Heart

Heart (cor) is a four-cavity muscle organ that acts as a continuously operating pump. It drives the blood through the blood vessels to all parts of the body and thus allows nutrition and metabolism in the tissues

Heart anatomy
The heart is placed behind the sternum in the mediastinum, two thirds to the left of the midline and one third to the right. The weight of heart averages around 300–350 g in men, in women it weighs around 250–300 g. An increase in heart weight above 400 g in men and above 350 g in women is called hypertrophy. The heart can hypertrophy in various pathological conditions or also in sports individuals. The whole muscle organ is enclosed in a envelope called the pericardium with a serous cavity.

Heart position
The heart muscle has the shape of an irregular cone and it is oriented ventrolaterally to the left with its tip (the longitudinal axis of the heart points from the mouth of the superior vena cava from top to right from back to front to left). The tip of the cone is projected into the 5th intercostal space near the medioclavicular line. The position of the tip changes with age and respiratory activity (approximately one intercostal space). In children it is moved one intercostal space higher and laterally, in older people it is located in the 6th intercostal space.

The projection of the heart is presented by four main points:
 * 1) Point A: on the right in the 2nd intercostal space, 1 cm from the sternum.
 * 2) Point T: located in the 5th intercostal space, at the right edge of the sternum, there is an auscultation point for the tricuspid valve.
 * 3) Point M: in the 5th intercostal space, internally from the medioclavicular line, auscultation point for the mitral valve.
 * 4) Point P: eft in the 2nd intercostal space, 2 cm from the sternum margin.
 * By connecting these points, we obtain the approximate dimensions of the cardiac silhouette.

Overall position of the heart is individual variable, depending on breathing, diaphragm position, chest shape, somatotype, etc. In the case of a wide and short chest, the position of the heart is more transverse - the longitudinal axis of the heart makes a smaller angle with the transverse plane. On the other hand, if there is a case of a long and narrow chest, the heart is placed more longitudinally - the longitudinal axis forms a larger angle with the transverse plane.

Heart description
At heart we can describe:


 * basis cordis – the cranial part with the atria, the main vessels enter and exit here;
 * apex cordis – tip of the heart;
 * facies sternocostalis (anterior) – anterior arched surface, facing the sternum and ribs;
 * facies diaphragmatica (inferior) – side facing the diaphragm;
 * facies pulmonalis – sometimes referred to as the left area facing the lungs;
 * margo acutus – the right edge of the heart in a sharp boundary line;
 * margo obtusus – left, rounded edge of the heart.

The atria and ventricles are macroscopically separated from each other by:
 * sulcus coronarius – separates atria from ventricles at the base of heart, the main coronary vessels are located there;
 * septum interatriale et septum interventriculare – are visible as cardiac septums;
 * sulcus interventricularis anterior et posterior – visible depressions separating the ventricles in front and back.

Muscle thickness
Cardiac muscle thickness varies in specific places:
 * Atria = 2–2,5 mm;
 * Right ventricle = 3–4,5 mm;
 * Left ventricle = 12–14 mm;
 * Interventricular septum = 12,5–15 mm.

Heart histology
From a histological point of view, the heart wall is made up of 3 layers, they are the endocardium, myocardium and epicardium.

Endocardium
Endocardium (inner layer; tunica intima) lines the heart cavity, is in contact with the flowing blood, smoothly changes into the tunic of the vascular intima, forms the heart valves. It consists of 4 layers:


 * 1) endotelium (endotelial cells);
 * 2) subendotelium (collagen ligament);
 * 3) elastic-musculár layer ollagen and elastic ligament, smooth muscle cells; this layer is especially strong in the atria);
 * 4) subendocardium (a sparse connective tissue, there is located electrical conduction system of the heart ).



Myocardium
Myocardium (tunica media) is the heart muscle that ensures regular heart contractions. This is the largest part of the heart wall, that is formed together from the endocardium, myocardium and epicardium. The strongest myocardium is found in the left ventricle, where the blood pressure is highest and where oxygenated blood is expelled into the large bloodstream.

Structure
The basic of the heart muscle is the cardiomyocyte. These are muscle cells that have a Y-shape. The cell nuclei that are located in the center of the cell are elongated and contain one to two nucleoli.

The main characteristics
Cardiac muscle tissue combines the characteristics of skeletal and smooth muscle. It consists of transversely striated heart tissue, which is not controlled by our will (involuntary muscle).

The innervation is based on the autonomic nervous system, which controls the frequency of contractions. The actual contractions arise spontaneously in the cardiac conduction system (known as cardiac automation).

The myocardium is nourished by coronary arteries that go directly from the aorta. If it is not adequately supplied with nutrients, complications in the form of diseases occur, especially diseases such as myocardial infarction and coronary artery disease.

Epicardium
Epicardium (outer layer of the heart wall; tunica serosa) is the mesothelial lining forming the visceral leaf of pericardium. It is furthest from the heart cavity, it communicates with about 50 ml of pericardial fluid. coronary arteries takes place in the subepicardium.

Heart chambers
Blood flows through four cavities - the right atrium, the right ventricle, the left atrium and the left ventricle. The individual cavities in the right and left heart are separated by valves that prevent blood flow back.

Right atrium (atrium dextrum)
The vena cava superior opens into the right atrium at the back from above, in ostium venae cavae superioris. Vena cava inferior comes from below in ostium venae cavae inferioris. The point of entry of both hollow veins is called "sinus venarum cavarum".  Sulcus terminalis  is a shallow depression to the right of the mouth of both veins, separating them from the rest of the vestibule. On the hollow side, it corresponds to the "crista terminalis", which is supported by a strip of muscle.

The blood flowing from the inferior vena cava to the heart is directed by the wall algae, valvula venae cavae inferioris, analogously the blood from vena cava superior is directed in the other way by the tuberculum intervenosum.

The actual right atrium is the area in front of the sinus venarum cavarum and contains several formations:
 * auricula dextra - right ear, which is a pin-shaped protrusion visible on the sternocostal surface of the heart;
 * musculi pectinati - the muscle beams that are most prominent in the auricule;
 * ostium sinus coronarii - the entrance of the main stem of the collecting veins of the heart into the right atrium, partially covered by  valvula sinus coronarii ;
 * on the inner surface there are other visible openings, which serve behind the entrances of the smaller collecting veins of the heart.

The medial wall is formed by the septum interatriale, with a striking fossa ovalis. During the embryonic development, it served as a transitional link between the two atria. The septum has its fibrous, thinned part without muscle - pars membranacea septi.

Inflow tract
The inflow part begins in the ostium atrioventriculare dextrum with a triple valve (valva atrioventricularis dextra; valva tricuspidalis). We distinguish three tips on it - cuspides anterior, posterior et septalis . Against the tips are stretched musculi papillares, which with their pull generated through the chordae tendinae prevent the valve from tipping into the atrium. In the right ventricle, the most important are m. papillaris anterior et posterior, in non-constant number are also mm. papillares septales.

Inflow part ends in ostium trunci pulmonalis with semilunar valves. (valva trunci pulmonalis)
 * on the walls there are located trabeculae carneae ventriculi dextri, which are muscle trabeculas similar to musculi pectinati in the atria. From the ventricular septum to the base of the anterior papillary muscle, there is a muscle bundle trabecula septomarginalis that contains part of cardiac conduction system.

Outflow tract
No trabeculae are present in this part, so the smooth part is marked as pars glabra. We distinguish the following departments:
 * conus arteriosus is the name for outflow part cranially in the direction of ostium trunci pulmonalis, it has a conical character;
 * ostium trunci pulmonalis has a valve valva trunci pulmonalis, which consist of three valvulae semilunares, semilunar valves;
 * valvula semilunaris anterior, dextra et sinistra – semilunar lamellas in the shape of a swallow's nest;
 * as lunula we describe the thinned edge, the middle of nach lamella contains nodulus valvulae semilunaris, which ensures the closure of the center of the valve.

Left atrium (atrium sinistrum)
In the left atrium, we distinguish the following units:
 * ostia venarum pulmonalium – the mouth of the pulmonary veins, usually two on the left and two on the right, without valves
 * auricula sinistra – left ear containing the same as the right ear musculi pectinati;
 * septum interatriale – atrial septum, in the place of the right-hand fossa ovalis is referred to as valvula foraminis ovalis;
 * ostium atrioventriculare sinistrum is the mouth of the left atrium into the left ventricle provided with a double valve (valva atrioventricularis sinistra; valva mitralis or valva bicuspidalis).

Left ventricle (ventriculus sinister)
The left ventricle looks round with a thicker muscle wall in cross section (approximately three times the mass of the muscle compared to the right ventricle).

Inflow tract is larger than the right ventricle, from the ostium atrioventriculare sinistrum forward down to the apex and to the anterior wall of the ventricle. We distinguish in it:
 * ostium atrioventriculare sinistrum – part of valva atrioventricularis sinistra (valva mitralis);
 * valva has two main points - – cuspis anterior et posterior;
 * two papillary muscles are stretched to the tips – m. papillaris anterior et posterior;
 * again by pulling over the chordae tendinae they ensure the correct position of the the valve;
 * trabeculae carneae – thicker and with larger depressions than in the right ventricle;
 * functionally, during the systole of the chamber, they fit tightly together and fills the cavity of the inflow part, which thanks to this mechanism empties completely.

Outflow tract is shorter than in the right heart a it is located je ventromedially from ostium atrioventriculare sinistrum, it points caudally kaudálně. We distinguish in it:
 * ostium aortae – right next to the atrioventricular orifice, more ventromedially positioned
 * contains valva aortae consisting of three crescent-shaped valves (valvulae semilunares);
 * valva semilunaris dextra, sinistra et posterior;
 * analogous to the pulmonary valve, they contain "lunulae" and "nodules" with the same function;;
 * sinus aortae is the dilated beginning of the aorta above each of the three lamellae of the valve, from which the two main coronary arteries depart (see below).

Seen from the left ventricle through the septum interventricularis, we can see a fibrous, thinned septal site, referred to as the pars membranacea septi interventricularis, can be seen. That means, that the "pars membranacea" is located between the inflow part of the right ventricle and the outflow part of the left ventricle.

Coronary circulation
The heart is supplied by two main coronary arteries, they are the first leaving branches of the aorty. The venous circulation is provided by the veins merging into the trunksinus coronarius, leading to the right atrium of the heart.



Cardiac skeleton
Cardiac skeleton it is made of dense fibrous ligament to which it is attached myocardium together with all heart valves. Skeleteon electrically separates myocardium of the atria from the myocardium of ventricles (the only link between the atrial myocardium and the ventricular myocardium is the so-called Bundle of His passing through the trigonum fibrosum dextrum). It consist of few parts:


 * Anuli fibrosi – čtyři vazivové prstence kolem srdečních chlopní:
 * anulus fibrosus dexter – at the right atrial orifice with a tricuspid valve;
 * anulus fibrosus sinister – at the left atrial orifice with mitral valve;
 * anulus aorticus – semilunar valve ring;
 * anulus trunci pulmonalis – ring of the semilunar pulmonary valve.

These rings are interconnedcted by the fibrous structures trigonum fibrosum dextrum (between anulus dexter, sinister and aorticus) and trigonum fibrosum sinistrum (between anulus sinister and aorticus). With the right trigonometry is connected pars membranacea septi.



Heart valves
Heart valves are valves that provide one-sided blood flow to the heart. They are not innervated and they are avascular (they open and close based on a pressure gradient). From a histological point of view, these are duplicatures of endocardium. They are formed by an internal fibrous plate (collagen and elastic fibers), on the surface they are covered with endothelium. They are connected to the fibrous rings of the heart skeleton. In the heart we find 4 heart valves, they are:
 * 1) tricuspid valve(valva atrioventricularis dextra seu tricuspidalis) - between the right atrium and the right ventricle;
 * 2) pulmonary valve (valva trunci pulmonalis) - between the right ventricle and the pulmonary artery;
 * 3) mitral valve (valva atrioventricularis sinistra seu bicuspidalis seu mitralis) - between left atrium and left ventricle;
 * 4) aortic valve (valva aortae) - between the left ventricle and the aorta.

Heart blood flow
Clinically, the heart is divided into left heartand right heart. The left heart includes the left atrium and left ventricle, the right heart contains the right atrium and right ventricle. The right and left hearts work together. We distinguish between small (pulmonary) circulation and large (body) circulation.



Right heart
Blood flows from superior and inferior cava to the right atrium'. Blood flows through the atrium to thetricuspid valve, through which it enters the Wright ventricle. In the wall of the right atrium is the first part of the heart conduction system, which creates excitement for regular heart contractions. Specifically, the SA and AV node.

Blood flows from the right atrium through tricuspid valve. In the ventricle, it first flows trhough the inflow part (trabeculae carnae) and aster it continues to the outflow part (conus arteriosus). Through pulmonal valve it flows to pulmonary artery and its branches to the lungs, in which where the blood gas exchange takes place. The right ventricle pumps blood at low pressure (approximately 20 mmHg).

Left heart
From lungs gets oxygenated blood through four pulmonary veins to the left atrium. It flows through mitral valve and gets to the left ventricle.

Blood flows from the let atrium through mitra valve. In the let ventricle it first flows through the inflow part (again composed oftrabeculae carnae) and then it passes into the outflow part (represented byvestibulum aortae). Through the aortic valve it flows into the aorta ascendens and its branches into the whole body. The left ventricle pumps blood under high pressure 'within the systemic circulation (at about 120 mmHg).

Cardiac conduction system
This system ensures the generation of action potentials for myocardial work independently of nerve connections - cardiac automation.

Lymphatic vessels of the heart
Lymphatic vessels of the heart begin with three knittings:
 * subendocardial;
 * myocardial;
 * subepicardial.

During the diastole, lymph flows from the subendocardial plexus to the myocardial plexus and from there during the systole to the subepicardial plexus. The right and left collectors of the heart are then collected from the subepicardial network.

Related links

 * Pericardium
 * Převodní systém srdeční
 * Cévní zásobení srdce
 * RTG obraz srdce
 * Vrozené srdeční vady
 * Cor pulmonale
 * Původci infekce srdce a cév

Externí odkazy

 * Srdce (česká wikipedie)
 * Heart (anglická wikipedie)
 * Gray's anatomy – heart