What is the myocardium?
The myocardium is the heart muscle, the working muscles of the heart. It is striated like skeletal muscle, but thinner and with a special structure: The surface of the cardiac muscle fibers is covered by a lattice fiber network, and the nuclei are longer than in skeletal muscle cells and are located centrally. The cardiac muscle fibers are branched and form a mesh-like network. The cells are interconnected by so-called glossy stripes.
In the area of the atria, the myocardium is weak (about one millimeter thick) and has a two-layer structure; in the area of the ventricles, it is stronger (two to four millimeters thick) and has three layers. The myocardium is strongest in the left ventricle, with a thickness of eight to eleven millimeters, because it is from here that the blood must be pumped via the aorta into the large circulatory system.
At the atria, the myocardium is much thinner, consisting of an outer layer and a transverse layer that run across both atria, and inner fibers that run across the roof of the atria.
What is the function of the myocardium?
The myocardium is the working muscle of the heart.
Contraction of the ring and inner longitudinal fibers of the myocardium constricts and shortens the ventricle and thickens the wall. As a result, the pressure in the ventricle increases, and blood is forced out of the heart and into the great vessels through the pulmonary and aortic valves, respectively. This ventricular shortening creates a suction that draws blood from the veins into the atria.
In some people, resistance in the periphery (vasoconstriction) or valve defects require the myocardium to perform permanent extra work or to deliver increased continuous physical effort (as in high-performance athletes). This causes the heart muscle fibers to lengthen and widen – the heart muscle enlarges, i.e. it “hypertrophies”.
From infancy, a pigment, lipfuscin, appears in the heart muscle, which increases in size as the heart ages, giving the aging heart a brownish color. Along with this, the muscle fibers become thinner and thinner.
Where is the myocardium located?
What problems can the myocardium cause?
A hypertrophied myocardium initially loses its strength. As it progresses, the heart muscles weaken overall, and the heart “leaks.”
Myocarditis is an inflammation of the heart muscle. The cause can be disease, radiation therapy, drug or medication use.
Myocardial infarction (heart attack) results from the narrowing or blockage of one or more coronary arteries that supply the heart muscle.
