Anatomy & Physiology

Anatomy & Physiology Study Guide

Chapter 19: The Heart 19.1 An Introduction to the Cardiovascular System Blood flows through a network of vessels that extend between the heart and peripheral tissues. Blood vessels are divided into two different circuits: the pulmonary circuit and systemic circuit. The pulmonary circuit is a network of blood vessels that carry blood to and from the gas exchange surfaces of the lungs, and the systemic circuit transports blood to and from the rest of the body. Blood travels through these circuits in one direction, beginning and ending at the heart. Thus, blood low in oxygen returning to the heart from the systemic circuit must complete the pulmonary circuit to pick up oxygen before reentering the systemic circuit. 19.2 The Pericardium The pericardium is the membrane that lines the pericardial cavity. As a delicate serous membrane, the pericardium can be subdivided into the visceral pericardium and the parietal pericardium . The epicardium is the visceral pericardium that covers and adheres closely to the outer surface of the heart; the inner surface of the pericardial sac, which surrounds the heart, is lined by the parietal pericardium. The pericardial sac is comprised of a dense network of collagen fibers, which form the fibrous pericardium. It stabilizes the position of the cardiovascular organs within the mediastinum. The small space between the parietal and visceral surfaces is the pericardial cavity. It normally contains 15– 50 mL of pericardial fluid, secreted by the pericardial membranes. This fluid acts as a lubricant, reducing friction between the opposing surfaces as the heart beats. Pathogens and inflammation can infect the pericardium, producing the condition pericarditis . The inflamed pericardial surfaces rub against one another, producing a distinctive scratching sound that can be heard through a stethoscope. The pericardial inflammation also commonly results in an increased production of pericardial fluid. Fluid then gathers in the pericardial cavity, restricting the movement of the heart. This condition, called cardiac tamponade , can also be caused by traumatic injuries (such as stab wounds) that produce bleeding into the pericardial cavity. 19.3 Superficial Anatomy of the Heart There are four cardiac chambers that can be identified in a superficial view of the heart. The two superior chambers are the atria. Anatomically, the atria possess relatively thin muscular walls and are highly expandable to allow for the filling of the chamber. When it is not filled with blood, the outer portion of each atrium is a deflated wrinkled flap. Each atrium has an atrial appendage, or an auricle , which is an expandable extension that appeared ear-like to early anatomists. The border between the superior chambers and inferior chambers is a deep groove called the coronary sulcus . The inferior chambers are the ventricles . The posterior interventricular sulcus

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