Each has its own characteristics, depending on the role it plays in the circulatory system.
Arteries are strong, flexible blood vessels that carry blood from the heart to the rest of the body. They expand to accept the blood pumped into them with each beat of the heart, and contract when the heart relaxes. As the arteries become smaller and narrower they turn into capillaries.
Capillaries, which look more like webs than vessels or tubes, lie in tangled "beds" in the tissues of the body. They are so tiny that blood cells must pass through them in single file. The exchange between the blood and the cells of the body takes place in the capillary beds. It is here that blood sends oxygen into the cells and removes waste. Special capillaries in the kidneys, liver and elsewhere take up waste products to be excreted. As the capillaries spread out of their beds, they thicken and merge into small vessels called "venules" which, in turn, lead to the larger veins that return blood to the heart.
Veins are less "active" and elastic than the arteries. They have valves that open to let blood through and close to prevent blood from pooling in the legs and elsewhere due to the pull of gravity.
Category : about heart

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