Heart Wall Histology

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Heart Wall

Endocardium:

Innermost layer of endothelial cells.
Its function is to line the chambers and valves of the heart, creating a smooth surface to reduce friction with the blood.
Site of endocarditis

Myocardium:

Muscle cells contract to pump blood from the heart; are arranged in bundles wrapped in connective tissue.
Myoendocrine cells that produce atrial natriuretic peptide (aka, factor or hormone) in response to high blood pressure.
Nodal cardiocytes control the rhythmic contraction of the myocardium (these cells are concentrated in the sinoatrial and atrioventricular nodes).

Details of cardiac muscle cells:

This arrangement increases intercellular connections, which are marked by intercalated discs, for efficient signal conduction.

Intercalated discs comprise interdigitating processes that hold adjacent cells together via complex junctions to rapidly spread contraction signals throughout the myocardium.
Purkinje fibers

Are lighter in the center and lie nearer the endocardium than do muscle cells Purkinje fibers are part of conduction system of the heart.

Epicardium:

Contributes to the serous layer of the pericardium, the protective sac that envelops the heart.
Comprises simple squamous epithelium.
Subepicardial connective tissue comprises adipose and other connective tissues, passage for coronary blood vessels and nerves.