1. Ear right
2. Left Ear
3. Vena cava higher
4. Aorta
5. Pulmonary artery
6. Pulmonary vein
7. Mitral Valve (atrioventricular)
8. Aortic Valve
9. Left Ventricle
10. Ventricule law
11. Vena cava inferior
12. Tricuspid valve (atrioventricular)
13. Valve sigmoid (lung)

The heart is a hollow and muscular body which ensures the circulation of blood in the blood pumping by rhythmic contractions to blood vessels and body cavities of an animal. The word heart means "which related to the heart" and it comes from the Greek word cardia, "heart" of Indo-European root kērd

The heart is the "engine", the pump of the circulatory system.

In the human body, the heart lies in the mediastinum. It is the middle part of the ribcage bounded by both lungs, sternum and spine. It is a little left of center of the chest, back, sternum, on the diaphragm. It is a hollow organ driven by a muscle, the myocardium, and coated the pericardium (pericardium) and is surrounded by the lungs.

The heart measuring 14 to 16 cm diameter and 12 to 14 cm. Its size is about 1.5 times the size of the closed fist of the person. Its volume is about 50 to 60 cc. A little less large in women than in men, it measures an average at this one 105 mm wide, 98 mm high, 205 mm circumference. The heart of an adult weighs 300 to 350 grams. These dimensions are often increased in heart disease. It consists of four rooms, called cardiac cavities: atria, or top atria and the ventricles below. Each day, the heart pump the equivalent of 8 000 litres of blood to an equivalent of 100 000 heartbeats.

A thick muscle wall, the septum, divides the atrium and left ventricle of the atrium and right ventricle, preventing the passage of blood between the two halves of the heart. The valves between the atria and ventricles ensure the passage-way coordinated blood from the atria to the ventricles. The central organ of the bloodstream is actually composed of two hearts joined to one another, but totally separate from one another: a heart venous said right (or segment capacitive), and said a heart left arterial (or segment resistive).

The ventricles have cardiac function is to pump blood to the body or to the lungs. Their walls are thicker than those of the atria and the ventricles of contraction is more important for the distribution of blood.

Blood oxygen depleted by its passage through the body enters the right atrium by three veins, the superior vena cava (superior vena cava), the inferior vena cava (inferior vena cava) and the coronary sinus. The blood then passes to the right ventricle. This pump to the lungs through the pulmonary artery (arteria pulmonalis).

After losing its carbon dioxide to the lungs and it be provided with oxygen, the blood passes through the pulmonary veins (venae pulmonales) to the left atrium. From there oxygenated blood enters the left ventricle. This is the pompante main room, designed to send the blood through the aorta (aorta) to all parts of the body except the lungs.

The left ventricle is much more massive than the right because it must exert considerable force to force blood through the body pressure against the body, while the right ventricle serves only the lungs.

Although the ventricles at the bottom of the atria, the two vessels through which blood leaves the heart (the pulmonary artery and aorta) are at the top of the heart.

The wall is composed of the heart muscle that does not fatigue. It consists of three distinct layers. The first is the epicardium (epicardium), which consists of a layer of epithelial cells and connective tissue. The second is the thick myocardial (myocardium) or cardiac muscle. Inside is the endocardium (endocardium), an additional layer of epithelial cells and connective tissue.

The heart needs a significant amount of blood, donated by the coronary arteries (whose circulation is called diastolic) left and right (arteriae coronariae), branch of the aorta.

The revolution heart
The heart rate at rest is 55 to 80 beats per minute, a rate of 4.5 to 5 liters of blood per minute. In total, the heart can beat more than 2 billion times in a lifetime. Each of its beats leads to a sequence of events collectively called the revolution heart. The latter consists of three major steps: systole atrial ventricular systole and diastole:

1. During atrial systole, the atria contract and eject blood to the ventricles (filling assets). Once the blood expelled from the atria, the atrio-ventricular valves between the atria and ventricles close. This prevents reflux of blood into the atria. The closure of these valves produces the sound of the familiar heart beat.
2. The ventricular systole implies contraction of the ventricles, expelling blood into the circulatory system. Once the blood expelled, the two valves sigmoïdes - the pulmonary valve on the right and left aortic valve - close. Thus the blood does not reflue to the ventricles. The closure of valves sigmoïdes noise produced a second cardiac more acute than the first. During the systole the atria now released, are filled with blood.
3. Finally, the diastole is the relaxation of all parts of the heart, allowing filling (liabilities) of the ventricles, by the right and left atrium and from the cellars and pulmonary veins.

The heart goes 1 / 3 time in systole and 2 / 3 in diastole.

Expulsion rhythmic blood and causes the pulse that can be tasting.

Automatism heart
The heart muscle is' myogenique '. This means that, unlike the skeletal muscle, which requires a stimulus conscious or reflex, the heart muscle s'excite itself. The rhythmic contractions occur spontaneously, though their frequency may be affected by nerve or hormonal influences such as exercise or the perception of danger.

The sequence rhythmic contractions is coordinated by a depolarization (reversing the polarity of the electric membrane by passing active ions through thereof) of the sinus node or hub and Keith Flack (nodus sinuatrialis) located in the upper wall the right atrium. The electric current induced in the order of millivolt, is transmitted throughout the atria and the ventricles happening in through the atrio-ventricular node. It spreads in the septum by the bundle of His, consisting of specialized fibers called Purkinje fibers and serving as a filter in the event of too rapid atria. The Purkinje fibers are specialized muscle fibers allowing a good electrical conduction, which ensures the simultaneous contraction of the ventricular walls. The electrical system explains the regularity of heartbeat and coordinates the atrio-ventricular contractions. This electrical activity that is being analysed by electrodes laid on the surface of the skin and which is the electrocardiogram, or ECG.

Regulation by the central nervous system
The strength and frequency of contractions are modulated by centres located in the medulla, through nerves cardiovascular moderator and cardiovascular pacemaker. These nerve centres are sensitive to blood conditions: pH, concentration of oxygen.

Hormonal regulation
The hormones such as adrenaline and noradrenaline (hormones adrenergic system or [ortho] nice) or thyroid hormone (T3) promote contractility. On the contrary, hormones such as acetylcholine (hormone system or cholinergic parasympatique) slow heartbeat.

The sympathetic system in addition to its direct action on the heart in particular will cause dilation of the coronary arteries (as well as bronchioles) vascularisent the heart while allowing an increase in blood flow and hence an increase in muscular effort is therefore possible increased frequency of contractions. The parasympathetic system on the contrary will produce a constriction of coronary arteries (and bronchioles) resulting then a decrease in blood flow decreased effort muscle potential, acting like a "brake engine."

Diseases and treatments
The study of heart disease called cardiology. The primary heart disease include:

* The coronary heart disease is a disease of the coronary arteries that deprives the heart muscle of oxygen. Reversible, it can cause severe chest pain called angina (angina pectoris). The acute obstruction of an artery causing the death of heart muscle cells (myocardial infarction).
* Heart failure is the progressive loss of the heart's ability to ensure blood flow. It manifests itself in dyspnea (shortness of breath), oedema of the lower limbs and can go as far as acute lung edema.
* Valvular heart: achieving valves sometimes manifested by a "blow to the heart."
* Endocarditis and myocarditis are inflammation of the heart cause bacterial or viral.
* The arrhythmia of the heart is an irregular heart beat. A conduction disorder causes bradycardia (heart or too slow).
* The pulmonary embolism is the obstruction of a pulmonary artery by a clot.
* Congenital heart diseases, ie a malformation of the heart, there may be inversions of the ventricles, earphones or both, malformation of blood vessels near the heart, or more frequently a bad partitioning by septa , Particularly the non-closure of the foramen oval between the atria.

If the coronary artery is narrowed or blocked, you can bypass the affected place with a coronary bypass, or expand with an angioplasty.

Beta-blockers are drugs that slow the heart beat and reduce the need heart of oxygen. The nitroglycerin and other compounds that emit nitric oxide are used in the treatment of heart disease because they cause the dilation of coronary vessels.

The first heart transplant was performed at Groote Schuur Hospital in Cape Town (South Africa) on December 3, 1967. Lewis Washkansky, 53, received a heart of a young woman died in a road accident. He died 18 days later of pneumonia. The surgical team was led by Christiaan Barnard. In France, Emmanuel Vitria lived from 1968 to 1987 with a transplanted heart.

First Aid
The failure of the heart, vital organ, may require care urgentissime:

* Cardiac arrest is an absolute medical emergency. It manifests itself in a state called "apparent death":

1. unconsciousness, ie the absence of reaction to pain or a simple verbal order,
2. the breathing, which can be seen observing the absence of movement of the chest and the absence of any respiratory noise,
3. and abolition of the pulse, in particular, carotid (this point is not a reliable element: with stress, the person seeking to take the pulse sometimes sent his own pulse at your fingertips).

In 90% of sudden deaths in adults, the heart is in ventricular fibrillation. When one is facing such a case, you should immediately call the relief and then immediately begin CPR until rescue to improve the chances of survival based on a medical care very rapidly allow an early defibrillation.

* Chest pain, a little prolonged, may be indicative of a myocardial infarction whose treatment of choice is revascularization fastest possible coronary artery occluse. Again, the call for emergency medical services remains imperative in any doubt.

* A malaise, shortness of breath importantly, palpitations poorly tolerated can be indicative of a heart failure may worsen quickly and justify the call urgent medical.

Beat the heart
The smaller animals are usually a heart beat faster. Young animals have a heart beat faster than adults of the same species.

Some heart rate depending on the species:
Grey whale 9 times per minute
Common Seal 10 times per minute (diving)
140 times per minute (on earth)
Elephant 25 times per minute
Being human 60-100 times per minute
Moineau 500 times per minute
Musaraigne 600 times per minute
Birds fly up-1 200 times per minute flight for some species

There is also a link between the average life in a kind and heart rate in this case. The species slow heart usually greater longevity.

From Antiquity to the Renaissance: uncertainty about the role of heart
The heart has long been regarded as the seat of sensations and voluntary movement. Without doubt the increase in heart rate during the emotions she is at the origin of this belief.

Aristotle (fourth century BC. AD) has assigned this role, while Galen (second century) ranged rather these functions in the brain.

The Middle Ages has long hesitated between these two approaches. Turisanus denied the heart of faculty status after a power of the soul.

It was not until the eighteenth century that the heart begins to be definitively dethroned of his office headquarters sensations, with the work of Franz Joseph Gall, then François Broussais on the brain.

Work is much more recent studies have shown the respective roles of the two hemispheres of the brain, with a specialization in each hemisphere. The right brain is thus seen as one who deals with emotions, and as more holistic (see on this point Symmetry brain). It will also consult the work done by the psychologist Tony Buzan in the years 1970 on the functions of the cerebral hemispheres.