Cardiovascular disease affects one in five people and remains the number one cause of mortality in the U.S. This course will review normal anatomy and physiology of the heart and circulatory system.
Anatomy of the heart
The heart is a hollow muscular, inverted cone-shaped muscular organ located in the thoracic cavity between the lungs. Its size is comparable to the adult fist. The weight and size depends upon age, gender, height, and nutritional status with male hearts (300 grams) weighing more than female hearts (250 grams). The heart is located in the mediastinal space, left of midline. The apex of the heart lies inferiorly between the fifth and sixth rib when a person is supine and between the sixth and seventh rib when a person is upright. The heart rests on the diaphragm and is tipped slightly forward and to the left in the chest. The great vessels enter the base of the heart at the superior aspect.
The epicardium, the myocardium, and the endocardium are the three layers of cardiac muscle that form the heart tissue. The outer most layer, the epicardium, is part of the pericardium, a multi-layered sac that covers and encloses the entire heart. The pericardium has two walls with the outer most being fibrous to prevent distention and dilation of the heart. This fibrous layer is attached to the great vessels, the sternum, and the diaphragm. The inner layer consists of the visceral and parietal portions. The visceral layer is also known as the epicardium and covers the entire heart and the great vessels. The epicardium folds over to become the parietal layer, which, in turn, lines the fibrous pericardium.
The pericardial space is located between the parietal layer and the epicardium. Normally this space contains 30-50 milliliters of serous fluid, which acts as a lubricant to decrease friction between the layers as the hearts expands and contracts. The phrenic nerve contains pain fibers and innervates the parietal layer. The epicardium has no pain fibers and is insensitive to pain.
The tissue of the myocardium is made up of striated muscle fibers interlaced into bundles. The myocardial cells have unique characteristics that enable the heart muscle to have automaticity or the innate ability to initiate rhythmic muscular contractions (rhythmaticity) in the absence of a stimulus. The myocardial cells can also conduct nerve impulses. However these cells cannot regenerate or repair if damaged and for that reason there is loss of myocardial function in the event of damage to the myocardium.
The innermost layer of the heart, the endocardium, is made up of endothelial tissue and lines the inside of the heart chambers and covers the heart valves.