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Preksha Dhyana :
The Functionting of the Heart
One sometimes woders how the heart manages to pump day and night for seventy years or more without resting. The answer, of course, is that the heart does Test, between every beat. The resting period is called diastole and, its duration is twice as long as that of systole, which is the period of muscular contraction. Blood-vessels--Arteries, Veins and Capillaries
There are more Than 100,000 kms. of blood vessels in a human body. Multitudinous branches of blood vessels of various sizes form a complex inter connceted net-work that reaches practically every cell in the body. The main types of blood vessels are arteries, veins and capillaries.
The blood vessel which carry the blood from the heart to the body are commonly known as arteries, while those which carry the blood in the opposite direction, i.e. toward the heart are called veins. Since, the pressure in the arteries is higher than in the veins, the walls of the former are thicker and stronger than those of the latter. Walls of the arteries consist of three layers of tissue. The outer layer consists of fibrous tissue, the middle layer of smooth muscle and elastic tissue and the inner lining of epithelium tissue. Although composed of the same layers of tissue, the walls of the veins are much thinner than those of the arteries.
Arteries vary in cross-section (size) from 25 mm. thick aorta down to less than 1.5 mm. in diameter. The bloodflow is helped along by rhythmic contractions in the mus. cular artery-walls.* Arteries are generally embedded deep into the muscles as a protection from all but severe injuries.
Oxygenated blood leaves the heart chamber via the aorta which emerges from the left ventricle and soon branches into two, one going upwards to the heart and the other downwards to the trunk and limbs. Aorta divides into arteries which again divide into smaller vessels called arterioles. The division progresses and ends into tiny thin. walled capillaries. These gassamer cobwebs link the smal. lest arterioles to the snallest venules. The wall of a capi.
When you take a pulse at the wrist, you are feeling the contractions a ateries and not those of beart.
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