Heart And Circulation (1937)

day and night in steady rhythm there operates within the human body a marvelous machine the heart from the slightly action of babyhood down through the years to the sedate pace of old age the heart beats about two and one-half billion times the heart is purely a muscular pump which maintains the circulation of our life's blood the force that starts each beat lies within the heart itself as we see in this turtle's heart it continues to beat long after it's removal from the body the automatic rhythmic action can be loaded in even a small part of heart muscle and even after such an isolated part of the heart has ceased to beat mechanical stimulation can produce contractions artificially in lamb the heart is a double pump in each cycle of its action the auricles above act as receiving chambers the right hora chol for venous blood returning from the body pouring oxygen and containing much waste carbon dioxide the left auricle receives purified blood through the pulmonary veins from the lungs these chambers empty their contents into the relaxed ventricles below the ventricles on contracting shortly after each beat of the auricles acted through pumps blood is forced from the right ventricle through the pulmonary artery to the lungs for purification while purified blood is forced out by the left ventricle through the aorta and other 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 back flow of blood the auricular ventricular valves open permitting the ventricles to fill with blood from the oracles now contraction of the ventricle starts and the mitral and tricuspid valves are forced shut the contraction of the ventricles also now forces open the arterial valve permitting free awkward flow of the blood here we see the action of one of the heart valves note that fluid passes freely in one direction but that the valves prevent it's going in the other there is one heart clown as the ventricles contract and a second when they relax and the exit valve snapshot this lead of about 70 per minute is normal for the average adult at rest during and for a time after exercise however the heart pumps much faster we will demonstrate with this turtle's heart some of the factors responsible for changes in the rate of heartbeat in exercise the body temperature rises we irrigate this heart with a warm salt solution note the increased rate of beating now it is again normal but carbon dioxide and adrenaline which increase in quantity in the blood during exercise likewise stimulate the heart to beat faster the heart is also equipped with a break device a pair of nerves which when stimulated slow down its action these heart movements are responsible for the arterial pulse the swelling of an artery with blood when the heart contracts and a partial collapse when the heart relaxes the blood is pumped to all parts of the body through the arteries in which the blood flows in spurts the arteries branch finally into microscopic capillaries found in every body tissue it is only through the thin capillary walls where the blood flows very slowly that oxygen can reach the blood from the lungs or food from the intestines or that waste products and other materials manufactured by the cells can migrate into the bloodstream to be carried to other cells or two organs of excretion from the capillaries the blood flows back to the heart through the veins we see that this flow is a steady stream the rate of flow is more rapid in the larger vessels but much slower through the tiny capillaries this difference in rate is purely mechanical in this model the total cross sectional area of the small vessels exceeds that of the larger one we know two slower flow in the smaller vessels this corresponds to the situation as between capillaries and arteries the blood vessels are not merely passive tubes formed by virtue of muscles that encircle their walls small arteries are able to constrictor to dilate to increase or decrease their internal caliber in this way they adjust the rate and amount of blood flow to meet the requirements of various organs or other parts of the body when skeletal muscles are active the blood vessels in the muscles are dilated there by the increased quantity of blood pumped by the heart it shunted away from such regions as a veteran where tissues are less active toward regions where activity is greatest such as arms and legs the muscles of the blood vessels are partially controlled by nerves in this rabbit ear we cut the cervical nerve and note the resultant dilatation of blood vessels but when the cervical nerve is stimulated we note that the vessels are constricted an important feature of the circulatory system is the arterial blood pressure unless this is kept sufficiently high temporary or permanent damage results if the pressure is too low to force blood to the head fainting may occur because of inadequate oxygen supply to the brain [Music] the arterial blood pressure is intimately dependent upon the rate of ejection of blood by the heart as we see in this anesthetized dog when the heart rate is slowed down we note that the pressure falls as the rate again increases the pressure rises the volume of blood in circulation is another factor in blood pressure here we approximate the loss of blood from a wound and note that the arterial blood pressure falls death may result from a continued inadequate supply of blood to vital centuries the transfusion of blood or even the injection of salt solution restore it to its normal level frequently saving life after extensive bleeding the third factor in blood pressure is the caliber of the blood vessels when large numbers of these vessels are constricted the pressure is elevated dilatation of a large number of blood vessels results in a lowering of the pressure in this film we have learned how the varying needs of the body that rest or in work are adequately and automatically met by adjustments of the heart and blood vessels most of this information has been gained from experimentation which has been carried on by men of medical science in their unending fight against the causes of disease and death