In the human body, more than 200 types of cells are isolated , each of which has the same hereditary code. All of them developed first from a unicellular, and then a multicellular embryo, which a little later divided into three germ layers. From each of its sites, body tissues developed, where approximately the same type of cells are located. Moreover, almost all of them developed from one group of predecessors. This process is called cell differentiation. This is a local adaptation of the cell to the real needs of the body, the implementation of the functions programmed in its hereditary code.
Characterization of cells and tissues
Somatic cells of the body have the same chromosomal set, regardless of functional purpose. However, they are different in phenotype, due to their preparation for various local tasks in biological tissues. A phenotype is the result of the expression of a particular genetic set in a particular habitat. And under different conditions, cells with the same genetic material develop in different ways, have different morphological characteristics, and perform specific functions.
A highly developed organism is necessary for the formation of many tissues of which its organs are composed. In this case, tissues are created from a homogeneous group of stem precursors. This process is called cell differentiation. This is a chain of events aimed at growing the cell population according to predetermined criteria for the growth and development of biological tissues of the body. It underlies the growth of the body and its multicellular organization.
Essence of differentiation
In terms of molecular biology, cell differentiation is the process of activating some parts of the chromosomes and deactivating others. That is, compact packaging or unwinding of chromosome sections, which makes them available for reading hereditary information. In the conjugated state, when the genes are packed into heterochromatin, reading is impossible, and in the expanded form the necessary sections of the genetic code become available for messenger RNA and subsequent expression. Therefore, cell differentiation is a non-strict regulated typification of chromatin packing of the same type.
Cytokines and messengers
As a result, in a group of cells differentiated under the same conditions and having similar morphological features, despiralization of the same chromosome regions is observed. And during the impact of intercellular messengers, local regulators of cellular differentiation, the necessary sections of the genes are activated, their expression occurs. And therefore, cells of biological tissues produce the same substances and perform similar functions, for which this process is provided. From this point of view, cell differentiation is a directed effect of molecular factors (cytokines) on the expression of genetic information.
Membrane receptors
Cells of the same tissue have a similar set of membrane receptors, the presence of which is controlled by the T-killers of the immune system. Loss of a cell receptor of the desired type or expression of another that is not intended for this location due to the risk of oncogenesis causes directed cell aggression against the “intruder”. The result will be the destruction of the cell, the differentiation of which was not according to the rules provided for by the influence of intercellular messengers from specialized regulators.
Immune differentiation
Immune cells have special receptor molecules called differentiation clusters. These are the so-called markers by which you can understand the conditions under which the immunocytes developed, and for what purposes they are intended. They undergo a long and complex process of differentiation, at each stage of which lymphocyte groups that have developed an insufficient number of receptors are eliminated and destroyed, or “inconsistencies with requirements” are noticed in their interaction with antibodies.
Cell groups and tissues
Most cells in the body divide in two during mitotic reproduction. At its preparatory stage, genetic information is doubled, after which two daughter cells with a similar set of genes are formed. Not only the active sections of chromosomes, but also conjugated ones are subject to copying. Therefore, in tissues, differentiated cells after division give two new daughter cells that have genetic material similar to a complete somatic set of chromosomes. However, they are unable to differentiate into other cells, since they cannot migrate naturally to other living conditions, that is, to other differentiation messengers.
Cell population growth
Immediately after the division of the two daughter cells, they receive a special set of organelles that they inherited from the mother. These smallest functional elements are already prepared to perform the necessary tasks in this biological tissue. Therefore, the daughter cell only needs to increase the volume of the cavities of the endoplasmic reticulum and increase in size.
Also, the goal of cell development is to obtain an adequate level of supply of nutrients and bound oxygen. For this, in the case of oxygen or energy starvation, it throws angiogenesis factors into the intercellular space. New capillary vessels sprout along these anchors, which will carry out the nutrition of a group of cells.
The process of increasing in size, obtaining an adequate supply of oxygen and energy substrates, as well as expanding intracellular organelles with an increase in the rate of protein production is called cell growth. It underlies the growth of a multicellular organism and is regulated by numerous proliferation factors. At some point, upon reaching the maximum size by a signal from the outside or by coincidence, the grown cell will again split in half, further increasing the size of the biological tissue and the body as a whole.
Mesodermal differentiation
As a clear demonstration of the differentiation of stem cells and their more developed "descendants", the transformation of the mesoderm germ layer of the human body should be considered. From mesoderm - a group of stem cells with the same structure and developing under the conditions of the presence of differentiation factors, such cell populations as nephrotome, somite, splanchnot, splanchnotomal mesenchyme and paramesonephral canal originate.
From each such population intermediate forms of differentiation will begin, which later will give rise to the cells of an adult organism. In particular, three cell groups develop from somitis: myotome, dermatome, and sclerotis. Myotoma cells give rise to muscle cells, sclerotoma to cartilage and bone, and a dermatome to connective skin tissue.
Nephrotomy gives rise to the epithelium of the kidneys and spermous ducts, and the epithelium of the fallopian tube and uterus will differentiate from the paramesonephral canal. The phenotype of the splanchnotome cells will be prepared by differentiation factors for their transformation into the mesothelium (pleura, pericardium and peritoneum), myocardium, and adrenal cortex. The splanchnotome mesenchyme is the starting material for the development of cell populations of blood, connective and smooth muscle tissue, blood vessels and microglial cells.
The growth of cells of these populations, their multiple division and differentiation is the basis for supporting the viability of a multicellular organism. This process is also called histogenesis - the development of tissues from cellular precursors as a result of their differentiation and phenotype transformation in accordance with the influence of extracellular factors that regulate their development.
Differentiation of plant cells
The functions of a plant cell depend on their location, as well as the presence of modulators and growth suppressors. The embryo of the plant as a part of seeds does not have vegetative and germinative sites, and therefore, after germination, it must develop them, which is necessary for reproduction and growth. And until the time comes for its germination, he will be at rest.
From the moment a growth signal is received, the functions of plant cells will begin to be realized along with an increase in size. Cell populations embedded in the embryo will go through the phase of differentiation and transform into transport routes, vegetative parts, and germinal structures.