Embryonic development of man

The development of the fetus inside the womb of a woman consists of three periods.

Stages of embryonic development.

The first period begins after penetration into the uterine cavity of the fetal egg and lasts throughout the first week. At this time, human embryonic development includes the laying of primary organs, the formation of extra-germplasm systems, which are called upon to ensure the fetal existence until the complete formation of all systems and organs.

The primary fixation in the uterus of the fetal egg is followed by its active growth. Cell layers form the basis, from which internal organs will subsequently be formed. The egg is fed by the dissolution of cells in the uterine mucosa by surface embryonic cells. Thus, the fetus moves deeper into the cavity and is anchored inside it. Complete adherence, as a rule, ends on the twelfth day after fertilization.

Next, the cell mass begins to increase significantly, it divides into two sheets: the inner (endoderm) and the outer (ectoderm) embryonic leaf. After the third week of gestation, a mesoderm is formed - the third leaf, located between the two others. The development of the human embryo, in particular its internal organs, will subsequently occur from these embryonic leaflets.

Ectoderm is the basis for the formation of tooth enamel, upper skin layers, peripheral (nodes) and central (spinal and brain) nervous system. Also, the sense organs (vision and hearing, olfactory and taste areas of the body) are laid.

The inner cellular layer (endoderm) is the basis for the formation of the respiratory and digestive systems.

Mesoderm participates in the formation of musculoskeletal, cardiovascular, excretory and reproductive systems.

Embryonic development of a person in the first period includes the distribution of cells. One part forms the chorion - the primary fetal membrane. The chorion is covered with small villi, which subsequently grow into the uterine mucosa and, thus, form the placenta. Another part of the cells participates in the creation of extra-germinal organs.

Embryonic development of a person passes into the second phase from the second week. This period is called the embryonic period. This stage continues after two months of gestation. During this period, all vital internal organs are formed.

At this time, the primary blood vessels are also formed. From the head region of the embryo, cells move to the part between the inner and outer cellular layer. As a result, the chord rudiment is formed.

An important moment during the second period is the formation of the placenta from the chorion.

From the ninth week of gestation to the very birth of the child, the third fruitful period lasts. Embryonic development of man at this time is characterized by the achievement of full maturation of all formed structures of the body.

From the ninth week, the endocrine system begins to develop . The intensive production of hormones necessary for growth begins. Particularly important is insulin. At the end of the third month, the placenta matures, which also begins to produce its own hormones.

There is a development of the brain, the ripened sections of which participate in the first movements of the fetus.

The formation of the immune system ends by the eighteenth week of fetal development. The development of leukocytes is activated in the child's body. Formed and components that make up the fetal congenital immune system - interferon and immunoglobulin. The spleen begins to work.

The most important changes in the pulmonary system occur on the twenty-fourth week. Terminal pouches are formed, with the help of which breathing becomes possible.

In the seventh month of gestation, the muscles and bones of the trunk grow, so the child's body becomes larger than his head.

During the ninth month, there is an active increase in body weight. The child becomes completely full and mature during this period.