Anatomy & Physiology

Anatomy & Physiology Study Guide

The Heart Wall The wall of the heart in dissection reveals three distinct layers: an outer epicardium, a middle myocardium, and an inner endocardium. • The epicardium covers the outer surface of the heart as the visceral pericardium. This serous membrane consists of an exposed mesothelium and an underlying layer of loose areolar connective tissue that adheres to the myocardium. • The myocardium defines the muscle layer that forms the bulk of both atria and ventricles. This layer contains cardiac muscle tissue, blood vessels, and nerves. The cardiac muscle tissue consists of concentric layers. Muscle bundles that form figure eights wrap around the atria and encircle the great vessels within the atrial myocardium. Superficial cardiac muscles wrap around both ventricles; deeper muscle layers spiral around and between the ventricles toward the apex in a figure-eight pattern. • Endocardium shields the inner surfaces of the heart, including those of the heart valves. This layer is composed of simple squamous epithelium that is continuous with the endothelium of the attached great vessels. Cardiac Muscle Tissue Cardiac muscle cells are interconnected by intercalated discs . At an intercalated disc, the interlocking membranes of adjacent cells are held together by desmosomes. Intercalated discs propagate action potentials and transfer the force of contraction quickly from cell to cell for an almost synchronized motion. 19.4 Internal Anatomy and Organization

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