Nursing Preparation Study Guide

Nursing Preparation Study Guide inferiorly into the posterior portion of the right atrium, and is responsible for carrying 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 (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. When the right ventricle contracts, the right AV valve closes, preventing the backflow of blood into the right atrium. The internal surface of the ventricle also contains a series ofmuscular ridges,the trabeculaecarneae. 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 the 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 flow from the left atrium into the left ventricle and prevents backflow during ventricular contraction. The Left Ventricle The two ventricles hold equal amounts of blood; however, the left ventricle has thicker walls and is much larger than the right ventricle. Its thick, muscular walls enable the left ventricle to develop pressure sufficient to push blood through the large systemic circuit, whereas the right ventricle needs to pump blood, at lower pressure, only about 15 cm (6 in.) to and from the lungs. The internal organization of the left ventricle generally resembles that of the right ventricle except for the absence of a moderator band.

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