What is proliferation?Proliferation in biology means the multiplication and growth of cells.
Proliferation refers to tissue proliferation consisting of mitotic cell divisions and cell growth. Cell growth involves a maximum volume increase of the cells to the size and shape that is preprogrammed in the DNA of the genes. The incentive to divide given certain hormones, neurotransmitters (messengers) and growth factors.
In the adult stage, some tissue or cell types are no longer capable of proliferation in humans, that is, they can no longer be divided and thus no longer able to reproduce. This applies, for example, to most of the nerve tissue and to most sensory cells.
However, renewal processes are constantly taking place in many tissue types, which are mostly made possible by proliferation-capable basic or even stem cells. The average age of human cells varies from a few hours to life, depending on the type of tissue. For example, the cornea renews every 28 days. The intestinal mucosa makes it much faster, within a few days. While the erythrocytes, the red blood cells released from the bone marrow, renew every 120 days, most white blood cells only become a few days old.
Function & Task
Proliferation of tissue cells is of great importance for embryonic and postnatal development in humans. Estimates say that at birth we have about 5 trillion cells. This number increases by the proliferation process to about 60 to 90 trillion in adults. The number of cells has thus increased to twelve to sixteen times. Upon completion of the growth phase, some types of cells lose their ability to proliferate. In other cell types, a limited proliferative capacity remains.
For tissues whose cells are unable to reproduce but still need to renew, the body relies on a type of stem cell that is often already specialized, that is, has lost its omnipotence and can only grow into cells of certain tissues. The limited possibility of replication is necessary in order to obtain the cell renewal process of different types of tissue of different lengths.
The extent to which the remaining ability to proliferate is expressed clearly by the fact that about 50 million cells die each second and are either recycled, broken down and excreted by the body's metabolism or, as in the case of the skin, simply shed to the outside. The constantly dying and degraded by the body metabolism cells must be replaced by the proliferation, so as not to lose cell substance.
A special role is played by the proliferation of injuries. Controlled by messenger substances during the healing phase of injuries involving hormones and enzymes a proliferation process. Non-lesioned connective tissue cells (fibrocytes), which are in the immediate vicinity of tendons and ligaments, migrate into the lesioned area and are able to contact each other with their processes and contract via contractile elements in their cytoskeleton, so that The torn ends of ribbons or tendons can tighten again. The repair mechanism shows that the proliferation ability of certain cells can be reactivated when needed.
Since the mid-1990s, it has been known that neurogenesis, ie the formation of new nerve cells in the central nervous system, is also possible in certain neuronal stem cells in adults, something which until then was not considered possible. Neural stem cells located in a limited area of the hippocampus produce precursor cells (progenitor cells), which also have proliferative capacity for a few days.
Diseases & complaints
The process of wound healing can be considered as an example of the body having the ability to switch on and off the proliferation capability of cells as needed. The question arises as to why this possibility does not exist with all types of tissue, so that organs destroyed by illness or limbs lost through an accident could regrow.
Apparently, nature has recognized evolutionarily that in an unlimited proliferation capacity of the cells, the risks would be greater than the potential benefits. The main danger associated with unrestricted proliferation is that the complex process is no longer controllable. This means that the cells no longer respond to messenger substances, enzymes and hormones after their proliferation ability. Unrestrained cell growth would be the result.
This is precisely the case with tumors whose tissue is subject to constant growth, so that the ability to proliferate can no longer be prevented. The main difference between benign (benign) and malignant (malignant) tumors lies in the fact that the malignant tumors in addition to their own ability to reproduce themselves can feed themselves, as they have the process of vascularization on its own network of vessels and are capable of metastasis.
In addition to the possibility of unrestrained proliferation, which can lead to cancer formation with very different orientations, there is also the problem of limited proliferative capacity. Often dysfunctions are triggered by toxins and by drugs such as alcohol and nicotine. For example, chronic alcohol abuse leads to a disruption of the proliferation and differentiation of T lymphocytes, which form an important part of the immune system.