Myocardium

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

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The myocardium is the heart muscle. It lies between the epicardium (outer skin of the heart), with which it is fused, and the endocardium (inner lining of the heart). It is constructed in a similar way to the skeletal muscles, but with a few special features. When cells of the myocardium are damaged, regeneration is only possible to an extremely limited extent. Read everything you need to know about the myocardium!

What is the myocardium?

The myocardium is the heart muscle, the working muscles of the heart. Like the skeletal muscles, it is striated across, but thinner and with a special structure: the surface of the heart muscle fibers is encased in a lattice fiber network, the cell nuclei are longer than in skeletal muscle cells and are located in the center. The heart muscle fibers are branched and form a network-like network. The cells are connected to one another by so-called glossy strips.

In the area of the atria, the heart muscles are weak (about one millimeter thick) and have two layers; in the area of the ventricles they are stronger (two to four millimeters thick) and have three layers. With a thickness of eight to eleven millimeters, the myocardium is strongest in the left ventricle, because from here the blood has to be pumped into the great circulation via the aorta.

As mentioned, the myocardium has three layers in the area of the heart chambers: an outer parallel-fiber inclined layer, a middle ring layer and an inner longitudinal layer. The outer layer arises from the top of the heart skeleton and winds helically to the left down to the apex of the heart, goes down at the lower end and then as an inner oblique fiber back up to the starting point. Individual fibers circle the ventricles individually and then go back up to the starting point as an inner layer. The middle ring layer circles each ventricle on its own.

In the atria, the myocardium is significantly thinner. It consists of an outer and a transverse layer, which run over both atria, and inner fibers, which run over the roof of the atria.

What is the function of the myocardium?

The myocardium is the heart's working muscles.

The contraction of the ring and inner longitudinal fibers of the heart muscles constricts and shortens the ventricle and thickens the wall. The pressure in the ventricle increases as a result, and the blood is pressed out of the heart into the large vessels through the pulmonary or aortic valve. This shortening of the chamber creates a suction that sucks the blood from the veins into the atria.

In some people, the myocardium has to do permanent extra work due to resistance in the periphery (vascular constrictions) or valve defects or to provide increased physical performance (as in high-performance athletes). This leads to the heart muscle fibers lengthening and widening - the heart muscle enlarges, which means that it is "hypertrophied".

From childhood on, a pigment appears in the heart muscles, lipfuscin, which spreads more and more with advancing age and gives the heart of old age a brownish color. As a result, the muscle fibers get thinner and thinner.

Where is the myocardium located?

The myocardium is the middle layer of the heart wall, the heart muscle. It is covered by the endocardium on the inside and the epicardium on the outside. The epicardium is connected by a film of serous fluid to the pericardium, the heart sac, in which the heart moves.