In the course of development, cells divide (reproduce), acquire new functions or structure (differencemode), move within the embryo (migrate) and undergo programmed death (often via apoptosis). These four major cellular process that act in different combinations and in different ways lead to growth and morphogenesis (literally “creation of form”), creating the embryo of normal size and shape containing the bodies of a corresponding size and shape in the desired position, tissues and cells with the right architecture, structure and function.
Although the increase may seem too obvious to discuss it, he carefully regulated during development, and unregulated growth can lead to catastrophic consequences. A simple doubling (one additional cycle of dividing cells) number of cells (hyperplasia) or increase their size (hypertrophy) will probably be fatal for the organism. Incorrect regulation of growth of segments of the body can cause severe deformity and dysfunction, as if hemihyperplasia and other disorders of segmental overgrowth. Additionally, differential regulation of growth can change the shape of the tissue or organ.
Morphogenesis occurs in the developing human organism through a variety of mechanisms, such as, for example, differential growth, differential-diverging pattern, regulated apoptosis, cell migration. In some circumstances the word “morphogenesis” is used as a General term that describes all of the development, but formally this is incorrect, as morphogenesis is associated with the process discussed here growth and leads to a properly formed and functioning tissue or organ. The human embryogenesis is the description of human development begins from the end of Chapter 2 — fertilization. After fertilization the product of conception undergoes a series of cell divisions without overall growth, called fragmentations. The fertilized egg undergoes four divisions to 3 day forming a 16-cell morula.
On the 4th day morula transferred in the blastocyst, the cells of the predecessor of the placenta form the wall, inside which the cells forming the embryo, going from one side, forming the inner cell mass. This is the point when the product of conception becomes the first clear manifestation of polarity, the axis of asymmetry, separating the inner cell mass (basically forming a ready-made body) from embryonic tissues that form the chorion and other extraembryonal education (placenta, etc.). The inner cell mass is then subdivided into epiblast, actually forming the embryo, and gipoblasta, creating the amniotic membrane. The embryo is implanted in the endometrium on 7-12 days after fertilization. After implantation, gastrulation occurs, the cells rearrange themselves into a structure consisting of three groups of cells, called the primary embryonic leaf of the ectoderm, mesoderm and endoderm
hree embryonic leaf form different structures. Cells SCS origin form a Central part of the bodies. It is the cells of the intestinal walls, the lining of the Airways and other similar structures. Mesodermal origin have kidney, heart, vessels, and structural or supporting tissue of the body. Almost exclusively mesodermal origin of the bones and muscles perform two basic functions — structural (physical support) and providing the necessary support and nutritional support of the hematopoietic system. From the ectoderm are formed the Central nervous system, peripheral nervous system and skin.
The following main stages of development — initiation of the nervous system, creating a basic structure of the body plan, organogenesis, and then continued from 4 to 8 weeks of gestation. The position and the basic structure of all bodies by this time established, and cellular components necessary for their full development, are in place. It is generally believed that the fetal period of development spans from 9 to 40 weeks of gestation, at that time primarily occur maturation and further differentiation of the organs. For some organ systems the development of birth does not stop. For example, the brain undergoes considerable development after birth, and the limbs continue epiphyseal growth, ending only after puberty.
Embryonic (germ) cells: transfer of genetic information
Apart from the growth and differentiation of somatic tissues, the body also needs to determine which cells will develop into gametes in the adult organism. This is the purpose of education sex (germ) cells. Sex cells commitied to the subsequent gametogenesis and meiosis in order that the individual could pass on their genetic traits, using recombination and random distribution of chromosomes. In addition, during the formation of reproductive cells should recover propeciacnce epigenetic imprinting required for some genes.
Stem cells: supports the regenerative capabilities of tissues
In addition to the program definition of differentiation required for development, the body must also establish tissue-specific stem cells capable of regenerating various cells in adult life. These cells are best studied in the hematopoietic system. Among 1011-1012 nuclear hematopoietic cells in an adult organism is almost 104-105 cells able to transform into any of the more specialized blood cells continuously throughout life. Hematopoietic stem cells can be transplanted to other people and completely reform their hematopoietic system. Required pool size of hematopoietic stem cells maintains a system of interacting gene products. These regulators strike a balance between the use of stem cells in replicating and creating cells-predecessors, capable of further development in the various Mature cells of the hematopoietic system.