Рефераты. Структура и заболевания сердца

Структура и заболевания сердца


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


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



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


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.

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