Heart is Courageous
DON’T worry too much about your heart, as so many healthy people seem to be doing nowadays; rejoice, rather, that nature has placed in your breast one of her most delicate yet durable marvels, an organ of surpassing patience, flexibility and strength. Rejoice, and try to understand how it works. It will work all the better for being understood.
Borrow a doctor’s stethoscope, and listen to the beating of your own heart. In its steady rhythm-lube-pud, lube dub you will hear the sound of life itself as blood courses through the valves and chambers of this inimitable pump. For the heart, mechanically speaking, is just that: a pressure pump which forces the blood, with its freight of oxygen, food or waste, through the vessels of the body.
Heart is Courageous
Driven by the heart, the approximately eleven pints of blood in the average human body make a round trip about once every minute. In twenty-four hours the heart receives and pumps out again between fourteen and eighteen thousand pints of blood. In a life span of the Biblical three score years and ten, the heart beats some two thousand five hundred million times, without a single shutdown for repairs. And-so it seems to one listening through the stethoscope-without a rest. Yet, without rest no muscle can endure, and the heart is a muscle. Though brief, the pauses between dub and the next lube are enough rest.
The normal heart, like man himself, spends twice as much time relaxing as it does at work. Besides, the heart draws extra rations. Though it weighs but one two-hundredth of the body’s weight, it requires one-twentieth of the blood in circulation for itself. Your heart is about the size of your fist and is snugly enclosed in a tough protective covering called the pericardium. Attached to the body only by the great blood vessels stemming from its base, it hangs within your chest, pointing diagonally downward towards your left breast. It is divided into two parts, right and left, by a blood-tight wall. Each part forms a separate pump.
And each of these two pumps, in turn, has two interacting chambers: the auricle, which receives blood into the heart from the veins, and the ventricle, which forces it out again into the body through the arteries. The heart’s specialised muscles are so cunningly layered and interwoven that they can squeeze, twist and literally wring out the contents of their chambers at every lube- in other words, at every contraction of the pump.
What causes the heart to beat? This question, asked almost eighteen hundred years ago by the anatomist Galen, was not answered until about 1890, when investigators began to suspect microelectronic energy. They were right. We now know that a kind of electrical timing apparatus called the pacemaker normally generates, about seventy times a minute, a tiny electrical impulse which sweeps down and across the muscle fibres, causing them to contract.
The heart, then, is a kind of elector muscular pump, contrived by millions of years of evolution, for the purpose of keeping the blood circulating in two main circuits. One, starting from the left chamber of the heart, is the great systemic circuit, which the blood makes through the entire body for the purpose of maintaining its tissues. A shorter, independent circuit goes from the right chamber of the heart to the lungs, to let the blood discharge its freight of carbon dioxide and pick up life-renewing oxygen. This is the pulmonary circulation.
In order to fully understand the action of the heart, let us trace More precisely the course of the blood. Dark venous blood, laden with carbon dioxide and waste matter picked up in its progress through the body’s veins, is drawn into the right auricle as the auricle lies momentarily relaxed. When the auricle is filled, the valve in its floor opens and the blood pours into the ventricle below.
When the ventricle is full, its smooth pumping pressure closes the valve, which bellies out like a parachute. This same pressure simultaneously opens another set of valves (half-moon-shaped) and forces blood out of the ventricle into the artery that leads directly to the lungs. In the thin-walled network of the lungs the dark blood is purified by exchanging its load of carbon dioxide for oxygen from the outer air. Thus freshened, the blood returns bright crimson to the heart-and the marvel of pulmonary circulation has been accomplished in less than ten seconds.
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Meanwhile, the left chamber of the heart, more powerful than the right, carries on the next phase in rhythmic unison with the first. Fresh from the lungs, the blood enters the left auricle. When the auricle is full, the valve opens and the ventricle begins to fill. A fraction of a second later the ventricle contracts, pushing its cupful of blood into the aorta, the huge artery that leads out from the base of the heart. When the pressure in the aorta exceeds that from the ventricle, the half-moon valves between them close. The brisk dub that you hear is the sound made by the valves as they slam shut.
From the aorta, widest of the rivers of life, the red flood branches out, ever more slowly, through arteries and arterioles and tiny capillaries, to every cell in the body. The heart repeats this process of contracting and relaxing, of systole and diastole, lube-dub, lube-dub, day after day, year in, year out, in disease and health, through sleep, love and battle, with the enduring constancy of time itself, with an efficiency not equalled by any of man’s inventions, and a courage that passes all understanding.