Why is the heart a muscular organ

heart

Synonym: Cor, Kardia
English: heart

1 definition

The human heart is the central organ of the bloodstream. It is a hollow muscular organ and functions as a pressure and suction pump that pumps around 5 to 6 liters of blood per minute through the human body. It is part of the cardiovascular system.

The study of the structure, function and diseases of the heart is cardiology. The heart's muscle cells are called cardiomyocytes.

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2 anatomy

2.1 Overview

The heart is located retrosternal in the middle mediastinum and is almost completely surrounded by the two-leaved pericardium. The largest part of the cardiac mass is formed by the heart muscles (myocardium), which are lined with endocardium towards the lumen and covered on the outside by the epicardium.

Anatomically, the heart is made up of two chambers (ventricles) and two atria (atria), the so-called heart cavities. They are separated from each other by heart valves and switched into the body and pulmonary circulation. The connective tissue separating layer between the atrial and ventricular myocardium in the valve plane of the heart is called the cardiac skeleton.

The surface of the heart facing cranially and dorsally, at which the large vascular trunks open, is called the heart base (base cordis), the opposite end is called the apex cordis (apex cordis).

The heart base is elastically fixed by the large vascular pedicels (porta arteriosa and porta venosa) and the bronchopericardiaca membrane. The freely moving apex of the heart is formed from the mass of the ventricles and extends ventrocaudally to the left medioclavicular line at the level of the 5th ICR.

The vein cross consisting of the two vena cava superior et inferior and the four pulmonary veins (venae pulmonales dextrae et sinistrae) in its entirety forms the porta venosa of the heart. The porta arteriosa comprises the aorta, which is spiraling at its origin, and the pulmonary trunk. The right and left coronary arteries, which are responsible for the proprietary blood supply to the heart, arise from the sturdy, thickened origin of the aorta (Bulbus aortae).

2.2 topography

The heart lies within the thorax in the middle mediastinum, with its contour projecting onto the 2nd to 5th rib. At the top, the base of the heart extends about two centimeters beyond the right sternal margin, and at the bottom the apex borders almost to the left medioclavicular line. The heart is laterally bounded by the two pleural leaves of the left and right lung. The left atrium is in direct dorsal contact with the esophagus. Ventral to the heart is the anterior chest wall with the sternum and the thymus behind it. The heart sits caudally on the diaphragm, which is fused with the pericardium.

The longitudinal axis of the heart lies obliquely in the thorax from right dorsocranial to left ventrocaudal. The inclination is approximately 45 ° in the horizontal as well as in the sagittal and frontal planes.

2.3 dimensions

The heart of an adult is about 12 cm long, and measures in cross section at the widest point 8 to 9 cm, at the deepest about 6 cm. The weight fluctuates between 280 and 340 grams for men and between 230 and 280 grams for women.

2.4 Classification

The heart is divided vertically into a right and a left half by septa, horizontally by a circular constriction and the leaflet valves into 2 atria and 2 ventricles. This results in a total of four heart cavities:

  • Right atrium (atrium cordis dextrum)
  • Right ventricle (right ventricle, ventriculus cordis dexter)
  • Left atrium (atrium cordis sinistrum)
  • Left ventricle (left ventricle, ventriculus cordis sinister)

This division of the heart can also be seen from outside. The coronary sulcus runs as a circular constriction between the atria and the ventricles. The anterior interventricular sulcus and the posterior interventricular sulcus are found between the chambers as retractions of the cardiac muscles.

The atria also have ear-shaped bulges, the so-called auricular ears.

2.5 Outside areas

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There are anatomically several outer surfaces of the heart:

2.6 Inner surfaces

The inner surface of the heart, which is covered with the endocardium, is not smooth and unstructured, but rather covered in the area of ​​the heart ventricles by cross-linked, rounded muscle trabeculae, the trabeculae carneae. The papillary muscles also arise here, which tighten the leaflet valves via tendon threads (Chordae tendineae).

2.7 blood supply

The heart is supplied with arterial blood via two large coronary vessels, the dextra coronary artery and the left coronary artery. They form numerous anastomoses with one another. However, these anastomoses are not sufficient to form a complete collateral circuit. One therefore speaks of functional end arteries. When a branch is closed, ischemia of the supply area occurs. Long-term ischemia leads to necrosis of the heart muscle tissue.

The venous blood is transported away via the coronary veins (including the vena cardiaca magna) and the coronary sinus.

The coronary arteries are responsible for the proprietary blood supply to the heart (vasa privata). Approximately 75% of the venous blood is collected in the coronary sinus and directed to the right atrium. About 25% of the blood flows through the Venae cardiacae minimae (Thebesius veins) directly into the atria and ventricles.

For more details see: Coronary arteries, cardiac veins

2.8 Innervation

The vegetative innervation of the heart takes place via sympathetic nerve fibers of the cervical ganglia, which are also known as cardiac nerves (nervi cardiaci), and parasympathetic fibers of the vagus nerve (X nerve). They radiate into a plexus of nerves, the cardiac plexus, at the base of the heart.

The internal electrical control of the heart's activity takes place via the heart's conduction system.

see main article: Innervation of the heart, conduction system of the heart

2.9 Lymph drainage

The heart has endocardial, myocardial and epicardial lymph vessels. Small lymph capillaries in the endomysium of the myocardium join together to form small collectors that mostly accompany the blood vessels. Larger collectors emerge from the epicardial lymphatic system and reach the ventral surface of the aorta and pulmonary trunk along the coronary arteries. Lymph nodes are embedded in these two lymphatic drainage areas (Nodi lymphatici cardiaci).

Lymph vessels on the wall of the large vessels pass through the envelope edge of the pericardium, pass to the bifurcatio tracheae and thus reach the nodes of the tracheobronchial and mediastinal anterior lymph nodes.

On the surface of the pericardium there is a separate pericardial lymphatic network, which drains the lymph from the pericardium and adjacent mediastinum into the lymphatic nodes prepericardiac and lateral pericardiac. The lymph then flows via mediastinal tracts and to the parasternal lymph nodes.

3 histology

Like skeletal muscles, the myocardium is striated muscles. Morphologically, it occupies an intermediate position between the smooth muscles and the skeletal muscles. The tissue consists of individual mononuclear or binuclear cells, the cardiomyocytes, which form a functional syncytium. In contrast to the peripherally located nuclei of the skeletal muscles, the cell nucleus of the cardiomyocytes is central.

A special feature of the mycard are the so-called glossy stripes between neighboring cardiomyocytes. Under the light microscope, they appear as bright, highly refractive cross-bands that stain more intensely than the cytoplasm of the cardiomyocytes. These are cell contacts that the cardiomyoctes coordinate mechanically and bioelectrically.

4 embryology

The heart anlage (cardiogenic plate) develops around the 18th day near the buccopharyngeal membrane from the lateral plate mesoderm (heart tube, vessels, epicardium, pericardium) and the neural crest (heart septum in the outflow tract). First, angioblasts form blood islands, from which a horseshoe-shaped vascular plexus is formed. The cells inside it become primitive blood cells, the peripheral cells endothelial cells.

The vascular plexus then fuses on both sides to form an endocardial tube. The lateral folding causes the endocardial tubes to move medially and merge there to form the unpaired heart tube. The mesenchymal cells of the visceral leaf surrounding it condense to form the myocardium. The cardiac jelly, which is the extracellular material of the mesenchyme, lies between the endothelium (endocardium) and the myocardium.

The cranio-caudal fold causes the descent (Descensus cordis) of these structures and the displacement into the pericardial cavity (see below) of the developing heart. The primary pericardial cavity, in which the cardiac tube is attached via the dorsal mesoderm, is created in the mesoderm by the formation of a gap. The middle part of the dorsal mesoderm degenerates, as a result of which the transversus pericardial sinus is formed.

Extensions of the primitive heart tube are:

On the 22nd day, the myocardium begins rhythmic contractions.

see main article: Embryonic heart development

5 physiology

The main task of the heart is to maintain blood circulation. The work or service performed in this process is referred to as cardiac work or cardiac output. In addition to the pumping function, the heart is also assigned a task in regulating blood pressure, which special endocrine cells (myoendocrine cells) perform, especially in the atria. In this context the atrial natriuretic peptide (ANP) is described. The heart is also able to respond to changes in blood volume. For example, the heart rate increases with increased volume (Bainbridge reflex). The contractility of the heart muscle cells is also increased (Frank-Starling mechanism).

6 clinic

6.1 Clinical anatomy

The AHA system of cardiac segmentation is used to localize clinical findings.

6.2 Clinical examination

The clinical examination of the heart is essentially based on the auscultation of the heart tones and murmurs as well as the palpation of the pulse.

6.3 Apparative diagnostics

There are numerous procedures available for examining the heart, which can be invasive or non-invasive. These include:

6.4 Laboratory diagnostics

There are a number of meaningful laboratory parameters for diagnosing heart disease. See, among other things, laboratory diagnostics for myocardial infarction and BNP.

6.5 Major illnesses

The diseases of the heart are the domain of cardiology. Since the heart is functionally closely related to the vascular system, one also speaks of cardiovascular diseases. Important diseases are:

7 literature

Herrmann-Lingen, C .: Depression and Coronary Heart Disease. In: Herzmedizin 26 (2009). H.2, pp.76-81. Get full text

8 web links

Further information on the topic can be found on the Heart topic.