The heart and circulation (1947)

day and night in steady rhythm there operates within the human body a marvelous machine the heart from baby hood to old age the heart beats about two and a half thousand million times the heart is simply a muscular pump maintaining the circulation of the blood in this turtle part it can be seen that the action of the heartbeat is automatic it continues to beat long after its removal from the body a small isolated part of heart muscle shows the automatic rhythmic action even after it has stopped beating mechanical stimulation can produce contractions in man the heart is a double pump the oracles above act as receiving chambers the right article for deoxygenated blood returning from the body containing much carbon dioxide the left article for oxygenated blood from the lungs by the pulmonary veins the oracles empty their contents into the relaxed ventricles below the muscular ventricles contract shortly after each beat of the article the right ventricle pumps blood through the pulmonary arteries to the lungs for re-oxygenation while oxygenated blood is pumped by the left ventricle through the aorta from which it is distributed by the arteries to all parts of the body note the efficient system of heart valves as the ventricles relax after contraction the valves of the two arteries close preventing the back flow of blood at the same time the valves between the oracles and ventricles open and blood flows from the articles into the ventricles now note the contraction of the ventricles this force closes the bicuspid and tricuspid valve and opens the semilunar valves of the arteries here we see the action of a semilunar valve this allows blood to pass freely away from the heart that prevents the backward flow there is one heart sound as the ventricles contract and a second when they relax and the semilunar valve snaps shut the heartbeat of about 70 per minute is normal for the average adult at rest during and for a time after exercise the heart beats much faster in this tessel chart we will show how certain textures alter the rate we irrigate the heart with a warm salt solution the rise of temperature as in exercise increases the rate of beating it becomes normal again but if stimulated by injection of carbon dioxide and adrenaline which increases in quantity in the blood during exercise it beats faster the beat of the heart is also under nervous control stimulation of certain nerves slows down its action as blood is pumped into the arteries it causes dilation of the muscular wall followed by relaxation when the ventricles relax this wave passing along the arteries produces the pulse the blood is pumped to all parts of the body through the arteries in which the blood flows in spurts as seen in this cut artery this diagram of circulation shows the tissues where the arteries branch into microscopic capillaries it is only through the thin capillary walls that substances in solution can diffuse into and out of the tissue diffusion takes place during circulation through the tissue the capillaries reunite to form the veins through which the blood is carried back to the heart in a steady stream as seen in this cut thing the rate of flow is more rapid in the larger vessel but much slower through the tiny capillaries the difference in rate is purely mechanical in this model the total cross-sectional area of the small tubes exceeds that of the larger one we note a slower flow in the smaller tube a corresponding difference occurs in the capillaries and arteries the blood vessels are not merely passive tubes the muscles of the arterial walls are able to contract or relax altering the diameter of the vessel in this way they adjust the quantity of blood supplied to the various body organs during physical exercise the blood vessels in the skeletal muscles are dilated therefore blood is drawn away from the less active organs the viscera and more blood passes to the active tissues the muscles the muscles of the blood vessels are partially controlled by nerves in this rabbit here the cervical nerve has been cut and the blood vessels have dilated but when the cervical nerve is stimulated the vessels are constricted the arterial blood pressure is very important in maintaining good health temporary or permanent damage may result from reduced blood pressure if the pressure is too low to force the blood to the head and the brain does not receive enough oxygen painting may result the arterial blood pressure depends on the rate at which blood is pumped from the heart this blood pressure apparatus is set up on a dog under an anesthetic stimulation of the vagus nerve slows down the rate of heartbeat and the pressure falls as the rate increases the pressure rises loss of blood from a wound results in a fall in blood pressure too greater loss may cause death blood transfusion or injection of a salt solution can restore pressure to its normal level and often save life after extensive bleeding the diameter of the blood vessels also affects blood pressure constriction of many vessels raises pressure dilation lowers pressure in this film we have learned how the varying needs of the body at rest or at work are automatically met by adjustments of the heart and blood vessels most of this information has been gained by experiments carried out by medical research workers in their attempts to fight disease you