BIO 255N Week 1 Study Guide (Chapter 20)

Anatomy and Physiology BIO 255N Week 1 Study Guide (Chapter 20) Mark Greco, MD I. ANATOMY OF THE HEART A. Location of the heart 1. The heart is situated between the lungs within the mediastinum mostly below the sternum with about two-thirds of its mass to the left of the midline (Figure 20.1). 2. Think of the heart as a cone lying on its side and resting on the diaphragm. The pointed apex is formed by the tip of the left ventricle (a lower chamber of the heart) and is directed downward to the left of midline. The base of the heart is opposite the apex, and is formed by the atria (upper chambers) of the heart. 3. Because the heart lies between two rigid structures, the vertebral column and the sternum, external compression on the chest (i.e., CPR) can be used to force blood out of the heart and into the circulation. (Clinical Correlation). B. Pericardium 1. The pericardium surrounds and protects the heart, and anchors the heart within the mediastinum. a. The pericardium consists of an outer fibrous pericardium and an inner serous pericardium (Figure 20.2). b. The serous pericardium is composed of a parietal layer (fused to the fibrous pericardium) and a visceral layer (adheres tightly to the heart surface). c. The visceral layer of the serous pericardium is also called the epicardium (see Section C below). d. Between the parietal and visceral layers of the serous pericardium is the pericardial cavity, a small potential space filled with pericardial fluid that reduces friction between the two membranes as the heart moves. e. An inflammation of the pericardium is known as pericarditis. Associated bleeding into the pericardial cavity compresses the heart (cardiac tamponade) and is potentially lethal (Clinical Correlation). C. Layers of the Heart Wall 1. The wall of the heart has three layers: epicardium (external layer), myocardium (middle layer), and endocardium (inner layer) (Figure 20.2). 2. The epicardium consists of