Anatomy & Physiology I and II

separated by the interventricular septum, which is much thicker. Atrioventricular (AV) valves , folds of fibrous tissue, extend into the openings between the atria and ventricles. By definition, valves permit blood flow in one direction only. These valves between the upper and lower chambers allow flow from the atria to the ventricles and block flow moving in the opposite direction. The Right Atrium The right atrium receives deoxygenated blood from the systemic circuit through the two great veins: the superior vena cava and the inferior vena cava. The superior vena cava delivers blood from the upper body. It opens into the superior region of the posterior right atrium and drains blood from the head, neck, upper limbs, and chest. The inferior vena cava , which opens inferiorly into the posterior portion of the right atrium, carries blood to the right atrium from the rest of the trunk, the viscera, and the lower limbs. The coronary sinus returns blood from cardiac veins of the heart. This sinus is a large, thin-walled vein that opens into the right atrium inferior to the connection with the superior vena cava. The posterior walls of the right atrium and the interatrial septum have smooth surfaces. In contrast, prominent muscular ridges, called the pectinate muscles, line the anterior wall and inner surface of the auricle. The Right Ventricl The right ventricle receives blood from the right atrium through a broad opening bounded by three fibrous flaps, also called cusps or leaflets. These flaps are part of the right atrioventricular (AV) valve, also known as the tricuspid valve . Connective tissue fibers called chordae tendineae attach to the free edge of each cusp. The fibers originate at the papillary muscles , which are conical muscular projections that arise from the inner surface of the right ventricle. The right AV

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

Anatomy & Physiology Study Guide

The right atrium interacts with the right ventricle and the left atrium with the left ventricle. A band of muscular tissue called a septum separates the right and left heart chambers. The thin interatrial septum separates the atria; the ventricles are

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