Реферати українською » Медицина, здоровье » Структура і захворювання серця

Реферат Структура і захворювання серця

Страница 1 из 2 | Следующая страница


The heart is a muscular organ whose interior is divided into two pairs of chambers, one on the right, the other on the left; the chambers of each pair are connected with each other by a valve. Lying in the mid-left section of the chest, close to the breastbone, the human heart weighs about 12 ounces, beats 70 to 80 times a minute, and is enclosed by a sturdy membrane called pericardium. Its chambers are lined by a delicate membrane, the endocardium, and its vigorous muscular and connective tissues are nourished by the heart’s own blood vessels, the coronary vessels.

How the Heart Works

This remarkable muscle serves as a pump controlling the blood stream in two circuits, the pulmonary and the systemic. The right side of the heart receives the blood from the large veins that drain the systemic circuit and propels it into the lungs where carbon dioxide is removed and oxygen is picked up. The oxygenated blood, collecting in the pulmonary veins, than enters the left side of the heart, from which it is pumped out again into the systemic circulation by way of the body’s largest blood vessel, the aorta. The rhythmic pumping is in the form of a repeated contraction ( systole ) and relaxation (diastole). Every 60 seconds, this precisely adjusted human pump drives about five quarts of blood through the body.

Auricles and Ventricles

The four chambers of the heart have special roles in the pumping process. The upper chambers are called the auricles; the lower chambers, the ventricles. The auricle and ventricle on each side together form an independent part of the heart, somewhat like a duplex apartment; in effect, they make up a “right heart” and a “left heart”. There is no connection for the blood into the pulmonary circuit, the left into the general body circuit.

Valves of the heart

Between the right auricle and right ventricle is a valve, called the tricuspid valve. Similarly, the left auricle and left ventricle are connected by the mitral valve, so named because of its apparent resemblance to a bishop’s miter or tall cap. The sounds of the valves opening and closing are heard by the doctor when he listens with his stethoscope. In addition to the valves between auricle and ventricle on each side of the heart, there are valves at the blood’s exit points: the pulmonary valve opening from the right ventricle into the pulmonary artery, and the aortic valve opening from the left ventricle into the aorta. All these valves, both within the heart and leading out of it, open shut in such a way is to keep the blood flowing only in one direction through the heart’s two separate pairs of chambers: from auricle to ventricle and out through its appropriate artery.

A Single Pumping Action

Although the right and left sides of the heart serve two separate branches of the circulation, each with its distinct function, they are co-ordinated so that the heart efficiently serves both sides with a single pumping action. The valve action on both sides is also co-ordinated with the two phases of the pumping action. Thus, during the diastole, or relaxation phase, the oxygen-poor blood which was accumulated in the right auricle returning from the systemic or body circulation pours into the right ventricle. At the same time, the oxygen-rich blood which was accumulated in the left auriclereturning from the pulmonary circulation pours into the left ventricle. The weak walls of both auricles contract to press the blood into the relaxed ventricles. In the next or contraction phase, the systole, the valve between auricle and ventricle on each side closes, and the muscular walls contract the ventricles and sweep the blood through each passage into the pulmonary artery and the aorta. At the end of the contraction the pulmonary and aortic valves snap shut, preventing any backward surge of the blood to the ventricles. The diastole follows, the ventricles again fill with the flow from their separate auricles and the cycle is repeated. This co-ordinated rhythmic action goes on tirelessly day and night throughout every individual’s lifetime.

The Valve Cusps

The valves, which must withstand considerable pressure, are composed of a special type of tough tissue. The mitral valve, between the left auricle and ventricle, has two cusps or leaflets. The tricuspid valve, between the right auricle and ventricle, has three cusps. Both valves function in the same manner. When blood pressure in auricle is higher than in the ventricle, the valve leaflets are swept open; as the blood flows downward, the auricular contraction at the start of the heart beat helps to push the blood along. As the blood fills the ventricle, the leaflets close, and with the contraction of the ventricle, pressure tightly shuts the valve. The valve leaflets are bolstered from below by a set of tough tendons with muscular attachments, enabling the leaflets to withstand the pressure and keep the valves from opening inward into the auricle.

The two valves which control the exit passages from the heart, the aortic valve and the pulmonary valve, have three leaflets each, and they also only for one-way flow. Other valves at special stations along the line in the circulatory system keep the blood from pooling in the lower extremities of the body.

Heart Disease.

Heart disease, the leading cause of death, is a term covering a variety of more than 20 different diseases of the heart and blood vessels. The most common of these are rheumatic heart disease, hypertension or high blood pressure, and coronary artery disease. Other forms of heart disease can be caused by congenital malformations of the heart and major vessels, syphilis, diphtheria, abnormal functioning of the thyroid gland, or diseases resulting from vitamin deficiencies.

Although approximately ten million Americans have some form of heart disease, the tremendous advances made by medical science have made it possible to treat and control these illnesses with increasing success. The majority of individuals who suffer a heart attack recover, and recurrent attacks of rheumatic fever which injure the heart can now frequently be prevented. By means of modern surgical techniques, heart defects and heart damage may often be repaired by HEART SURGERY.

To clarify various descriptions of heart ailments, it should be understood that a “heart attack” is not strictly the same as “heart disease”. A heart attack usually signifies the sudden obstruction of a coronary artery, one of the blood vessels feeding blood to the heart muscle; the clogging of the artery by a blood clot cuts off the blood supply to an area of the heart muscle. There is also a distinction between a heart attack, heart disease, and “heart failure”. Heart failure does not mean that the heart has stopped beating but that the heart is not pumping efficiently and the body’s blood circulation is being affected by the change.

One of the most prevalent of the diseases involving the heart is arteriosclerosis, commonly known as hardening of the arteries. Diseases of other organs of the body can also produce heart disease; one of these is nephritis, a disease of the kidneys which affects the tiny blood vessels or capillaries. Another such disease is diabetes which in some individuals may injure the blood vessels in much the same fashion as does high blood pressure.


Symptoms of heart disease may include certain types of palpitation, shortness of breath, a particular type of chest pain in the region of the left breast (angina pectoris), swelling of the ankles and feet, dizziness, fainting spells, extreme weariness, bluish lips, coughing up of blood, or a persistent cough. A person suffering from such symptoms should consult a doctor to determine whether heart disease is present. After taking the patient’s medical history and making a thorough examination, which may include an electrocardiogram, the doctor will diagnose the condition and prescribe any treatment that may be required.


An unusually rapid, strong, or irregular heartbeat of which a person is aware is called palpitation. In the majority of cases, palpitation is completely normal; almost everyone, for example, feels his heart pounding more rapidly and strongly after exertion or when he is excited or nervous. Many people are also apt to be especially conscious of heartbeat when they are lying in bed, especially when lying on the left side. There are also palpitations that are abnormal but that do not of themselves indicate heart disorder, though they may cause annoyance or discomfort. Commonest is the “skipped beat”, or extrasystole; in some cases this may occur because of excessive smoking o coffee drinking or as a reaction to some kinds of medicine.

The various types of palpitation that may indicate heart disorder in some instances include paroxysmal tachycardia and “flutter”, abnormal rhythms in which the heart executes runs of rapid beats. Another is auricular fibrillation, in which the beats are rapid but irregular, seeming to occur at random.

These palpitations may be caused by organic heart disease, but they also can result from other factors. Similarly, emotional pressures rather than organic changes may cause the so-called “nervous heart”, or functional heart disease. Although these symptoms do not prove definitely that the heart is in a trouble, they should prompt a person to consult his doctor. If the doctor’s examination shows no heart disease, the individual can be reassured. If not, the doctor will be able to begin immediate treatment.

Shortness of Breath

This may occur after only moderate exercise, such as climbing one flight of steps. A person who finds himself continually in a breathless state after activities which he once did without efforts should consult a physician. Awakening at night short of breath may also be warning of heart difficulties. This type of night breathlessness often takes the form of feeling of suffocation or a choking sensation. Shortness of breath may also indicate other disorders; some of these are described more fully in the article on BREATHLESSNESS.

Chest Pain (Angina Pectoris)

This type of pain, usually over the heart or in the mid-chest, may follow some excitement, a heavy meal, or exertion. It may not last more than a minute or two, and may fade when the person rests or stands still. Such pain may frequently be confused with similar symptoms arising from gas pains or indigestion, but only a physician should diagnose the complaint. Self-diagnosis can be dangerous.

Swelling of the Ankles and Feet

Deterioration of the heart’s pumping efficiency, or heart failure, can throw the blood circulation odd balance and cause fluid to collect in the tissues (edema). Swelling may be caused by varicose veins or by standing for long periods of time, but puffiness of a different type which may interfere with putting on shoes, or which can be deeply indented by pressure with a finger, should be checked with a doctor.

Kinds of Heart Disease

The diseases affecting the heart and blood vessels range from defects present at birth to damage of the organs caused by other diseases or injuries. They include congenital, syphilitic, and rheumatic heart disease; bacterial endocarditis, coronary insufficiency, coronary thrombosis, heart failure, and related disorders.  

Congenital Heart Defects

Between 30000 and 40000 children with one or more heart defects are born annually in the USA. A quite common defect is the tetralogy of Fallot, sometimes inaccurately called Blue Baby. Another defect consists of passage between the aorta and pulmonary artery which normally closes right after birth. There may be an opening between the ventricles, the two pumping chambers of the heart (ventricular septal defect).  Defective valves affecting the flow of blood to and

Страница 1 из 2 | Следующая страница

Схожі реферати: