The cardiovascular system consists of the heart, which works like a pump, and more than 60,000 miles of blood vessels. Its main purpose is to transport oxygen and nutrients to the body and remove metabolic waste. Approximately the size of an adult fist, the heart weighs between 250 and 350g, according to Anthony S. Kaleth Ph.D, co-author of "ACSM's Resource Manual for Guidelines for Exercise Testing and Prescription." Four types of tissue compose the heart.
Fibrous Pericardium
Similar to a slippery sac, the pericardium covers the heart in providing protection and lubrication. This specialized tissue has two layers--the outer layer, or fibrous pericardium, and inner layer, or serous pericardium. Composed of areolar connective tissue, the fibrous pericardial layer protects the heart and holds it in place by attaching to walls of the surrounding chest cavity. When this tissue becomes inflamed due to disease or injury, a painful condition known as pericarditis can develop, says Dr. Michael H. Crawford, author of "Current Diagnosis and Treatment in Cardiology."
Serous Pericardium
Serous pericardium, the inner layer of the pericardial sac, divides into two sections--the parietal and visceral layers. The parietal layer adheres to the fibrous pericardium and consists of connective tissue. Coming in direct contact with the heart, the visceral layer is considered the heart's epicardium or outer membrane layer. In addition to providing another line of protection for the heart, the visceral layer produces pericardial fluid, a slippery liquid responsible for lubricating the heart as it beats.
Myocardium
The tissue responsible for making the heart beat is referred to as the myocardium. It consists of cardiac muscle tissue and makes up most of the heart's anatomical mass. This specialized muscle tissue contains conduction cells, called intercalated discs, that enable the heart to beat automatically. In addition to movement, the myocardium provides structure in dividing the heart into four chambers, as well as support for holding the heart's valves in place. As with skeletal muscle, this tissue constantly requires oxygen. Physician-author Crawford explains, during a heart attack, when oxygen delivery to the heart muscle is cut off, this tissue becomes irreversibly damaged.
Endocardium
Endocardium is the layer of tissue that lines the heart's inside. Consisting primarily of endothelial cells, the endocardium provides a smooth lining for the the heart's valves and chambers for blood to flow. This tissue controls heart development in human embryos and adults, says Kaleth, professor of health science at Indiana University-Purdue.
References
- "ACSM's Resource Manual for Guidelines for Exercise Testing and Prescription"; Functional Anatomy; Anthony S. Kaleth, Ph.D; 2010
- "Current Diagnosis and Treatment in Cardiology"; Pericarditis; Michael H. Crawford, M.D.; 2009
