TYPES AND TASKS OF STEM CELLS
ALL-ROUNDERS WITH SPECIAL PROPERTIES
There are various types of stem cells. They are categorised by three different methods:
⦁ By Cell Type
⦁ By Ontogenetic Age
⦁ By Differentiation Potential
CLASSIFICATION BY CELL TYPE
The tissues or cell types of precursor cells are capable of differentiating by the classification of cell types. For example, a blood stem cell cannot differentiate into a new neuron or bone cell.
HEMATOPOIETIC STEM CELLS
Another term for hematopoietic stem cells is blood stem cells. Their significance for the entire haematopoiesis is quite clear and they have a very short lifespan. An adult must produce approximately 200 billion erythrocytes (red blood cells), 120 billion leukocytes (white blood cells), and 150 billion thrombocytes (platelets) each day.
MESENCHYMAL STEM CELLS
The cells that make up connective tissue are called mesenchymal stem cells. Along with muscles, tendons, and ligaments, they also evolve into bone and cartilage. They are particularly present in the umbilical cord tissue. Adult mesenchymal stem cells and mature fat cells, both can be found abundantly in human fat tissue, making it a valuable source of stem cells.
NEURONAL STEM CELLS
Brain cells are produced from neurons, or neural stem cells. They are very fascinating for the study of traumatic injuries, such as those following strokes or severe brain injuries caused by accidents, or neurodegenerative illnesses, such as Parkinson's or dementia. The hope in this regard is that neuronal stem cells may trigger repair processes and thus minimise damages.
CLASSIFICATION BY ONTOGENETIC AGE
In biology, ontogenesis refers to the process by which an organism develops from an egg cell to a sexually mature creature. As a result, the ontogenetic age classification distinguishes between embryonic, foetal, and adult stem cells. The various stages of human development, starting with the fertilised egg cell and ending with the adult are illustrated. The lifespan of embryonic stem cells is very limited whereas adult stem cells continue to divide throughout life.
ADULT STEM CELLS
Adult stem cells from bone marrow and other organs are the reservists of our organism. They create substitutes for dead cells and they cannot differentiate into all types of cells in an organism anymore. Like embryonic stem cells, they are not as viable as stem cells from umbilical cord blood. Furthermore, their later extraction is time-consuming, risky, and expensive.
EMBRYONIC STEM CELLS
Long before birth, embryonic stem cells play an important role in the origin of human life. They are like the "mothers of all cells," as they can develop into any kind of specific cell. However, their existence is very limited time, specifically as the embryo develops into the blastocyst, which occurs in about three to four days after fertilisation. This implies that to use embryos for medicinal purposes, they would need to be grown and then destroyed. Because of this, the ethical use of embryonic stem cells is very controversial.
NEONATAL STEM CELLS
Despite being very young and potent, stem cells from umbilical cord blood fall under the category of adult cells. Therefore, neonatal stem cells have their own group. Collecting umbilical cord blood at birth and storing it is the simplest and most ethical way of extracting young and potent stem cells, thus securing them for medical precaution.
CLASSIFICATION BY POTENTIAL DIFFERENTIATION
The human body contains stem cells, which are unspecialized cells. They possess the ability to develop into any type of organism cell and self-renewal. The specialisation process involves multiple stages. Developmental potency is reduced with each step, which means that a unipotent stem cell is not able to differentiate into as many types of cells as a pluripotent one.
Depending upon the differentiation potential into different lineages, stem cells are categorized as totipotent, pluripotent, multipotent, oligopotent, and unipotent.
Totipotent stem cells
have the ability to divide and give rise to all types of cells in an organism. Totipotency, which enables cells to produce both extra-embryonic and embryonic structures, has the highest differentiation potential. A zygote is a type of totipotent cell that is created when an egg and a sperm are fertilised. These cells may eventually develop into either a placenta or one of the three germ layers. After 4 days, the blastocyst's inner cell mass begins to exhibit pluripotency. Pluripotent cells are produced in this organelle.
Oligopotent stem cells
can differentiate into several cell types. The myeloid stem cell is one type of stem cell that can divide into white blood cells but not red blood 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. The inner cell mass of preimplantation embryos is where ESCs are derived. Induced pluripotent stem cells (iPSCs), which are produced from the epiblast layer of implanted embryos, form another example. Their pluripotency is a continuum that ranges from fully pluripotent cells like ESCs and iPSCs to representations with less potency—multi-, oligo-, or unipotent cells. Teratoma development test is one approach to evaluate their activity and range. iPSCs are produced synthetically from somatic cells and have similar properties to PSCs. Their cultivation and use hold great promise for both the present and the future of regenerative medicine.
Multipotent stem cells
have a narrower spectrum of differentiation than PSCs, but they can specialise in discrete cells of specific cell lineages. A hematopoietic stem cell, which may give rise to various blood cell types, is one example. An oligopotent cell develops from a hematopoietic stem cell. The only cells that can differentiate are those in its lineage. However, the term "pluripotent cell" is more suitable because some multipotent cells have the capacity to develop into distinct cell types.
Unipotent stem cells
are characterised by the narrowest differentiation capabilities and a special property of dividing cells repeatedly. They are a good option for therapeutic usage in regenerative medicine because of its latter quality. Dermatophytes are the only cell type that can be formed from these cells.
