Endokard

Endokard, also known as the endocardium, is the thin, highly specialized inner lining of the heart. It lines the heart chambers and covers the heart valves, and is continuous with the endothelial lining of the great vessels as they exit the heart. The endocardium consists of an endothelial cell layer (simple squamous epithelium) and a subendocardial connective tissue region. In the ventricles, the subendocardial layer contains parts of the heart’s conducting system, including Purkinje fibers, which help coordinate ventricular contraction.

Functionally, the endocardium provides a smooth, low-friction surface within the heart to minimize turbulence as blood flows through the chambers and across the valves. It participates in signaling to the myocardium and helps organize the architecture of the valvular apparatus. The endocardial lining also forms part of the heart’s conduction network in the subendocardial zone and is closely involved in valve structure and function.

Developmentally, the endocardium originates from the heart tube endothelium and undergoes cellular transitions that contribute to the formation of subendocardial tissue and the cardiac valves. Endocardial cushions contribute to the development of the atrioventricular septum and the semilunar valve apparatus during embryogenesis.

Clinical significance, endocarditis is an inflammatory or infectious process affecting the endocardial surface, often involving valves, with risks including congenital heart disease, prosthetic valves, rheumatic disease, and intravenous drug use. Other conditions affecting the endocardium include endocardial fibroelastosis and post-injury scar formation.