Anatomy and Disease
The human body is remarkably well designed. Most of its organs have a great deal of extra capacity or reserve: They can still function adequately even when damaged. For example, more than two thirds of the liver must be destroyed before serious consequences occur, and a person can survive after an entire lung is surgically removed as long as the other lung is functioning normally. Other organs can tolerate little damage before they malfunction and symptoms occur. For example, if a stroke destroys a small amount of vital brain tissue, a person may be unable to speak, move a limb, or maintain balance. A heart attack, which destroys heart tissue, may slightly impair the heart's ability to pump blood or may result in death.
Disease often affects anatomy, and changes in anatomy can cause disease. If the blood supply to a tissue is blocked or cut off, the tissue dies (infarction), as in a heart attack (myocardial infarction) or stroke (cerebral infarction). An abnormal heart valve can cause heart malfunction. Trauma to the skin may damage its ability to act as a barrier, which may lead to infection. Abnormal growths, such as cancer, can directly destroy normal tissue or produce pressure that ultimately destroys it.
Because of the relationship between disease and anatomy, methods of seeing into the body have become a mainstay of the diagnosis and treatment of disease. The first breakthrough came with x-rays, which enabled doctors to see into the body and examine internal structures without surgery. Another major advance was computed tomography (CT), in which x-rays are linked with computers. A CT scan produces detailed cross-sectional (two-dimensional) images of the body's interior.
Other methods of producing images of internal structures include ultrasound scanning, which uses sound waves; magnetic resonance imaging (MRI), which uses the movement of atoms in a magnetic field; and radionuclide imaging, which uses radioactive chemicals injected into the body (see Appendix II). These are noninvasive ways to see into the body, in contrast to surgery, which is an invasive procedure.
Anatomy in This Book
Because anatomy is so important to medicine, almost every section of this book begins with a description of the anatomy of an organ system. Illustrations throughout the book focus on the part of the anatomy being discussed. Additionally, color pictures are located in two separate areas in the book to help illustrate various important aspects of the human body.
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