Heart

The human heart

Structure

In the Human body, the heart is located in the Médiastin. It is the median part of the Rib cage delimited by both Poumon S, the Sternum and the Spinal column. It is a little on the left center of the Thorax, behind of the sternum, on the diaphragm. It is a body hollow mû by a Muscle, the Myocarde, and coated with the Péricarde ( pericardium ); it is surrounded by the lungs.

The heart measures from 14 to 16 cm and its diameter from 12 to 14 cm. Its size is approximately 1,5 times the size of the closed fist of the person. Its volume is worth approximately 50 to 60 cm ³. A little less large at the woman than at the man, it measures on average at that Ci 105 mm of width, 98 mm height, 205 mm of circumference. The heart of an adult weighs from 300 to 350 Gram S. These dimensions are often increased in the cardiac affections. It consists of four rooms, called cardiac cavities: the atria or auricles in top, and the ventricles in bottom.

A thick muscular wall, the septum , divides the atrium and the left ventricle of the atrium and the ventricle right, avoiding the passage of blood between the two halves of the heart. valve S between the auricles and the ventricles ensure the one-way passage coordinated of blood since the atria towards the ventricles. The central body of blood circulation, actually, is composed of two hearts coupled one with the other, but however completely distinct one from the other: a heart right known as venous (or capacitive segment), and a left heart known as arterial (or resistive segment).

The Ventricule S have as a function to pump blood towards the body or the lungs. Their walls are thicker than those of the atria, and the contraction of the ventricles is more important for the distribution of blood.

Blood impoverished of Oxygène by its passage in the body enters the right atrium by three Veine S, the higher Vena cava ( vena undermined superior ), the lower Vena cava ( vena undermined inferior ) and the coronary sine. Blood passes then towards the ventricle right. This one pumps it towards the lungs by the pulmonary Artère ( arteria pulmonalis ).

After having lost its Carbon dioxide with the lungs and to be themselves equipped with oxygen there, blood passes by the pulmonary veins ( venae pulmonales ) towards the left auricle. From there oxygenated blood enters the left ventricle. This one is the pumping room principal, having for goal to send blood by the Aorte ( aorta ) towards all the parts of the body except the lungs. The left ventricle is much more massive than the right because it must exert a considerable force to force blood to cross all the body against the body pressure, while the ventricle right serves only the lungs.

Although the ventricles are in bottom of the atria, the two vessels by which blood leaves the heart (the pulmonary artery and the aorta) find in top of the heart. The wall of the heart is made up of muscle which is not tired. It consists of three distinct layers. The first is the épicarde ( epicardium ) which is composed of a layer of epithelial cells and of conjunctive Tissu. The second is the thick Myocarde ( myocardium ) or cardiac muscle. Inside the Endocarde ( endocardium ) is, an additional layer of epithelial cells and conjunctive fabric.

The heart needs an significant amount of blood, offered by the coronary arteries (of which circulation is known as diastolic) left and right ( arteriae coronariae ), of the junctions of the aorta.

The cardiac revolution

Diastole and
auricular Systole

ventricular Systole

The heart rate at rest is from 60 to 80 beats per minute, for a flow from 4,5 to 5 liters of blood per minute. Each beat of the heart involves a sequence of events collectively called the cardiac revolution. This one consists of three major stages: the auricular Systole , the ventricular systole and the Diastole :

During the auricular systole , the auricles contracts and ejects blood towards the ventricles (active filling). Once the expelled blood of the auricles, the auriculo-ventricular valves between the auricles and the ventricles are closed. This avoids a backward flow of blood towards the auricles. The closing of these valves produces the sound familiar of the beat of the heart.
the ventricular systole implies the contraction of the ventricles, expelling blood towards the circulatory system. Once expelled blood, both sigmoid valves - the pulmonary valve on the right and the aortic valve on the left - are closed. Thus blood does not ebb towards the ventricles. The closing of the sigmoid valvules produces a second cardiac noise acuter than the first. During this systole the now slackened auricles, fill of blood.
Lastly, the diastole is the relieving of all the parts of the heart, allowing the filling (passive) ventricles, by the right and left auricles and since the venas cava and pulmonary.

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

The rhythmic expulsion of blood thus causes the Pouls which one can touch.

Regulation of the cardiac contractions

Cardiac automatism

The cardiac muscle is “myogenic”. This wants to say that with the difference of the skeletal Muscle, which has need for a conscious stimulus or reflex, the cardiac muscle excites itself. The rhythmic contractions occur spontaneously, although their frequency can be affected by nervous or hormonal influences the such exercise or the perception of danger.

The rhythmic sequence of the contractions is coordinated by a depolarization (inversion of the electric polarity of the membrane by active passage of ions through this one) of the sinusal Nœud or node of Keith and Flack ( nodus sinuatrialis ) located in the higher wall of the right atrium. The induced electric current, about the microvolt, is transmitted in the whole of the auricles and passes in the ventricles via the atrio-ventricular node. It is propagated in the septum by the Faisceau of His , made up of called specialized fibers fibers of Purkinje and being used as filter in the event of too fast activity of the auricles. The fibers of Purkinje are muscle fibers specialized allowing a good electric conduction, which ensures the simultaneous contraction of the ventricular walls. This electric system explains the regularity of the cardiac rhythm and ensures the coordination of the auriculo-ventricular contractions. It is this electric activity which is analyzed by electrodes posed on the surface of the skin and which constitutes the electrocardiogram or ECG.

Regulation by the central nervous system

The power and the frequency of the contractions are modulated by centers located in the Medulla, by the means of Nerf S cardio-regulator and cardio-stimulative. These nerve centres are sensitive to the blood conditions: pH, concentration in Dioxygène.

Hormonal regulation

August 1st the hormones such as the thyroid adrenalin or hormones support the contractility.

Diseases and treatments

First aid

The failure of the heart, vital body, can require a catch of load urgentissime:

the cardiac arrest is a absolute Medical emergency. It appears by a state known as of “sudden death”: a total loss of consciousness with stop of the breathing, and abolition of the pulses, in particular, carotidien (this point does not constitute a reliable element: with the Stress , the person seeking to take the pulse feels sometimes her own pulse at the end of the fingers). In 90 % of sudden deaths of the adult, the heart is in ventricular Fibrillation. When one is face of such a case, it is necessary immediately to invite the helps then to begin the cardiorespiratory Réanimation immediately while waiting for the helps, in order to improve the chances of survival which rest on a very fast medical assumption of responsibility being able to allow an early defibrillation.

the thoracic Pain, so much is prolonged little, can be revealing of a Myocardial infarction whose treatment of choice is the fastest possible revascularisation of the occluded coronary artery. There too, the call to the medical departments of urgencies remains imperative with the slightest doubt.

a faintness, important breathlessness, badly tolerated palpitations can be revealing of a Cardiac failure being able to worsen quickly and justify the urgent medical call.

Media

Modeling of the cardiac cycle (animation flash).
Vidéos of echocardiography, the University of Grenoble.

The heart of the other animals

Structure

The structure of the Mammalian heart of the others S and the Oiseau X is similar to that of the man with his four rooms.

The Amphibien S have a heart with three rooms. The Poisson S rather have a simple circulatory system than double, as well as a heart with two rooms. The hearts of the Arthropod S and the Mollusque S have only one room.

Beat of the heart

Smaller animals have a beat of the faster heart in general. The young animals have a beat of the heart faster than the adults of the same species.

Some heart rates according to the species:

There exists also a bond between average longevity in a species and the heart rate in this species. The species in slow heart have usually a greater longevity.

History and symbolic system

Antiquity with the Rebirth: hesitations on the role of the heart

The heart was regarded for a long time as the seat of the feelings and the voluntary movement. No doubt the increase in the cardiac rhythm at the time of the emotions is at the origin of this belief.

Aristote (IVe front century JC) allotted this role to him, while Galien (2nd century) rather located these functions in the Cerveau.

The Moyen-âge hesitated a long time between these two designs. Turisanus denied in the middle the statute of faculty resulting from a power from the heart.

It is only as from the 18th century that the heart starts to be détrôné definitively of its function of seat of the feelings, with work of François Joseph Gall, then of François Broussais on the Cerveau.

Work much more recent showed the respective role of both Hémisphères of the brain, with a specialization of each hemisphere. The right brain is thus regarded that which treat the emotion S, and as more Holistique (see on this point cerebral Symétrie). One will consult also the work carried out by the psychologist Tony Buzan in the Années 1970 on the functions of the cerebral Hémisphères.

The heart preserves its function symbolic system

The heart is not only a Organe essential with the Vie, it represents also the Amour (♥). The heart is the symbol of the love: one gives in a metaphorical way his heart to the person whom one likes to mean to him that his life is entrusted to him. This probably comes from the cardiac acceleration caused by the agitation (the Stress ) when one thinks of the loved being (because of rise in the blood Pressure, one feels to beat the heart in its chest, the heart “is beating wildly”).

In fact, the word heart more largely indicates what is in the center (the heart of the problem, in the middle of the night…). The heart is symbolically attached to all that there is of more important, of more essential; we need as much our Poumon S as of our heart to live, but it would seem that this last is however infinitely more important in our Inconscient since he acquired a paramount place in our Langue by representing the Amour, the Générosité, the Franchise, the Courage…

In religion, the Sacré-coeur is the royal Heart of Jesus-Christ.

Here some expressions containing the word heart:

To learn by heart. Why this expression?

Logic would like that one learns " by cerveau". However, in the Antiquity, the treated S of anatomy regarded the heart as the seat of the emotions, passions, the will, courage, the thought, the intelligence and the memory. This is why starting from the XIIIe century, one learned " by heart ". The expression crossed the centuries and is always used today.

To have a stony heart; to be without heart
To have the heart on the hand
To have the heart broken
to have of It on the heart
Of good heart
In open heart
To listen to its heart
To be of any heart with somebody
To have a heave
To have heart (to have courage)
To have heart with the work
Heart of rockor

Note

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