What Are Blood Vessels

The network of blood vessels in the human body consists of arterioles, arteries, capillaries, veins and venules. All the blood flowing through the human body is carried through these blood vessels. The arteries are flexible, strong as well as resilient and carry away the blood from the heart. The arteries bear the highest blood pressures among all the blood vessels present in the human body. The arteries can handle the highest blood pressures because they are elastic and they can also recoil passively when the heart is relaxing two heartbeats. The arteries narrow down passively so that they can maintain the blood pressure in the human body. When the arteries branch out into smaller blood vessels they are known as arterioles. The arterioles and arteries have adjustable muscular walls and hence can adjust their diameter to accommodate the increasing or decreasing flow of blood to different parts of the body.

The capillaries are one of the smallest blood vessels in the human body and are also among the most thin-walled blood vessels. The capillaries typically act as bridges between the arteries which are carrying blood away from the heart. The capillaries also act as bridges between the veins which are carrying blood back into the heart. The capillaries have thin walls so that nutrients and oxygen can pass from the blood passing through the capillaries into the tissues. Similarly the waste products can also pass from the tissues into the blood being carried through the capillaries.

The blood flows into small veins commonly known as venules (arising from the capillaries) and subsequently the blood flows back into the veins which lead the blood back into the heart. The veins have much thinner walls in comparison to the arteries mostly because the blood pressure exerted on the veins is much lower than that exerted on the arteries. In case the amount of fluid passing through the veins increases the veins can dilate or widen in diameter to accommodate the increase in flow. The larger veins in the human body such as the veins in the legs have valves in them so that the blood in his veins does not flow backwards. In case the valves in such veins are leaking the backflow of the blood in his veins can cause them to stretch as well as become convoluted and elongated. When the veins become convoluted and elongated near the surface of the body they are known as varicose veins.

In case a blood vessel tears, breaks or is cut then the blood passing through the blood vessel starts to leak out and causes bleeding. Often the blood may flow out of the body which is known as external bleeding and it can also flow into cavities in the human body such as into spaces around the organs. The blood can also flow directly into the organs and it is known as internal bleeding.

Aging Blood Vessels

With age the walls of the arterioles and that of the arteries become thicker and the space within the arteries also begins to expand slightly. The elastic tissue contained in the walls of the arterioles and arteries is also lost with age. When combined, these changes can make the blood vessels less resilient and much stiffer.

Since the blood vessels like the arterioles and arteries become less elastic with age older people cannot relax fast during the rhythmic pumping of their heart. It is because of this reason that the blood pressures increases during the contraction cycle of the heart that is during systole. The blood pressure often increases above normal in comparison to the younger people who can relax quickly even during the rhythmic pumping of the heart. It is thus very common to observe high blood pressure during systole in older people. It is also quite common to observe normal blood pressure during diastole in older people. Abnormally high blood pressure during systole and normal blood pressure during diastole is known as isolated systolic hypertension.

These effects of aging on blood vessels and the heart can be reduced by regular exercise since the exercise helps maintain fitness of the cardiovascular system in human beings. Exercise can also help maintain the muscular fitness of people as they begin to age. Exercise is thus considered to be extremely beneficial irrespective of their age at which it started.

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Yasser Elnahas

MD, PHD, Professor Of CardioVascular Surgery
Dr. Yasser Elnahas, Is an associate Professor of Cardiovascular Surgery. Dr. Elnahas was trained as a fellow At Texas Heart Institute And Mayo Clinic Foundation.Dr. Elnahas is dedicated to educating the general public about different disease conditions and simplifying the medical knowledge in an easy to understand terminology.

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