Structure and Functions (Magill’s Medical Guide, Sixth Edition)
All the cells in the human body are dependent on the blood in the cardiovascular system (the heart and blood vessels) for the transport of gases, nutrients, hormones, and other factors. Likewise, the tissues must have a way to dispose of waste products so that they do not build to harmful levels. All these substances are dissolved in the blood, but something must provide the force to transport the blood to all parts of the body at all times—the heart. This organ must beat continuously from early in development to death. It beats without conscious control and can vary how quickly it moves blood throughout the body depending on the needs and activities of the tissues.
In humans, an individual’s heart is about the size of his or her fist and is enclosed in the center of the chest cavity between the lungs. The heart contains specialized muscle cells known as cardiac muscle. These cardiac cells make up most of the thickness of the walls of the heart; they are responsible for moving blood out of the heart and are also involved in maintaining the rhythm of the heartbeat. This heavily muscled layer is referred to as the myocardium. The inner lining of the heart is called the endocardium; it is continuous with the lining of all the blood vessels in the body. The outermost layer of the heart is the epicardium, which covers the myocardium. The heart moves as it beats and is contained within a fluid-filled bag called the...
(The entire section is 1289 words.)
Disorders and Diseases (Magill’s Medical Guide, Sixth Edition)
Even though the heart seems to be adaptable to a variety of situations throughout one’s life, it can malfunction. In fact, diseases of the heart and blood vessels are the number-one killer in the United States. One common disease that affects the heart directly is coronary artery disease, which can lead to life-threatening heart attacks. Although medical researchers are still investigating the causes of coronary artery disease, most of the evidence points to hypertension (high blood pressure) and atherosclerosis (a buildup of fatty plaque in the walls of arteries).
Hypertension is usually defined as a blood pressure greater than 140/90 millimeters of mercury (mmHg) at rest. A typical blood pressure for a young, healthy adult is 120/80 mmHg. The top number measures the force of blood against an artery wall during the contraction of the heart; this is referred to as the systolic pressure. The bottom number, the diastolic pressure, is a measurement of force when the heart is relaxed. If either systolic or diastolic pressure exceeds 140/90 mmHg, the patient is considered hypertensive. The cause of hypertension has not been determined, but it is known that with hypertension the heart must work harder to push the blood through the arteries, including the coronary arteries. Physicians treat hypertension by prescribing drugs that block the effect of the sympathetic nervous system on the heart, such as metoprolol (Lopressor)....
(The entire section is 1227 words.)
Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
The role of the heart in the functioning of the human body was questioned by the ancient Egyptians, who attributed breathing to the heart. It was the Chinese who first documented that the heart is responsible for the pulse and movement of blood. They also believed that the heart was the seat of happiness. The ancient Greeks had a different idea about the function of the heart, believing that it was the region where thinking originated.
It was not until William Harvey (1578-1657), an English physiologist, published his experiments on the heart and circulation that scientists believed blood was pumped continuously by the heart. He observed that both ventricles of the heart contracted and expanded at the same time. Harvey also noted that when the heart was removed from an animal, it continued to contract and relax; that is, it had an automatic rhythm.
More than one hundred years after Harvey published his work, Stephen Hales made the first blood pressure measurements. He did so by inserting a tube into the neck artery of a horse and watching the blood rise 3 meters above the animal. Then early in the twentieth century Willem Einthoven invented an instrument to measure electrical currents. This instrument was used by Thomas Lewis to measure the electrical activity in the heart, the first electrocardiograph (ECG).
By the mid-twentieth century, heart surgeries were being performed to correct heart defects....
(The entire section is 396 words.)
For Further Information: (Magill’s Medical Guide, Sixth Edition)
American Heart Association. http://www.americanheart.org. Site provides comprehensive information on heart disease and conditions, healthy lifestyles, and resources, and provides interactive health tools.
Hales, Dianne. An Invitation to Health Brief. Updated ed. Belmont, Calif.: Wadsworth/Cengage Learning, 2010. This updated text should be read by anyone who wishes an overview of health topics. Several chapters deal with the function of the heart and how lifestyle influences its health.
The Incredible Machine. Washington, D.C.: National Geographic Society, 1994. A colorful book that describes for the layperson how the body works and how one alters one’s own health. The chapter on the cardiovascular system is well written and contains exciting photographs and drawings of the heart.
McGoon, M. The Mayo Clinic Heart Book. 2d ed. New York: William Morrow, 2000. One of the most respected texts for laypersons on heart disease. Covers all aspects of anatomy, physiology, diagnosis, treatment, and prevention.
Mackenna, B. R., and R. Callander. Illustrated Physiology. 6th ed. New York: Churchill Livingstone, 1997. Provides the reader with a visual explanation of physiology on a basic level. Chapter 5 contains many excellent diagrams, illustrations, and explanations of cardiovascular anatomy and physiology.
Marieb, Elaine N., and Katja Hoehn. Human Anatomy...
(The entire section is 311 words.)
Heart (Encyclopedia of Science)
In humans, the heart is a pulsating organ that pumps blood throughout the body. On average, the heart weighs about 10.5 ounces (300 grams). It is a four-chambered, cone-shaped organ about the size of a closed fist. It lies under the sternum (breastbone), nestled between the lungs. The heart is covered by a triple-layered, fibrous sac called the pericardium. This important organ is protected within a bony cage formed by the ribs, sternum, and spine.
(The entire section is 1727 words.)
Heart (Encyclopedia of Nursing & Allied Health)
The heart is a muscular organ of the cardiovascular system that contracts to cause movement of the blood throughout the body.
The heart is approximately fist-sized and located in the chest between the two lungs and behind the ribs and breastbone (sternum). It rests at a slight tilt from vertical, which makes it appear to be on the left side of the body. The walls of the heart are made up of three layers of tissue: epicardium, myocardium, and endocardium. The epicardium is a thin layer on the outer surface of the heart. The myocardium is the muscular layer, made up of cardiac muscle that contracts to do the work of the heart moving the blood. The endocardium is the smooth inner lining of the heart.
The entire structure of the heart is enclosed in a fibrous sac called the pericardium. A small amount of liquid is normally found in the space between the heart and the pericardium, which helps reduce the friction between the epicardial and pericardial membranes.
The heart is divided by a central wall (or septum) into its right and left sides. Each of these sides contains a smaller, upper chamber known as an atrium, and a lower, larger chamber known as a ventricle. The atria and ventricles are separated by a valve made of flaps of tissue that prevent blood flow in the wrong direction. The valve on the left side of the heart is the mitral (or bicupsid) valve, which has two flaps. The right atria and ventricle are separated by the tricupsid valve, which has three flaps.
There are five great vessels branching off from the heart that are responsible for carrying blood into or out of the organ. These five vessels are the aorta, the pulmonary artery and vein, and the superior and inferior venae cavae. The aorta is the main artery, carrying oxygenated blood from the heart out into the body. The pulmonary artery carries blood away from the heart to the lungs, and the pulmonary vein carries blood from the lungs to the heart. The superior and inferior venae cavae carry deoxygenated blood from the upper and lower parts of the body back to the heart.
Unidirectional valves separate two of the great vessels from the chambers of the heart. The pulmonic (or pulmonary valve) separates the right ventricle and the pulmonary artery. The aorta and left ventricle are separated by the aortic valve.
The coronary arteries are two vessels that divide off the aorta and branch out over the entire surface of the heart. These vessels bring oxygenated blood to the heart tissue itself.
The heart functions as a strong, four-chambered muscular pump. It can move more than five quarts of blood through the body each minute, the equivalent of about 2,000 gallons per day. At a typical heart rate of 72 beats per minute, the heart contracts on average 100,000 times per day. This adds up to more than 2.5 billion beats in a 70-year lifetime.
One key to the functioning of the heart is the unique characteristics of its muscular tissue. Cardiac muscle differs from other muscles of the body in that its normal function is a rhythmic contraction, which is the basis for the tissue's ability to respond to the electrical impulses that govern the beating of the heart. The natural pacemaker of the heart, the sinoatrial (SA) node, is located in the right atrium. Cardiac muscle cells that naturally contract at the fastest rate when compared to the other cells of the heart surround this cluster of nerve cells. This area of the heart therefore has the ability to initiate the contraction by sending wavelike electrical signals throughout the organ.
First, the electrical signal causes the two atria to contract, when sends the blood from those chambers into the two ventricles. Then the signal passes down through a group of nerve cells known as the atrioventricular (AV) node. This nerve cluster is located near the center of the heart. The travel through this area slows down the signal so that it reaches the ventricles after the atria have finished their contraction. Then the ventricles contract, moving the blood out of the heart, and the cycle starts again. The heart's electrical activity can be measured using electrocardiography.
The physical functions of the full heartbeat is known as the cardiac cycle. The cycle can be divided into two phases: diastole and systole. Diastole occurs when the heart relaxes and the myocardial fibers lengthen. As the heart dilates, the cavities fill with blood. Diastole of the atria occurs slightly before the diastole of the ventricles.
Systole happens when the part of the heart is in contraction and the myocardial fibers shorten. Again, systole of the atria precedes systolic phase of the ventricles. Systole of the ventricles cause blood to surge out of the heart and into the aorta and pulmonary artery.
Over time, the cardiac cycle occurs as follows. It begins with the diastole of the atrium, where both the left and right atria relax and fill with blood. The right atria fills with deoxygenated blood from the superior and inferior venae cavae. The pulmonary artery fills the left atria with newly oxygenated blood from the lungs. The SA node signals the beginning of systole and the atrium contract, sending blood through the tricuspid and mitral valves into the right and left ventricles, respectively. During ventricle filling, the valves of the great vessels are closed so blood already pumped out of the heart does not leak back.
The electrical signal has now reached the ventricles and they contract, sending the deoxygenated blood of the right ventricle into the pulmonary artery to the lungs and the oxygenated blood of left ventricle into the aorta to the body. During contraction, the tricupsid and mitral valves close to prevent flow back into the atrium. This cycle is repeated continuously.
Role in human health
The heart is the centerpiece of the elaborate and extensive human cardiovascular system. Responsible for moving the blood throughout the body, this system transports the necessities for lifexygen, nutrients, hormones, immune functionso the cells. The system also transports wastes such as carbon dioxide away from the cells to the organs responsible for their elimination from the body. The heart is the driving force behind this essential
Diastolehase of the heartbeat where the ventricles relax and fill with blood.
Endocardiumhe thin, innermost layer of the heart.
Epicardiumhe outermost layer of the heart.
Myocardiumhe middle, working layer of the heart containing the heart muscle cells.
Regurgitation defect of the heart valves that interferes with its ability to close completely, allowing blood to leak in the direction opposite of circulation.
Septum physical divider between chambers, found between the atria and the ventricles.
Stenosis stiffening of the heart valves, which narrows its opening and can interfere with function.
Systolehase of the heartbeat where the ventricles contract and force blood from the heart.
transport. Therefore it is not surprising that a healthy heart is necessary for a healthy body.
There are several risk factors for heart problems that can be controlled through preventative measures. These include lowering blood cholesterol levels with diet, exercise, or in extreme cases, medications. Lower cholesterol levels lower the probability of coronary artery disease (clogging of the arteries that bring oxygenated blood to the heart), a major cause of heart failure. Keeping blood pressure, blood sugar levels, and body weight within normal levels also greatly decreases the chance for heart problems. Other controllable risk factors include a sedentary lifestyle, stress and anger, and smoking.
Common diseases and disorders
According to 1999 estimates, approximately 58.8 million Americans have one or more types of heart disease, as it is most broadly defined. Although the cause and effect of various heart diseases can be examined in a particular patient, it is difficult to make generalizations about different diseases and disorders. Often one disease of the cardiovascular system will contribute or even cause another. In any case, the various symptoms of an unhealthy heart, whatever the cause, are quite common.
Several diseases of the heart are related to athero-sclerosis, the accumulation of cholesterol in the arteries. When this problem occurs in the coronary arteries, it is known as coronary artery disease. Three conditions which can follow from the loss of blood flow to the heart due to the clogged arteries are angina pectoris, a severe chest pain, myocardial infarction (commonly called a heart attack), or congestive heart failure, where the heart is unable to efficiently pump the blood throughout the body.
Angina pectoris is the result of temporary deprivation of oxygen and often occurs after stress or exertion. Heart attacks occur because a portion of the heart is permanently deprived of blood and the cells become damaged. Congestive heart failure involves a cascade reaction of the body to inefficient heart action that results in accumulation of fluids in the outer reaches of the body. In each of these cases, the trigger cause of the condition was the blockage of the arteries that supply the heart.
A second set of heart diseases involves an abnormality in the electrical system of the heart. Called arrhythmias, these diseases occur when the heart no longer beats in the standard pattern. Altered beat function can greatly reduce the efficiency of the heart and can result in fainting (due to lack of blood to the brain), palpitations (an unpleasant awareness of the beating of the heart), shortness of breath, and chest pain. Some common types of arrhythmia include brachycardia (slow heart beat), atrial fibrillation, and ventricular fibrillation.
Brachycardia is commonly treated using pacemakers, an inplanted device that keeps the heart's rhythm steady. Fibrillations are very fast, inefficient beats of the atrium or ventricles. Fibrillation can be treated with medication or an implanted cardiac defibrillator (ICD) that delivers a shock to the heart to restart normal beating. Arrhythmias can be caused by coronary heart disease, high blood pressure, or a previous heart attack, emphasizing the interrelation of the various heart diseases.
A third kind of heart disease involves damage to one of the four valves of the heart. The frequency of damage to these structures is related to the work that they doith the structures undergoing the greatest amount of pressure having the highest frequency of disease. Thus, valve problems occurs most frequently with the mitral valve, then the aortic, tricupsid, and pulmonic. Mitral valve prolapse is the most common condition, where excess valve tissue prevents it from closing properly. Surgery may not be necessary, however, until leaking of the valve, known as valve regurgitation, accompanies the prolapse. Regurgitation is a symptom of stenosis, a condition where the valve has become too stiff to function properly.
Untreated rheumatic fever, a bacterial infection, is the most prevalent cause of valve problems. The use of antibiotics to treat strep throat has greatly reduced the incidence of this disease in the United States. Congential defects are the second most common cause of heart valve conditions.
Congenital heart defects, in the valves and other structures, occur when the heart or its vessels do not develop normally before birth. The most common congenital heart defect is a combination of four problems called the teralogy of Fallot. With this problem the ventricular septum is incomplete, there is an obstruction to blood flow beneath the pulmonary artery, the aorta is shifted rightward, and the right ventricular wall is thickened.
A final kind of heart disease is cardiomyopathy. This disorder occurs when the muscle of the heart degenerates. There are multiple causes of cardiomyopathy and it is the number one reason people undergo heart transplants. Categorized by the type of muscle damage, there are three general types of cardiomyopathy: dilated, hypertrophic, and restrictive. Dilated cardiomyopathy refers to the enlargement of the heart that is a response to the overall myocardial weakness. Many problems can cause dilated cardiomyopathy including viral infections, excessive alcohol intake, and myocarditis (inflammation of the heart).
Hypertrophic cardiomyopathy is an abnormal over-growth of the heart muscle. An inherited disease, the overgrown muscle blocks the movement of blood both into and out of the heart. Restrictive cardiomyopathy is due to a stiffening of the heart muscle that prevents it from fully relaxing during diastole. This problem is a symptom of other diseases such as hemochromatosis (a defect in iron use by the body) or amyloidosis (overproduction of antibodies by the bone marrow that cannot be broken down).
Baum, Seth J. The Total Guide to a Healthy Heart. New York: Kensington Books, 1999.
Topol, Eric J., ed. Cleveland Clinic Heart Book. New York: Hyperion, 2000.
Crumlish, Christine, et al. "When Time is Muscle." American Journal of Nursing 100 (January 2000): 26.
Thomas, Donna Jean G., and Barbara F. Harrah, "A New Look at Heart Failure." Home Healthcare Nurse 18 (March 2000).
American Heart Association. 7272 Greenville Avenue, Dallas, Texas 75231. (800) AHA-USA1. <<a href="http://www.americanheart.org">http://www.americanheart.org>.
Heart Information Network. June 29, 2001. <<a href="http://www.heartinfo.org">http://www.heartinfo.org> (July 2, 2001).
Michelle L. Johnson, M.S., J.D.
Heart (Contemporary Musicians)
Heart is one of the few rock groups to feature womeneattle-born sisters Ann and Nancy Wilsons lead performers. The band has been working together, with some personnel changes, since the early 1970s, when the members were living in western Canada. Since their first album, Dreamboat Annie, went platinum in 1975, the entertainers in Heart have known every extreme that plagues famous rock bands, from the most dizzying heights of success to the most frustrating lulls in appeal.
As Gwenda Blair noted in Ms. magazine, however, the Wilson sisters "have always managed to hold up, whether they were facing . . . breakneck superstar tours, or. . . the seemingly endless uphill struggle to break out of. . . obscurity." Blair attributed the group's tenacity to the Wilsons' special bond, "the easy camaraderie of best girlfriends mixed with the special familiarity and sensitivity of sisterhood." The reporter added: "The continuity and companionship provided by that combination have carried the Wilsons a great distance over the years."
Indeed, Heart has enjoyed an impressive level of success throughout most of its two-decade-long existence: four platinum albums, scores of sold-out tours, and number-one hits in the 1970s and 1980s. Blair described the group's draw on its listeners: "Heart's music, with its . . . bouncing-up-and-down-in-your-seat sound is what millions of people like. To some critics Heart's sound may be sheer bubblegum blare fit only for undisceming and voracious teen appetites. But to Ann and Nancy, escape and fantasy, not heavy messages or avant-garde music, is what rock is all about."
Press coverage of Heart has centered on the Wilson sisters almost since the band began playing together in a one-room house in Vancouver. By all accounts, including their own, Ann and Nancy were ordinary, middle-class young women who grew up in Bellevue, a suburb of Seattle, Washington. They were teens in the 1960s, daughters of parents who embraced the radical causes and experimental lifestyles of that era. "We were pretty normal for the time we grew up in," Ann told Rolling Stone. "What we experienced was going on in suburbs all over the country. We weren't that different." On the other hand, high school chum Sue Ennis, who has since written songs for Heart, recalled that the Wilsons were aloof from most of their peers, disdainful of the standard high school popularity contests, and happiest when they were alone in a bedroom, composing or listening to rock music. To quote Rolling Stone contributor Daisann McLane, as teenagers Ann and Nancy "played and wrote songs constantly, moody evocations of late-adolescent alienation."
Ann graduated from Sammamish High School in 1968 with one ambition: to sing in a band. She began working with Tex Blaine and the Skyway Ranch Boys, but soon joined a psychedelic rock band called White Heart, staffed by guitarist Roger Fisher and bassist Steve Fossen. After doing a few gigs under the name HocusPocus, the group members opted to call themselves Heart. Ann began a long romantic relationship with Michael Fisher, Roger's brother, and Nancy eventually became involved with both the band (as a guitarist and flute player) and with Roger Fisher. Blair wrote of the Wilsons: "Two real-life Barbies, they . . . acquired their very own Kenswo handsome brothers who were also members of Heart."
Heart's early existence can hardly be described as a Barbie-and-Ken dream life. The band members moved to Vancouver and subsisted on brown rice and stolen fruit while trying to build a following. Laura Fissinger describes the group's struggle, and ultimate success, in Rolling Stone: "In the early Seventies, Heart was just one more club band, doing six nights a week, four sets a night, and letter-perfect carbons of 'Stairway to Heaven.' Guitarist Howard Leesehe only other Heart member still around from the early daysas working for Mushroom records in Vancouver when he was tapped to produce the group's first demo. Leese's employers initially courted Ann as a solo act. When she said no, they took the whole passel."
That "whole passel" turned out a debut album, Dreamboat Annie, that went platinum in seven months despite its obscure Canadian label and minimal promotion budget. The best known song from the album, a mysterious rocker called "Magic Man," is today considered a classic. Heart turned out several more hit albumsLittle Queen (1977), Magazine (1978), Dog and Butterfly (1978), and Bebe Le Strange (1980)nd had smash singles with "Crazy on You," "Barracuda," and "Dog and Butterfly." McLane noted that the most successful Heart songs "graft heavy-metal musicianship to emotional, image-laden lyrics. This unlikely combination is held together by Ann's powerful, three-octave soprano. She can belt and screech the hardest rock tune, then slide through every delicate nuance of a tender folk ballad."
Nonstop touring also helped to promote Heart as a top rock band. The group's dynamicswo sisters romantically involved with two brothersade for frenzied press coverage and, at first, energetic live shows. Then problems began to beset Heart. First the group broke its contract with Mushroom and underwent a costly court battle over some unfinished tapes the label wanted to release. Then Ann ended her involvement with Mike Fisher, even though she credited him with the band's success and suffered pangs of anxiety without his support. Nancy followed suit by breaking up with Roger Fisher and then firing him from the band. For a variety of reasonshe loss of Roger's riveting concert presence among themeart went into a nosedive in the early 1980s.
The group continued to tour relentlessly, and continued to produce albums, but popular support faded. "Our management had us on the road nonstop," Nancy told Rolling Stone. "We surfaced from our exhaustion just long enough to see that we were being mishandled and swept under the carpet." Having taken responsibility for the direction of the band, the Wilsons switched from Epic to Capitol records in 1984. The following yearnd on into 1986eart experienced a major come-back with their ninth album, Heart, and two top-selling singles, "What About Love" and "These Dreams."
Ann and Nancy, whose titillating music videos have occasionally angered censorious critics, admit that their music is "wrong for any given time for what was in"n observation echoed by some rock writers. The media may be condescending toward Heart's "basic blueprint of heavy metal meets Joni Mitchell," to quote Fissinger, but audiences respond to it warmly. According to Ariel Swartley in Rolling Stone, the members of Heart "need no showmanship to carry them: conviction has already been built into the melody, tension embedded in the harmonies." Swartley also concluded that in Ann Wilson, Heart has "possibly the greatest female rock & roll singer ever. . . . And when she's hot. . . the only reserved you're thinking about is your seat for the next show."
Dreamboat Annie, Mushroom, 1976
Little Queen, Portrait, 1977
Magazine, Mushroom, 1978.
Dog and Butterfly, Portrait, 1978
Bebe Le Strange, Epic, 1980
Greatest Hits Live, Epic, 1980
Private Audition, Epic, 1982
Passionworks, Epic, 1983.
Heart, Capitol, 1985.
Bad Animals, Capitol, 1987.
High Fidelity, February, 1978.
Mademoiselle, June, 1982.
Rolling Stone, November 30, 1978; March 22, 1979; April 24, 1986.
Anne Janette Johnson