Question

Write an essay about "stem cells biologiy" in a word file with the following format

Main body in the word(text) 12 pnt times new roman, headings 14 pnt Times new roman, line spacing 1.0, margins 2.5 from each side of the page.

Dont leave gaps between the paragraphs. I need to use references and give them at the end of the text. Referances should given in 8pnt times new roman , use at least 5 of them

Answer 1

Ans:

STEM CELL BIOLOGY:

Stem cells are unspecialized cells of the human body. They are able to differentiate into any cell of an organism and have the ability of self-renewal. Stem cells exist both in embryos and adult cells. Stem cells are operationally defined as cells that have the potential for unlimited or prolonged self-renewal, as well as the ability to give rise to at least one type of mature, differentiated cells.

Embryonic Stem Cells
In humans, the embryo is defined as the organism from the time of implantation in the uterus until the end of the second month of gestation. Embryonic stem cells (ESCs), however, refer to a much more restricted period, resulting from the isolation and cultivation of cells from the blastocyst, which forms at approximately 5 days after fertilization.

Adult Stem Cells
Adult or somatic stem cells (ASCs) are rare, quiescent cells with a more limited self-renewal and differentiation capacity. Numerous types of precursor cells have been isolated in adult tissues, leading to the concept that all tissues have their own compartment of stem cells. They are responsible for replenishing cells that die within a given organ, either due to physiological (wear and tear) or pathological processes.

Stem Cell Classification:

• Totipotent stem cells are able to divide and differentiate into cells of the whole organism. Totipotency has the highest differentiation potential and allows cells to form both embryo and extra-embryonic structures. One example of a totipotent cell is a zygote, which is formed after a sperm fertilizes an egg. These cells can later develop either into any of the three germ layers or form a placenta. After approximately 4 days, the blastocyst’s inner cell mass becomes pluripotent. This structure is the source of pluripotent cells.
• Pluripotent stem cells (PSCs) form cells of all germ layers but not extraembryonic structures, such as the placenta. Embryonic stem cells (ESCs) are an example. ESCs are derived from the inner cell mass of preimplantation embryos. Another example is induced pluripotent stem cells (iPSCs) derived from the epiblast layer of implanted embryos. Their pluripotency is a continuum, starting from completely pluripotent cells such as ESCs and iPSCs and ending on representatives with less potency—multi-, oligo- or unipotent cells. One of the methods to assess their activity and spectrum is the teratoma formation assay. iPSCs are artificially generated from somatic cells, and they function similarly to PSCs. Their culturing and utilization are very promising for present and future regenerative medicine.
• Multipotent stem cells have a narrower spectrum of differentiation than PSCs, but they can specialize in discrete cells of specific cell lineages. One example is a haematopoietic stem cell, which can develop into several types of blood cells. After differentiation, a haematopoietic stem cell becomes an oligopotent cell. Its differentiation abilities are then restricted to cells of its lineage. However, some multipotent cells are capable of conversion into unrelated cell types, which suggests naming them pluripotent cells.
• Oligopotent stem cells can differentiate into several cell types. A myeloid stem cell is an example that can divide into white blood cells but not red blood cells.
• Unipotent stem cells are characterized by the narrowest differentiation capabilities and a special property of dividing repeatedly. Their latter feature makes them a promising candidate for therapeutic use in regenerative medicine. These cells are only able to form one cell type, e.g. dermatocytes.

Stem Cell: A Biological View

A blastocyst is formed after the fusion of sperm and ovum fertilization. Its inner wall is lined with short-lived stem cells, namely, embryonic stem cells. Blastocysts are composed of two distinct cell types: the inner cell mass (ICM), which develops into epiblasts and induces the development of a foetus, and the trophectoderm (TE). Blastocysts are responsible for the regulation of the ICM microenvironment. The TE continues to develop and forms the extraembryonic support structures needed for the successful origin of the embryo, such as the placenta. As the TE begins to form a specialized support structure, the ICM cells remain undifferentiated, fully pluripotent and proliferative. The pluripotency of stem cells allows them to form any cell of the organism. Human embryonic stem cells (hESCs) are derived from the ICM. During the process of embryogenesis, cells form aggregations called germ layers: endoderm, mesoderm and ectoderm, each eventually giving rise to differentiated cells and tissues of the foetus and, later on, the adult organism. After hESCs differentiate into one of the germ layers, they become multipotent stem cells, whose potency is limited to only the cells of the germ layer. This process is short in human development. After that, pluripotent stem cells occur all over the organism as undifferentiated cells, and their key abilities are proliferation by the formation of the next generation of stem cells and differentiation into specialized cells under certain physiological conditions.

Signals that influence the stem cell specialization process can be divided into external, such as physical contact between cells or chemical secretion by surrounding tissue, and internal, which are signals controlled by genes in DNA. Stem cells also act as internal repair systems of the body. The replenishment and formation of new cells are unlimited as long as an organism is alive. Stem cell activity depends on the organ in which they are in; for example, in bone marrow, their division is constant, although in organs such as the pancreas, division only occurs under special physiological conditions.

References:

1. Till JE, McCulloch EA. Hemopoietic stem cell differentiation. Biochim Biophys Acta 1980; 605: 431-459.

2. Weissman IL. Stem cells: units of development, units of regeneration, and units in evolution. Cell 2000; 100: 157-168.

3. Alison MR, Islam S. Attributes of adult stem cells. J Pathol 2009; 217: 144-160.

4. Sukoyan MA, Vatolin SY, Golubitsa AN, Zhelezova AI, Semenova LA, Serov OL. Embryonic stem cells derived from morulae, inner cell mass, and blastocysts of mink: comparisons of their pluripotencies. Embryo Dev. 1993; 36(2): 148-158.

5. Larijani B, Esfahani EN, Amini P, Nikbin B, Alimoghaddam K, Amiri S, Malekzadeh R, Yazdi NM, Ghodsi M, Dowlati Y, Sahraian MA, Ghavamzadeh A. Stem cell therapy in treatment of different diseases. Acta Medica Iranica. 2012; 50(2): 79-96.