The placenta or afterbirth (diagram 129) forms at the beginning of the third week of embryo life. The length of its vessels, drawn together, as high

Placentation in humans [formation]

The placenta or afterbirth (diagram 129) forms at the beginning of the third week of embryo life. The length of its vessels, drawn together, as high as 50 km! By the time of the child's birth the placenta reaches a diameter of 15-20 cm, and weight of 500-600 g. It is an essential interim body for fetus and it continuously grows along with fetus. The placenta should be attached to the wall of the uterus above the head of the fetus. If it happens on the contrary, it will depart earlier, and it can cause fetal death and fatal bleeding in mother.

The umbilical cord (diagrams 128, 129) connects placenta with the fetus. Blood vessels of the mother and fetus are working closely together in the placenta. This ensures an uninterrupted supply of nutrients, oxygen to the future child and the removal of recycled and harmful products of metabolism from his body. Taken from http://worldofschool.org

Diagram 128. Human fetus at 9-10 weeks
Diagram 129. The placenta and the umbilical cord: 1 — uterine wall; 2 — the fetus; 3 — the umbilical cord; 4 — placenta; 5 — the blood vessels; 6 — umbilical artery; 7 — umbilical vein; 8 — the umbilical cord; 9 — amniotic fluid

Protecting the fetus from various harmful substances, placenta, unfortunately, cannot resist alcohol, nicotine and drugs. It has been found that the nicotine accumulates therein and in the amniotic fluid, and carbon dioxide as well as other constituents of tobacco smoke impair the oxygen supply to the fetus.

Self-treatment of various diseases during pregnancy is unacceptable since most drugs also penetrate through the placenta to the fetus and poison it, causing developmental defects. The placenta can be called a temporary endocrine gland because it secretes hormones that stimulate the preparation of mammary glands to feed the baby, prevent premature contraction of uterine muscles, and inhibit the process of ovulation during pregnancy (menstruating ceases in pregnant women).

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Questions:
  • Identify features of the structure and functioning of the placenta and the umbilical cord.

  • Prove extremely important role of placenta and umbilical cord.