Types Of Organ Transplant Biology Essay

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There are several different types of organ transplant, each come from either type of donation; living donation, and non living donation. Any organ transplant can be categorised as being either an allograft or an isograft. Allograft being the transplantation of organs, cells, and tissues from a non-genetically identical member of the same species to another, A transplanted organ or tissue from a genetically identical donor, i.e., an identical twin, is termed an isograft. Furthermore, when a tissue is transplanted from one site to another on the same patient, it is termed an autograft (Hood, A. F. et al, 1987).

Live donation is where a person chooses to donate an organ to save another human being's life. The most common is Kidney donation. This is when one person donates a healthy kidney, in order to provide the recipient with a functioning kidney. There are certain risks involved, yet the remaining kidney will still provide the necessary function needed to remove waste from the body you cant cite this, it's a website -(organdonor.gov). It is also possible for a living donor to donate a lobe of their liver, in order to save a patient suffering from any number of liver ailments. This is made possible due to the liver's regenerative properties, meaning that after a short period of time, the liver will have grown back to almost full size, the same applies the transplanted lobe, it too will regenerate - eventually providing the recipient with a healthy fully functional liver. Furthermore, in some cases live donors can donate a portion of a lung, a partial section of their pancreas, and in some cases, a portion of their intestines. Although these organs will never regenerate, both the donated portion and the donor's remaining organ- will both provide adequate function for both donor and recipient. However because living donation can only provide small portions of these organs (lungs, pancreas, and intestine), they are not as common as non living donations, which can ideally provide whole organs.

Non living donations are strictly broken down into two categories; Heart Beating and Non Heart Beating. Heart beating donation which is otherwise known as "donation after brain death." This means the donor has died but is being supported by a ventilator until the donated organs have been retrieved. This method has a greater success rate because the organs are maintained by oxygenated blood until removal. you cant cite this, it's a website (www.nhs.uk) Most of these cases are of patients who have suffered severe head trauma leading to irreparable damage to the brainstem and the brain itself, a Cerebral infarction (ischemic stroke), fatal Cerebral aneurysm etc, - all causing brain death, (incidentally once brain death is declared, the person becomes legally dead.) due to brain death, there is no Central nervous system in operation, therefore the heart and other vital organs are crucially kept functioning via artificial means in intensive care units. This is kept going long enough for the desired organs to be removed, because it allows them to remain oxygenated for as long as possible prior to the transplant procedure, and this boosts the success rate of the operation. However, these organs need to be removed quickly, as major electrocardiographic, haemodynamic, and histopathological changes take place during the development of brain death; myocardial and pulmonary injury may result - leading to deterioration of function (Cooper, D. K. et al, 1989). Consequently, organs that are harvested promptly will be significantly less damaged.

Non heart beating donations (also known as donations post cardiac death) are where the patient's heart has stopped indefinitely and cannot be resuscitated. Although the sinus rhythm of the heart has ceased, blood flow has halted, and the patient has been officially declared dead. Several hours may allowed lapse before organ removal occurs, any longer than this and the organs will no longer be considered viable for transplantation, as they will be too severely compromised from the de-oxygenation due to the anaerobic conditions. It is very rare for kidneys to be removed after any more than an hour after cardiac death, where as the corneas from the eyes can last up to 24 hours, the skin can last up to 24 hours, even bone can last up to 36 hours, and the heart valves are the longest viable, with up to 72 hours you cant cite this, it's a website (direct.gov.uk). Thus enabling certain tissues to be stored or "banked", such as skin, blood stem cells, bone marrow, and corneas (although these can only remain viable for a certain period before they become damaged.)

The vital thoracic organs donated from either form of Non Living donation, - the Heart and Lungs- can be used in a procedure known as a Domino Transplant. Domino organ transplantation was probably mentioned for the first time to describe the transplantation of a heart graft retrieved from a patient undergoing a heart-lung transplantation (Furtado, A. J. L. 2000). His original heart was then in turn further donated. This happens because the procedure is usually done to treat patients with cystic fibrosis, the heart is also explanted because it is usually healthy, as cystic fibrosis only effects the lungs, and the entire operation is considered easier. The Domino transplant principal is also applied to a form of liver transplant, one where a patient suffering from familial amyloidotic polyneuropathy, a condition in which the liver produces excess insoluble fibrous protein aggregates which are known as Amyloids, these accumulate over time and eventually become harmful to other organs Therefore this patient's liver can be replaced with a healthy donation, and then transplanted into an older patient whose life expectancy is significantly less than the time it would take for the Amyloidotic polyneuropathy to cause noticeable damage (Furtado, A. J. L. 2000). However, the lungs do not have to be transplanted via the domino procedure, a double-lung transplant, also known as a bilateral transplant, can be executed either sequentially, en bloc (whats this?), or simultaneously. Sequential is more common than en bloc. This is effectively like having two separate single-lung transplants (Patterson, G. A. et al 1988). Furthermore, the transplantation of the lungs is often only used as a measure of last resort for patients with severe end stage pulmonary disease- patients who have exhausted all other available treatments. This is due to the extensive technicalities and requirements that need to be met by both the donor and the recipient- the lungs need to be the right size (adequate enough to fit inside the recipient's thoracic cavity yet sufficiently oxygenate the recipient), the blood group (HLA) needs to match, plus the actual procurement is rare, which makes it a premium.

Another type of transplant is Hematopoietic stem cell transplantation (HSCT). This is a procedure in which progenitor cells capable of reconstituting normal bone marrow function are administered to a patient. This procedure is often performed as part of therapy to eliminate a bone marrow infiltrative process, such as leukaemia, or to correct congenital immunodeficiency disorders (Powell, J. L. et al 2009). There are three different types of Hematopoietic stem cell transplant, they are each categorised based on where the cells are taken from. The three most typical sources are, a donor (allogeneic transplant), the patient themselves (autologous transplant), and donated umbilical cord blood (cord blood transplant). Autologous transplant is often where a portion of a patient's stem cells (typically marrow) are collected prior to the patients treatment with high-dose myeloablative therapy (Powell, J. L. et al 2009). (A treatment for tumours to eliminate malignant cells, a process which severely or entirely depletes the patient's bone marrow cells). After this chemotherapy treatment, the autologous transplant takes place; the patient's marrow is "rescued" using the previously collected stem cells. Allogeneic transplants basically refer to the use of stem cells collected from a living donor (or donor source) other than the patient themselves. The donor may be genetically related or completely un related to the recipient patient. However, the genetically related donors are likely to have a greater human leukocyte antigen (HLA) match between themselves and the patient, which means that there is significantly less chance of the patient's body rejecting the donor marrow, because the patient's autoimmune system is more likely to recognise and accept the matching leukocyte antigens of the donor marrow. These Allogeneic stem cell transplants are usually applied in the context of many malignant and non malignant disorders, to replace a defective host marrow or immune system with a normal donor marrow and immune system (Powell, J. L. et al 2009).

A Cord blood transplant is the use of Hematopoietic stem cells harvested from the placenta and the umbilical cord. This type of Hematopoietic stem cell transplant is regarded as the process with the fewest question marks for risk, because it is a valuable alternative source of hematopoietic stem cells (HSCs). It has unique advantages of easy procurement, absence of risk to donors, low risk of transmitting infections, immediate availability, greater tolerance of human leukocyte antigen (H LA) disparity, and lower incidence of inducing severe graft-versus-host disease (GVHD) (Zhong, X. Y. et al 2008). The mother agrees to donate her placenta and umbilical cord and once her child is born, the cord is clamped and cut, then the blood is collected immediately after then stored, via freezing.