ZOO 3603C - Assignment #3 CH - ZOO 3603C December 9 2016 Assignment#3 Topic#1 Stem Cells Cells are the smallest and most basic units of life that are

ZOO 3603C - Assignment #3 CH - ZOO 3603C December 9 2016...

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Unformatted text preview: ZOO 3603C December 9, 2016 Assignment #3: Topic #1 – Stem Cells Cells are the smallest and most basic units of life that are able to sustain all living organisms as small as single-­‐celled prokaryotes and as large as multicellular eukaryotes. There are approximately 200 different types of cells, totaling to about 37.2 trillion cells, in the human body alone. From this large pool of cells, one family is particularly fascinating. Stem cells are blank slates. They have the ability to differentiate into any type of cell and are able to help replace the injured cells lost every day. Defining stem cells and the countless research surrounding its abilities can help us understand the potential of these cells. What are stem cells? As described earlier, stem cells are unique and extremely important to the survival of multicellular organisms. These special cells have two main functions – to self-­‐renew so the supply of stem cells can be maintained, and the ability to differentiate into specialized cells to contribute to the growth of new tissues. Though stem cells are able to generate specialized cells, their abilities are limited by potency. Totipotent stem cells can differentiate into any cell possible, and can include the first few cells divided from a zygote. Pluripotent stem cells are similar, but they can specialize into almost any kind of cells with a few exceptions. These cells can be derived from the endoderm, mesoderm and ectoderm germ layers of a developing blastocyst. Multipotent stem cells can differentiate into cells of the same family, like red and white blood cells. Oligopotent stem cells have the ability to specialize into a small number of cells, like lymphoid, while unipotent stem cells are strictly limited to producing one kind of cell, like muscle stem cells. (1) There are two main categories of stem cells: embryonic stem cells and adult stem cells. Embryonic stem cells are pluripotent and have the ability to become almost any cell in the body. These cells are obtained “from embryos produced by in vitro fertilization (IVF), a process in which oocytes and sperm are placed together to allow fertilization to take place in a culture dish,” (2). After four or five days have passed and the embryo is now a blastocyst, the embryonic stem (ES) cells can be harvested from the inner cell mass. However, the extraction of these cells has been deemed controversial because by removing the ES cells, the entire embryo is being destroyed and preventing the potential for a new life. On the other hand, the majority of adult stem cells are considered multipotent, as their fates are more limited. There are many types of adult stem cells, including hematopoietic stem cells. These cells are able to specialize into all kinds of blood cells (“red blood cells, B and T lymphocytes, natural killer cells, neutrophils, basophils, eosinophils, monocytes and macrophages” (3)). Additionally, there are mesenchymal stem cells (MSC) that can differentiate into skeletal tissues, including “bone cells (osteoblasts and osteocytes), cartilage cells (chondrocytes), fat cells (adipocytes) and stromal cells” (3). Neural stem cells are also essential in the formation of neurons, astrocytes and oligodendrocytes to support the functions of the brain. Additional adult stem cells include epithelial and skin stem cells that can specialize to help maintain the lining of the digestive system and skin. While ES cells have been controversial, adult stem cells are widely accepted because the body’s organs utilize them on a daily basis to restore injured or dying cells. Where are stem cells found in the body? Stem cells are located in multiple parts of the body. As previously mentioned, ES cells are found in the inner cell mass of the developing blastocyst. Adult stem cells can be “found in tissues such as the brain, bone marrow, blood, blood vessels, skeletal muscles, skin and the liver” (1). Located directly in blood, peripheral blood stem cells can be extracted through a process known as apheresis, in which blood is taken from the donor, circulated through a machine, which gathers the stem cells, and returns the rest of the blood back to the donor. Additionally, hematopoietic and mesenchymal stem cells can be found in umbilical cord blood, but are mainly found by drilling into bone marrow. An interesting place to find stem cells in the body is in adipose tissue, extracted by liposuction. Manipulating lipid cells and isolating certain cellular constituents can produce adipose-­‐derived stem cells for therapeutic uses (4). There may be other areas of the body that contain stem cells, but more research still needs to be conducted. What are stem cells currently used for in contemporary medicine? In contemporary medicine, stem cells are utilized for multiple uses. One of the most common uses is through bone marrow transplantation, which can help treat disorders like leukemia, lymphoma and other blood disorders. Leukemia is a progressive disease in which an excessive number of leukocytes is produced and are unable to mature properly. Thus, these immature cells, known as leukemic blasts, cannot “perform the functions of normal mature blood cells which is to defend the body against infection and disease,” (5). As a result, the unwarranted amount of leukemic blasts collects in the blood and bone marrow and prevents normal leukocytes from forming. Thus, the body is unable to fight infections without operational white blood cells and causes this disease to become fatal. However, through the advancement of technology, researchers have found ways to suppress this harmful disease with the help of stem cells. Individuals affected with this disorder are able to receive a bone marrow or stem cell transplant. With bone marrow transplants, doctors first collect bone marrow stem cells either from the patient or the donor. Similarly, with stem cell transplants, doctors place a transplant catheter in a large vein to collect the peripheral blood and hematopoietic stem cells. Then, the patient is put through extensive chemotherapy in order to kill the effected cancerous cells. Finally, doctors are able to place the collected stem cells back into the patient’s blood through IV. “It takes about 24 hours for the stem cells to reach the bone marrow. Then they start to grow, multiply, and help the marrow make healthy blood cells again,” (6). Though stem cell transplants have been very effective with treating leukemia and other blood disorders, many complications can still arise. For example, during recovery, patients are highly susceptible to infections due to a reduced immune system. Additionally, patients can become infected with graft-­‐versus-­‐host disease (GvHD) in which the “donor’s blood cells attack the patient’s own normal tissues,” (5) and causes an even lower immune response. Not only can hematopoietic and bone marrow stem cells be used to treat cancerous blood disorders, but cord blood stem cells can also be used to particularly treat children. These stem cells are extracted from the umbilical cord after the birth of a baby. Blood diseases like Fanconi anemia and leukemia also occur in children, and so cord blood stem cells are utilized to help boost the child’s immune system with healthy blood cells. However, “there are limitations to the types of disease that can be treated: cord blood stem cells can only be used to make new blood cells for blood disease therapies,” (7). Furthermore, “skin stem cells have been used since the 1980s to grow sheets of new skin in the lab for severe burn patients,” (7). These cells are able “to grow sheets of epidermis in the lab” (7) and then be grafted onto the patient’s skin as a skin graft. Currently, skin stem cells are utilized to help third degree burn victims heal quicker and replace the epidermis that is unable to produce new skin. Unfortunately, “only the epidermis can be replaced with this method; the new skin has no hair follicles, sweat glands or sebaceous glands,” (7), but further research is being conducted to help with this issue. Moreover, the eye has a reservoir of special stem cells that help replace those damaged by blinking or trauma caused by the environment. These stem cells are known as limbal stem cells and they are located near the edge of the cornea. “If the cornea is severely damaged, for example by a chemical burn, limbal stem cells can be taken from the patient, multiplied in the lab and transplanted back onto the patient’s damaged eye(s) to restore sight,” (7). What promises do stem cells hold for the treatment of human diseases? Stem cells hold endless possibilities for the treatment of human diseases. Even though there are treatments to help with grafting new skin for burn victims, there are still some challenges with treating skin-­‐related human diseases. For instance, a genetic disorder, known as epidermolysis bullosa (EB), affects over 500,000 people in the world. This condition causes the skin to become very fragile, resulting in excessive blistering and patches of missing skin. To combat this disease, Dr. Marius Wernig has been conducting research on a certain gene that controls the secretion of collagen-­‐7. He harvested regular skin cells from the EB patients and dedifferentiated them to become stem cells. With these pluripotent cells, “a segment of the collagen-­‐7 gene in the pluripotent cells where the mutations occurred was then replaced with the correct segment, which made the pluripotent cells healthy,” (8). The correction in the collagen-­‐7 gene allowed Dr. Wernig to grow healthy skin cell patches, and graft them onto mice. The researchers found that the correction in the collagen-­‐7 gene allowed the human skin to grow properly and heal the missing skin patches,” (8). Though the results of this experiment referred to mice and not humans, they still show promising evidence that stem cells can be manipulated with corrected genetic codes to help treat certain diseases. Furthermore, mesenchymal stem cells can differentiate into adipocytes, chondrocytes, and osteocytes to help support the skeletal structure of the body. Currently, there are no therapies available to treat bone and cartilage diseases, but there are many promises in this direction. For example, osteoarthritis is a disease in which the cartilage between the joints erodes away and results in the very painful movement of joints against each other. “Because MSCs can differentiate into cartilage cells, scientists hope MSCs could be injected into patients to repair and maintain the cartilage in their joints,” (9). However, this feat proves challenging because the body’s immune system responds negatively to MSC transplantation. Moreover, to combat “blood vessel damage linked to heart attacks or diseases, such as critical limb ischemia,” (9), the use of MSCs shows noteworthy potential. Research has shown that MSCs can help with neovascularization, or the making of new blood vessels, in mice. These results indicate that MSCs may be responsible for stimulating blood vessel growth through endothelial precursors and current endothelial cells in humans (9). Additionally, new advancements in technology have allowed researchers to develop induced pluripotent stem cells (iPSCs). By introducing certain genes into adult cells, researchers are able to reprogram these cells to act like ES cells so they can self-­‐renew and have the ability to differentiate into almost any kind of cell. In terms of leukemia treatments, iPSCs can be used to grow leukemic cells, which researchers can study and manipulate to find new and less toxic therapies (5). “Researchers have been able to generate brain cells from iPSCs made from skin samples belonging to patients with neurological disorders, such as Down’s syndrome or Parkinson’s disease,” (7). These brain cells can be studied carefully and manipulated with new drugs to identify potential advancements with treating neurological diseases. Likewise, because stem cells are undifferentiated, they have the ability to specialize into a myriad of cells and tissues. But most interestingly, stem cells can be used to generate entire, functional organs. Doctors have been performing organ transplantations for damaged livers and kidneys for many decades now. The future of stem cell research shows great potential for these organs to be made directly from the body’s cells (10). The use of stem cells will surely help solve one of the leading problems of having a shortage of organ donors. Though this is not a viable option presently, the future of stem cells possibly indicates this method to be the leading choice for in organ transplantation. In summation, stem cells are very essential to the survival of life. Not only do stem cells restore the damaged or dead cells everyday, but they are also crucial in rebuilding tissues and organs during extreme damage. Even though there is already a myriad of research surrounding stem cells, there is still a need for more research to be conducted to further explore the full potential of stem cells. References: (1) Crosta, Peter. "What Are Stem Cells?" Medical News Today. MediLexicon International, 1 Sept. 2008. Web. 09 Dec. 2016. (2) Yu, Junying, and James A. Thomson. "Embryonic Stem Cells." National Institutes of Health. U.S. Department of Health and Human Services, n.d. Web. 09 Dec. 2016. (3) "Stem Cell Basics IV." National Institutes of Health. U.S. Department of Health and Human Services, n.d. Web. 09 Dec. 2016. (4) "FDA to Put Mushrooming Fat Stem Cell Clinics on Crash Diet?" The Niche. N.p., 05 Jan. 2015. Web. 09 Dec. 2016. (5) Weber, Christine. "Leukaemia: How Can Stem Cells Help?" EuroStemCell. N.p., 24 Mar. 2016. Web. 09 Dec. 2016. (6) "What Is a Stem Cell Transplant (Bone Marrow Transplant)?" Cancer.Net. Cancer.Net Editorial Board, 28 Jan. 2016. Web. 09 Dec. 2016. (7) "Types of Stem Cells and Their Current Uses." EuroStemCell. N.p., 17 Aug. 2012. Web. 09 Dec. 2016. (8) Naik, Gautam. "Stem Cells Hold Promise for Skin Disease Treatment." The Wall Street Journal. Dow Jones & Company, 26 Nov. 2014. Web. 09 Dec. 2016. (9) "Mesenchymal Stem Cells: The 'other' Bone Marrow Stem Cells." EuroStemCell. N.p., 5 Nov. 2015. Web. 09 Dec. 2016. (10) Liu, Yunying, Ru Yang, Zuping He, and Wei-­‐Qiang Gao. "Generation of Functional Organs from Stem Cells." Cell Regeneration. BioMed Central, 22 Jan. 2013. Web. 09 Dec. 2016. ...
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