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How does the Circulatory System Work?

Michael Anissimov
Updated Feb 16, 2024
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The circulatory system brings the body's cells what they need to survive - oxygen and nutrients. Only the most primitive animals lack a circulatory system.

The center of the circulatory, or cardiovascular system, is the heart, a powerful pump organ designed to beat many millions of times over the lifetime of an organism. The heart circulates blood throughout the veins and arteries. Arteries carry oxygen-rich blood away from the heart, providing it to tissues, then returning the depleted red bloods cells back to the heart through the veins for reoxygenation.

All the body's stationary cells are surrounded by interstitial fluid, also known as extracellular fluid, which is designed to draw oxygen and nutrients from red blood cells passing by. Red blood cells float in a medium called plasma which is similar to interstitial fluid, and makes up most of the volume of the blood, the primary fluid of the circulatory system.

The largest artery in the human body is the aorta, running through the neck and immediately proximate to the heart. The heart oxygenates red blood cells in its ventricles, or compartments, regulated by valves. The lungs receive fresh oxygen from the air outside, then relaying it to the heart. Complex multicellular organisms such as human beings need air with a fair amount of oxygen (15-25%) in it to survive. Plants, and many microbes, can survive in oxygen-free environments - unlike animals, they require carbon dioxide for respiration.

If the operation of the heart is interrupted, the organism is likely to quickly die, after brain damage begins to set in. This sometimes happens during major heart attacks. By using artificial heart stimulation systems, modern medicine is able to keep the circulatory systems of such victims alive long enough for surgery.

Anthropods and molluscs lack typical circulatory systems - in their bodies, there is no distinction between blood and the interstitial fluid - a material taking both properties simply bathes the organs in the necessary oxygen.

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Michael Anissimov
By Michael Anissimov
Michael Anissimov is a dedicated WiseGeek contributor and brings his expertise in paleontology, physics, biology, astronomy, chemistry, and futurism to his articles. An avid blogger, Michael is deeply passionate about stem cell research, regenerative medicine, and life extension therapies. His professional experience includes work with the Methuselah Foundation, Singularity Institute for Artificial Intelligence, and Lifeboat Foundation, further showcasing his commitment to scientific advancement.
Discussion Comments
By anon321038 — On Feb 20, 2013

@peasy: When your oxygen levels are down, your carbon dioxide goes up, which means your body works harder to compensate for the lack of oxygen and your heart rate goes up. In general, it affects your respiratory system and cardiovascular system.

By visionary — On Jan 31, 2011

@extrordinary -- The tissue valve used in some surgeries that are made using the valve leaflets of a pig valve, has recently been shown to last at least 14 years in patients over 70 years old. The benefit of using this type of valve is no blood thinners are needed.

By extrordinary — On Jan 30, 2011

@anon51972 -- What is the survival rate for someone who has had a transplant with a pig heart?

By donbri5 — On Jan 27, 2011

@peasy -- When the oxygen levels in the body are not adequate, you can begin to have many types of symptoms. Usually, fatique and shortness of breath are the common complaints. However, it can also become a precursor to inflammation, thyroid disease, hormone imbalance to name a few. One should always have the oxygen levels tested as part of annual visit.

By peasy — On Jan 24, 2011

I wonder, since the circulatory system works to move oxygen through the body, what happens when the oxygen level starts to decline, not specifically from a heart attack, but in general?

By anon51972 — On Nov 10, 2009

Did you know that other then the artificial heart simulation system, there is another way. Some doctors use pig hearts as a transplant for they are the closest animal with our organs.

Michael Anissimov
Michael Anissimov
Michael Anissimov is a dedicated WiseGeek contributor and brings his expertise in paleontology, physics, biology,...
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