TRANSPLANT REJECTION
For medical transplantation to be successful, physicians must elude the combative efforts of the bodys complex immune system, which fights to protect the body from infections of all sorts. Central to the functioning of the immune system is its ability to distinguish between invading or foreign matter, which should be attacked, and matter that is a normal part of the body, which should not be attacked. This recognition system causes the immune system to attack transplanted tissues because it has no way to distinguish between harmful and beneficial foreign matter.
Because of this rejection, the recipient must take drugs to suppress the immune response. The first drugs that were used were azathioprine and prednisone. But these drugs suppress the entire immune system, leaving the recipient vulnerable to infections and certain cancers. They also have toxic side effects. A major breakthrough in immune suppression was the development of cyclosporine, a natural product derived from a fungus found in the soil. Cyclosporine suppresses the part of the immune system involved in organ rejection with less severe impact on other parts of the immune system.
KIDNEY TRANSPLANTS
The diseases that most often create a need for kidney transplantation are glomerulonephritis (inflammation of the kidneys), diabetes, hypertension and cystic kidney failure. People with these diseases who have failing kidneys have to undergo regular treatment with an artificial kidney (haemodialysis). Kidney dialysis is the procedure in which blood is circulated through a machine that removes wastes and excess fluids from the bloodstream. The patient must be hooked up to the dialysis machine two to three times each week for as long as 12 hours at a time. Some patients use dialysis for a short time, while their kidneys recover from injury or disease. Others must use dialysis for their entire lives or until they undergo a kidney transplant. However, dialysis can only replace about 5% of the function of two healthy kidneys, and for many people their quality of life on dialysis is very poor. Additionally, life expectancy is lower for people on dialysis than for the normal population.
Kidney transplantation is the best treatment possible for kidney failure. Kidney transplants are also the most common of all transplant operations and have excellent success rates. It can improve quality of life dramatically and increase life expectancy.
One year after transplantation of a kidney from a brain-dead donor around 90% of transplants are still functioning well. After five years over 60% are still healthy and overcoming any need for dialysis. Some kidney transplant patients have survived more than 25 years.
Because people have two kidneys but need only one, a living relative often serves as a donor, retaining one kidney for his or her own use. About one-third of transplanted kidneys come from living relatives and about two-thirds are from someone who recently died.
LIVER TRANSPLANTS
For people with severe liver disease, transplantation can sometimes be the only effective treatment available. The most common diseases that cause a need for liver transplantation are cirrhosis, some types of chronic hepatitis, acute liver failure, or inflammation of the bile ducts that lead into the liver (primary sclerosing cholangitis).
The liver is the only internal organ with the capacity to regenerate. This capacity provides the surgeon additional flexibility in treating liver damage. For instance, if the damage is not very severe, a temporary transplant can take over the livers function while the patients own liver recovers. It is also possible to remove part of a liver from a living donor and transplant it. After the surgery both the donors liver and the transplanted portion will grow to full size.
Fortunately, waiting lists for liver transplants are shorter than for kidneys. At one year, around 80% of liver transplants are working well. This falls to 60 65% after five years.
HEART AND HEART / LUNG TRANSPLANTS
Heart transplants are perhaps the most dramatic of all organ transplants because without a functioning heart, a patient cannot survive more than a few minutes. On December 3, 1967, Christiaan Barnard performed the first human heart transplant, transferring the heart of a 25-year-old woman into the body of Louis Washkansky, a 55-year-old grocer, Washkansky died 18 days later. The second transplant, on January 2, 1968, was for Philip Blaiberg, who lived for 563 days after the operation. However, heart transplant surgery later became standard after the development of powerful drugs that prevented the bodys immune system from rejecting the transplant.
The most common cause of heart failure is coronary heart failure. The final stage in almost any type of heart disease is heart failure, also known as congestive heart failure, in which the heart muscle weakens and is unable to pump enough blood to the body. In response to this shortfall, the kidneys conserve water in an attempt to increase blood volume, and the heart is stimulated to pump harder. Eventually excess fluid seeps through the walls of tiny blood vessels and into the tissues. Fluid may collect in the lungs, making breathing difficult, especially when a patient is lying down at night. Many patients with heart failure must sleep propped up on pillows to be able to breathe. Fluid may also build up in the ankles, legs or abdomen. In the later stages of heart failure, any type of physical activity becomes next to impossible. Heart failure can sometimes be reversed and can often be effectively treated for long periods with a combination of drugs. A last resort in the treatment of heart failure is heart transplantation, in which a diseased heart is replaced with a healthy heart from a person who has died of other causes.
Heart transplantation is an effective option: Most patients are able to resume a normal life about six months after surgery and 85% of heart transplants are still working well after a year, and almost 70% after five years. However, because there is only a limited supply of donor hearts, many people who could potentially benefit from heart transplantation are not placed on the waiting list.
LUNG TRANSPLANTS
Increasingly, cystic fibrosis patients with severe, irreparable lung damage turn to lung transplantation surgery. Although complications with transplantation surgery may pose problems for some patients, lung or combination heart and lung transplants provide nearly 80% of cystic fibrosis patients with severe lung damage an entirely new lease on life.
In nearly 20% of all cases, the first symptom is intestinal blockage in newborns. In other babies, the first evidence is bulky stool, poor weight gain, flabby muscle tone, or slow growth, all products of low levels of digestive enzymes in the intestines. About half of all children with cystic fibrosis first see the doctor for coughing, wheezing, or respiratory tract infections. Teenagers with cystic fibrosis may grow slowly and enter puberty later than their peers. Cystic fibrosis often causes impaired reproductive function. Cystic fibrosis patients of all ages are prone to dehydration because they lose so much salt in their sweat. Infections, particularly in the lungs, plague people with cystic fibrosis throughout their lives. These chronic infections destroy lung tissue, a complication that ultimately takes the lives of most people with cystic fibrosis.
CORNEA TRANSPLANTS
Eye banks concentrate on retrieving tissues used in eye surgery that restores or improves sight. Most eye banks focus on retrieving corneas. The cornea is the clear front window of the eye, about the size and shape of a coin. It transmits light to the interior of the eye allowing us to see clearly. Corneal injury, disease or hereditary conditions can cause clouding, distortion and scarring that may result in blindness. But corneal blindness is one of the few forms of blindness that can be cured. In a delicate procedure, the surgeon removes the damaged cornea and replaces it with a cornea donated by a recently deceased person. Cornea transplants are very successful, with a success rate of more than 90% if the cornea is placed on the eye in such a manner that blood vessels do not come into contact with it. Without blood vessels, the body cannot send immune cells to attack the cornea.
SKIN
A burn is an injury to the skin caused when heat, chemicals, electricity, or radiation destroy tissue. Extensive burns, involving 30% or more of the bodys surface, can be life threatening because they disrupt the skins ability to fight infection, prevent fluid loss, and regulate body temperature. Deep burns are often treated with skin grafts. In this procedure, healthy skin removed from another area on the body is transferred to the burned area to cover the wound. If the burned area is not too large, the grafted skin will grow in its new location and eventually fuse with the healthy skin at the edges of the burn. But if burns cover a large portion of a patients body and not enough healthy skin remains to use for a graft, patients may receive grafts from dead bodies. Although the patients immune system eventually rejects and destroys this foreign tissue, these temporary skin grafts help prevent fluid loss and infection while the patients own skin heals.
Skin was the first tissue transplanted, and researchers used skin transplants in the late 1950s and early 1960s to decipher the immune system response to transplants.
BONE MARROW
Bone marrow is the living tissue found in the centre of many large bones of the body. Special cells on the bone marrow, called stem cells, are the source of both red blood cells, the primary component of blood, and white blood cells, the workhorses of the immune system. Certain blood diseases, including leukaemia and sickle cell anaemia, are the result of the stem cells in the bone marrow producing faulty blood cells. In some cases, these diseases can be treated by destroying all of the patients bone marrow and replacing it with new donor bone marrow that does not produce the faulty blood cells. Bone marrow transplants are also used in fighting breast cancers and other cancers because intensive radiation or chemotherapy used to cure the cancer also kills the patients bone marrow, which must then be replaced with a transplant.
Stem cell transplants require a closer matching of donor and recipient than is the case with other types of transplants. If the match is not good enough, the recipients body may reject the bone marrow or the white blood cells generated by the donor marrow can attack the recipients body, a phenomenon known as graft-versus-host disease. Formerly, stem cells could only be transplanted from the bone marrow of the donor, and the procedure was known as bone marrow transplantation. Recent advances now make it possible to recover stem cells from circulating blood, making the transplant procedure much simpler and less risky for the donor. A live donor is able to simply donate blood, from which the necessary cells and components are removed.
BONE
Bone is used for facial reconstruction of motor vehicle accident victims. Bone is also used in replacing cancerous growths in arms or legs of patients. In the past we used to have to amputate the limb.
Heart valves can also be replaced through transplantation. Pancreases can also be transplanted, although they are not done in South Africa. In America they have also started with small intestine transplants. Reliable survival data for intestine transplant patients are not yet available because the procedure is still experimental. Techniques are improving all the time and it may soon be practical to transplant other parts of the body.
ARTIFICIAL ORGANS AND TISSUES
One way to get around the shortage of donors is to use wholly or partially artificial organs made of plastic, metal, and other synthetic materials. A kidney dialysis machine, for example, is an artificial organ, even if it is too large to implant in the body. The first permanent artificial heart was transplanted in 1982, but the patient survived only for 112 days. Artificial hearts are not widely used today because of the risk of infection and bleeding and concerns about their reliability. In addition, the synthetic materials used to fashion artificial hearts can cause blood clots to form in the heart. These blood clots may travel to a vessel in the neck or head, resulting in a stroke. Instead, emphasis has shifted to the use of left-ventricular assist devices (LVADs), which are implanted beside a patients heart to help it pump blood. LVADs keep patients alive until a donor heart is available. Many artificial devices work to restore the operation of malfunctioning organs without replacing the whole organ. Examples include artificial heart valves and pacemakers to help the heart function properly, and cochlear implants to restore hearing.
XENOTRANSPLANTS
The shortage of donors has led some surgeons to consider using animals as donors. Chimpanzee kidneys were successfully transplanted in 1963, with one recipient living for nine months after the surgery. Although the kidneys were not rejected, they proved too small to keep the recipient alive. Efforts to transplant chimpanzee and baboon hearts into humans in the 1960s and 1970s also failed because the hearts were too small. The first successful baboon organ transplant occurred in 1984, when a baboon's heart was transplanted into a two-week-old premature baby whose heart was congenitally malformed. The baby survived for 20 days before her body rejected the organ. Because of problems with the small size of chimpanzee and baboon organs, doctors are now turning to other species as potential organ donors.
One animal receiving a lot of attention from the medical community is the pig. Pigs have organs that are the right size for human use, they have large litters, and they mature quickly so there is a ready supply of donating animals. Human bodies do not reject some pig tissues, such as heart valves. Surgeons in the United States transplant about 60,000 pig heart valves into humans annually. However, other transplanted pig organs undergo a phenomenon called hyperacute rejection. The recipient's immune system recognizes that the blood vessels in the transplanted organ are foreign and shuts off blood flow to the new organ within hours or even minutes, causing the transplanted organ to blacken and die. Recently, scientists have used genetic engineering techniques to breed pigs whose blood vessels contain the marker antigens found in human blood vessels. Livers from these pigs have been successfully connected to the bloodstream of several patients to clear toxic wastes while the patients' own livers recovered. Fetal pig brain cells have also been used to treat Parkinson disease, and research is underway on using other organs from these pigs.
One of the big drawbacks of xenotransplants is the fear that unknown, possibly deadly viruses could be transferred from animals to humans. Once the animal viruses get into humans, they might spread to other humans. In 1997, scientists showed that pig viruses could infect humans with unpredictable results. The unresolved questions surrounding xenotransplantation mean that future research must be done cautiously.
source: odf.org.za
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