Transplant, in medicine, is the transfer of any tissue or organ from one person to another. Transplanted tissues and organs replace diseased, damaged, or destroyed body parts. They can help restore the health of a person who might otherwise have died or been seriously disabled. Transfers of tissue from one part of a person's own body to another part are also called transplants. These procedures include skin grafts and hair transplants.

Doctors often divide transplants into two major types--organ transplants and tissue transplants. Organs, such as the heart and kidney, are complex structures that require a blood supply and oxygen to survive. Some organs, such as the heart and lungs, cannot be preserved for more than a few hours outside of the body. Doctors must transplant these organs very quickly. Tissues are also complex, but those that are commonly transplanted--bone, corneas, and skin--can be stored for much longer periods of time. Transplant tissues can be preserved in refrigerators or freezers at special tissue banks.

Another major difference between organ and tissue transplants involves the body's disease-fighting immune system. The immune system reacts differently to transplanted organs than it does to certain transplanted tissues. The immune system frequently attacks transplanted organs. As a result, doctors use special techniques and drugs to protect the new organs. Transplants of certain tissues, however, do not usually require these procedures.

Excerpt from the "Transplant" article, The World Book Encyclopedia © 1999