The heart is a hollow, thick-walled muscular, cone-shaped
organ about the size of our first. It is like a pump in the body which brings
about the circulation of the blood. The heart lies in the thorax. It is about
10 cm long and weighs about 250 grams in women and it it is heavier in men. The
human heart has four chambers. The heart is divided (from base to apex) into right and left halves
by a muscular portion called the septum. Each half of the heart again is
subdivided into the upper and lower chamber. The upper chamber is called an
atrium and the lower is called the ventricle. The atrium and ventricle of each
side communicate with one another through the atrio-ventricualr orifice, which
is guarded by valves. The right atrium collects the impure (deoxygenated) blood
from the whole body, whereas the left atrium collects the pure (oxygenated)
blood from the lungs. In the same way, the right ventricle pumps the blood
toward the lungs, whereas left ventricle distributes the blood to various parts
of our body.
Friday, July 8, 2016
The Heart
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The two
auricles contract at the same time. Then the two ventricles contract, after
which the heart takes a little rest. The beat of the heart is between sixty to
hundred times a minute. But as each cycle last about 0.8 of a second and consists
of arterial systole (0.1 sec), ventricular systole (0.3 sec) and cardiac
diastole (0.4 sec), the average normal cardiac cycle is assumed to beat 73-75
times per minute in normal conditions.
The major
functions of the heart are as follows:
. It collects the
impure (deoxygenated) blood from the whole body.
. It pumps the
impure blood toward the lungs for purification.
. It distributes
the pure (oxygenated) blood to various parts of our body.
. It helps to
supply the oxygen and nutritive elements to various parts of our body.
. It helps to
control the blood pressure.
The Blood Vessels
The blood flows
through blood vessels, which are elastic tubes. There are mainly three types of
blood vessels in our body. Those are:
(i)
Arteries,
(ii)
The Capillaries, and
(iii)
The veins.
(i)
Arteries: Arteries
are the blood vessels the transport blood from the heart. Generally, they carry
only the pure (oxygenated) blood, but pulmonary artery carries away impure
(deoxygenated) blood from the heart to the lungs for the purpose of
purification. The largest artery is the Aorta, through which pure blood leaves
from the heart and gets distributed to the whole body through the various
branches of arteries. The arteries, at last, merge into capillaries.
(ii)
The Capillaries:
As the arteries get farther away from the heart, they get smaller. Each one
divides into a series of smaller ones like branches of a tree. Finally, when
they reach tissues, they are sub-divided into tiny tubes called capillaries.
The blood passes through the thin walls of the capillaries into the tiny cells
of the entire body. At last, the capillaries combine to form venules.
(iii)
The Veins:
after the blood has given its nourishment to the body cells through the
capillaries, the impure materials are received from the cells through the
capillaries. These materials pass into another set of the blood vessels called
veins, which carry the impure (deoxygenated) blood back to the heart. The
veins, at last merge in superior and inferior vena cava. In fact, the veins are
the blood vessels that transport impure blood to the heart. The only exception
to this is pulmonary vein whose function is to carry pure (oxygenated) blood at
the left atrium of the heart from the lungs.
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