The History Of Transplants, Transplantation And The Immune System, Types Of Transplants, Donor Organ And Tissue Networks
A surgical transplant involves the removal of body parts, organs, or tissues from one person and implanting them into the body of another person. Although the idea of transplantation to cure disease dates back several centuries, transplantation has been considered a viable therapy for only a few decades. The relatively recent growth in transplantation stems primarily from expanding knowledge about the body's immune system and the ability to suppress its natural response to attack foreign tissue. Another advance has been the ability to preserve organs out of the body for longer periods of time until they can be transplanted. Although most transplants involve the transference of tissues or organs between two humans, research is rapidly advancing toward using animal organs for transplantation into humans. Unfortunately donor organs are scarce, which has led to ethical questions concerning what patients would most benefit from receiving a transplant. For example, some believe that alcoholics suffering from cirrhosis of the liver should not receive a liver transplant that they may eventually destroy again because of alcohol abuse.
The immune responses
Although there are probably many types of immune responses, scientists have only identified a few associated with organ rejection. Hyperacute rejection occurs when the patient's body has already produced a large number of antibodies (proteins manufactured by the immune system to battle disease and infection) that immediately recognize the antigens from the donor organ. This type of rejection, which usually occurs because of incompatible blood types, is often instantaneous, sometimes causing the patient to die even before the surgery is completed.
Acute rejection usually takes several days to occur because the immune system's white blood cells called lymphocytes, which are integral to its functioning because they initiate the production of antibodies, are lying dormant until the patient receives the organ. As the immune system initiates a response to the antigens in the donor organ, specific immune cells in the blood begin to attack. Acute rejection is combated by the use of immunosuppressive drugs. The longer the patient survives without a immune response attacking the organ, the greater the chances for keeping the immune system under control and for long-term survival.
However, chronic rejection can occur several months or years later. Although this type of rejection is rare, when it occurs, the donor organ slowly deteriorates despite all efforts at immunosuppression. Scientists do not fully understand why the immune response may kick in months or years after an organ has been successfully transplanted.
By far, organ transplantation has received the most attention in the popular press. People who would be severely debilitated or die because of failing organs are the recipients of organ transplants. The primary organ transplants are heart, liver, pancreas, lung, and kidney transplants. Under certain circumstances, a patient may receive more than one transplant, the most common multiple transplant procedure is the dual heart/lung transplant.
Kidney transplants are designed to treat patients whose kidneys are failing, making them unable to process body waste products. These transplants have approached a 90% success rate. If the transplant fails, the patient may be put on dialysis until a new donor kidney can be found. Dialysis uses a machine to artificially remove blood from the body, clean the waste products by filtering the blood, and then return the blood to the body.
Other transplantable organs include the liver, the heart, and the lungs. With the development of immunosuppressive drugs, liver transplants have been growing in their success rates, although many patients still die because of organ rejection or from infections. Heart and lung transplants are often performed simultaneously since they share an interrelated vascular system and survival rates are higher for lung transplant patients when they also receive a new heart.
Organ transplants are delicate and complex procedures that require a well trained staff and usually take several hours or much longer to perform. As the surgeon removes the organ, sutures (wire or some other material) are used to close or tie off arteries and other connections to the organ. The new organ is then placed in position and the painstaking task of reconnecting the organ begins. Although the techniques, like vascular anastomosis, for making these connections are well established, they can be difficult procedures. For example, many of the connections to the liver lie underneath the liver and out of the surgeons' immediate view.
Unlike tissues or cells, which can be maintained in functioning condition by placing them in life sustaining cultures (specially prepared nourishing fluids places in a dish or a bowl), organs that have been donated for transplantation require a more complex approach for their preservation. Perfusion is the process of using a pump or other mechanical device to circulate specific electrolyte solutions through the organ's vascular system.
These solutions may support the organ's metabolic (or chemical and physical) functioning. Some solutions are used, in effect, to freeze the organ. For instance, in cornea, skin, kidney, liver, heart, and pancreas transplants, some solutions are designed to cause hypothermia (subnormal body temperatures) in the organ. Organ tissues maintain their ability to function 10 or more times longer when kept at a temperature of 32–39°F (0–4°C), and kidneys have been preserved for more than 50 hours using this approach.
Artificial organs and xenografts
Due to the lack of available organs for transplantation, researchers are constantly experimenting with developing new sources of organs and tissues for transplantation. Artificial organs, for example, are being developed. These include electronic devices to make the heart beat and pumps implanted into the body that can supply necessary substances like insulin. Many of these devices are used as "bridges" to transplantation. In other words, they are temporary therapies to keep the patient alive while a suitable donor organ can be found. Artificial skin is also under development as are mechanical implants to help cure deafness.
Although current transplantation deals primarily in allografts, or transplantation within the same species, transplantation between species, called xenografts, is also a rapidly advancing area of study. The first partially successful xenografts were performed over a quarter of a century ago when surgeons transplanted organs from chimpanzees to humans.
But since the use of primates, which are closer to humans in nature, raises certain ethical questions, recent research has focused on non-primate animals. Pigs, for example, are relatively easy to breed and have large litters. They also share with humans many similar anatomical structures, like the heart, that function in similar ways in the body. Although pig organ transplants have, to date, been unsuccessful, advances in the development of immunosuppressive drugs have led some transplant scientists to think that success in this area can be achieved. Another advance in medical science, the ability to manipulate genes (hereditary components found in cells), has led to genetic engineering. This process involves manipulating and combining specific genetic components to achieve desirable traits or effects. In the case of pig organs, the goal is to make them more compatible to humans. However, the primary obstacle to xenografts remains rejection by the host's immune system. Even using immunosuppressant drugs does not guarantee the immune system will not eventually recognize and destroy the non-human organ.
- Transpiration - Why Do Organisms Transpire Water?, Transpiration As An Ecological Process, Effects Of Human Activities On Transpiration
- Surgical Transplant - The History Of Transplants
- Surgical Transplant - Transplantation And The Immune System
- Surgical Transplant - Types Of Transplants
- Surgical Transplant - Donor Organ And Tissue Networks
- Surgical Transplant - The Future Of Transplantation
- Surgical Transplant - Ethical Issues Surrounding Transplantation
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