From the moment of conception, the body undergoes many changes. Developing from just one cell containing the hereditary material of the parents, it grows due to the reproduction and differentiation of cells. This is a constant process of maintaining the life of a multicellular organism, which is based on many intercellular interactions. At each stage of life, the specialization of cells changes and becomes more and more narrow.
Cells and tissues
A group of cells with the same morphophysiological characteristics, located in the same place and solving the same tasks, is called a tissue. Organs are made up of tissues, and organisms are made up of organ systems. But in order to go from the germ cell to the organism, it is necessary to overcome many stages of cell differentiation. This process is the preparation of cells to perform the functions assigned to them, as a result of which, at high levels,development, they lose the ability to share.
Regeneration
The need for long-term differentiation explains the impossibility of true regeneration of highly specific tissues and organs, the cells of which are at a high degree of their development. In these organs, mechanical damage is restored by fusion of living areas with connective tissue. That is, a complete recovery of cells that were in this place before, if they were highly differentiated, will never happen.
As an example, it is appropriate to cite the formation of scars when muscles are damaged, including in the heart. Also, as a result of damage to the brain or nerves, there is no recovery of neurons. After damage to a highly differentiated tissue, the body is forced to put up with the loss of its functions. And only the use of stem cells that have not yet passed the stage of transformation under the influence of local cytokines and conditions of stay leaves hope for true regeneration. But for now, this is the technology of the future.
Growth of the body
Differentiation of cells in the body occurs in stages, depending on the mediators and the signals they receive from the regulator. Without an external factor, transformation is impossible in the direction in which it is required for development. And when it is received, the process has a directed strictly typified character, where at each stage there is a system for monitoring and screening out failed cytological populations.
Because the process of growth from embryo to matureorganism is a programmed in a strict sequence of cell differentiation. This order must be strictly observed, and until one important stage has occurred, another stage of separation and cytological specification should not occur. Otherwise, development and growth will initially occur with an error, which leads to the formation of malformations or developmental anomalies.
Evolution of multicellularity
In an adult organism, this mechanism underlies the formation of tumor cells. It is difficult to imagine how a huge number of stages must replace each other in the strictest sequence for the correct differentiation of cells and tissues. This is an incredible mechanism by which a multicellular organism functions. It is also a clear demonstration of the thesis that ontogeny is a brief repetition of phylogeny. This means that cell differentiation occurs in the sequence in which evolution moved.
Hematopoietic differentiation
Differentiation of blood cells is a clear example of the staging of this process in a highly developed organism. In humans, it originates from a common precursor called the hematopoietic stem cell. It is pluripotent, that is, any blood cell can be formed from it under the influence of various types of cytokines. More importantly, it is also the product of a long development and preparation to become the forerunner of hematopoiesis. She went through the stage of stem cell differentiation, preparing only forone goal - to become the beginning of hematopoietic germs. No other tissue will be made from it, which distinguishes it from undifferentiated stem cells.
Initial hematopoiesis
At the first stage, two populations develop from a stem cell under the influence of two fundamentally different factors. Under the influence of thrombopoietin and colony-stimulating factor (CSF), a large cellular group of myelopoiesis precursors is formed. All monocytes, granular leukocytes, platelets and erythrocytes will develop from this group. Just the formation of a primitive precursor cell is the starting stage of the division of hematopoiesis into two streams. The first stream is myelopoiesis and the second stream is leukopoiesis.
During it, from the same pluripotent precursor cell, but already under the influence of interleukin, a cell population of leukopoiesis is formed. It will develop T and B lymphocytes with natural killer cells. Splitting into two streams is an example of initial cell differentiation. This means that before the formation of functioning blood cells, several stages will pass, at each of which the phenotype and receptor set will change. Many will change locations, where separation and cytological specification will be influenced by cytokines and antigens with antibodies.
Myelopoiesis
The main dividing cell that gives rise to all myelocytes is the myeloid germ. Its development follows two streams: the first is the formation of a precursor common with platelets and erythrocytes, and the second isthe formation of a protoleukocyte, from which the monocyte and granulocyte will originate. The first stream of cell differentiation is the process of their development under the influence of colony-stimulating factor, thrombopoietin and interleukin type 3.
Precursors of leukocytes and monocytes are formed under the action of the hematopoietic colony-stimulating factor. From the common precursor of platelets and erythrocytes, under the action of thrombopoietin and erythropoietin, respectively, intermediate forms of cells develop. Of these, through the so-called aging and additional development, adult cells of erythrocytes and platelets will be formed.
It is noteworthy that platelets are, rather, fragments of the cell that preceded them, since at the stage of differentiation they lost unnecessary organelles and the nucleus. In erythrocytes, the nucleus was also eliminated, and the cytoplasm was filled with hemoglobin. Leukocytes, as cells developing in the second stream of myelopoiesis, have a nucleus, although their degree of differentiation is also very high.
Leukopoiesis
Lymphocytic cell differentiation is the process of formation of lymphocytes and natural killer cells from a common precursor of lymphopoiesis. It is carried out mainly under the influence of interleukins and is also initially divided into two streams - B-lymphopoiesis and T-lymphopoiesis. This stage of controlled development gives rise to two populations of unipotent cells, destined only to become an intermediate form for the formation of one lymphocytic lineage.
The precursor of T-killers and T-lymphocytes is formed from the T-growth zone, and from the B-cell precursor, the influence of interleukin-4 forms the B-lymphocyte germ zone. T-killers are formed under the influence of interleukin-15, an expression factor of the corresponding receptors - clusters of differentiation (CD). On their basis, the entire population of lymphocytes will be divided into groups depending on the type of their CD antigen. Accordingly, the immune cells will perform different functions.
