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This research paper is about stem cells. It includes the basic idea of stem cells, the different types of stem cells, how they are distinguished into the different types, their function, and how they can be used for our benefit. I chose this topic for my research because it helps me understand a part of science I have always been curious about. By the end of the research, the reader will have the basic idea about stem cells - what they are and how they work.
Stem cells are unspecialized cells that can develop into different types of cells and replicate many times. This ability of stem cells to replicate is known as proliferation. Stem cells can either self-renew to divide into more stem cells, or differentiate into specialized cells that can perform specific functions. Stem cells can also divide to repair or replace damaged cells.
There are mainly two different types of stem cells; embryonic stem cells and adult stem cells. Embryonic stem cells can divide many times and into all types of cells while adult stem cells are limited to differentiating into specific types of cells. Stem cells have many sources - embryos, fetuses, umbilical cord blood, placenta, bone marrow, etc.
Functions of stem cells
Stem cells during developmenthttp://upload.wikimedia.org/wikipedia/commons/thumb/1/18/Stem_cell_division_and_differentiation.svg/220px-Stem_cell_division_and_differentiation.svg.png
Stem cells can undergo self-renewal, which is a process by which stem cells replicate many times, but the resulting cell is similar to the parent cell; it is undifferentiated or unspecialized. Another property of stem cells is the
ir potency, which is their capability to differentiate into types of specialized cells. This property is also used to distinguish stem cell types.
A stem cell can self-renew, or produce more stem cells, by two different methods, symmetric and asymmetric. Symmetric division happens when one stem cell divides into two cells that similar to the parent cell. Asymmetric division occurs when one stem cell divides into two different cells - one stem cell and one progenitor cell. A progenitor cell is a cell that is more specialized than a stem cell and can differentiate further into a completely specialized cell. Another difference between a stem cell and a progenitor cell is that a stem cell can undergo division indefinitely, while a progenitor cell is said to divide only a limited number of times.
The cell potency of a stem cell classifies it into the different types. During development, the potential of the cell decreases, but the specialization increases. This process is called determination.
Type of cell
These cells are produced when a sperm cell fuses with an egg cell. They can differentiate into all types of cells, including embryonic cells.
These cells are produced when totipotent cells differentiate. They can differentiate into almost all types of cells.
Embryonic stem cell
These cells can different into many different cells, but only the ones related to the family of cells.
Germ layer stem cell
These cells can differentiate into only some types of cells.
Lineage stem cell
These cells can differentiate into only their own type, but can self renew.
Muscle stem cell
Stem cells during repair of cells
Another function of stem cells is to repair damaged cells in the body. Most adult cells are used for this function. Regeneration of cells can be achieved by two different methods. Stem cells that circulate can replace cells when signaled appropriately, or differentiated cells that can divide again can undergo a process of self-reparation. Recently, with the help of cell lineage tracking, it has been discovered that stem cells from one organ divided to replace cells of another organ. This is known as plasticity, which is an increase in the potency of a cell.
Research and clinical applications
Types of stem cells used
Embryonic Stem cells
The embryonic stem cells used in clinics are the pluripotent cells taken from the blastocyst of the embryo. Since around the 1980s, embryonic stem cells have been cultured, but these were the cells from mouse embryos. Later researches included cells from embryos of hamsters, pigs, cows, etc.
Embryonic stem cells are best characterized for cultured stem cells because - firstly, they are pluripotent, and can divide into almost all types of cells. Moreover, they are immortal and can divide indefinitely. This makes it easier to maintain the cells in a laboratory culture.
Adult stem cells
The adult stem cells are multipotent, and are found in many places of the body such as the brain, liver, the epidermis, etc. One recently discovered characteristic of the adult stem cells is plasticity, which is the ability of a stem cell to increase its potency. Another characteristic of adult stem cells is transdifferentiation, which is the ability of the cell to convert directly to another type of a cell.
Treatments and stem cell therapies
The adult stem cells are considered to be ideal for stem cell therapies mainly due to one reason - they have a less potency than embryonic stem cells. Since embryonic stem cells can divide into almost any type of cell, if they are used for cell therapies, the chance of development of cancer is very high. The cells can immediately divide into many different cell types and develop into a teratoma. The use of adult stem cells greatly reduces these chances. Moreover, the use of adult stem cells does not raise ethical concerns. The only downside is that not all types of adult stem cells can easily be obtained. Stem cell therapy has been used in many diseases including heart diseases, diabetes, parkinson's disease, etc.
Induced pluripotent stem cells (iPSCs)
iPSCs normal adult cells that are genetically programmed to express the properties of a pluripotent stem cell. The research for iPSCs is still under progress, but they are already being used for development of drugs, and are expected to be used for further important aspects, like treatments. Like other treatments, the rejection of the cells and production of cancerous tumors is possible. The research also helps scientists understand the structure of pluripotent cells and thus hopefully will help them know how to repair a damaged cell in the body.
Stem cells are found in many parts of the body, indicated by their name. Embryonic stem cells are found in the embryo, fetal stem cells in the fetus, umbilical cord blood stem cells in the umbilical cord blood, etc. The potency of the stem cells is used to further distinguish them into different types. Stem cells have different functions, like self renewal or differentiation, and repairing of damaged cells in an organ or tissue. The Stem cells can also be used for other purposes such as stem cell therapies.