Difference between revisions of "Heart" - New World Encyclopedia

From New World Encyclopedia
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[[Image:Heart-and-lungs.jpg|thumb|right|230px|The heart and lungs, from an older edition of '' [[Gray's Anatomy]]''.]]
 
[[Image:Heart-and-lungs.jpg|thumb|right|230px|The heart and lungs, from an older edition of '' [[Gray's Anatomy]]''.]]
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The '''heart''' is a [[muscle|muscular]] [[organ (anatomy)|organ]] responsible for pumping [[blood]] through the [[blood vessel]]s by repeated, rhythmic contractions, or a similar structure in the [[annelid]]s, [[mollusk]]s, and [[arthropod]]s.<ref>{{cite web | url = http://www.kmle.com/search.php?Search=heart | title = ''KMLE Medical Dictionary Definition of heart'' | author = [http://www.kmle.com The American Heritage Stedman's Medical Dictionary]}}.</ref> The term ''cardiac'' (as in [[cardiology]]) means "related to the heart" and comes from the [[Greek language|Greek]] καρδία, ''kardia'', for "heart." The heart is composed of [[cardiac muscle]], an [[involuntary muscle]] tissue which is found only within this organ.<ref>{{cite web | url = http://www.kmle.com/search.php?Search=cardiac | title = ''KMLE Medical Dictionary Definition of cardiac'' | author = [http://www.kmle.com The American Heritage Stedman's Medical Dictionary]}}</ref> The average human heart beating at 72 BPM, will beat approximately 2.5 billion times during a lifetime of 66 years.
  
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The '''heart''' is a hollow, [[muscle|muscular]] [[organ (anatomy)|organ]] in [[vertebrate]]s, responsible for [[pumping]] [[blood]] through the [[blood vessel]]s by repeated, rhythmic contractions, or a similar structure in [[annelid]]s, [[mollusk]]s, and [[arthropod]]s. The term ''cardiac'' (as in [[cardiology]]) means "related to the heart" and comes from the [[Greek language|Greek]] καρδιά, ''kardia'', for "heart." The heart is composed of [[cardiac muscle]], an [[involuntary muscle]] tissue which is found only within this organ.  
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==Overview==
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===Open circulatory system==
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An '''open circulatory system''' is an arrangement of internal transport in which circulatory fluid, in a cavity called the hemocoel (also spelled haemocoel), bathes the organs directly. There is no distinction between [[blood]] and interstitial fluid; this combined fluid is called '''hemolymph''' (also spelled haemolymph).  
  
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==Early development==
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Open systems are present in some [[invertebrate]]s, like [[mollusk]]s and [[arthropod]]s. Muscular movements during locomotion by animals with such a system can facilitate hemolymph movement, but diverting flow from one area to another is limited. When the [[heart]] relaxes, blood is drawn back toward the heart through open-ended pores.  
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[[Image:EHR-BBII.jpg|thumb|right|300px|At 21 days after [[Fertilisation|conception]], the human heart rate begins beating at 75-80 beats per minute and accelerates linearly for the first month of beating.]]
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The human embryonic heart begins beating approximately 21 days after conception, or five weeks after the last normal menstrual period (LMP), which is the date normally used to date 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 linearly for the first month of beating, peaking at 165-185 bpm during the early 7th week, (early 9th week after the LMP). This acceleration is approximately 3.3 bpm per day, or about 10 bpm every three days, an increase of 100 bpm in the first month. [http://www.obgyn.net/us/us.asp?page=/us/cotm/0001/ehr2000]
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Hemolymph fills all of the interior hemocoel of the body and surrounds all [[cell (biology)|cell]]s. Hemolymph is composed of [[water]], inorganic salts (mostly [[Sodium|Na<sup>+</sup>]], [[Chlorine|Cl<sup>-</sup>]], [[Potassium|K<sup>+</sup>]], [[Magnesium|Mg<sup>2+</sup>]], and [[Calcium|Ca<sup>2+</sup>]]), and [[organic chemistry|organic compounds]] (mostly [[carbohydrate]]s, [[protein]]s, and [[lipid]]s). The primary oxygen transporter molecule is ''hemocyanin''.
  
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After peaking at about 9.2 weeks after the LMP, it decelerates to about 150 bpm (+/-25 bpm) during the 15th week after the LMP. After the 15th week the deceleration slows reaching 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:
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There are free-floating cells, the hemocytes, within the hemolymph. They play a role in the arthropod [[immune system]].
  
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Age in days = EHR(0.3)+6
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===Closed circulatory system===
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The circulatory systems of all [[vertebrate]]s, [[annelid]]s (for example, [[earthworm]]s), and [[cephalopod]]s (squid and octopus) are '''closed,''' meaning that the [[blood]] never leaves the system of blood vessels, which consists of [[arteries]], [[vein]]s, and [[capillaries]].
  
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See: [http://www.obgyn.net/us/us.asp?page=/us/cotm/0001/ehr2000 Embryonic Heart Rates Compared in Assisted and Non-Assisted Pregnancies]
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The main components of the closed circulatory system are the [[heart]], the [[blood]], and the blood vessels. Arteries bring oxygenated blood to the tissues (except pulmonary arteries), and veins bring deoxygenated blood back to the heart (except pulmonary veins). Blood passes from arteries to veins through capillaries, which are the thinnest and most numerous of the blood vessels.
  
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There is no difference in male and female heart rates before birth.<ref>Terry J. DuBose [http://www.obgyn.net/english/pubs/features/dubose/ehr-age.htm Sex, Heart Rate and Age]</ref>
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The closed circulatory systems of [[fish]], [[amphibian]]s, [[reptile]]s, [[bird]]s, and [[mammal]]s show various stages of sophistication.
  
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==Structure==
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In fish, the system has only one circuit, with the blood being pumped through the capillaries of the gills and on to the capillaries of the body tissues. This is known as ''single'' circulation. The heart of fish is therefore only a single pump (consisting of two chambers).
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[[Image:3DScience_Human_Heart.jpg|thumb|300px|right|Anterior (frontal) view of the opened heart. Arrows indicate normal blood flow. Image provided courtesy of www.3dscience.com.]]
 
  
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In the human body, the heart is normally situated slightly to the left of the middle of the [[thorax]], underneath the [[breastbone]] (see [http://www.easyrashi.com/TEFILLIN/Position_of_heart.htm diagrams]). 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 enclosed by a sac known as the [[pericardium]] and is surrounded by the [[lung]]s. The pericardium is a double membrane structure containing a [[serous]] fluid to reduce friction during heart contractions. The [[mediastinum]], a subdivision of the thoracic cavity, is the name of the heart cavity.  
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In amphibians and most reptiles, a double circulatory system is used, but the heart is not always completely separated into two pumps. Amphibians have a three-chambered heart.
  
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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. This physical location is between the sixth and seventh rib, just to the left of the sternum [http://www.easyrashi.com/TEFILLIN/sternum.htm]. In normal adults, the mass of the heart is 250-350 [[gram|g]] (9-16 oz), but extremely diseased hearts can be up to 1000 g (2 lb) in mass due to [[Organ hypertrophy|hypertrophy]]. It consists of four chambers, the two upper ''atria'' (singular: atrium
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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 birds evolved independently of that of mammals.
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) and the two lower ''ventricles''.  On the left is a picture of a fresh human heart which was removed from a 64-year-old British male.
 
  
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[[Image:Humhrt2.jpg|thumb|200px|left|Human Heart]]
 
  
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The function of the right side of the heart (see [[right heart]]) is to collect deoxygenated blood, in the [[right atrium]], from the body and pump it, 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 a passive process called [[diffusion]]. The left side (see [[left heart]]) collects oxygenated blood from the [[lung]]s into the [[left atrium]]. From the left atrium the blood moves to the [[left ventricle]] which pumps it out to the body. On both sides, the lower ventricles are thicker and stronger than the upper atria.
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==Early development==
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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]].
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{{main|Heart development}}
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[[Image:EHR-BBII.jpg|thumb|right|300px|At 21 days after [[Fertilization|conception]], the human heart begins beating at 70 to 80 beats per minute and accelerates linearly for the first month of beating.]]
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It is unknown how blood in the embryo circulates for the first 21 days in the absence of a functioning heart, although some have hypothesized that the heart is not so much a pump, as a [[Hydraulic Ram]] — an organ built-up from cumulative peripheral activity. [http://www.rsarchive.org/RelArtic/Marinelli/]
  
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==Regulation of the cardiac cycle==
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When the human [[embryon]]ic heart begins beating — around 21 days after conception, or five weeks after the last normal [[menstrual period]] (LMP), which is the date normally used to date pregnancy.  The human heart begins beating at a rate near the mother’s, about 75-80 beats per minute (BPM).
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Cardiac muscle is myogenic (able to contract and relax on its own). It is a specialized muscle found nowhere else but in the heart because it has its own conducting system. This is in contrast with [[skeletal muscle]], which requires either conscious or reflex nervous stimuli. The heart's rhythmic contractions occur spontaneously, although the [[waves]] or [[nerves]] can be changed by nervous frequency influences such as [[exercise]] or the perception of danger.  
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The embryonic heart rate (EHR) then accelerates linearly for the first month of beating, peaking at 165-185 BPM during the early 7th week, (early 9th week after the LMP). This acceleration is approximately 3.3 BPM per day, or about 10 BPM every three days, an increase of 100 BPM in the first month.<ref>http://www.obgyn.net/us/us.asp?page=/us/cotm/0001/ehr2000</ref>
  
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The rhythmic sequence of contractions is coordinated by the [[sinoatrial node|sinoatrial]] and [[atrioventricular node]]s. The sinoatrial node, often known as the [[cardiac pacemaker]], is located in the upper wall of the right atrium and is responsible for the wave of electrical stimulation (See ''[[action potential]]'') that initiates atria contraction. Once the wave reaches the atrioventricular node, situated in the lower right atrium, it is conducted through the [[bundle of His|bundles of His]] and causes contraction of the ventricles. The time taken for the wave to reach this node from the sinoatrial nerve creates a delay between contraction of the two chambers and ensures that each contraction is coordinated simultaneously throughout all of the heart. In the event of severe pathology, the [[Purkinje fibers]] can also act as a pacemaker; this is usually not the case because their rate of spontaneous firing is considerably lower than that of the other pacemakers and hence is overridden
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After peaking at about 9.2 weeks after the LMP, it decelerates to about 152 BPM (+/-25 BPM) during the 15th week after the LMP. After the 15th week the deceleration slows reaching 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 Age in days = EHR(0.3)+6
  
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==Other physiological functions==
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There is no difference in male and female heart rates before birth.<ref>Terry J. DuBose http://www.obgyn.net/english/pubs/features/dubose/ehr-age.htm Sex, Heart Rate and Age]</ref>
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The heart also secretes [[atrial natriuretic factor]] (ANF), a powerful [[peptide hormone]] that affects the blood vessels, the adrenal glands, the kidneys, and the regulatory regions of the brain in order to regulate blood pressure and volume.
 
  
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==First aid==
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==Structure==
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''See [[cardiac arrest]] for emergencies involving the heart''
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[[Image:3DScience Human Heart.jpg|thumb|300px|right|Anterior (frontal) view of the opened heart. Arrows indicate normal blood flow. Image provided courtesy of www.3dscience.com.]]
  
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If a person is encountered in cardiac arrest (no heartbeat), [[cardiopulmonary resuscitation]] (CPR) should be started, and [[call for help|help called]]. If an [[automated external defibrillator]] is available, this device may automatically administer [[defibrillation]] if this is indicated.
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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 [[breastbone]] (see [http://www.easyrashi.com/TEFILLIN/Position_of_heart.htm diagrams]). 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 enclosed by a sac known as the [[pericardium]] and is surrounded by the [[lung]]s. The pericardium comprises two parts: the fibrous pericardium, made of [[Dense connective tissue|dense fibrous connective tissue]]; and a double membrane structure containing a [[serous]] fluid to reduce friction during heart contractions (the serous pericardium). The [[mediastinum]], a subdivision of the thoracic cavity, is the name of the heart cavity.  
  
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==The hearts of other animals==
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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 in the left mid-clavicular line. In normal adults, the mass of the heart is 250-350 [[gram|g]] (9-12 oz), or about three quarters the size of a clenched fist, but extremely diseased hearts can be up to 1000 g (2 lb) in mass due to [[Organ hypertrophy|hypertrophy]]. It consists of four chambers, the two upper ''atria'' (singular: atrium
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{{main|Circulatory system#Types of circulatory systems}}
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) and the two lower ''ventricles''.  On the left is a picture of a fresh human heart which was removed from a 64-year-old male.
  
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===[[Vertebrate]]s===
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==Functioning==
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The hearts of [[fish]] have only two chambers: one [[atrium]] and one [[ventricle]]. In fish, the system has only one circuit. The blood pumps through the gills and on to the bodily tissues before returning to the heart.
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[[Image:Humhrt2.jpg|thumb|200px|left|Human heart]]
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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 and pump it, 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 [[lung]]s into the [[left atrium]].  From the left atrium the blood moves to the [[left ventricle]] which pumps it out to the body.  On both sides, the lower ventricles are thicker and stronger than the upper atria.
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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]].
  
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[[Amphibian]]s and most [[reptile]]s have a three-chambered heart, in which oxygenated blood from the lungs and de-oxygenated blood from the respiring tissues enter by separate atria, and are directed via a spiral valve to the appropriate vessel—aorta for oxygenated blood and pulmonary artery for deoxygenated blood. The spiral valve is essential to keeping the mixing of the two types of blood to a minimum, enabling the animal to have higher metabolic rates, and be more active than otherwise.
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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, blood flows back through the pulmonary [[vein]] to the left atrium. It then travels through the bicuspid 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, 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.
  
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[[Mammal]]s (a class of vertebrate), [[bird]]s and [[crocodile]]s 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 birds evolved independently of that of mammals.
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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. Its pumping is so strong, that if the [[aorta]] would be cut off, then the blood would squirt to a level of 4 meters <ref> [[Ian Holm]] in From Hell </ref>.
  
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===[[Invertebrates]]===
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==First aid==
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Many invertebrates, such as [[bivalve]]s and [[arthropod]]s, exhibit an [[open circulatory system]] where blood flows both in vessels and freely in the body cavity. In these animals the blood usually collects in a series of specialised [[sinus]]es, or cavities, where it directly comes in contact with tissues. It is then returned to the heart and is again released into the body.
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[[Image:heart.jpg|thumb|right|Heart]]
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''See [[cardiac arrest]] for emergencies involving the heart''
  
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The [[earthworm]] doesn't have a heart; it has five aortic arches that serve the same purpose.  
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If a person is encountered in cardiac arrest (no heartbeat), [[cardiopulmonary resuscitation]] (CPR) should be started and [[call for help|help called]]. If an [[automated external defibrillator]] is available, this device may automatically administer [[defibrillation]] if this is indicated. Usually, if there is enough time, the person can be rushed to the hospital where he or she will be cared for by a cardiologist, a doctor who specializes in the heart and lungs.
  
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{{sectstub}}
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Electrical innervation of the heart in health is supplied by two closely intertwined mechanisms. The first mechanism is well demonstrated in electrical coil systole (interpreted by the electrocardiogram as QRS)as an individualized myocardial electrical tree initiated by the sinoatrial node. Secondary diastolic electrical control is posited to represent autonomic recoil control from the vagus nerve and cardiac branches and the thoracic ganglia.
  
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===[[Heartbeat]]===
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==Food use==
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Smaller animals have faster heartbeats. This is evident within a species as well, as the young beat their hearts faster than the adults. See "Early development" above for information about the early human heart rates.
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The hearts of [[cattle]], [[sheep]], [[pig]]s, [[chicken]]s and certain [[fowl]] are consumed in many countries. They are counted among [[offal]], but being a muscle, the taste of heart is like regular meat. It resembles [[venison]] in structure and taste.
  
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The [[Gray Whale]]'s heart beats 9 times per [[minute]], [[Common Seal|Harbour Seal]] 10 when diving, 140 when on land, [[elephant]] 25, [[human]] 72, [[sparrow]] 500, [[shrew]] 600, and [[hummingbird]] 1,200 when hovering.  These heart rates usually vary on the animal's ratio of surface area to body mass; an elephant with relatively less surface area than a mouse loses proportionally less heat and requires comparatively less blood to be pumped throughout their body.  An [[Cold-blooded|ectothermic]] animal will usually have a slower, and more variable heartbeat than an [[Warm-blooded|endothermic]] animal of similar size.
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==Aztec heart removal==
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The [[Aztec]] civilization used the heart as a sacrificial token during the sacrifice of a human being. The priest used a stone knife to cut into the thoracic cavity and remove the heart, upon which it would be placed on a stone [[altar]] as an offering to the gods. The greatest sacrifice under the reign of [[Montezuma II|Montezuma]] involved the removal of the hearts of over 12,000 enemy soldiers.
  
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==Food use==
 
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The hearts of [[cattle]], [[sheep]], [[pig]]s, [[chicken]]s and certain [[fowl]] are consumed as [[food]] in many countries. They are counted among [[offal]], but being a muscle, the taste of heart is much more like regular meat than that of other offal. It resembles [[venison]] in structure and taste.
 
  
 
=="Heart" as a symbol==
 
=="Heart" as a symbol==
 
[[image:BigPinkHeart.jpg|thumb|The traditional "heart shape" appears on a [[1910]] [[St. Valentine's Day]] card.]]
 
[[image:BigPinkHeart.jpg|thumb|The traditional "heart shape" appears on a [[1910]] [[St. Valentine's Day]] card.]]
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The '''heart''' ('''{{unicode|♥}}''') has long been used as a [[symbol]] to refer to the [[spirituality|spiritual]], [[emotion]]al, [[morality|moral]], and in the past also [[intelligence (trait)|intellectual]] core of a human being. As the heart was once widely believed to be the seat of the human [[mind]], the word ''[[wikt:heart|heart]]'' continues to be used poetically to refer to the [[soul]], and stylized depictions of hearts are extremely prevalent symbols representing [[love]]. However, more realistic depictions of human [[heart]]s tend to have [[macabre]] [[connotation]]s of [[death]] and [[violence]], quite unlike the concepts associated with the poetic and symbolic heart. This discrepancy is a common source of [[black comedy|dark humor]].
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The '''heart''' ('''{{unicode|♥}}''') has long been used as a [[symbol]] to refer to the [[spirituality|spiritual]], [[emotion]]al, [[morality|moral]], and in the past also [[intelligence (trait)|intellectual]] core of a human being. As the heart was once widely believed to be the seat of the human [[mind]], the word ''[[wikt:heart|heart]]'' continues to be used poetically to refer to the [[soul]], and stylized depictions of hearts are extremely prevalent symbols representing [[love]]. However, more realistic depictions of human [[heart]]s tend to have [[macabre]] [[connotation]]s of [[death]] and [[violence]], quite unlike the concepts associated with the poetic and symbolic heart. This discrepancy is a common source of [[black comedy|dark humor]].
  
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==As metaphor==
 
===In mythology, spirituality and religion===
 
===In mythology, spirituality and religion===
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In religious texts such as the [[Bible]] [http://www.jewishencyclopedia.com/view.jsp?artid=468&letter=H&search=heart], the heart has historically been ascribed much mystical significance, either as [[metaphor]] or as an organ genuinely believed to have spiritual or divine attributes.
 
In religious texts such as the [[Bible]] [http://www.jewishencyclopedia.com/view.jsp?artid=468&letter=H&search=heart], the heart has historically been ascribed much mystical significance, either as [[metaphor]] or as an organ genuinely believed to have spiritual or divine attributes.
  
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In the Bible, this idea emerges in the earliest passages; [[Genesis]] 6:5 situates the thoughts of evil men in their hearts, and [[Exodus]] 5 through 12 speak repeatedly of the Lord "hardening [[Pharaoh (Book of Abraham)|Pharaoh]]'s heart." By this it is meant that God made Pharaoh resolve not to let the Israelite slaves leave Egypt, in order to bring judgment against Pharaoh and demonstrate his power: "'Go to Pharaoh, for I have hardened his heart and the hearts of his officials so that I may perform these miraculous signs of mine among them'" (Exodus 10:1).
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In the Bible, this idea emerges in the earliest passages; [[Genesis]] 6:5 situates the thoughts of evil men in their hearts, and [[Exodus]] 5 through 12 speak repeatedly of the Lord "hardening [[Pharaoh (Book of Abraham)|Pharaoh]]'s heart." By this it is meant that God made Pharaoh resolve not to let the Israelite slaves leave Egypt, in order to bring judgment against Pharaoh and demonstrate his power: "'Go to Pharaoh, for I have hardened his heart and the hearts of his officials so that I may perform these miraculous signs of mine among them'" (Exodus 10:1).  In the [[Book of Jeremiah]] 17:9, it is written that the "heart is deceitful above all things, and desperately wicked," and that the Lord is the judge who "tries" the human heart.
  
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In the [[Book of Jeremiah]] 17:9, it is written that the "heart is deceitful above all things, and desperately wicked," and that the Lord is the judge who "tries" the human heart.
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The [[Sacred Heart of Jesus]] and the [[Immaculate Heart of Mary]] are traditional [[Roman Catholic Church|Roman Catholic]] [[devotion]]al images.  
  
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Similarly, in [[Egyptian mythology]], the heart was weighed in a balance against the [[feather]] of [[Ma'at]], symbolising [[truth]], in the judgment of the dead in the Egyptian ''[[Book of the Dead]]''. Should the heart be heavier than the feather, the judged person would suffer in hell, since his heart was weighed down with sins. However, if the heart was lighter than the feather, the owner of the heart was admitted to paradise (See also [[Egyptian soul]]).
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Similarly, in [[Egyptian mythology]], the heart was weighed in a balance against the [[feather]] of [[Ma'at]], symbolising [[truth]], in the judgment of the dead in the Egyptian ''[[Book of the Dead]]''. Egyptian sources do not actually reveal whether the heart had to be lighter or heavier than the feather for the deceased to pass into paradise - all depictions show only the weighing of the heart, not the actual results, heavier or lighter. (See also [[Egyptian soul]]).
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[[Image:Corazón.svg|thumb|right|128px|European traditional heart symbol.]]
  
 
===In early science and philosophy===
 
===In early science and philosophy===
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The [[Stoicism|Stoics]] taught that the heart was the seat of the human soul.
 
The [[Stoicism|Stoics]] taught that the heart was the seat of the human soul.
  
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===As icon===
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==As icon==
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[[Image:Corazón.svg|thumb|right|128px|European traditional heart symbol.]]
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{{unreferencedsection|date=December 2007}}
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In [[Europe]]an traditional art and folklore, the heart symbol is drawn in a stylized shape. This shape is typically colored [[red]], suggesting both [[blood]] and, in many cultures, passion and strong emotion. The hearts and the diamonds are the two red [[suit (cards)|suits]] in most [[playing card]] decks. The shape is particularly associated with [[romantic love|romantic]] [[poetry]]; it is often seen on [[St. Valentine's Day]] [[greeting card|cards]], [[candy]] boxes, and similar [[popular culture]] artifacts as a symbol of [[romantic love]].
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In [[Europe]]an traditional art and folklore, the heart symbol is drawn in a stylized shape. This shape is typically colored [[red]], suggesting both [[blood]] and, in many cultures, passion and strong emotion. It and diamonds are the two red [[suit (cards)|suits]] in most [[playing card]] decks. The shape is particularly associated with [[romantic love|romantic]] [[poetry]]; it is often seen on [[St. Valentine's Day]] [[greeting card|cards]], [[candy]] boxes, and similar [[popular culture]] artifacts as a symbol of [[romantic love]].
 
  
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What the traditional "heart shape" actually depicts is a matter of some controversy.  It only vaguely resembles the human heart. Some people claim that it actually depicts the heart of a cow, a more readily available sight to most people in past centuries than an actual human heart. However, while beef hearts are ''more'' similar to the iconic heart shape, the resemblance is still slight. The shape ''does'' resemble that of the three-chambered heart of the turtle, and that of the human male [[prostate gland]], but it is very unlikely that the image was patterned after either of these organs.  
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What the traditional "heart shape" actually depicts is a matter of some controversy.  It only vaguely resembles the human heart. Some people claim that it actually depicts the heart of a cow, a more readily available sight to most people in past centuries than an actual human heart. However, while bovine hearts are ''more'' similar to the iconic heart shape, the resemblance is still slight. The shape ''does'' resemble that of the three-chambered heart of the turtle, and that of the human male [[prostate gland]], but it is very unlikely that the image was patterned after either of these organs.
  
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[[Image:Cyrenecoin.jpg|thumb|left|200px|Ancient silver coin from [[Cyrene, Libya|Cyrene]] depicting a [[silphium]] seed or fruit.]]
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The "heart" shape could also be considered to depict features of the human female body, such as the female's [[mons pubis|pubic mound]] or spread [[vulva]].  The tantric symbol of the "[[Yoni]]" is another example of a heart-shaped abstraction of a woman's vulva. In fact, the symmetry resembles the vulva far more than the asymmetry of the organ. In the introduction to the Vagina Monologues [[Gloria Steinem]] writes, "[The heart] was reduced from power to romance by centuries of male dominance."
  
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The "heart" shape could also be considered to depict features of the human female body, such as the female's [[mons pubis|pubic mound]] or [[vulva]].  A [[Sumerian language|Sumerian]] [[Cuneiform script|cuneiform]] symbol for "woman" closely resembles the heart shape, and is believed to directly depict the pubic mound. Others maintain that the heart resembles the shape of the female [[breast]]s or the female [[buttock]]s.
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Others maintain that the heart resembles the shape of the female [[breast]]s or the female [[buttock]]s.   
 +
[[Image:Cyrenecoin.jpg|thumb|right|200px|Ancient silver coin from [[Cyrene, Libya|Cyrene]] depicting a [[silphium]] seed or fruit.]]
  
 
Another possible origin can be seen on the coins of the ancient city of [[Cyrene, Libya|Cyrene]], some of which depict the seeds or fruit of the now-extinct [[silphium]] plant. The seeds are distinctly heart-shaped. Since this plant was widely used as an ancient [[herbal contraceptive]] or ''abortifacient'', this shape may have come to be associated with sexuality and [[love]].
 
Another possible origin can be seen on the coins of the ancient city of [[Cyrene, Libya|Cyrene]], some of which depict the seeds or fruit of the now-extinct [[silphium]] plant. The seeds are distinctly heart-shaped. Since this plant was widely used as an ancient [[herbal contraceptive]] or ''abortifacient'', this shape may have come to be associated with sexuality and [[love]].
  
−
[[Image:SwansHeart.jpg|thumb|right|250px|Mating [[Mute Swan]]s may appear to make a [[negative space]] heart.]]
+
The "heart" shape is formed by the back and wings of a [[dove]], which was associated with [[Aphrodite]], the ancient [[Greek mythology|Greek]] [[goddess]] of [[love]].
 +
 
 +
It may also be a stylised form of the combination of the [[silhouettes]] of two people kissing.
 +
[[Image:heartleaf.jpg|thumb|right|The heart-shaped hole made by nature on a leaf]]
  
 
The most common [[emoticon]] for the heart is <tt>&lt;3</tt>. In [[Unicode]], the heart symbol is U+2665, and it can thus be generated in [[HTML]] by typing &amp;#x2665; or &amp;#9829;, or by the HTML entity &amp;hearts;. Mathematically, a heart-shaped figure, called a [[cardioid]], can be represented by plotting a graph of either <math>(x^2 + y^2 - 1)^3 = x^2y^3</math> or, in polar form, <math>r = 1 - sin(\theta)</math>
 
The most common [[emoticon]] for the heart is <tt>&lt;3</tt>. In [[Unicode]], the heart symbol is U+2665, and it can thus be generated in [[HTML]] by typing &amp;#x2665; or &amp;#9829;, or by the HTML entity &amp;hearts;. Mathematically, a heart-shaped figure, called a [[cardioid]], can be represented by plotting a graph of either <math>(x^2 + y^2 - 1)^3 = x^2y^3</math> or, in polar form, <math>r = 1 - sin(\theta)</math>
 +
 +
 +
 +
==Additional images==
 +
<gallery>
 +
Image:2cb.jpg| [[2C-B]] pill.
 +
 +
Image:SwansHeart.jpg| Mating [[Mute Swan]]s may appear to make a [[negative space]] heart.
 +
 +
Image:Heart potato.jpg| A red potato exhibiting [[gemination]], an effect brought about by a  partial twinning during development.
 +
 +
Image:HeartCarvedInTrea.jpg | Heart carved in tree
 +
 +
</gallery>
 +
 +
 +
 +
==See also==
 +
*[[Cardiac cycle]]
 +
*[[Electrocardiogram]]
 +
*[[Electrical conduction system of the heart]]
 +
 +
== References ==
 +
{{reflist|2}}
 +
 +
== External links ==
 +
{{wiktionary}}
 +
{{commonscat|Heart}}
 +
*[http://www.emedicine.com/ped/topic2902.htm eMedicine: Surgical anatomy of the heart]
 +
*[http://library.thinkquest.org/C003758/home.htm Very Comprehensive Heart Site]
 +
*[http://www.abc.net.au/sydney/stories/s1572459.htm Self Improvement Wednesday] - ABC 702 Drive audio
 +
*[http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookcircSYS.html The circulatory system]
 +
*[http://www.easyrashi.com/TEFILLIN/sternum.htm The position of the heart]
 +
*[http://thevirtualheart.org/anatomyindex.html Interactive 3D heart] This realistic heart can be rotated, and all its components can be studied from any angle.
 +
*[http://www.rotaractmumbaighatkopar.org/Heartcare Heart care] How to take care of your heart.
 +
 +
==References==
 +
*[http://www.slate.com/id/2159800/?GT1=9129 The Shape of My Heart: Where did the ubiquitous Valentine's symbol come from?] by Keelin McDonell, [[Slate.com]].
 +
 +
*[http://www.heartsymbol.com www.heartsymbol.com: The Heart Symbol - Origin, History And Significance] by Prof. Armin Dietz
  
  
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*[http://www.americanheart.org  American Heart Association]
 
*[http://www.americanheart.org  American Heart Association]
  
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{{Heart}}
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{{cardiovascular_system}}
  
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{{credit2|Heart|88399124|Heart_(symbol)|88107937}}
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{{credit|Heart|178512122|Heart_(symbol)|179283511}}
 
[[Category:Life sciences]]
 
[[Category:Life sciences]]

Revision as of 03:47, 21 December 2007

The heart and lungs, from an older edition of Gray's Anatomy.

The heart is a muscular organ responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in the annelids, mollusks, and arthropods.[1] The term cardiac (as in cardiology) means "related to the heart" and comes from the Greek καρδία, kardia, for "heart." The heart is composed of cardiac muscle, an involuntary muscle tissue which is found only within this organ.[2] The average human heart beating at 72 BPM, will beat approximately 2.5 billion times during a lifetime of 66 years.

Overview

=Open circulatory system

An open circulatory system is an arrangement of internal transport in which circulatory fluid, in a cavity called the hemocoel (also spelled haemocoel), bathes the organs directly. There is no distinction between blood and interstitial fluid; this combined fluid is called hemolymph (also spelled haemolymph).

Open systems are present in some invertebrates, like mollusks and arthropods. Muscular movements during locomotion by animals with such a system can facilitate hemolymph movement, but diverting flow from one area to another is limited. When the heart relaxes, blood is drawn back toward the heart through open-ended pores.

Hemolymph fills all of the interior hemocoel of the body and surrounds all cells. Hemolymph is composed of water, inorganic salts (mostly Na+, Cl-, K+, Mg2+, and Ca2+), and organic compounds (mostly carbohydrates, proteins, and lipids). The primary oxygen transporter molecule is hemocyanin.

There are free-floating cells, the hemocytes, within the hemolymph. They play a role in the arthropod immune system.

Closed circulatory system

The circulatory systems of all vertebrates, annelids (for example, earthworms), and cephalopods (squid and octopus) are closed, meaning that the blood never leaves the system of blood vessels, which consists of arteries, veins, and capillaries.

The main components of the closed circulatory system are the heart, the blood, and the blood vessels. Arteries bring oxygenated blood to the tissues (except pulmonary arteries), and veins bring deoxygenated blood back to the heart (except pulmonary veins). Blood passes from arteries to veins through capillaries, which are the thinnest and most numerous of the blood vessels.

The closed circulatory systems of fish, amphibians, reptiles, birds, and mammals show various stages of sophistication.

In fish, the system has only one circuit, with the blood being pumped through the capillaries of the gills and on to the capillaries of the body tissues. This is known as single circulation. The heart of fish is therefore only a single pump (consisting of two chambers).

In amphibians and most reptiles, a double circulatory system is used, but the heart is not always completely separated into two pumps. Amphibians have a three-chambered heart.

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 birds evolved independently of that of mammals.


Early development

At 21 days after conception, the human heart begins beating at 70 to 80 beats per minute and accelerates linearly for the first month of beating.

It is unknown how blood in the embryo circulates for the first 21 days in the absence of a functioning heart, although some have hypothesized that the heart is not so much a pump, as a Hydraulic Ram — an organ built-up from cumulative peripheral activity. [1]

When the human embryonic heart begins beating — around 21 days after conception, or five weeks after the last normal menstrual period (LMP), which is the date normally used to date 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 linearly for the first month of beating, peaking at 165-185 BPM during the early 7th week, (early 9th week after the LMP). This acceleration is approximately 3.3 BPM per day, or about 10 BPM every three days, an increase of 100 BPM in the first month.[3]

After peaking at about 9.2 weeks after the LMP, it decelerates to about 152 BPM (+/-25 BPM) during the 15th week after the LMP. After the 15th week the deceleration slows reaching 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 Age in days = EHR(0.3)+6

There is no difference in male and female heart rates before birth.[4]

Structure

File:3DScience Human Heart.jpg
Anterior (frontal) view of the opened heart. Arrows indicate normal blood flow. Image provided courtesy of www.3dscience.com.

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 breastbone (see diagrams). 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 enclosed by a sac known as the pericardium and is surrounded by the lungs. The pericardium comprises two parts: the fibrous pericardium, made of dense fibrous connective tissue; and a double membrane structure containing a serous fluid to reduce friction during heart contractions (the serous pericardium). The mediastinum, a subdivision of the thoracic cavity, is the name of the heart cavity.

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 in the left mid-clavicular line. In normal adults, the mass of the heart is 250-350 g (9-12 oz), or about three quarters the size of a clenched fist, but extremely diseased hearts can be up to 1000 g (2 lb) in mass due to hypertrophy. It consists of four chambers, the two upper atria (singular: atrium ) and the two lower ventricles. On the left is a picture of a fresh human heart which was removed from a 64-year-old male.

Functioning

Human heart

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 and pump it, 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 which pumps it out to the body. 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, blood flows back through the pulmonary vein to the left atrium. It then travels through the bicuspid 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, 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. Its pumping is so strong, that if the aorta would be cut off, then the blood would squirt to a level of 4 meters [5].

First aid

File:Heart.jpg
Heart

See cardiac arrest for emergencies involving the heart

If a person is encountered in cardiac arrest (no heartbeat), cardiopulmonary resuscitation (CPR) should be started and help called. If an automated external defibrillator is available, this device may automatically administer defibrillation if this is indicated. Usually, if there is enough time, the person can be rushed to the hospital where he or she will be cared for by a cardiologist, a doctor who specializes in the heart and lungs.

Electrical innervation of the heart in health is supplied by two closely intertwined mechanisms. The first mechanism is well demonstrated in electrical coil systole (interpreted by the electrocardiogram as QRS)as an individualized myocardial electrical tree initiated by the sinoatrial node. Secondary diastolic electrical control is posited to represent autonomic recoil control from the vagus nerve and cardiac branches and the thoracic ganglia.

Food use

The hearts of cattle, sheep, pigs, chickens and certain fowl are consumed in many countries. They are counted among offal, but being a muscle, the taste of heart is like regular meat. It resembles venison in structure and taste.

Aztec heart removal

The Aztec civilization used the heart as a sacrificial token during the sacrifice of a human being. The priest used a stone knife to cut into the thoracic cavity and remove the heart, upon which it would be placed on a stone altar as an offering to the gods. The greatest sacrifice under the reign of Montezuma involved the removal of the hearts of over 12,000 enemy soldiers.


"Heart" as a symbol

The traditional "heart shape" appears on a 1910 St. Valentine's Day card.

The heart (♥) has long been used as a symbol to refer to the spiritual, emotional, moral, and in the past also intellectual core of a human being. As the heart was once widely believed to be the seat of the human mind, the word heart continues to be used poetically to refer to the soul, and stylized depictions of hearts are extremely prevalent symbols representing love. However, more realistic depictions of human hearts tend to have macabre connotations of death and violence, quite unlike the concepts associated with the poetic and symbolic heart. This discrepancy is a common source of dark humor.

As metaphor

In mythology, spirituality and religion

In religious texts such as the Bible [2], the heart has historically been ascribed much mystical significance, either as metaphor or as an organ genuinely believed to have spiritual or divine attributes.

In the Bible, this idea emerges in the earliest passages; Genesis 6:5 situates the thoughts of evil men in their hearts, and Exodus 5 through 12 speak repeatedly of the Lord "hardening Pharaoh's heart." By this it is meant that God made Pharaoh resolve not to let the Israelite slaves leave Egypt, in order to bring judgment against Pharaoh and demonstrate his power: "'Go to Pharaoh, for I have hardened his heart and the hearts of his officials so that I may perform these miraculous signs of mine among them'" (Exodus 10:1). In the Book of Jeremiah 17:9, it is written that the "heart is deceitful above all things, and desperately wicked," and that the Lord is the judge who "tries" the human heart.

The Sacred Heart of Jesus and the Immaculate Heart of Mary are traditional Roman Catholic devotional images.

Similarly, in Egyptian mythology, the heart was weighed in a balance against the feather of Ma'at, symbolising truth, in the judgment of the dead in the Egyptian Book of the Dead. Egyptian sources do not actually reveal whether the heart had to be lighter or heavier than the feather for the deceased to pass into paradise - all depictions show only the weighing of the heart, not the actual results, heavier or lighter. (See also Egyptian soul).

File:Corazón.svg
European traditional heart symbol.

In early science and philosophy

Many classical and medieval philosophers and scientists, including Aristotle, considered the heart the seat of thought, reason or emotion, often rejecting the value of the brain.

The Roman physician Galen located the seat of the passions in the liver, the seat of reason in the brain, and considered the heart to be the seat of the emotions. While Galen's identification of the heart with emotion were proposed as a part of his theory of the circulatory system, the heart has continued to be used as a symbolic source of human emotions even after the rejection of such beliefs.

The Stoics taught that the heart was the seat of the human soul.

As icon

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In European traditional art and folklore, the heart symbol is drawn in a stylized shape. This shape is typically colored red, suggesting both blood and, in many cultures, passion and strong emotion. The hearts and the diamonds are the two red suits in most playing card decks. The shape is particularly associated with romantic poetry; it is often seen on St. Valentine's Day cards, candy boxes, and similar popular culture artifacts as a symbol of romantic love.

What the traditional "heart shape" actually depicts is a matter of some controversy. It only vaguely resembles the human heart. Some people claim that it actually depicts the heart of a cow, a more readily available sight to most people in past centuries than an actual human heart. However, while bovine hearts are more similar to the iconic heart shape, the resemblance is still slight. The shape does resemble that of the three-chambered heart of the turtle, and that of the human male prostate gland, but it is very unlikely that the image was patterned after either of these organs.

The "heart" shape could also be considered to depict features of the human female body, such as the female's pubic mound or spread vulva. The tantric symbol of the "Yoni" is another example of a heart-shaped abstraction of a woman's vulva. In fact, the symmetry resembles the vulva far more than the asymmetry of the organ. In the introduction to the Vagina Monologues Gloria Steinem writes, "[The heart] was reduced from power to romance by centuries of male dominance."

Others maintain that the heart resembles the shape of the female breasts or the female buttocks.

File:Cyrenecoin.jpg
Ancient silver coin from Cyrene depicting a silphium seed or fruit.

Another possible origin can be seen on the coins of the ancient city of Cyrene, some of which depict the seeds or fruit of the now-extinct silphium plant. The seeds are distinctly heart-shaped. Since this plant was widely used as an ancient herbal contraceptive or abortifacient, this shape may have come to be associated with sexuality and love.

The "heart" shape is formed by the back and wings of a dove, which was associated with Aphrodite, the ancient Greek goddess of love.

It may also be a stylised form of the combination of the silhouettes of two people kissing.

File:Heartleaf.jpg
The heart-shaped hole made by nature on a leaf

The most common emoticon for the heart is <3. In Unicode, the heart symbol is U+2665, and it can thus be generated in HTML by typing &#x2665; or &#9829;, or by the HTML entity &hearts;. Mathematically, a heart-shaped figure, called a cardioid, can be represented by plotting a graph of either or, in polar form,


Additional images

  • 2cb.jpg

    2C-B pill.

  • Mating Mute Swans may appear to make a negative space heart.

  • A red potato exhibiting gemination, an effect brought about by a partial twinning during development.

  • Heart carved in tree


See also

  • Cardiac cycle
  • Electrocardiogram
  • Electrical conduction system of the heart

References
ISBN links support NWE through referral fees

  1. ↑ The American Heritage Stedman's Medical Dictionary. KMLE Medical Dictionary Definition of heart..
  2. ↑ The American Heritage Stedman's Medical Dictionary. KMLE Medical Dictionary Definition of cardiac.
  3. ↑ http://www.obgyn.net/us/us.asp?page=/us/cotm/0001/ehr2000
  4. ↑ Terry J. DuBose http://www.obgyn.net/english/pubs/features/dubose/ehr-age.htm Sex, Heart Rate and Age]
  5. ↑ Ian Holm in From Hell

External links

Commons-logo.svg
Wikimedia Commons has media related to:

References


References


See also

  • Artificial heart
  • Atrium
  • Blood pressure
  • Cardiology
  • Cardiothoracic surgery
  • Cardiovascular pathology
  • Circulatory system
  • Echocardiography
  • Electrical conduction system of the heart
  • Haemodynamics
  • Heart cancer
  • Heart defects
  • Heart rate
  • Heart transplant
  • Pulse
  • Ventricle
  • Ventricular hypertrophy
  • Holiday heart syndrome
  • Circle map — simplified mathematical model of the beating heart.
  • MUGA scan
  • Cardiac stress test

External links

Anatomy of torso, cardiovascular system: heart
Structures
atria (interatrial septum, musculi pectinati) • ventricles (interventricular septum, trabeculae carneae, chordae tendinae, papillary muscle) • valves • cusps
Regions
base • apex • grooves (coronary/atrioventricular, interatrial, anterior interventricula, posterior interventricular) • surfaces (sternocostal, diaphragmatic) • borders (right, left)
Right heart
(vena cavae, coronary sinus) → right atrium (auricle, fossa ovalis, limbus of fossa ovalis, crista terminalis, valve of the inferior vena cava, valve of the coronary sinus) → tricuspid valve → right ventricle (conus arteriosus, moderator band/septomarginal trabecula)  → pulmonary valve → (pulmonary artery and pulmonary circulation)
Left heart
(pulmonary veins) → left atrium (auricle) → mitral valve → left ventricle → aortic valve (aortic sinus) → (aorta and systemic circulation)
Layers
pericardium: fibrous pericardium • serous pericardium (pericardial cavity, epicardium/visceral layer) • pericardial sinus
myocardium • endocardium • cardiac skeleton (fibrous trigone, fibrous rings)
Conduction system
Cardiac pacemaker • SA node • AV node• bundle of His • Purkinje fibers
Cardiovascular system - edit
Blood  |  Heart → Aorta → Arteries → Arterioles → Capillaries → Venules → Veins → Vena cava → Heart → Pulmonary arteries → Lungs → Pulmonary veins → Heart

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