The Heart - PDF

The Heart Pericardium, layers of heart and fibrous skeleton  Describe the structure and function of the pericardium Intended Describe the structure (histological composition) and function of the three layers Learning of the heart (epicardium, myocardium...

The Heart Pericardium, layers of heart and fibrous skeleton  Describe the structure and function of the pericardium Intended Describe the structure (histological composition) and function of the three layers Learning of the heart (epicardium, myocardium Outcomes (differences between chambers) and endocardium). Structure and Function of Pericardium Loading… Layers of the heart Myocardium Loading… Fibrous Skeleton of the Heart Summary - Pericardium The membrane that surrounds and protects the heart is the pericardium. It confines the heart to its position in the mediastinum, while allowing sufficient freedom of movement for vigorous and rapid contraction. Consists of two main parts: the fibrous pericardium and the serous pericardium Superficial fibrous pericardium is composed of tough, inelastic, dense irregular connective tissue. It resembles a bag that rests on and attaches to the diaphragm; its open end is fused to the connective tissues of the blood vessels entering and leaving the heart. The fibrous pericardium prevents overstretching of the heart, provides protection, and anchors the heart in the mediastinum. The fibrous pericardium near the apex of the heart is partially fused to the central tendon of the diaphragm and therefore movement of the diaphragm, as in deep breathing, facilitates the movement of blood by the heart. The deeper serous pericardium is a thinner, more delicate membrane that forms a double layer around the heart The outer parietal layer of the serous pericardium is fused to the fibrous pericardium. The inner visceral layer of the serous pericardium, which is also called the epicardium is one of the layers of the heart wall and adheres tightly to the surface of the heart. Between the parietal and visceral layers of the serous pericardium is a thin film of lubricating serous fluid. This slippery secretion of the pericardial cells, known as pericardial fluid, reduces friction between the layers of the serous pericardium as the heart moves. The space that contains the few milliliters of pericardial fluid is called the pericardial cavity. Summary – Layers of the heart The wall of the heart consists of three layers - the epicardium (external layer), the myocardium (middle layer), and the endocardium (inner layer). The epicardium is composed of two tissue layers. The outermost is called the visceral layer of the serous pericardium. This thin, transparent outer layer of the heart wall is composed of mesothelium. Beneath the mesothelium is a variable layer of delicate fibroelastic tissue and adipose tissue. The adipose tissue predominates and becomes thickest over the ventricular surfaces, where it houses the major coronary and cardiac vessels of the heart. The epicardium imparts a smooth, slippery texture to the outermost surface of the heart. The epicardium contains blood vessels, lymphatics, and vessels that supply the myocardium. The middle myocardium is responsible for the pumping action of the heart and is composed of cardiac muscle tissue. It makes up approximately 95% of the heart wall. The muscle fibers (cells), like those of striated skeletal muscle tissue, are wrapped and bundled with connective tissue sheaths composed of endomysium and perimysium. The cardiac muscle fibers are organized in bundles that swirl diagonally around the heart and generate the strong pumping actions of the heart. The innermost endocardium is a thin layer of endothelium overlying a thin layer of connective tissue. It provides a smooth lining for the chambers of the heart and covers the valves of the heart. The smooth endothelial lining minimizes the surface friction as blood passes through the heart. The endocardium is continuous with the endothelial lining of the large blood vessels attached to the heart. Summary – Fibrous skeleton of the heart The fibrous skeleton consists of four dense connective tissue rings that surround the valves of the heart, fuse with one another, and merge with the interventricular septum. In addition to forming a structural foundation for the heart valves, the fibrous skeleton prevents overstretching of the valves as blood passes through them. It also serves as a point of insertion for bundles of cardiac muscle fibers and acts as an electrical insulator between the atria and ventricles.