Cardiac Histology

HEART WALL

Comprises three layers

  • Endocardium, Myocardium, Epicardium

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:

  • Striated.
  • Have 1-2 centrally located nuclei.
  • Cells branch to connect with multiple adjacent 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.

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