Human heart with coronary arteries.

The heart is a muscular organ in all vertebrates responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in annelids, mollusks, and arthropods. Muscle (from Latin musculus, diminutive of mus "mouse" is contractile tissue of the body and is derived from the In Biology, an organ ( Latin: organum, "instrument tool" from Greek όργανον - organon "organ instrument Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes Blood is a specialized Bodily fluid that delivers necessary substances to the body's cells ��such as nutrients and oxygen—and transports Waste products The blood vessels are part of the Circulatory system and function to transport Blood throughout the body The annelids, collectively called Annelida (from Latin anellus "little ring" are a large phylum of Animals comprising Molluscs are animals belonging to the phylum Mollusca. There are around 250000 extant Species within the phylum with an estimated 70000 Arthropods are Animals belonging to the Phylum Arthropoda (from Greek ἄρθρον arthron, " Joint " The term cardiac (as in cardiology) means "related to the heart" and comes from the Greek καρδία, kardia, for "heart. Cardiology (from Greek grc καρδίᾱ kardiā, "heart" and grc -λογία -logia) is the branch of Internal medicine Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly "

The heart of a vertebrate is composed of cardiac muscle, an involuntary muscle tissue which is found only within this organ. The cardiac muscle is a type of involuntary striated Muscle found in the walls of the Heart. Involuntary muscles are smooth uni nucleated non-branching muscles that are not directly controllable at will The average human heart beating at 72 BPM, will beat approximately 2. 5 billion times during a lifetime spanning 66 years.

Early development

Main article: Heart 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. The Heart is the first functional organ in a vertebrate embryo For soil improvement see Fertilization (soil.

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. An embryo (from Greek:, plural, lit "that which grows" from en- "in" + bryein "to swell be full" is a multicellular The menstrual cycle is a recurring cycle of physiologic changes that occurs in reproductive-age Females Overt menstruation (where there is blood flow from the It is unknown how blood in the human embryo circulates for the first 21 days in the absence of a functioning heart. 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. ^[1]

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. ^[2]

Structure

The structure of the heart varies among the different branches of the animal kingdom. (See Circulatory system. This is an article about the rock music band "Circulatory System" ) Cephalopods have two "gill hearts" and one "systemic heart". The cephalopods ( Greek plural (kephalópoda "head-feet" are the Mollusc class Cephalopoda characterized by Fish have a two-chambered heart that pumps the blood to the gills and from there it goes on to the rest of the body. Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two A gill is an anatomical structure found in many aquatic organisms In amphibians and most reptiles, a double circulatory system is used, but the heart is not always completely separated into two pumps. Prehistoric amphibian Amphibians (class Amphibia such as Frogs Toads Salamanders Newts Gymnophiona, Sirens and Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers The double circulatory system of blood flow refers to the separate systems of Pulmonary circulation and the Systemic circulation in Amphibians 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 from that of mammals. Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Heart chamber is a general term used to refer to any of the four chambers of the Mammalian Heart (an organ) Right atrium

Human heart removed from a 64-year-old male.

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 thorax is a division of an Animal 's body that lies between the head and the Abdomen. Dextrocardia refers to the Heart being situated on the right side of the body The sternum (from Greek στέρνον sternon, "chest" or breastbone) is a long flat Bone located in the center of the thorax (chest 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). Left heart is a term used to refer collectively to the Left atrium and Left ventricle of the Heart; occasionally this term is intended to reference the The left lung is smaller than the right lung because the heart occupies more of the left hemithorax. lung is the essential Respiration organ in air-breathing Animals including most Tetrapods a few Fish and a few Snails The most primitive The heart is enclosed by a sac known as the pericardium and is surrounded by the lungs. The pericardium is a double-walled sac that contains the Heart and the roots of the Great vessels. lung is the essential Respiration organ in air-breathing Animals including most Tetrapods a few Fish and a few Snails The most primitive 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). In Physiology, the term serous fluid is used for various Bodily fluids that are typically pale yellow and transparent and of a Benign nature The mediastinum, a subdivision of the thoracic cavity, is the name of the heart cavity. The mediastinum is a non-delineated group of structures in the Thorax (chest surrounded by Loose connective tissue. ^[3]

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. For other uses of the words gram or gramme see Gram (disambiguation. Hypertrophy is the increase of the size of an organ or in a select area of the tissue It consists of four chambers, the two upper atria (singular: atrium ) and the two lower ventricles.

Functioning

In humans, 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). Right heart is a term used to refer collectively to the Right atrium and Right ventricle of the Heart; occasionally this term is intended to reference The right atrium (in older texts termed the "right auricle" is one of four chambers (two atria and two ventricles in the Human The right ventricle is one of four chambers (two atria and two ventricles in the Human Heart. Pulmonary circulation is the portion of the Cardiovascular system which carries Oxygen -depleted Blood away from the heart to the Lungs, and Gas exchange or respiration takes place at a respiratory surface—a boundary between the external environment and the interior of the body This happens through the passive process of diffusion. Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement The left side (see left heart) collects oxygenated blood from the lungs into the left atrium. Left heart is a term used to refer collectively to the Left atrium and Left ventricle of the Heart; occasionally this term is intended to reference the lung is the essential Respiration organ in air-breathing Animals including most Tetrapods a few Fish and a few Snails The most primitive The left atrium is one of the four chambers in the Human Heart. From the left atrium the blood moves to the left ventricle which pumps it out to the body. The left ventricle is one of four chambers (two atria and two ventricles in the Human Heart. 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. Systemic circulation is the portion of the Cardiovascular system which carries Oxygenated Blood away from the heart to the Body, and returns

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. Arteries are Blood vessels that carry blood away from the Heart. From there, blood flows back through the pulmonary vein to the left atrium. In the Circulatory system, a vein is a Blood vessel that carries Blood back toward the Heart (as opposed to Artery, a blood vessel 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, 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. In Biology, a syncytium ( plural syncytia) is a large cell-like structure filled with Cytoplasm containing many nuclei This relates to electrical stimulation of one cell spreading to neighboring cells.

First aid

Heart

The heart is one of the critical organs of an animal's body, as it pumps oxygenated blood to feed the body's biological functions. The cessation of the heartbeat, referred to as cardiac arrest, is a critical emergency. A cardiac arrest, also known as cardiorespiratory arrest, cardiopulmonary arrest or circulatory arrest, is the abrupt cessation of normal circulation of Without intervention, death can occur within minutes of cardiac arrest since the brain requires a continuous supply of oxygen and cannot survive for long if that supply is cut off. The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain

If a person is encountered in cardiac arrest, cardiopulmonary resuscitation (CPR) should be started and help called. Use of a defibrillator is preferred, if available, to attempt to restore a normal heartbeat; many public areas have portable defibrillators available for such emergencies. Defibrillation is the definitive treatment for the life-threatening Cardiac arrhythmias Ventricular fibrillation and Ventricular tachycardia. 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.

History of discoveries

The valves of the heart were discovered by a physician of the Hippocratean school around the 4th century BC. Hippocrates of Cos II or Hippokrates of Kos ( ca. 460 BC – ca However their function was not properly understood then. Because blood pools in the veins after death, arteries look empty. Ancient anatomists assumed they were filled with air and that they were for transport of air.

Herophilos distinguished veins from arteries but thought that the pulse was a property of arteries themselves. Herophilos, sometimes Latinized Herophilus (335-280 BC was a Greek physician Erasistratos observed that arteries that were cut during life bleed. Erasistratus of Chios (304 BC- 250 BC was a Greek anatomist and royal physician under Seleucus I Nicator of Syria He ascribed the fact to the phenomenon that air escaping from an artery is replaced with blood that entered by very small vessels between veins and arteries. Thus he apparently postulated capillaries but with reversed flow of blood. Capillaries are the smallest of a body's Blood vessels measuring 5-10 μm in diameter which connect Arterioles and Venules and enable the interchange

The 2nd century AD, Greek physician Galenos (Galen) knew that blood vessels carried blood and identified venous (dark red) and arterial (brighter and thinner) blood, each with distinct and separate functions. Galen ( Greek: Γαληνός Galēnos; Latin: Claudius Galenus, Aelius Galenus, Claudius Aelius Galenus, or 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. The liver is a vital organ in the human body and is present in Vertebrates and some other animals Chyle is a milky Fluid ( Bodily fluid) consisting of Lymph and emulsified Fats or free Fatty acids (FFAs 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 that the arterial blood was created by venous blood passing from the left ventricle to the right by passing through 'pores' in the interventricular septum, 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.

Food use

The hearts of cattle, sheep, pigs, chickens and certain fowl are consumed in many countries. Cattle, colloquially referred to as cows, are domesticated Ungulates a member of the Subfamily Bovinae of the family Pigs, also called hogs or' swine', are Ungulates which have been domesticated as sources of food leather and similar products since ancient times The chicken ( Gallus gallus, sometimes G gallus domesticus) is a domesticated Fowl which is traditionally believed to have descended from Most or all Birds collectively referred to as fowl belong to one of two orders namely the gamefowl or landfowl ( Galliformes) and the waterfowl They are counted among offal, but being a muscle, the taste of heart is like regular meat. Offal is the Entrails and Internal organs of a Butchered Animal. It resembles venison in structure and taste. Venison is the Culinary name for Meat from the family Cervidae.

See also

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

References

External links

• Heart contraction and blood flow (animation)
• eMedicine: Surgical anatomy of the heart
• Very Comprehensive Heart Site
• Self Improvement Wednesday - ABC 702 Drive audio
• The circulatory system
• The position of the heart
• Interactive 3D heart This realistic heart can be rotated, and all its components can be studied from any angle.
• Heart care How to take care of your heart.
• BioArtificialHearts.com Information about bioartificial hearts.