|
| (Click to enlarge) |
| heart |
A. superior vena cava B. pulmonary artery C. left atrium D. left ventricle E. right ventricle F. inferior vena cava G. right atrium H. aorta (Carlyn Iverson) |

at heart
[Middle English hert, from Old English heorte.]
Heart is a red variety meat. Calf, lamb and chicken hearts are small and tender, and therefore the most sought after. Pig heart is moderately tender. Beef heart is larger, firmer and has the strongest flavor.
Buying
Choose: a fleshy heart with a fresh appearance and red-brown (lamb and beef), bright red (pig and chicken) or pale red (calf) in color.
Preparing
Remove the fat around the heart, the membranes and veins, wash and, if desired, soak the heart for at least 1 hr in the fridge in cold water to which 1 tablespoon (15 ml) of vinegar per 4 cups (1 l) of water has been added (to tenderize, especially for beef heart). Rinse well, then wipe.
Heart is often cooked as a stew or a casserole. Peruvians are fond of anticuchos, marinated and grilled beef hearts.
Storing
In the fridge: 1-2 days.
In the freezer: 3-4 months.
Cooking
Braised or simmered: pig and beef hearts (3-4 hr, add liquid as needed). The hearts of young animals (2-3 hr).
Broiled, grilled or roasted.
Sautéed: sliced heart (5-7 min).
Serve slightly pink.
Nutritional Information
| simmered beef heart | braised lamb heart | braised pig heart | braised calf heart | simmered chicken heart | |
| protein | 29 g | 25 g | 24 g | 29 g | 26 g |
| fat | 6 g | 8 g | 5 g | 7 g | 8 g |
| cholesterol | 193 mg | 249 mg | 221 mg | 176 mg | 242 mg |
| calories | 175 | 185 | 148 | 186 | 185 |
| per 3.5 oz/100 g | |||||
Browse other variety meats:
Browse other foods: Vegetables | Legumes | Fruits | Nuts and Seeds | Seaweeds | Mushrooms | Cereals and Grains | Fish | Crustaceans | Mollusks | Herbs, Spices and Seasonings | Meats | Variety Meats | Delicatessen Meats | Poultry | Dairy Products | Sugars, Cocoa and Carob | Fats and Oils | Binders and Leavenings | Coffee, Tea and Herbal Teas
For more information on heart, visit Britannica.com.
(invertebrate)
Hearts of invertebrates can be categorized according to the source of the electrical rhythmicity that underlies their beat. Rhythmic electrical activity can arise in the muscle itself (myogenic hearts) or in neurons that drive the heart muscle (neurogenic hearts). Most mollusks and some insects appear to have purely myogenic hearts; these hearts beat normally when isolated from neural inputs. Conversely, the hearts of the higher crustaceans and the xiphosuran Limulus are usually considered to be purely neurogenic: motor neurons impose their rhythmic electrical activity on heart muscle fibers by means of direct excitatory synapses. Without neural input, the heart ceases to beat. Other invertebrates, including gnathobdellid leeches and some insects, have hearts that can produce a myogenic beat but require rhythmic neural input to coordinate that beat and maintain the proper rate.
In the marine snail Aplysia, an organism with a myogenic heart, a muscular heart consisting of an auricle and a ventricle is located in a dorsal pericardial cavity. The rhythmic contractions of the auricle fill the ventricle with hemolymph, which is then pumped through the open circulatory system by the rhythmic contractions of the ventricle. The normal heartbeat period lasts about 3 s. A pair of semilunar valves prevents backflow of hemolymph into the auricle during ventricular contraction. Three arteries issue from the ventricle toward the anterior, and a single semilunar valve prevents backflow from them during ventricular expansion. The arteries carry the hemolymph to the various body organs, where they end in tissue spaces. The hemolymph then collects in the hemocoel and returns to the heart by two parallel veins, one through the kidney and one through the gill. Although the Aplysia heart is innervated, its normal beat persists after denervation.
The lobster is an example of an organism with a neurogenic heart. A muscular heart pumps hemolymph through the open circulatory system. This heart is located dorsally along the thoracic midline and is suspended within a pericardial cavity by ligaments. The heartbeat period lasts about 2 s. Large anterior- and posterior-going arteries, which branch extensively to supply various body organs, issue from the heart. Semilunar valves, located at the juncture of each artery with the heart, prevent backflow of blood into the heart when it relaxes. Hemolymph enters the heart from the pericardial sinus through six ostia, which have valves to ensure unidirectional flow. The rhythmic discharge of motor neurons innervating the heart by way of excitatory chemical synapses produces the heartbeat. These motor neurons are located in the cardiac ganglion on the inner dorsal surface of the heart. The cardiac ganglion contains only nine neurons, which generate a simple two-phased rhythm of electrical activity. The four posterior small cells (cells 6–9) are interneurons, and the five anterior large cells (cells 1–5) are the motor neurons. See also Nervous system (invertebrate).
Heart (anatomy)
The muscular pumping organ of the cardiovascular system. The heart typically lies ventrally, near the anterior end of the trunk; it is ventral and medial to the gills in fish and at the base of the neck or in the chest region of tetrapods. In humans it is located behind the breastbone and ribs between the third and fifth costal cartilages. Its anterior portion or base is directed to the right and dorsally and is the area where the great vessels enter and leave the heart. The lower muscular portion ends in a blunt apex which lies behind the fifth costal cartilage on the left.
The muscular wall of the heart, the myocardium, is lined by an inner endocardium and is covered externally by membranous visceral pericardium. There are coronary arteries and veins to and from the heart, which has a specialized neuromuscular conducting system and autonomic nerve supply.
In fishes the heart is basically a simple tube which becomes subdivided into four successive chambers, the sinus venosus, atrium, ventricle, and conus arteriosus. Blood from the body enters the sinus and leaves the conus to go to the gills to be oxygenated. The ventricle supplies the main pumping force.
When lungs are introduced into the system in lungfish and tetrapods, the mixing of oxygenated and nonoxygenated blood becomes a problem. In brief, the sinus venosus and conus arteriosus disappear, becoming incorporated into the other chambers or the bases of the great vessels. At the same time the atrium and later the ventricle become divided into right and left chambers by a median septum.
In birds and mammals including humans (see illustration) the medial fibromuscular septum divides the heart into two lateral halves, each consisting of a thin-walled receiving chamber or atrium and a thicker, muscular pumping chamber or ventricle. Blood enters the right atrium from the superior and inferior venae cavae which drain most of the body. It passes through the tricuspid valve to the right ventricle and is pumped to the lungs during systole, or contraction of the heart. Blood returns from the lungs by way of the pulmonary veins to the left atrium, passes into the left ventricle through the mitral valve, and during contraction is pumped out into the aorta. See also Cardiovascular system.

Internal structure of four-chambered mammalian heart, ventral view. (After C. K. Weichert, Anatomy of the Chordates, 2d ed., McGraw-Hill, 1958)
Usually from ox, lamb, pig, or sheep; a 150-g portion is a rich source of protein, niacin, iron, and vitamins B1 and B2, also, unusually for a meat product, a good source of vitamin C; contains about 9 g of fat, of which half is saturated; supplies 270 kcal (1130 kJ).
The heart is an amazing pump. It maintains the circulation of blood by beating approximately 70 times a minute, more than 36 million times each year. The heart is about the size of a clenched fist and lies in the chest cavity between the two lungs. Its walls consist mainly of cardiac muscle. It is divided into a left side and a right side, each of which has two chambers: an atrium and a ventricle. Deoxygenated blood from the veins enters the right atrium and is passed through the tricuspid valve into the right ventricle. This contracts and pumps blood through the pulmonary artery into the lungs. Oxygenated blood returns through the pulmonary vein into the left atrium and then into the left ventricle. This contracts forcefully to pump oxygenated blood to the rest of the body. The unidirectional flow of blood is maintained by heart valves.
The heart is a very active organ, and it needs a good supply of oxygen to keep it alive. Some of the oxygenated blood pumped out of the left ventricle goes directly to the heart through the coronary arteries. These branch out to supply the thick heart muscle with oxygen and nutrients. Disease of these arteries causes a heart attack.
Since heart consists almost entirely of muscle, it tends to be quite tough. In general, the younger the animal, the more tender the heart. Beef heart is the largest of those commonly available, followed by those of calves, lambs and chickens. Choose hearts that are fresh-smelling, plump and red, avoiding those with a brown or gray hue. Refrigerate, loosely wrapped, for no more than a day or two. Before using, remove any excess fat and wash thoroughly. Heart can be braised, stewed or chopped and added to cooked dishes such as stews. Small hearts, such as those from young lambs and pigs, are often stuffed and sautéed or roasted and served one per person. Chicken hearts from a young bird can also be sautéed. See also variety meats.
Throughout human history the rhythmic beat of the heart has quintessentially represented life. Until the advent of the heart-lung machine, the lack of a heart beat, unless reversed within a few minutes, invariably signalled death. The beat of our own heart can be apparent to us in the pulse felt, or seen, at various parts of the body, occasionally heard or — because of an unusual rhythm or ‘skipped’ beat — noticeable in the chest.
The heart is a hollow muscular organ. It acts as the ‘prime mover’ for the circulation of the blood and the maintenance of the blood pressure. A certain volume of blood is delivered with each beat, and a further key aspect is the pressure at which this flow is delivered. Vital functions such as those of lungs and kidneys, or the exchange of components of the blood and tissue fluid at the capillaries, are critically dependent on the pressure achieved within the circulatory system.
Anatomy
The heart comprises a series of blood-filled chambers; the walls are composed virtually entirely of muscle cells of a type unique to the heart (cardiac myocytes). The heart is actually two double pumps acting in series; there are four chambers in all. The right side receives blood returning from the entire body (in the great veins) and pumps it into the pulmonary artery, which supplies only the alveoli (gas exchange sites) in the lungs. The left side receives blood from the lungs and pumps it into the aorta, the largest artery. (The heart is generally illustrated as seen from the front, so ‘left’ and ‘right’ appear mirrored.) The aorta branches to form the arterial tree that supplies blood to the whole body. The heart, appropriately, is itself the first organ supplied with blood from the aorta. The coronary arteries open from the beginning of the aorta and take blood to all parts of the heart tissue. Each side of the heart has an upper chamber, the atrium (plural: ‘atria’), into which the veins drain. They serve as antechambers to the respective ventricles, the thicker-walled chambers that lie below them.
Atria and valves The arrangement of one-way valves and the prevailing pressures mainly determine blood flow from vein-to-atrium-to- ventricle during the cyclic activity of the heart beat, but some pumping of blood by the atria into the ventricles also occurs. The valves preventing back-flow from ventricle to atrium are tough, parachute-like structures partly anchored in the connective tissue plate which forms the physical union of the ventricular and atrial portions of the heart. Their free edges are restrained by several papillary muscles. These are slim extensions from the inner wall of the ventricles, each with a tendinous end fused with the valve; acting like parachute cords, they prevent the valve being pushed through into the atrium as its flaps become filled when the ventricle contracts and puts pressure on its contents. The mitral (or bicuspid) valve on the left side has two flaps, and the tricuspid valve on the right has three. The ‘parachutes’ press together forming a complete closure preventing regress of blood into the respective atrium whence it came. Instead, when the pressure has risen sufficiently, blood is directed into the pulmonary artery and the aorta through one-way valves which separate them from, and prevent back-flow into, their respective ventricles (see Figure).
The heart beat
The heart beats between 60 and 220 times per minute in a typical young adult; 40 to 50 million beats per year. The rate alters, often rather obviously, according to one's state of physical and mental activity. This results in pumping over 3 million litres of blood (per year) through the body and an equal volume through the lungs. The pump work done by the heart is equivalent to lifting a 1 kg weight to about twice the height of Mount Everest each day. This level of persistent, rhythmic, and decidedly dynamic activity may provoke a sense of awe, although it is hardly more remarkable than the prosaic activity of every other organ — except in its absolute necessity to keep at it! We will first consider the electrical processes of the heart since, like many muscles, it is triggered into activity (contraction, the heart beat) by an electrical wave. This section is followed by consideration of contraction itself.
Electrical aspects The left and right atria beat virtually simultaneously and then, after a fraction of a second's delay, both ventricles contract. Electrical activity, as in most other muscles, triggers the contraction. This activity arises not from excitatory nerve fibres, but spontaneously within the heart itself from a small clump of pacemaker cells near the point where the vena cava joins the right atrium: the sino-atrial (SA) node. The electrical wave, or action potential, spreads across the heart from cell to cell. This spread is made possible because each heart cell is connected to its immediate neighbours at several contact regions which offer a relatively low resistance to the flow of electrical current. All the muscle cells of the heart are thus electrically linked together. This means that the activity spreads as a wave, its direction determined by the cell-to-cell couplings available. It also means that, as far as we know, every cardiac myocyte is active at some stage during every heart beat. The muscle cells of the atria and ventricles only make electrical contact in one small region, the atrio-ventricular (AV) node at the centre of the heart. Thus, activity follows a predictable, regular path — across the right and left atria, through the AV node, along specialized faster-conducting heart cells (Purkinje fibres) on the internal face of the muscular wall between the two ventricles (interventricular septum), and thence through the substance of both ventricles. Heart cells, like other electrically excitable cells, become inexcitable (refractory) for a brief period after each action potential. Consequently, once the wave has passed right through the ventricles it ceases, since there are no non-refractory cells available to excite. A new wave is spontaneously initiated at the pacemaker region.
Contractile (mechanical) aspects All the heart muscle cells are thus electrically excited and it is this that triggers them to contract. The wave of contraction, therefore, follows the same sequence: atria first, then ventricles. The electrical activity triggers an abrupt rise in the concentration of ‘free’ calcium ions inside the cells — a common feature in signalling contraction in muscle of every type. The calcium ions required are derived in part by influx from the extracellular fluid, in part by release from intracellular stores in the sarcoplasmic reticulum. The influx is through calcium-selective channels in the surface membrane which are opened by the depolarization. The influx itself transiently promotes further influx, and also triggers the release of more calcium from the intracellular store.
In each ventricle, as the muscular walls contract (develop tension and shorten) they press upon the blood they enclose. The pressure rises and the AV valve fills out and closes. At this stage of the cycle, the exit valve into the relevant artery (pulmonary artery or aorta) is also closed because the pressure in the arteries is higher than that in the ventricles. Temporarily, each ventricle is thus a closed chamber, it can neither lose nor gain blood, so pressure rises quickly until it exceeds that in the exit artery; the exit valve is then pushed open and blood is ejected, squirted from the ventricles as their muscular walls continue to shorten. The pressure at which the valve opens is much higher on the left side than on the right side, in accordance with the higher blood pressure in the aorta and its branches than in the pulmonary artery and its branches. The resistance offered by the lungs to blood flow is much less than that by the body generally; thus the pressures required of the right ventricle can be lower, yet achieve the same flow rate. Both ventricles eject the same volume of blood (the stroke volume): in the adult heart, about 70 ml (half a teacup) which is half or less of the volume it contained. As action potential finishes, the intracellular calcium concentration has already started to reduce again: some calcium is being ‘pumped’ back into the store, and some is leaving the cell by an ion exchange process. With the raised calcium concentration signal thereby removed, the force of contraction quickly wanes in the muscle, so ventricular pressure falls. The elasticity of the arteries, which were dilated when blood was ejected into them, now ensures that a higher pressure is sustained in them than in the rapidly relaxing ventricles (the ‘garden hose’ effect, familiar to those who have turned off a hose-pipe supply tap only to see water continue squirting as the elastic pipe collapses). The respective exit valves are thus pushed closed again, preventing reflux into the ventricles. Blood pressure, therefore, falls more slowly in the arteries than in the ventricles. At this stage about 90 ml of blood remains in each ventricle. Pressure continues to fall quickly until it is below that in the atria. Thus, the AV valves are pushed open, allowing blood to flow from the atria into the ventricles ‘topping them up’ with more blood. (Despite the appearance in some published schematic diagrams and ‘cartoon’ sequences, at all stages of the heart beat the chambers are ‘full’ of blood. It is the enclosed volume which changes, depending on the tension and elasticity of the muscular walls and the status of the inlet and outlet valves.)
The return of the ventricle to its ‘resting’ shape between beats is due to its own elasticity. Like a squeezed sponge or hollow rubber ball, this significantly ‘sucks’ blood from the atria, thereby contributing to its own filling. The reduction of this factor in old age or its enhancement by athletic training have a major effect on overall cardiac function. These effects are analogous to problems associated with ‘stiff’ inelastic valves which perhaps more obviously compromise effective flow in and out of the chambers of the heart.
The state when the heart is contracting is termed systole (sis'-toe-lee) ; the relaxed state is termed diastole (di-a'-stoe-lee).
Control of pump function
The cardiac output is the volume of blood pumped per minute by each ventricle — some 5 litres/minute at ‘rest’ — and is simply the product of heart rate and stroke volume. Cardiac output will thus alter if either varies. The stroke volume is in turn influenced by cardiac filling and by the contractility of the cardiac muscle itself — its intrinsic ability to contract (shorten and/or produce tension).
Heart rate The earliest human hunters will have noticed, like later horror film makers, that even when removed from the body, the heart continues to beat for a time. Other organs also continue to live, but their activity is hardly as impressive as that of the heart.
Because all the cells of the heart are electrically connected to their neighbours, the whole behaves as a unit. Most regions are inactive, unless artificially stimulated. The activity of the regions with the property of ‘firing’ spontaneously is conducted to all their inactive neighbours, so they act as pacemakers. The inherent pacemaker firing rate, typically about 100 per minute, is influenced by nerve actions of the autonomic nervous system: sympathetic nerves release noradrenaline which increases rate, and parasympathetic (vagus) nerve fibres release acetylcholine which slows the rate. Heart rate typically varies between 60 per minute (in deep sleep) to approaching 200 per minute (during brief bursts of maximal exercise). The normal ‘resting’ rate while sitting, relaxed, is about 70 per minute, but shows wide variation amongst entirely healthy individuals. (In one university class of 350 twenty-year-old students, the range was 48 to 90 per minute.) One common feature is a marked variation within the breathing cycle: breathing in usually increases the rate. Physical fitness, particularly that associated with endurance rather than muscle strength, is often associated with a low resting rate. Extremes such as the tennis player Bjorn Borg, or the professional cyclist Miguel Indurain, with resting values in the low 30s per minute, are well known. Young children have higher resting rates; whilst still in the womb, a baby will have a rate of 120 to 160 beats per minute; it is often reported that rates above 140 indicates a female baby, but there are more reliable tests!
Cardiac filling ‘Filling’ reflects the flow of blood back into the heart (venous return from the lungs and the body). William Harvey observed that the presence of valves requires that blood in the larger veins can only flow towards the heart, the key to recognizing that blood circulates. Amongst other factors, the extent of muscular activity, breathing movements, and body positions (standing, lying, arms or legs raised) all affect the rate of return of blood to the heart. Cardiac muscle shows the unusual property that, within limits, it contracts more powerfully when starting from stretched lengths, so that the ventricle ‘empties’ more forcibly when it is ‘filled’ more than usual. This is achieved at trivial extra metabolic cost; the efficiency of pumping thus increases as output increases; surely a paradigm for ‘productivity gains’. This property allows the heart to compensate automatically when the volume of blood within it at the start of the beat (the end diastolic volume) is greater than previously, by pumping more forcefully, thus ejecting a larger volume. This feature is termed Starling's ‘Law of the Heart’, after one of its discoverers.
Contractility It is obvious that an intrinsically stronger heart will be able to eject blood more forcefully and more completely. Unlike our voluntary (skeletal) muscles, the ‘strength’ of heart muscle can vary quickly, even from one beat to the next. This is because it is sensitive to chemical influences (especially of adrenaline/noradrenaline) and electrical influences that can rapidly modify the intracellular processes that underlie contraction. Additionally, as with voluntary muscle, the extent of growth and development of the heart muscle will affect the overall strength of the organ; athletes generally have thicker heart walls which match the larger muscles in their thicker limbs. A normal, sudden increase in contractility is associated with the onset of physical activity or even with its anticipation; this is signalled to the heart, along with the increase in heart rate, by activity in the sympathetic nerve fibres which release noradrenaline. The combination of higher rate and stronger, more rapid contraction tends to match cardiac output to the increased ‘demands’ for blood flow to the exercising muscles.
The heart of the matter and the matter of the heart
The control systems which influence the heart rate and strength of beating are the same as those implicated in such apparently diverse processes as blushing, breathing rate, sexual arousal, mental stress, or alertness. These links seem to have been recognized by our forebears in advance of the definitive precision of the discoveries of cardiovascular physiology. Poets report that hearts leap, hearts are strong, hearts are united, hearts are hot, heart strings are plucked, hearts are ‘in the mouth’, hearts become feeble, hearts are chilled, hearts tremble, and hearts are broken. In human history, the nature of the circulation of the blood and the (quite literally) central role of the heart in this system are still recent discoveries, even though they rank with the very earliest of the truly ‘modern’ scientific method. Nevertheless, the heart (with perhaps the eye) is the organ most quoted in literature and song to define the essential qualities of life and even its very presence. The ready perception of the action of the heart, its racing rate when we are excited or surprised, aroused or shocked, the shallow, rapid beat encountered in feverish poor health, the occasional irregularity of beat that can concern us all (often, thankfully, quite unnecessarily), together form the shared ‘heart’ experiences of mankind that writers and poets have ever drawn upon. We are generally blissfully unaware of the other hives of metabolic industry that contribute to our physiology. The liver, the thyroid, the hypothalamus, the pituitary, the spleen, the pancreas, not one of these is dignified with a property recognizable to their owners. It is surely the literal vitality of the heart's rhythmic beating, the recognition of its link to the movements of blood, the necessary identity between this continual activity and life itself (outside an operating theatre) that validates the continuing truth of poetic notions of ‘heart’
— David J. Miller
See cardiovascular system. See also autonomic nervous system; blood pressure; blood circulation; blood vessels; cardiac muscle; heart attack; heart block; heart failure; heart sound.
noun
Idioms beginning with heart:
heart of the matter
hearty
heart and soul
heart goes out to, one's
heart in one's mouth, have one's
heart in the right place, have one's
heart stands still
heart of gold
heart of stone
heart sinks, one's
heart to heart
See also absence makes the heart grow fonder; after one's own heart; at heart; break someone's heart; by heart; change of heart; cold hands, warm heart; cross my heart; cry one's eyes (heart) out; cut to the quick (heart); do one (one's heart) good; eat one's heart out; find it in one's heart; from the bottom of one's heart; get to the heart of; give someone heart failure; half a heart; harden one's heart; have a heart; have no heart for; heavy heart; in one's heart of hearts; lose heart; lose one's heart to; near to one's heart; not have the heart to; open one's heart; pour out one's heart; set one's heart on; sick at heart; steal someone's heart; steel one's heart against; take heart; take to heart; to one's heart's content; warm heart; warm the cockles of one's heart; wear one's heart on one's sleeve; with all one's heart; young at heart.
Definition: courage
Antonyms: cowardice, fear
n
Definition: essence, central part
Antonyms: edge, exterior, exteriority, outside, periphery, surface
n
Definition: person's emotions
Antonyms: head
The center portion of a log, usually referring to heartwood or duramen.
A hollow, four-chambered muscular organ lying in the thoracic cavity between the lungs. Its wall consists mainly of cardiac muscle. The heart is divided by a septum into a right and left side, each of which has two chambers: an atrium and a ventricle. Deoxygenated blood from the veins enters the right atrium and is passed into the right ventricle. This contracts and pumps the blood through the pulmonary artery into the lungs. Oxygenated blood returns through the pulmonary vein into the left atrium and then into the left ventricle. This contracts forcefully to pump the oxygenated blood to the rest of the body. Unidirectional flow of blood is maintained by heart valves.
Anatomy and Function
The human heart is a pear-shaped structure about the size of a fist. It lies obliquely within the chest cavity just left of center, with the apex pointing downward. The heart is constructed of a special kind of muscle called myocardium or cardiac muscle, and is enclosed in a double-layered, membranous sac known as the pericardium. A wall of muscle divides the heart into two cavities: the left cavity pumps blood throughout the body, while the right cavity pumps blood only through the lungs. Each cavity is in turn divided into two chambers, the upper ones called atria, the lower ones ventricles. Venous blood from the body, containing large amounts of carbon dioxide, returns to the right atrium. It enters the right ventricle, which contracts, pumping blood through the pulmonary artery to the lungs. Oxygenated blood returns from the lungs to the left atrium and enters the left ventricle, which contracts, forcing the blood into the aorta, from which it is distributed throughout the body. In addition, the heart employs a separate vascular system to obtain blood for its own nourishment. Two major coronary arteries regulate this blood supply.
Cardiac Cycle
Blood flows through the heart in one direction only. It is prevented from backing up by a series of valves at various openings: the tricuspid valve between the right atrium and right ventricle; the bicuspid, or mitral, valve between the left atrium and left ventricle; and the semilunar valves in the aorta and the pulmonary artery. Each heartbeat, or cardiac cycle, is divided into two phases. In the first phase, a short period of ventricular contraction known as the systole, the tricuspid and mitral valves snap shut, producing the familiar "lub" sound heard in the physician's stethoscope. In the second phase, a slightly longer period of ventricular relaxation known as the diastole, the pulmonary and aortic valves close up, producing the characteristic "dub" sound. Both sides of the heart contract, empty, relax, and fill simultaneously; therefore, only one systole and one diastole are felt. The normal heart has a rate of 72 beats per minute, but in infants the rate may be as high as 120 beats, and in children about 90 beats, per minute. Each heartbeat is stimulated by an electrical impulse that originates in a small strip of heart tissue known as the sinoatrial (S-A) node, or pacemaker.
Advances in Cardiology
One of the important advances in cardiology is the artificial pacemaker used to electrically initiate a normal heartbeat when the patient's own pacemaker is defective (see arrhythmia); it may be surgically implanted in the patient's body. Similarly, an internal defibrillator may be implanted to deliver an electrical shock to the heart in order to stop certain forms of rapid heart rhythm disturbances. Another familiar tool of the cardiologist is the electrocardiograph (EKG), which is used to detect abnormalities that are not evident from a physical examination (see electrocardiography).
One of the most important advances in heart surgery during the 1960s was the transplantation of the healthy heart immediately after the death of an individual (the donor) to a recipient suffering from incurable heart disease (see transplantation, medical). In the 1980s new advances in the design and construction of an artificial heart-both the entire organ and such parts as the valves and large blood vessels-showed some promise in treating cardiovascular disease (see heart, artificial), but the limited success that has characterized artificial heart implantation thus far has led many experts to question the efficacy of such measures. Although the artificial heart has often been used as a temporary measure until a permanent human donor heart can be located, a number of recipients have not fared well, even for a limited duration. In addition, it is often unclear how long the recipient will have to wait for a donor. Proponents of the artificial heart hope that technological advances will allow the permanent replacement of human hearts with artificial ones.
See circulatory system; heart disease.
Bibliography
See J. Peto, The Heart (2005).
The hollow muscular organ that is the center of the circulatory system. The heart pumps blood throughout the intricate system of blood vessels in the body.
n.
An automatic, muscular blood-pump. Figuratively, this useful organ is said to be the esat of emotions and sentiments -- a very pretty fancy which, however, is nothing but a survival of a once universal belief. It is now known that the sentiments and emotions reside in the stomach, being evolved from food by chemical action of the gastric fluid. The exact process by which a beefsteak becomes a feeling -- tender or not, according to the age of the animal from which it was cut; the successive stages of elaboration through which a caviar sandwich is transmuted to a quaint fancy and reappears as a pungent epigram; the marvelous functional methods of converting a hard-boiled egg into religious contrition, or a cream-puff into a sigh of sensibility -- these things have been patiently ascertained by M. Pasteur, and by him expounded with convincing lucidity. (See, also, my monograph, The Essential Identity of the Spiritual Affections and Certain Intestinal Gases Freed in Digestion -- 4to, 687 pp.) In a scientific work entitled, I believe, Delectatio Demonorum (John Camden Hotton, London, 1873) this view of the sentiments receives a striking illustration; and for further light consult Professor Dam's famous treatise on Love as a Product of Alimentary Maceration.
Quotes:
"The eyes see what the heart loves. If the heart loves God and is single in this devotion, then the eyes will see God whether others see Him or not."
- Warren Wiersbe
"Have thy heart in heaven and thy hands upon the earth. Ascend in piety and descend in charity. For this is the Nature of Light and the way of the children."
- Thomas Vaughan
"Doubt obscures the true vision of the heart."
- Source Unknown
"Advice from a veteran trapeze performer: Throw your heart over the bars and your body will follow."
- Source Unknown
"Use your head and your heart, its not everything but its a start."
- Source Unknown
"I like people and I like them to like me, but I wear my heart where God put it -- on the inside."
- Source Unknown
See more famous quotes about Heart
The heart is the eternal symbol of love, romance, and the very life force within all of humankind. Getting to the "heart of the matter" suggests that the heart rules the source of truth and love. When one is unfair in a particularly insensitive manner, the person and the act are described as "heartless." Friendship, courage, romantic bonds, and emotional expression are also embodied in this symbol.
The hollow muscular organ lying on the sternum that serves as a pump controlling the blood flow in two circuits, the pulmonary and the systemic. See also circulatory system.

|
|
This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (July 2009) |
|
|
|
| Problems listening to this file? See media help. | |
The heart is a myogenic muscular organ found in all animals with a circulatory system (including all vertebrates), which pumps blood throughout the blood vessels by repeated, rhythmic contractions. The term cardiac (as in cardiology) means "related to the heart" and comes from the Greek καρδιά, kardia, for "heart".
The vertebrate heart is principally composed of cardiac muscle and connective tissue. Cardiac muscle is an involuntary striated muscle tissue found only in this organ and responsible for the ability of the heart to pump blood. The average human heart, beating at 72 beats per minute, will beat approximately 2.5 billion times during an average 66 year lifespan. It weighs approximately 250 to 300 grams (9 to 11 oz) in females and 300 to 350 grams (11 to 12 oz) in males.[1]
In invertebrates that possess a circulatory system, the heart is typically a tube or small sac and pumps fluid that contains water and nutrients such as proteins, fats, and sugars. In insects, the "heart" is often called the dorsal tube and insect "blood" is almost always not oxygenated since they usually respirate (breathe) directly from their body surfaces (internal and external) to air. However, the hearts of some other arthropods (including spiders and crustaceans such as crabs and shrimp) and some other animals pump hemolymph, which contains the copper-based protein hemocyanin as an oxygen transporter similar to the iron-based hemoglobin in red blood cells found in vertebrates.
|
Contents
|
The mammalian heart is derived from embryonic mesoderm germ-layer cells that differentiate after gastrulation into mesothelium, endothelium, and myocardium. Mesothelial pericardium forms the outer lining of the heart. The inner lining of the heart, lymphatic and blood vessels, develop from endothelium. Heart muscle is termed myocardium.[2]
From splanchnopleuric mesoderm tissue, the cardiogenic plates develops cranially and laterally to the neural plate. In the cardiogenic plates, two separate angiogenic cell clusters form on either side of the embryo. The cell clusters coalesce to form an endocardial tube continuous with a dorsal aorta and a vitteloumbilical vein. As embryonic tissue continues to fold, the two endocardial tubes are pushed into the thoracic cavity, begin to fuse together, and complete the fusing process at approximately 22 days.[3]
The human embryonic heart begins beating at around 22 days after conception, or five weeks after the last normal menstrual period (LMP). The first day of the LMP is normally used to date the start of the gestation (pregnancy). The human heart begins beating at a rate near the mother’s, about 75–80 beats per minute (BPM).
The embryonic heart rate (EHR) then accelerates by approximately 100 BPM during the first month to peak at 165–185 BPM during the early 7th week afer conception, (early 9th week after the LMP). This acceleration is approximately 3.3 BPM per day, or about 10 BPM every three days, which is an increase of 100 BPM in the first month.[4][5][6]
After 9.1 weeks after the LMP, it decelerates to about 152 BPM (+/-25 BPM) during the 15th week post LMP. After the 15th week, the deceleration slows to an average rate of about 145 (+/-25 BPM) BPM, at term. The regression formula, which describes this acceleration before the embryo reaches 25 mm in crown-rump length, or 9.2 LMP weeks, is: the Age in days = EHR(0.3)+6. There is no difference in female and male heart rates before birth.[7]
The structure of the heart varies among the different branches of the animal kingdom. (See Circulatory system.) Cephalopods have two "gill hearts" and one "systemic heart". In vertebrates, the heart lies in the anterior part of the body cavity, dorsal to the gut. It is always surrounded by a pericardium, which is usually a distinct structure, but may be continuous with the peritoneum in jawless and cartilaginous fish. Hagfishes, uniquely among vertebrates, also possess a second heart-like structure in the tail.[8]
The human heart has a mass of between 250 and 350 grams and is about the size of a fist.[9] It is located anterior to the vertebral column and posterior to the sternum.
It is enclosed in a double-walled sac called the pericardium. The superficial part of this sac is called the fibrous pericardium. This sac protects the heart, anchors its surrounding structures, and prevents overfilling of the heart with blood.
The outer wall of the human heart is composed of three layers. The outer layer is called the epicardium, or visceral pericardium since it is also the inner wall of the pericardium. The middle layer is called the myocardium and is composed of cardiac muscle which contracts. The inner layer is called the endocardium and is in contact with the blood that the heart pumps. Also, it merges with the inner lining (endothelium) of blood vessels and covers heart valves.[10]
The human heart has four chambers, two superior atria and two inferior ventricles. The atria are the receiving chambers and the ventricles are the discharging chambers. The pathway of blood through the human heart consists of a pulmonary circuit[11] and a systemic circuit. Deoxygenated blood flows through the heart in one direction, entering through the superior vena cava into the right atrium and is pumped through the tricuspid valve into the right ventricle before being pumped out through the pulmonary valve to the pulmonary arteries into the lungs. It returns from the lungs through the pulmonary veins to the left atrium where it is pumped through the mitral valve into the left ventricle before leaving through the aortic valve to the aorta.[12][13]
Primitive fish have a four-chambered heart, but the chambers are arranged sequentially so that this primitive heart is quite unlike the four-chambered hearts of mammals and birds. The first chamber is the sinus venosus, which collects de-oxygenated blood, from the body, through the hepatic and cardinal veins. From here, blood flows into the atrium and then to the powerful muscular ventricle where the main pumping action will take place. The fourth and final chamber is the conus arteriosus which contains several valves and sends blood to the ventral aorta. The ventral aorta delivers blood to the gills where it is oxygenated and flows, through the dorsal aorta, into the rest of the body. (In tetrapods, the ventral aorta has divided in two; one half forms the ascending aorta, while the other forms the pulmonary artery).[8]
In the adult fish, the four chambers are not arranged in a straight row but, instead form an S-shape with the latter two chambers lying above the former two. This relatively simpler pattern is found in cartilaginous fish and in the ray-finned fish. In teleosts, the conus arteriosus is very small and can more accurately be described as part of the aorta rather than of the heart proper. The conus arteriosus is not present in any amniotes, presumably having been absorbed into the ventricles over the course of evolution. Similarly, while the sinus venosus is present as a vestigial structure in some reptiles and birds, it is otherwise absorbed into the right atrium and is no longer distinguishable.[8]
In amphibians and most reptiles, a double circulatory system is used but the heart is not completely separated into two pumps. The development of the double system is necessitated by the presence of lungs which deliver oxygenated blood directly to the heart.
In living amphibians, the atrium is divided into two separate chambers by the presence of a muscular septum even though there is only one ventricle. The sinus venosus, which remains large in amphibians but connects only to the right atrium, receives blood from the vena cavae, with the pulmonary vein by-passing it entirely to enter the left atrium.
In the heart of lungfish, the septum extends part-way into the ventricle. This allows for some degree of separation between the de-oxygenated bloodstream destined for the lungs and the oxygenated stream that is delivered to the rest of the body. The absence of such a division in living amphibian species may be at least partly due to the amount of respiration that occurs through the skin in such species; thus, the blood returned to the heart through the vena cavae is, in fact, already partially oxygenated. As a result, there may be less need for a finer division between the two bloodstreams than in lungfish or other tetrapods. Nonetheless, in at least some species of amphibian, the spongy nature of the ventricle seems to maintain more of a separation between the bloodstreams than appears the case at first glance. Furthermore, the conus arteriosus has lost its original valves and contains a spiral valve, instead, that divides it into two parallel parts, thus helping to keep the two bloodstreams separate.[8]
The heart of most reptiles (except for crocodilians; see below) has a similar structure to that of lungfish but, here, the septum is generally much larger. This divides the ventricle into two halves but, because the septum does not reach the whole length of the heart, there is a considerable gap near the openings to the pulmonary artery and the aorta. In practice, however, in the majority of reptilian species, there appears to be little, if any, mixing between the bloodstreams, so the aorta receives, essentially, only oxygenated blood.[8]
Archosaurs (crocodilians and birds) and mammals show complete separation of the heart into two pumps for a total of four heart chambers; it is thought that the four-chambered heart of archosaurs evolved independently from that of mammals. In crocodilians, there is a small opening, the foramen of Panizza, at the base of the arterial trunks and there is some degree of mixing between the blood in each side of the heart; thus, only in birds and mammals are the two streams of blood – those to the pulmonary and systemic circulations – kept entirely separate by a physical barrier.[8]
In the human body, the heart is usually situated in the middle of the thorax with the largest part of the heart slightly offset to the left, although sometimes it is on the right (see dextrocardia), underneath the sternum. The heart is usually felt to be on the left side because the left heart (left ventricle) is stronger (it pumps to all body parts). The left lung is smaller than the right lung because the heart occupies more of the left hemithorax. The heart is fed by the coronary circulation and is enclosed by a sac known as the pericardium; it is also surrounded by the lungs. The pericardium comprises two parts: the fibrous pericardium, made of dense fibrous connective tissue, and a double membrane structure (parietal and visceral pericardium) containing a serous fluid to reduce friction during heart contractions. The heart is located in the mediastinum, which is the central sub-division of the thoracic cavity. The mediastinum also contains other structures, such as the esophagus and trachea, and is flanked on either side by the right and left pulmonary cavities; these cavities house the lungs.[15]
The apex is the blunt point situated in an inferior (pointing down and left) direction. A stethoscope can be placed directly over the apex so that the beats can be counted. It is located posterior to the 5th intercostal space just medial of the left mid-clavicular line. In normal adults, the mass of the heart is 250–350 grams (9–12 oz), or about twice the size of a clenched fist (it is about the size of a clenched fist in children), but an extremely diseased heart can be up to 1000 g (2 lb) in mass due to hypertrophy. It consists of four chambers, the two upper atria and the two lower ventricles.
|
|
This article may require cleanup to meet Wikipedia's quality standards. No cleanup reason specified. Please add a |reason= parameter to this template. Please help improve this article if you can. The talk page may contain suggestions. (April 2012) |
In mammals, the function of the right side of the heart (see right heart) is to collect de-oxygenated blood, in the right atrium, from the body (via superior and inferior vena cavae) and pump it, through the tricuspid valve, via the right ventricle, into the lungs (pulmonary circulation) so that carbon dioxide can be dropped off and oxygen picked up (gas exchange). This happens through the passive process of diffusion. The left side (see left heart) collects oxygenated blood from the lungs into the left atrium. From the left atrium the blood moves to the left ventricle, through the bicuspid valve (mitral valve), which pumps it out to the body (via the aorta). On both sides, the lower ventricles are thicker and stronger than the upper atria. The muscle wall surrounding the left ventricle is thicker than the wall surrounding the right ventricle due to the higher force needed to pump the blood through the systemic circulation.
Starting in the right atrium, the blood flows through the tricuspid valve to the right ventricle. Here, it is pumped out the pulmonary semilunar valve and travels through the pulmonary artery to the lungs. From there, oxygenated blood flows back through the pulmonary vein to the left atrium. It then travels through the mitral valve to the left ventricle, from where it is pumped through the aortic semilunar valve to the aorta. The aorta forks and the blood is divided between major arteries which supply the upper and lower body. The blood travels in the arteries to the smaller arterioles and then, finally, to the tiny capillaries which feed each cell. The (relatively) deoxygenated blood then travels to the venules, which coalesce into veins, then to the inferior and superior venae cavae and finally back to the right atrium where the process began.
The heart is effectively a syncytium, a meshwork of cardiac muscle cells interconnected by contiguous cytoplasmic bridges. This relates to electrical stimulation of one cell spreading to neighboring cells.
Some cardiac cells are self-excitable, contracting without any signal from the nervous system, even if removed from the heart and placed in culture. Each of these cells have their own intrinsic contraction rhythm. A region of the human heart called the sinoatrial (SA) node, or pacemaker, sets the rate and timing at which all cardiac muscle cells contract. The SA node generates electrical impulses, much like those produced by nerve cells. Because cardiac muscle cells are electrically coupled by inter-calated disks between adjacent cells, impulses from the SA node spread rapidly through the walls of the artria, causing both artria to contract in unison. The impulses also pass to another region of specialized cardiac muscle tissue, a relay point called the atrioventricular node, located in the wall between the right atrium and the right ventricle. Here, the impulses are delayed for about 0.1s before spreading to the walls of the ventricle. The delay ensures that the artria empty completely before the ventricles contract. Specialized muscle fibers called Purkinje fibers then conduct the signals to the apex of the heart along and throughout the ventricular walls. The Purkinje fibres form conducting pathways called bundle branches. This entire cycle, a single heart beat, lasts about 0.8 seconds. The impulses generated during the heart cycle produce electrical currents, which are conducted through body fluids to the skin, where they can be detected by electrodes and recorded as an electrocardiogram (ECG or EKG).[16] The events related to the flow or blood pressure that occurs from the beginning of one heartbeat to the beginning of the next can be referred to a cardiac cycle. [17]
The SA node is found in all amniotes but not in more primitive vertebrates. In these animals, the muscles of the heart are relatively continuous and the sinus venosus coordinates the beat which passes in a wave through the remaining chambers. Indeed, since the sinus venosus is incorporated into the right atrium in amniotes, it is likely homologous with the SA node. In teleosts, with their vestigial sinus venosus, the main centre of coordination is, instead, in the atrium. The rate of heartbeat varies enormously between different species, ranging from around 20 beats per minute in codfish to around 600 in hummingbirds.[8]
Cardiac arrest is the sudden cessation of normal heart rhythm which can include a number of pathologies such as tachycardia, an extremely rapid heart beat which prevents the heart from effectively pumping blood, which is an irregular and ineffective heart rhythm, and asystole, which is the cessation of heart rhythm entirely.
Cardiac tamponade is a condition in which the fibrous sac surrounding the heart fills with excess fluid or blood, suppressing the heart's ability to beat properly. Tamponade is treated by pericardiocentesis, the gentle insertion of the needle of a syringe into the pericardial sac (avoiding the heart itself) on an angle, usually from just below the sternum, and gently withdrawing the tamponading fluids.
The valves of the heart were discovered by a physician of the Hippocratean school around the 4th century BC, although their function was not fully understood. On dissection, arteries are typically empty of blood because blood pools in the veins after death. Ancient anatomists subsequently assumed they were filled with air and served to transport it around the body.
Philosophers distinguished veins from arteries, but thought the pulse was a property of arteries themselves. Erasistratos observed that arteries cut during life bleed. He ascribed the fact to the phenomenon that air escaping from an artery is replaced with blood which entered by very small vessels between veins and arteries. Thus he apparently postulated capillaries, but with reversed flow of blood.
The Greek physician Galen (2nd century AD) knew blood vessels carried blood and identified venous (dark red) and arterial (brighter and thinner) blood, each with distinct and separate functions. Growth and energy were derived from venous blood created in the liver from chyle, while arterial blood gave vitality by containing pneuma (air) and originated in the heart. Blood flowed from both creating organs to all parts of the body, where it was consumed and there was no return of blood to the heart or liver. The heart did not pump blood around, the heart's motion sucked blood in during diastole and the blood moved by the pulsation of the arteries themselves.
Galen believed the arterial blood was created by venous blood passing from the left ventricle to the right through 'pores' in the interventricular septum, while air passed from the lungs via the pulmonary artery to the left side of the heart. As the arterial blood was created, "sooty" vapors were created and passed to the lungs, also via the pulmonary artery, to be exhaled.
For more recent technological developments, see Cardiac surgery.
| Look up heart in Wiktionary, the free dictionary. |
| Wikimedia Commons has media related to: Heart (organ) |
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Dansk (Danish)
n. - hjerte, mod, centrum, kerne
v. tr. - opmuntre
idioms:
Nederlands (Dutch)
hart, innerlijk, binnenste, gemoed, wil, karakter, emoties, (voor) liefde, verlangens, goedhartigheid, kern, boezem, hartklop, tikker, pit, hartspier/-klep na aan het hart
Français (French)
n. - (Anat) c¯ur, c¯ur (sentiments), sentiments profonds, nature, pitié, courage, centre, en pleine (jungle, campagne), fond (du problème), c¯ur (cartes), c¯ur (de laitue, d'artichaut)
v. tr. - encourager
idioms:
Deutsch (German)
n. - (Anat.)(Psych.) Herz, Kern(holz), Mittelpunkt, Zentrum, Herz (Spielkarte)
v. - ermutigen, ermuntern
idioms:
Ελληνική (Greek)
n. - καρδιά, (για παιγνιόχαρτα) κούπα, (μτφ.) ανθρωπιά, ευσπλαχνία, ψυχή, θάρρος, τόλμη
idioms:
Italiano (Italian)
cuore, essenza
idioms:
Português (Portuguese)
n. - coração (m), centro (m), o essencial (m), coragem (f), peito (m), copas (f pl)
idioms:
Русский (Russian)
сердце, душа, чувства, любовь, мужество, центральная часть, суть, интеллект, желудок
idioms:
Español (Spanish)
n. - corazón, fondo, fuero interno, lo esencial, centro
v. tr. - animar
idioms:
Svenska (Swedish)
n. - hjärta (äv. bildl.), kärna, hjärtekort, mod, ollon
中文(简体)(Chinese (Simplified))
心, 中心, 心脏, 把...放在中心
idioms:
中文(繁體)(Chinese (Traditional))
n. - 心, 中心, 心臟
v. tr. - 把...放在中心
idioms:
한국어 (Korean)
n. - 심장, 마음, 애정, 핵심
v. tr. - 마음에 새기다, 격려하다
idioms:
日本語 (Japanese)
n. - 心臓, 胸部, 胸, 感情, 勇気, 気力, 熱意, 愛情, 中心, 核心, 真ん中
v. - 結球する, 心に銘記させる, 心材を詰める
idioms:
العربيه (Arabic)
(الاسم) قلب, فؤاد, الكوبه ورقه لعب تحمل صورة قلب, شخصيه الفرد بسماتها العاطفيه والعقليه, ذاكرة, طبيعه المرء العاطفيه والاخلاقيه, رأي, موقف, حنان, مزاج, حب, شجاعه, هم, رغبه ثابته, شخص مخلوق, لب, لباب
עברית (Hebrew)
n. - לב, חזה, אמצע
v. tr. - עודד, חיזק לב, המריץ, נסך אומץ ב-
If you are unable to view some languages clearly, click here.