Every year, more than 100,000 Americans need to have damaged or failing organs replaced. Healthy body parts come from either a living or a deceased donor. The latter is most common. In the U.S., a living donor can provide a recipient with a kidney, liver, lung or part of an intestine. A deceased donor can also supply a new heart, pancreas or stomach. Unfortunately, only a third of all transplant candidates receive the life-saving surgery each year. The remaining hopefuls are placed on a decadelong waiting list. For many, the lengthy delay has devastating consequences.

TRIAL AND ERROR

Organ transplantation has a long history of failure. Throughout the early 20th century, physicians attempted a multitude of complicated transplants. Only one succeeded. In 1905, a farmer had both transparent front layers of his eyes replaced. One eye was repaired, the other stayed blind.

For the next 50 years, no organ transplant recipient lived longer than 30 days. In the mid-1950s, the first kidney was successfully transplanted. However, the key was the relationship between the patient and his living donor: They were twin brothers, therefore it was easier for the recipient's immune system to accept the familiar organ. The unprecedented achievement led to the development of essential immunosuppressant medications.

RULES AND REGULATIONS

A physician can determine if a patient needs an organ transplant -- but can't control how soon that organ will become available. Without a living donor in place, an intended recipient is placed on the waiting list. To receive an organ from a deceased donor, a patient's blood type and body size must match the prospective provider, to prevent his or her own body from rejecting the transplant. A heart or lung must fit comfortably inside the patient's chest.

Additionally, the geographic proximity between the donor and the receiver is taken into account. At most, a heart or lung can survive about six hours outside a body, so those nearest the donor's hospital are given first priority. Since a kidney or liver has a longer shelf life, those organs are usually transported to the sickest person on the waiting list rather than those who've been waiting the longest. Tragically, more than a dozen people on the list die every day.

IN AND OUT

Kidneys are the most commonly transplanted organs. Most kidney transplant recipients are over the age of 50. The transplant patient is given general anesthesia for the approximately four-hour surgery. For kidney transplants, the removal of the old kidney is only necessary if the organ is toxic. Otherwise, the new organ is attached to a different area in the lower abdomen. In the U.S., a kidney transplant can cost $100,000; a liver may run twice that; and a heart can exceed $500,000. Typically, an organ replacement lasts about five years.

PAIN AND SUFFERING

Although hospital recovery time is usually less than a week, complications can occur. Excessive bleeding and deadly infections are common. The body can also reject the transplant within a few days or even months after surgery. A rejected organ will require immediate removal. The organ may then be re-donated if feasible.

GIVE AND GET

In an effort to save more lives, physicians are developing ways to turn one donation into two. Transplant candidates who require new lungs have greater results when they receive the same donor's heart as well. This is done even when the recipient's heart is healthy. The extracted heart is then given to another patient. Younger recipients whose replaced organs have gradual degenerative diseases may also donate those organs. These are then given to elderly recipients whose mortality won't be drastically affected by the long-term affliction.

* More than 30,000 organ transplants are performed in the U.S. each year.