Health Centers
 loading...
if not loaded., try Site map to view all
 
 
 
 
bookmark | print this page | mail to friend | site map | help

Alphabetical Disease Lookup

FONT SIZE

T T T

Heart

 

The heart which is the central organ of the cardiovascularsystem, is located between the two lungs in the middle of the chest. Two-thirds of the heart lies to the left of the breastbone and onethird to the right.

Placing a hand on the chest, we can feel the heartbeat on the left side of the rib cage because there at the bottom left corner of the heart, which is somewhat tilted forward, comes closest tothe surface of the body.

The adult heart is about the size of two clenched fists. It is shaped like a cone and weighs about 7 to 15 ounces, depending on the size and weight of the individual.

Cardiac Cycle

Electrical activity coordinates the rhythmic contraction and relaxation of the heartís chambers known as the cardiac cycle. Most currents in the heart are less than a millionth of an ampere (the current running through a 100-watt bulb is approximately 1 ampere),but they exert a powerful influence on the heart muscle. The cardiac cycle consists of two phases, called diastole and systole.

Diastole :
Diastole, during which the heartís ventricles are relaxed, is the longer phase, taking up approximately two-thirds of the cycle. During diastole, the sinus node generates an impulse that forces the two atria to contract. In this phase, the tricuspid and mitral valves are open, and blood is propelled from the atria into the relaxedventricles. By the end of diastole, the electric impulse reaches the ventricles, causing them to contract.

Systole :
Systole in which blood is ejected from the ventricles, takes up the remaining one third. During systole, the contracting ventricles close the tricuspid and mitral valves. Shortly afterward, the pressure of the blood inside the ventricles rises sufficiently to force the pulmonary and aortic valves to open, and blood is ejected into the pulmonary artery and the aorta. As the ventricles relax again, blood backs up from the pulmonary artery and the aorta, closing down the pulmonary and aortic valves. The pressure in the relaxed ventricles is now lower than in the atria, the tricuspid and mitral valves open again, and the cardiac cycle starts anew.

This seemingly lengthy sequence of events in fact takes approximately a second. The familiar double throb (lub dub) of the beating heart corresponds to the two sets of synchronized contractions that occur during the cardiac cycle. The throbbing sound we hear comes not only from the snapping of the valves, but also from the accompanying vibrations of other heart structures and from the turbulence produced by the flow of blood.

Circulation

The circulatory system is an intricate network of vessels that supplies blood to all body organs and tissues. The part of the network that delivers blood to all parts of the body except the lungs is called the systemic circulation, while the flow of blood through the lungs is referred to as the pulmonary circulation. Placed end to end, all the blood vessels of the body would stretch some 60,000 miles in length.

The Systemic Circulation : The arteries and capillaries
Blood that has been oxygenated in the lungs which is bright red in color is pumped out of the heart through the aorta which is the bodyís largest artery and it measures approximately 1 inch in diameter. The coronary arteries which provide the heart's own blood supply, branch out from the aorta just above the aortic valve.

The aorta arches upward from the left ventricle to the upper chest then runs down the chest into the abdomen. It forms the main trunk of the arterial part of the circulation, which again branches off into numerous arteries that deliver oxygen-rich blood to various tissues. The arteries are further subdivided into smaller tubes, the arterioles, which in turn branch off into even smaller vessels, the capillaries.

While the walls of larger and medium-sized blood vessels are made of a layer of connective tissue and muscle cells with a very thin inner lining called the endothelium, the walls of the capillaries consist of endothelium alone. Most capillary walls are only one cell thick, and sists of a single red blood cell at a time. It is in the capillaries that the exchange of substances between the blood and the tissues takes place. Through the walls of the capillaries, the blood gives off its oxygen and nutrients and picks up carbon dioxide and waste products. A large part of the waste is extracted from blood as it flows through the kidneys, where the plasma which is the fluid component of blood , seeps through the capillary walls of the kidneys excreting mechanism. Most of the fluid is reabsorbed into the bloodstream;A fraction of a percent and some waste is removed from the body as urine, which accumulates at a rate of about a quart a day in a healthy adult. The blood pressure on the arterial side of the circulatory system is relatively high, but it decreases as the arteries branch off into arterioles and capillaries. On the venous side, the blood pressure is relativelylow. The difference in pressure contributes to the driving force that propels the blood through the circulatory system.

The Veins
The capillaries carrying blood that now has a lower oxygen content merge to form the venules, which in turn converge into successively larger veins. Venous blood, looks purplish or dark red color. Venous blood enters the right atrium through two major vessels: the superior vena cava, which brings blood from the upper part of the body including the brain; and the inferior vena cava, which brings blood from the lower part.

Since the pressure in the veins is normally significantly lower than in the arteries, the walls of the veins are considerably thinner than arterial walls. The larger veins have a system of internal one-way valves that prevents the blood from flowing downward under the pull of gravity when an individual stands up. When he or she moves, the veins are squeezed by the surrounding muscle, which helps propel more blood toward the heart. Without valves in the veins, blood would pool in the legs, which would then be perpetually swollen.

The Pulmonary Circulation
The main function of the pulmonary circulation is to deliver oxygen to the blood and free it of carbon dioxide. This goal is accomplished as the blood flows through the lungs. The pressure in this part of the system is only about one-sixth as great as in the systemic circulation, and the walls of pulmonary arteries and veins are significantly thinner than the walls of corresponding vessels in the rest of the body.

In the pulmonary circulation, the roles of arteries and veins are the opposite of what they are in the systemic circulation. Blood in the arteries has less oxygen, while blood in the veins is oxygen-rich. The circuit starts with the pulmonary artery, which extends from the right ventricle and carries blood with a low oxygen content to the lungs. In the lungs, it branches off into the two arteries, one for each lung, and then into arterioles and capillaries.

The gas exchange between the air we breathe in and the blood takes place in the pulmonary capillaries. Their walls act like filters by allowing molecules of gas but not molecules of fluid to pass through. The total surface area of the capillaries in the lungs ranges from 500 to 1,000 square feet.The carbon dioxide and waste products are removed from the blood in the pulmonary arteries across capillary walls and leave the body through the mouth and nose. The blood that has picked up oxygen returns to the heart through four pulmonary veins and into the left atrium.

Heart Attack

When a coronary artery is completely or almost completely blocked, either by an atherosclerotic plaque or by a blood clot, the result is a heart attack, or myocardial infarction which is called as death of heart muscle. Heart attack causes the heart muscle to change. After about four to six hours, the portion of the affected muscle will have deteriorated to a nonfunctioning state.

The symptoms of heart attack are :
chest pain, usually severe and persistentólasting longer than two minutes;
sweating;
nausea;
dizziness; and
fainting.

Some heart attacks result from spasm of a coronary artery rather than from arteriosclerosis, but the symptoms are essentially the same. About 60 percent of the deaths occur within the first hour after the onset of symptoms (sudden death), before the victim reaches the hospital. The individual who sustains a heart attack and gets to the hospital quickly now has a much better chance of survival, by the treatment known as throm-bolysis, in which a clot-dissolving drug is injected into the bloodstream, where it can dissolves clot in a coronary artery, restoring some blood flow.

After receiving thrombolytic therapy, patients have several treatment options as :
continued medical therapy,
balloon angioplasty,
or a coronary artery bypass graft.
Long-term medical treatment can involve any of the drugs used to treat angina, as well as aspirin, which causes the blood to be less susceptible to clotting.

Heart Failure

Unlike a heart attack, heart failure is usually a slow process. There are several major causes of heart failure:

Long-standing hypertension : As the heart strains under increased pressure, it begins to enlarge and weaken.

Narrowed exit valves in the heart [especially the aortic]: These increase the demand on the heart; the heart must pump harder to push the circulating blood.

Leaky heart valves : Each time the heart pumps, some blood goes forward but some leaks back into its chamber.The heart must work harder to get adequate blood to tissues.

Viral infections : These may damage the heart muscle and weaken it to the point of heart failure.

Alcoho : May cause similar damage to the heart.

Inefficiency : Following a heart attack the heart muscle may not be able to pump efficiently, andblood backs up. This is the most common cause of heart failure.

When the heart cannot able to do its job, blood flow slows. Blood returning to the heart from the veins backs up into the tissues, Like the way water builds up behind a dam. Sometimes fluid collects in the lungs and makes breathing more difficult, especially when lying down or during exercise.

Other symptoms include :
easy fatigue,
an inability to exercise,
swelling in the ankles, legs, and abdomen.

Some nonmedical treatments include :
Rest,
a low-sodium diet,
a slower pace

Medical treatment include :
use of drugs that increase the pumping action of the heart, help the body eliminate excess salt and water, or expand the blood vessels and decrease the resistance in those vessels, making the heartís work easier.

Heart Disorders

Pericarditis
This is caused by a virus or other infection. Pericarditis is an inflammation of the pericardium, which is the outer sac, or membrane, that surrounds the heart like a cellophane wrapping.

In some rare cases, pericarditis appears as part of a collagen vascular disease such as systemic lupus erythematosus, or as a complication of a tumor of the lung or of lymphoma (lymphatic cancer). It may also appear in the late stage of kidney disease, in patients having radiation therapy of the chest, or occasionally as a reaction to medications such as certain antiarrhythmic or antihypertensive drugs.

Pericarditis caused by a viral infection tends to be less serious than pericarditis from other causes. Because the viral infection usually runs its course and disappears. At times viral pericarditis may be a recurrent illness.

Symptoms of Pericarditis :
variable types of chest pain,which often worsens when the individual lies down and improves when he or she sits up.
Sometimes pericarditis is accompanied by fever or shortness of breath.

The treatments for this include :
bed rest,
aspirin or nonsteroidal anti-inflammatory drugs (NSAIDS) for reducing inflammation,
in persistent cases, cortisone.

If pericarditis proves to be a relapsing condition, the pericardium may have to be removed surgically.

Myocarditis
Myocarditis occurs when the heart muscle itself becomes inflamed .Years ago, rheumatic fever wa a common cause, but today, myocarditis is most often idiopathic. No cause can be found, or it is secondary to a viral condition. In myocarditis, the heart muscle degenerates, becomes soft, and may no longer be able to function as an efficient pump. Patients who have it may develop heart failure or arrhythmias.

Cardiologists can sometimes control the svnmtoms of myocarditis with medication, and sometimes myocarditis goes away on its own. Sometimes, myocarditis is an inexorable progressive illness, and it is one of the reasons for cardiac transplants. This is not common, however. Researchers are now looking into treatment of some forms of myocarditis with immunosuppressive drugs, but this therapy is still considered experimental.

Endocarditis
Endocarditis is an infection of a heart valve or inner lining of the heart muscle. Because bacteria can destroy hear t tissue, a valve can develop a leak if it is infected.Infection most often develops on a valve that was previously abnormal in some way either scarred by rheumatic fever, congenitally abnormal, or prolapsed.Today, cardiologists are seeing endocarditis with increasing frequency in patients with normal valves who have used illicit intravenous drugs.

Symtoms include :
Fever, which is the most common symptom,
fatigue,
weight loss,
heart failure may also be present.

There are about 19,000 cases of bacterial endocarditis. fewer than 2,000 of them are fatal. Many of the fatalities occur in intravenous drug abusers.

Treatment:
Antibiotics are usually effective against the bacteria that cause endocarditis.
Anyone with a known heart valve problem should take antibiotics before having dental work, because bacteria from the mouth are capable of entering the bloodstream and causing endocarditis.
This is true of any surgical procedure in which there is the possibility of bacterial contamination of the blood.

Cardiomyopathies
Cardiomyopathy is a term for a number of primary diseases of the heart muscle. In hypertrophic cardiomyopathy, the heart muscle, particularly the left ventricle, thickens. Sometimes the thickening of the heart muscle in the region directly below the aortic valve leads to a partial obstruction of blood leaving the left ventricle.

Restrictive cardiomyopathy is characterized by the replacement of good heart muscle fibers with rigid, less elastic tissue, so that the heart particularly the ventricles cannot fill normally.Amyloid heart disease and sarcoidosis are rare types of restrictive cardiomyopathy.

 


 
Your feedback?




 
Other navigational links under Alphabetical Disease Lookup
 
 

Rate this page?
Good Average Poor



Rating accepted

Thanks for your note! Suggestion if any, will be taken up by the editor squad on a prority. We appreciate your gesture.
Hecapedia squad
Improve hecapedia - Join the squad


 
 
Nothing on this web site, in any way to be viewed as medical advice. All contents should be viewed as general information only.
All health care decisions should only be made with consultation from your physician.

About us | Link to us | Contact us | Associates | Media Center | Business services | Feedback | Report Bugs | Sitemap | Help
privacy policy | disclaimer | terms and conditions | accessibility | anti-spam policy
© 2006 hecapedia