The Heart


Categories: THE CARE OF THE HEART-PUMP AND ITS PIPE-LINES
Sources: A Handbook Of Health

Structure and Action of the Heart. Now what is it that keeps the blood

whirling round and round the body in this wonderful way? It is done by a

central pump (or more correctly, a little explosive engine), with thick

muscular walls, called the heart, which every one knows how to find by

putting the hand upon the left side of the chest and feeling it beat.

The heart is really a bulb, or pouch, which has ballooned out from the

central feed pipe of the blood supply system, somewhat in the same way

that the stomach has ballooned out from the food tube.



The walls of this pouch, or bulb, are formed of a thick layer of very

elastic and powerful muscles almost as thick as the palm of your hand.

When the great vein trunk has poured blood into this pouch until it is

swollen full and tight, these muscles in its walls shut down sharply and

squirt or squeeze the blood in the heart-pouch into the great

artery-pipe, the aorta. In fact, you can get a very fair, but rough,

idea of the way in which the heart acts by putting your half-closed hand

down into a bowl of water and then suddenly squeezing it till it is shut

tight, driving the water out of the hollow of your hand in a jet, or

squirt.



But, some of you will ask at once, what is to prevent the blood in

the heart, when the muscle wall squeezes down upon it, from shooting

backward into the vena cava, instead of forward into the aorta?



Nature thought of that long ago, and ingeniously but very simply

guarded against it by causing two little folds of the lining of the

blood pipes to stick up both where the vena cava enters the heart and

where the aorta leaves it, so as to form little flaps which act as

valves. These valves allow the blood to flow forward, but snap together

and close the opening as soon as it tries to flow backward. While

largest and best developed in the heart, these valves are found at

intervals of an inch or two all through the veins in most parts of the

body, allowing the blood to flow freely toward the heart, but preventing

it from flowing back.



As the heart has to pump all the blood in the body twice,--once around

and through the lungs, and once around and through the whole of the

body,--it has become divided into two halves, a right half, which pumps

the blood through the lungs and is slightly the smaller and the thinner

walled of the two; and a left half, which pumps the purified blood,

after it has come back from the lungs, all over the rest of the body.





Each half, or side, of the heart has again divided itself into a

receiving cavity, or pouch, known as the auricle; and a pumping or

delivering pouch, known as the ventricle. And another set of valves

has grown up between the auricle and the ventricle on each side of the

heart. These valves have become very strong and tough, and are tied back

in a curious and ingenious manner by tough little guy ropes of tendon,

or fibrous tissues, such as you can see quite plainly in the heart of an

ox. It is important for you to remember this much about them, because,

as we shall see in the next chapter, these valves are one of the parts

of the heart most likely to wear out, or become diseased.





Heart Beat and Pulse. The heart fills and empties itself about eighty

times a minute, varying from one hundred and twenty times for a baby,

and ninety for a child of seven, to eighty for a woman, and seventy-two

for a full-grown man.



When the walls of the ventricles squeeze down to drive out their blood

into the lungs and around the body, like all other muscles they harden

as they contract and thump the pointed lower end, or apex, of the

heart against the wall of the chest, thus making what is known as the

beat of the heart, which you can readily feel by laying your hand upon

the left side of your chest, especially after you have been running or

going quickly upstairs. As each time the heart beats, it throws out half

a teacupful of blood into the aorta, this jet sends a wave of swelling

down the arteries all over the body, which can be felt clearly as far

away as the small arteries of the wrist and the ankle. This wave of

swelling, which, of course, occurs as often as the heart beats, is

called the pulse; and we take it, or count and feel its force and

fullness, to estimate how fast the heart is beating and how well it is

doing its work. We generally use an artery in the wrist (radial) for

this purpose because it is one of the largest arteries in the body which

run close to the surface and can be easily reached.



Summary of the Circulation of the Blood. We will now sum up, and put

together in their order, the different things we have learned about the

circulation of the blood through the body.





Starting from the great vein trunk, the vena cava, it pours into the

receiving chamber, or auricle, of the right side of the heart, passes

between the valves of the opening into the lower chamber, the right

ventricle. When this is full, the muscles in the wall of the ventricle

contract, the valve flaps fly up, and the blood is squirted out through

the pulmonary artery to the lungs. Here it passes through the

capillaries round the air cells, loses its carbon dioxid, takes in

oxygen, and is gathered up and returned through great return pipes to

the receiving chamber, or auricle, of the left side of the heart. Here

it collects while the ventricle below is emptying itself, then pours

down between the valve flaps through the opening to the left ventricle.

When this is full, it contracts; the valves fly up and close the

orifice; and the blood is squirted out through another valve-guarded

opening, into the great main artery, the aorta. This carries it, through

its different branches, all over the body, where the tissues suck out

their food and oxygen through the walls of the capillaries, and return

it through the small veins into the large vein pipes, which again

deliver it into the vena cava, and so to the right side of the heart

from which we started to trace it.



Although the two sides of the heart are doing different work, they

contract and empty themselves, and relax and fill themselves, at the

same time, so that we feel only one beat of the whole heart.



One of the most wonderful things about the entire system of blood tubes

is the way in which each particular part and organ of the body is

supplied with exactly the amount of blood it needs. If the whole body is

put to work, so that a quicker circulation of blood, with its millions

of little baskets of oxygen, is needed to enable the tissues to breathe

faster, the heart meets the situation by beating faster and harder.

This, as you all know, you can readily cause by running, or jumping, or

wrestling.





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