Myokards

Myokards, more commonly referred to as the myocardium, is the muscular layer of the heart. It forms the thick middle portion of the heart wall and is responsible for the heart’s contractile force that pumps blood.

Structure: The myocardium consists of cardiac muscle cells called cardiomyocytes that are branched and connected end-to-end at intercalated discs, which contain gap junctions and desmosomes. This arrangement enables rapid electrical coupling and mechanical synchronization. The tissue is striated and rich in mitochondria to meet high energy demands, and it contains elements of the conduction system embedded within the muscle tissue.

Function: Cardiomyocytes contract in response to electrical impulses that propagate through the myocardium via the cardiac conduction system. Excitation-contraction coupling involves calcium-induced calcium release from the sarcoplasmic reticulum, with calcium entering through L-type channels during the action potential plateau. The autonomic nervous system modulates heart rate and force, while the coronary circulation provides oxygen and nutrients.

Anatomy and blood supply: The myocardium is supplied by the coronary arteries and drained by coronary veins. Blood flow to the tissue is greatest during diastole. The heart wall comprises the epicardium (outer), myocardium (muscular middle), and endocardium (inner), with the myocardium forming the bulk of the tissue that generates contractile force.

Clinical relevance: Ischemia or infarction damages myocardium, reducing contractile function. Various cardiomyopathies alter its structure or performance, and arrhythmias can arise from disturbances within the myocardial conduction apparatus. Proper myocardial function is essential for sustaining systemic circulation and organ perfusion.