Anatomy & Physiology

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 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 Ventricle 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 valve closes when the right ventricle contracts, preventing the backflow of blood into the right atrium. The internal surface of the ventricle also includes a series of muscular ridges: the trabeculae carneae . The conus arteriosus forms the superior end of the right ventricle and ends at the pulmonary valve. The pulmonary valve consists of three semilunar cusps of thick connective tissue. Deoxygenated blood travels through the valve to the pulmonary arteries, which carry blood to the lungs for oxygenation by way of diffusion at the level of the pulmonary capillaries. The Left Atrium From the pulmonary capillaries, blood collects into small veins that ultimately unite to form the four pulmonary veins. The left atrium receives blood through entrances in its posterior wall from two right and two left pulmonary veins. The left atrium has an auricle like the right atrium. A valve, the left atrioventricular (AV) valve, also called bicuspid or mitral valve, guards the entrance to the left ventricle. As the name bicuspid implies, the left AV valve contains a pair, not a trio, of cusps. The bicuspid valve permits blood to flow from the left atrium into the left ventricle but prevents backflow during ventricular contraction.

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