development of the fetus inside the woman's womb consists of three periods.
stages of embryonic development.
first period begins after penetration into the uterine cavity of the ovum, and continues during the first week.At this time, human embryonic development involves a bookmark primary organs, the formation of extraembryonic systems to subsequently ensure the existence of the fetus to full education for all systems and organs.
For primary fixation in the uterus ovum should actively its growth.Formed cell layers - the foundation of which will be subsequently formed by the internal organs.Eating an egg gets by dissolving cells in the endometrium surface embryonic cells.Thus, the fruit is moving deeper into the cavity and fixed therein.Full adherence, usually ends on the twelfth day after fertilization.Next
cell mass begins to increase significantly, there is its division into two pieces: the inner (endoderm) and outer (ectoderm) embryonic leaf.At the end of the third week of gestation formed mesoderm - the third piece, located between the other two.The development of the human embryo, in particular its internal organs in consequence will occur from these germ layers.
ectoderm is the basis for the formation of dental enamel, the upper layers of skin, peripheral (kt) and central (brain and spinal cord) nervous system.And also lays the senses (vision and hearing, olfactory and gustatory areas of the body).
inner cell layer (endoderm) is the basis for the formation of the respiratory and digestive systems.
mesoderm participates in the formation of the musculoskeletal, cardiovascular, excretory, and reproductive systems.
human embryonic development in the first period includes the distribution of the cells.One of them forms the chorion - primary fetal membranes.Chorion villi covered with small that subsequently grow in the lining of the uterus and thus form the placenta.Another part of the cell involved in the creation of extraembryonic organs.
human embryonic development into the second phase of the second week.It is called the embryonic period.Continue this step after two months of gestation.During this period there is the formation of all the vital organs.
At this time also form primary blood vessels.From the head region of the embryo cells are moved to the portion between the inner and outer cell layer.The result is a rudiment of the notochord.
important point during the second period is the formation of chorionic placenta.
From the ninth week of gestation and birth of the child until the last third - fetal - period.Embryonic development of man at this time is characterized by the achievement of full maturity of the formed structures of the body.
with nine weeks begins to develop the endocrine system.An intensified production of hormones necessary for growth.Particularly important is the insulin.At the end of the third month ending maturation of the placenta, which is also beginning to produce its own hormones.
is the development of the brain matured departments which are involved in the first movement of the fetus.
Education immune system to the end of the eighteenth week of fetal development.The body of the child generation is activated leukocytes.Generators and components that make up the innate immune system of the fetus - interferon and immunoglobulin.Starts spleen.
important changes in the pulmonary system occur on the twenty-fourth week.Formed terminal sacs, through which it becomes possible to carry out a breath.
the seventh month of gestation there is a growth of muscles and bones of the body, so a child's body becomes larger than his head.
During the ninth month actively there is an increase in body weight.The child in this period becomes fully mature and mature.
