Liver Transplantation
Gale Encyclopedia of Surgery: A Guide for Patients and Caregivers
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2004
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Copyright 2004, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company. (Hide copyright information)
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Liver transplantation
Definition
Liver transplantation is a surgery that removes a diseased liver and replaces it with a healthy donor liver.
Purpose
A liver transplant is needed when the liver's function is reduced to the point that the life of the patient is threatened.
Demographics
Compared to whites, those with African-American, Asian, Pacific Islander, or Hispanic descent are three times more likely to suffer from end-stage renal disease (ESRD). Both children and adults can suffer from liver failure and require a transplant.
Patients with advanced heart and lung disease, who are human immunodeficiency virus (HIV) positive, and who abuse drugs and alcohol are poor candidates for liver transplantation. Their ability to survive the surgery and the difficult recovery period, as well as their long-term prognosis, is hindered by their conditions.
Description
The liver is the body's principle chemical factory. It receives all nutrients, drugs, and toxins, which are absorbed from the intestines, and performs the final stages of digestion, converting food into energy and replacement parts for the body. The liver also filters the blood of all waste products, removes and detoxifies poisons, and excretes many of these into the bile. It further processes other chemicals for excretion by the kidneys. The liver is also an energy storage organ, converting food energy to a chemical called glycogen that can be rapidly converted to fuel.
When other medical treatment interferes with the functioning of a damaged liver, a transplant is necessary. Since 1963, when the first human liver transplant was performed, thousands more have been performed each year. Cirrhosis, a disease that kills healthy liver cells, replacing them with scar tissue, is the most common reason for liver transplantation in adults. The most frequent reason for transplantation in children is biliary atresia—a disease in which the ducts that carry bile out of the liver, are missing or damaged.
Included among the many causes of liver failure that bring patients to transplant surgery are:
- Progressive hepatitis, mostly due to virus infection, accounts for more than one-third of all liver transplants.
- Alcohol damage accounts for approximately 20% of transplants.
- Scarring, or abnormality of the biliary system, accounts for roughly another 20% of liver transplants.
- The remainder of transplants come from various cancers, uncommon diseases, and a disease known as fulminant liver failure.
Fulminant liver failure most commonly happens during acute viral hepatitis, but is also the result of mushroom poisoning by Amanita phalloides and toxic reactions to overdose of some medicines, such as acetaminophen—a medicine commonly used to relieve pain and reduce fever. The person who is the victim of mushroom poisoning is a special category of candidate for a liver transplant because of the speed of the disease and the immediate need for treatment.
As the liver fails, all of its functions diminish. Nutrition suffers, toxins build, and waste products accumulate. Scar tissue accumulates on the liver as the disease progresses. Blood flow is increasingly restricted in the portal vein, which carries blood from the stomach and abdominal organs to the liver. The resulting high blood pressure (hypertension) causes swelling of and bleeding from the blood vessels of the esophagus. Toxins build-up in the blood (liver encephalopathy), resulting in severe jaundice (yellowing of the skin and eyes), fluid accumulation in the abdomen (ascites), and deterioration of mental function. Eventually, death occurs.
There are three types of liver transplantation methods. They include:
- Orthotopic transplantation, the replacement of a whole diseased liver with a healthy donor liver.
- Heterotrophic transplantation, the addition of a donor liver at another site, while the diseased liver is left intact.
- Reduced-size liver transplantation, the replacement of a whole diseased liver with a portion of a healthy donor liver. Reduced-size liver transplants are most often performed on children.
When an orthotropic transplantation is performed, a segment of the inferior vena cava (the body's main vein to the heart) attached to the liver is taken from the donor, as well. The same parts are removed from the recipient and replaced by connecting the inferior vena cava, the hepatic artery, the portal vein, and the bile ducts.
When there is a possibility that the afflicted liver may recover, a heterotypic transplantation is performed. The donor liver is placed in a different site, but it still has to have the same connections. It is usually attached very close to the patient's original liver; if the original liver recovers, the donor liver will wither away. If the patient's original liver does not recover, that liver will dry up, leaving the donor in place.
Reduced-size liver transplantation puts part of a donor liver into a patient. A liver can actually be divided into eight pieces—each supplied by a different set of blood vessels. In the past, just two of these sections have been enough to save a patient suffering from liver failure, especially if it is a child. It is possible, therefore, to transplant one liver into at least two patients and to transplant part of a liver from a living donor—and for both the donor and recipients to survive. Liver tissue grows to accommodate its job provided that the organ is large enough initially. Patients have survived with only 15–20% of their original liver intact, assuming that that portion was healthy from the beginning.
As of 2003, the availability of organs for transplant was in crisis. In October 1997, a national distribution system was established that gives priority to patients who are most ill and in closest proximity to the donor livers. Livers, however, are available nationally. It is now possible to preserve a liver out of the body for 10 to 20 hours by flushing it with cooled solutions of special chemicals and nutrients, if necessary. This enables transport cross-country.
Description
Once a donor liver has been located and the patient is in the operating room and under general anesthesia, the patient's heart and blood pressure are monitored. A long cut is made alongside of the ribs; sometimes, an upwards cut may also be made. When the liver is removed, four blood vessels that connect the liver to the rest of the body are cut and clamped shut. After getting the donor liver ready, the transplant surgeon connects these vessels to the donor vessels. A connection is made from the bile duct (a tube that drains the bile from the liver) of the donor liver to the bile duct of the liver of the patient's bile duct. In some cases, a small piece of the intestine is connected to the new donor bile duct. This connection is called Roux-en-Y. The operation usually takes between six and eight hours; another two hours is spent preparing the patient for surgery. Therefore, a patient will likely be in the operating room for eight to 10 hours.
The United Network for Organ Sharing (UNOS) data indicates that patients in need of organ transplants outnumber available organs three to one.
Diagnosis/Preparation
The liver starts to fail only when more than half of it is damaged. Thus, once a person demonstrates symptoms of liver failure, there is not much liver function left. Signs and symptoms of liver failure include:
- jaundice
- muscle wasting (loss of muscle)
- forgetfulness, confusion, or coma
- fatigue
- itching
- poor blood clotting
- build-up of fluid in the stomach (ascites)
- infections
- bleeding in the stomach
A doctor will diagnose liver disease; a liver specialist, a transplant surgeon, and other doctors will have to be consulted, as well, before a patient can be considered for a liver transplant. Before transplantation takes place, the patient is first determined to be a good candidate for transplantation by going through a rigorous medical examination. Blood tests, consultations, and x rays will be needed to determine if the patient is a good candidate. Other tests that may be conducted are: computed tomography (CAT or CT) scan, magnetic resonance image (MRI), ultrasound, routine chest x ray , endoscopy, sclerotherapy and rubber-band ligation, transjugular intrahepatic portosystemic shunt (TIPS), creatinine clearance, cardiac testing (echocardiogram [ECHO]) and/or electrocardiogram [EKG or ECG]), and pulmonary function test [PFTs]), liver biopsy , and nutritional evaluation. A dietitian will evaluate the patient's nutritional needs and design an eating plan. Since a patient's emotional state is as important as their physical state, a psychosocial evaluation will be administered.
Once test results are reviewed and given to the liver transplant selection committee, the patient will be assessed for whether he or she is an appropriate candidate. Some patients are deemed too healthy for a transplant and will be followed and retested at a later date if their liver gets worse. Other patients are determined to be too sick to survive a transplant. The committee will not approve a transplant for these patients. Once a patient is approved, they will be placed on a waiting list for a donor liver. When placed on the waiting list, a patient will be given a score based on the results of the blood tests. The higher a patient's score, the sicker the patient is. This results in the patient earning a higher place on the waiting list.
Suitable candidates boost their nutritional intakes to ensure that they are as healthy as possible before surgery. Drugs are administered that will decrease organ rejection after surgery. The medical committee consults with the patient and family, if available, to explain the surgery and any potential complications. Many problems can arise during the waiting period. Medicines should be changed as needed, and blood tests should be done to assure a patient is in the best possible health for the transplant surgery. Psychological counseling during this period is recommended, as well.
When a donor is found, it is important that the transplant team be able to contact the patient. The patient awaiting the organ must not eat or drink anything from the moment the hospital calls. On the other hand, the liver may not be good enough for transplantation. Then, the operation will be cancelled, although this does not happen often.
Aftercare
Following surgery, the patient will wake up in the surgical intensive care unit (SICU). During this time, a tube will be inserted into the windpipe to facilitate breathing. It is removed when the patient is fully awake and strong enough to breathe on his or her own. There may be other tubes that are removed as the patient recovers. When safe to leave the SICU, the patient is moved to the transplant floor. Walking and eating will become the primary focus. Physical therapy may be started to help the patient become active, as it is an important part of recovery. When the patient begins to feel hungry and the bowels are working, regular food that is low in salt will be given.
A patient should expect to spend about 10 to 14 days in the hospital, although some stays may be shorter or longer. Before leaving the hospital, a patient will be advised of: signs of infection or rejection, how to take medications and change dressings, and how to understand general health problems. Infection can be a real danger, because the medications taken compromise the body's defense systems. The doctors will conduct blood tests, ultrasounds, and x rays to ensure that the patient is doing well.
The first three months after transplant are the most risky for getting such infections as the flu, so patients should follow these precautions:
- Avoid people who are ill.
- Wash hands frequently.
- Tell the doctor if you are exposed to any disease.
- Tell the doctor if a cold sore, rash, or water blister appears on the body or spots appear in the throat or on the tongue.
- Stay out of crowds and rooms with poor circulation.
- Do not swim in lakes or community pools during the three months following transplant.
- Eat meats that are well-cooked.
- Stay away from soil, including those in which house-plants are grown, and gardens, during the three months following transplant.
- Take all medications as directed.
- Learn to report the early symptoms of infection.
To ensure that the transplant is successful and that the patient has a long and healthy life, a patient must get good medical care, prevent and treat complications, keep in touch with doctors and nurses, and follow their advice. Nutrition plays a big part in the success of a liver transplant, so what a patient eats after the transplant is very important.
Medications needed following liver transplantation
Successfully receiving a transplanted liver is only the beginning of a lifelong process. Patients with transplanted livers have to stay on immunosuppressant drugs for the rest of their lives to prevent organ rejection. Although many patients can reduce the dosage after the initial few months, virtually none can discontinue drugs altogether. For adolescent transplant recipients, post transplantation is a particularly difficult time, as they must learn to take responsibility for their own behavior and medication, as well as balance their developing sexuality in a body that has been transformed by the adverse effects of immuno-suppression. Long-term outcome and tailoring of immunosuppression is of great importance.
Cyclosporine has long been the drug of experimentation in the immunosuppression regimen, and has been well-tolerated and effective. Hypertension, nephrotoxicity, and posttransplant lymphoproliferative disease (PTLD) are some of the long-term adverse effects. Tacrolimus has been developed more recently, and has improved the cosmetic adverse effects of cyclosporine, but has similar rates of hypertension and nephrotoxicity, and possibly a higher rate of PTLD. Prednisone, azathioprine, and tacrolimus are often combined with cyclosporine for better results. Newer immunosuppressive agents promise even better results.
There has been a recent, welcome development in renal sparing drugs, such as mycophenolate mofetil, which has no cosmetic adverse effects, does not require drug level monitoring, and is thus particularly attractive to teenagers. If started prior to irreversible renal dysfunction, recent research demonstrates recovery of renal function with mycophenolate mofetil. There is little published data on the use of sirolimus (rapamycin) in the pediatric population, but preliminary studies suggest that the future use of interleukin-2 receptor antibodies may be beneficial for immediate post-transplant induction of immunosuppression. When planning immunosuppression for adolescents, it is important to consider the effects of drug therapy on both males and females in order to maintain fertility and to ensure safety in pregnancy. Adequate practical measures and support should reduce noncompliance in this age group, and allow good, long-term function of the transplanted liver.
Risks
Early failure of the transplant occurs in every one in four surgeries and has to be repeated. Some transplants never work, some patients succumb to infection, and some suffer immune rejection. Primary failure is apparent within one or two days. Rejection usually starts at the end of the first week. There may be problems like bleeding of the bile duct after surgery, or blood vessels of the liver may become too narrow. The surgery itself may need revision because of narrowing, leaking, or blood clots at the connections. These issues may be solved with or without more surgery depending on the severity.
Infections are a constant risk while on immunosuppressive agents, because the immune system is supposed to prevent them. A method has not yet been devised to control rejection without hampering immune defenses against infections. Not only do ordinary infections pose a threat, but because of the impaired immunity, transplant patients are susceptible to the same opportunistic infections (OIs) that threaten acquired immune deficiency syndrome (AIDS) patients—pneumocystis pneumonia, herpes and cytomegalovirus (CMV) infections, fungi, and a host of bacteria.
Drug reactions are also a continuing threat. Every drug used to suppress the immune system has potential problems. As previously stated, hypertension, nephrotoxicity, and PTLD are some of the long-term adverse effects with immunosupressive drugs like cyclosporine. Immunosuppressants also hinder the body's ability to resist cancer. All drugs used to prevent rejection increase the risk of leukemias and lymphomas.
There is also a risk of the original disease returning. In the case of hepatitis C, reoccurrence is a risk factor for orthotropic liver transplants. Newer antiviral drugs hold out promise for dealing with hepatitis. In alcoholics, the urge to drink alcohol will still be a problem. Alcoholics Anonymous (AA) is the most effective treatment known for alcoholism.
Transplant recipients can get high blood pressure, diabetes, high cholesterol, thinning of the bones, and can become obese. Close medical care is needed to prevent these conditions.
Normal results
For a successful transplant, good medical care is important. Patients and families must stay in touch with their medical teams and drugs must be taken as advised to prevent infection and rejection of the new organ. However, sometimes because of the way it is preserved, the new liver doesn't function as it should, and a patient may have to go back on to the waiting list to receive a new liver.
Morbidity and mortality
Twenty-five million or one in 10 Americans are or have been afflicted with liver or biliary diseases. As of June 2003, there were 17,239 patients on the UNOS National Transplant Waiting List who were waiting for a liver transplantation. For the previous year (July 1, 2001 to June 30, 2002), there were a total of 5,261 liver transplants performed. Of those, 4,785 were cadaver donors (already deceased) and 476 living donors. For liver transplants performed from July 1, 1999 to June 30, 2001, the one-year survival rate was 86% for adults; 1,861 patients died while on the UNOS waiting list for the year ending June 30, 2002. More than 80% of children survive transplantation to adolescence and adulthood.
Since the introduction of cyclosporine and tacrolimus (drugs that suppress the immune response and keep it from attacking and damaging the new liver), success rates for liver transplantation have reached 80–90%.
Infections occur in about half of transplant patients and often appear during the first week. Biliary complications are apparent in about 22% of recipient patients (and 6% of donors), and vascular complications occur in 9.8% of recipient patients. Other complications in donors include re-operation (4.5%) and death (0.2%).
There are potential social, economic, and psychological problems, and a vast array of possible medical and surgical complications. Close medical surveillance must continue for the rest of the patient's life.
Alternatives
There is no treatment that can help the liver with all of its functions; thus, when a person reaches a certain stage of liver disease, a liver transplant may be the only way to save the patient's life.
Resources
books
Abhinav, Humar, M.D., I. Hertz Marshall, M.D., Laura J., Blakemore, M.D., eds. Manual of Liver Transplant Medical Care. Minneapolis, MN: Fairview Press, 2002.
Beauchamp, Daniel R., M.D., Mark B. Evers, M.D., Kenneth L. Mattox, M.D., Courtney M. Townsend, and David C. Sabiston, eds. Sabiston Textbook of Surgery: The Biological Basis of Modern Surgical Practice, 16th ed. London: W. B. Saunders Co., 2001.
Lawrence, Peter F., Richard M. Bell, and Merril T. Dayton, eds. Essentials of General Surgery, 3rd ed. Philadelphia, PA: Lippincott, Williams & Wilkins, 2000.
periodicals
Brown, R.S., Jr., M. W. Russo, M. Lai, M. L. Shiffman, M. C. Richardson, J. E. Everhart, et al. "A survey of liver transplantation from living adult donors in the United States." New England Journal of Medicine 348, no. 9 (February, 2003):818–25.
Goldstein, M. J., E. Salame, S. Kapur, M. Kinkhabwala, D. La-Pointe-Rudow, N. P. P. Harren, et al. "Analysis of failure in living donor liver transplantation: differential outcomes in children and adults." World Journal of Surgery 27, no. 3 (2003):356–64.
Kelly, D. A. "Strategies for optimizing immunosuppression in adolescent transplant recipients: a focus on liver transplantation." Paediatric Drugs 5, no. 3 (2003):177–83.
Longheval, G., P. Vereerstraeten, P. Thiry, M. Delhaye, O. Le Moine, J. Deviere, et al. "Predictive models of short- and long-term survival in patients with nonbiliary cirrhosis." Liver Transplantation: Official Publication of the American Association for the Study of Liver Diseases and the International Liver Transplantation Society 9, no. 3 (March, 2003):260–7.
Neff, G. W., A. Bonham, A. G. Tzakis, M. Ragni, D. Jayaweera, E. R. Schiff, et al. "Orthotopic liver transplantation in patients with human immunodeficiency virus and end-stage liver disease." Liver Transplantation: official publication of the American Association for the Study of Liver Diseases and the International Liver Transplantation Society 9, no. 3 (March, 2003):239–47.
Papatheodoridis, G. V., V. Sevastianos, and A. K. Burrouhs. "Prevention of and treatment for hepatitis B virus infection after liver transplantation in the nucleoside analogues era." American Journal of Transplantation 3, no. 3 (March, 2003):250–8.
Rudow, D. L., M. W. Russo, S. Haflige, J. C. Emond, and R. S. Brown, Jr. "Clinical and ethnic differences in candidates listed for liver transplantation with and without potential living donors." Liver Transplantation: Official Publication of the American Association for the Study of Liver Diseases and the International Liver Transplantation Society 9, no. 3 (March, 2003):254–9.
Wong, F. "Liver and kidney diseases." Clinics in Liver Disease 6, no. 4 (November, 2002):981–1011.
organizations
American Liver Foundation. 75 Maiden Lane, Suite 603, New York, NY. 10038. (800) 465-4837 or (888) 443-7872. Fax: (212) 483.8179. info@liverfoundation.org. <http://www.liverfoundation.org>.
Hepatitis Foundation International (HFI). 504 Blick Drive, Silver Spring, MD. 20904-2901. (800) 891-0707 or (301) 622-4200. Fax: (301) 622-4702. hfi@comcast.net. <http://www.hepfi.org>
National Digestive Diseases, Information Clearinghouse. 2 Information Way, Bethesda, MD. 20892-3570. nddic@info.niddk.nih.gov.
National Institutes of Health, 9000 Rockville Pike, Bethesda, Maryland. 20892. (301) 496-4000. NIHInfo@OD.NIH.GOV. <http://www.nih.gov.>
United Network for Organ Sharing. 500-1100 Boulders Parkway, P.O. Box 13770. Richmond, VA. 23225. (888) 894-6361 or (804) 330-8500. <http://www.unos.org>
other
U.S. National Library of Medicine and the National Institutes of Health. Liver Transplantation. 2003 [cited March 13, 2003]. <www.nlm.nih.gov/medlineplus/livertransplantation.html>.
J. Ricker Polsdorfer, M.D.
Crystal H. Kaczkowski, M.Sc.
WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?
A transplant surgeon will perform the surgery in a hospital that has a special unit called a transplant center.
QUESTIONS TO ASK THE DOCTOR
- What should I do to prepare for this operation?
- Who will tell me about the transplant process?
- Can I tour the transplant center?
- Who are the members of the transplant team and what are their jobs?
- Is there a special nursing unit for transplant patients?
- How many attending surgeons are available to do my type of transplant?
- Does the hospital do living donor transplants?
- Is a living donor transplant a choice in my case? If so, where will the living donor evaluation be done?
- What is the organ recovery cost if I have a living donor?
- Will I also need to change my lifestyle?
- How long will I have to stay in the hospital?
- Why is recovery such a slow process?
Cite this article
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Proximal visceral endoderm and extraembryonic ectoderm regulate the formation of primordial germ cell precursors.(Research article)
Magazine article from: BMC Developmental Biology; 12/20/2007; ; 700+ words
; ...cells adjacent to the extraembryonic ectoderm. The population of PGC precursors increases...endoderm (VE) and the extraembryonic ectoderm (ExE) play an important role in the...from epiblast; ExE, extraembryonic ectoderm; thick black line, endoderm. (I...
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Embryonic stem cells develop into ectoderm cells in damaged inner ear.
Newspaper article from: Immunotherapy Weekly; 6/2/2004; 700+ words
; ...amp; NewsRx.net) -- Embryonic stem cells develop into ectoderm cells in damaged inner ears. "The potential of embryonic...ear may have some activity inducing ES cells to develop into ectoderm cells, but the effect was insufficient to induce inner ear...
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Neural tube derived Wnt signals cooperate with FGF signaling in the formation and differentiation of the trigeminal placodes.(Research article)(fibroblast growth factor)(Report)
Magazine article from: Neural Development; 12/15/2008; ; 700+ words
; ...and focal thickenings of the embryonic ectoderm, the neurogenic placodes [1, 2...cells extend anterior-laterally in the ectoderm and then delaminate into the underlying...follows. At the three somite stage, head ectoderm rostral to the first somite is competent...
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Early Development of Zooxanthella-Containing Eggs of the Corals Pocillopora verrucosa and P. eydouxi with Special Reference to the Distribution of Zooxanthellae.
Magazine article from: The Biological Bulletin; 8/1/2000; ; 700+ words
; ...at least temporarily observed in the ectoderm of planulae of some corals and soft corals...because infection first occurred in the ectoderm cells of embryos or early planulae...daughter cells, including presumptive ectoderm cells (Benayahu, 1997; Benayahu and...
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Function of FGF8 during embryonic development elucidated.
Newspaper article from: Biotech Business Week; 2/9/2004; 700+ words
; ...and to determine whether the pharyngeal ectoderm and endoderm Fgf8 expression domains...gene function in the pharyngeal arch ectoderm and endoderm," the researchers wrote...ablating FGF8 protein in the pharyngeal arch ectoderm causes failure of formation of the fourth...
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ECTODERMAL DYSPLASIAS
Magazine article from: Dental Assistant; 5/1/2004; ; 700+ words
; ...or more derivatives of the embryonic ectoderm. To say that the EDs are inherited means...say that derivatives of the embryonic ectoderm are involved means that the hair, nails...this juncture to illustrate that the ectoderm does not develop in a vacuum. There...
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Ectodermal dysplasias.
Magazine article from: The Dental Assistant; 5/1/2004; ; 700+ words
; ...or more derivatives of the embryonic ectoderm. To say that the EDs are inherited means...say that derivatives of the embryonic ectoderm are involved means that the hair, nails...this juncture to illustrate that the ectoderm does not develop in a vacuum. There...
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Defective Decapentaplegic Signaling Results in Heart Overgrowth and Reduced Cardiac Output in Drosophila
Magazine article from: Genetics; 7/1/2007; ; 700+ words
; ...Decapentaplegic (Dpp) signals from the dorsal ectoderm to maintain Tinman (Tin) expression...that a second Dpp signal from the dorsal ectoderm restricts the number of pericardial cells...Decapentaplegic (Dpp) signals from the dorsal ectoderm to the dorsal mesoderm for a second time...
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Churchill regulates cell movement and mesoderm specification by repressing Nodal signaling.(Research article)
Magazine article from: BMC Developmental Biology; 11/2/2007; ; 700+ words
; ...mesoderm comes at the expense of the ectoderm; conversely, repression of mesoderm results in an expansion of the ectoderm [2, 3, 4, 5]. FGF signaling...patterning of the mesoderm and neural ectoderm in mice, frogs, fish and the chick...
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A global view of gene expression in lithium and zinc treated sea urchin embryos: new components of gene regulatory networks.(Research)(Clinical report)
Magazine article from: Genome Biology (Online Edition); 5/16/2007; ; 700+ words
; ...but also on genes that are involved in ectoderm differentiation and patterning. We then...territories. During gastrulation the ectoderm is divided into an oral side, which...increase in endoderm at the expense of the ectoderm, but without alterating the mesodermal...
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ectoderm
Book article from: The Columbia Encyclopedia, Sixth Edition
ectoderm layer of cells that covers the surface of an animal embryo after the process...Chordata , a third, middle layer, the mesoderm , is formed between the ectoderm and endoderm during gastrulation, and the process is termed triploblastic...
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Hans Spemann
Encyclopedia entry from: Encyclopedia of World Biography
...influence exerted by the cup on the overlying ectoderm. Spemann's Classical Experiments This...the implanted material, so that the ectoderm (upper layer) of the implant formed...embryo was formed by induction from the ectoderm of the host tissue. To decide the point...
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Growth and Differentiation of the Nervous System
Book article from: Animal Sciences
...which also gives rise to the skin. All ectoderm cells have the ability to develop into...releases chemicals onto the overlying ectoderm, causing those cells to differentiate...structure is formed from rapidly dividing ectoderm cells. In the second step, the continued...
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embryo
Book article from: The Columbia Encyclopedia, Sixth Edition
...The outer layer of cells is called the ectoderm , the inner layer the endoderm . Among...however, a later invagination of the ectoderm results in a gut that is open at both...and tissues develop. In general the ectoderm gives rise to the skin, or integument...
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optic vesicle
Book article from: A Dictionary of Biology
...the retina of the eye. When the optic vesicle comes into contact with the ectoderm covering the head of the embryo, these ectodermal cells become thicker: the ectoderm in this region invaginates and eventually becomes detached from the adjacent...
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