myokardiumiin

Myocardium, the muscular middle layer of the heart wall, forms the bulk of the heart’s mass and is responsible for the heart’s pumping action. It lies between the endocardium, which lines the chambers, and the epicardium, the outer surface. In Finnish, myokardiumiin would be a grammatical form meaning into the myocardium; there is no separate anatomical entity by that name in English. The myocardium consists mainly of cardiomyocytes arranged in layered, helical bundles. These muscle cells are striated and often contain a single, or occasionally two, nuclei. Intercalated discs connect cardiomyocytes and house gap junctions and desmosomes, enabling rapid electrical coupling and mechanical continuity essential for coordinated contraction. The tissue is highly vascularized and rich in mitochondria to support continuous, energy-demanding activity.

Functionally, the myocardium generates contractile force that ejects blood from the heart chambers. Contraction is regulated by the cardiac conduction system, including the sinoatrial node, atrioventricular node, and Purkinje fibers, which produce a rhythmic, automatic heartbeat. Cardiac muscle relies on calcium-induced calcium release for excitation–contraction coupling and typically contracts spontaneously with a controlled autonomic influence.

The myocardium receives blood supply from the coronary arteries, with perfusion primarily during diastole. It has limited regenerative capacity; after injury such as ischemia, damaged tissue is replaced by fibrous scar rather than renewed muscle.

Clinically, myocardial dysfunction is central to conditions such as myocardial infarction, myocarditis, and cardiomyopathies (dilated, hypertrophic, restrictive). Diagnosis often involves imaging modalities like echocardiography and cardiac MRI, alongside ECG and biomarker assessment.