miokard

Miokard, or myocardium, is the thick muscular middle layer of the heart wall. It lies between the endocardium, the inner lining, and the epicardium, the outer layer, and forms the bulk of the heart chambers. The myocardium contracts to pump blood; its coordinated activity sustains systemic and pulmonary circulation. Cardiomyocytes, the muscle cells of the myocardium, are striated, branched cells connected by intercalated discs that include gap junctions and desmosomes. This arrangement enables rapid electrical coupling and synchronized contraction. The tissue is rich in mitochondria and capillaries, reflecting its high energy demand. The heart's conducting system, including pacemaker cells and Purkinje fibers, modulates rhythm and coordinates the timing of contraction.

Blood supply is provided by the coronary arteries; perfusion occurs mainly during diastole. The left ventricle has the thickest wall because it must generate higher pressure to propel blood into the systemic circulation, while the right ventricle has a thinner wall suited for pulmonary circulation.

Developmentally, the myocardium arises from mesoderm and grows largely by hypertrophy after birth; adult cardiomyocytes have limited regenerative capacity, so injuries often form scar tissue rather than new muscle.

Clinical relevance: injury to the myocardium can result from ischemia or inflammation. Myocardial infarction damages contractile tissue; myocarditis involves inflammation; cardiomyopathy refers to diseases of the myocardium that can impair contraction and cause heart failure. Biomarkers such as troponin aid diagnosis, and imaging techniques like echocardiography or MRI assess function and structure.