Answer to Question #50543 in Biology for Abby

Question #50543
1. a) What organogenesis?
b) At what stage of pregnancy the embryo he now carries the fetus name? Why?
c) What is the duration of a typical pregnancy?
d) In which quarter there he has the most development and differentiation?
e) What is the minimum age (in weeks) to which a premature fetus could survive without much critical care?

2.Décris briefly the three stages of parturition. Why they say it is a phenomenon of retro activation.

3. How is it that lactation is controlled by hormonal secretions of the pituitary gland? What is the external factor that indirectly stimulates the lactation?
Expert's answer
a) Organogenesis is a process of organs development from the germ layers: ectoderm, mesoderm, endoderm.
b) Fetus is a term describing that the embryo can be recognized as belonging to its own species. In this period embryo has heart, brain and muscles, though they don't function completely. The embryo is called fetus from the ninth week.
c) The duration of pregnancy is 9 month (40 weeks).
d) Embryo (the first quarter) has the most differentiation and development because embryonic stem cells differentiate into all cell types.
e) Beginning from the 24-25 weeks fetus can survive with the probability of 50%.
First stage (dilation stage): it begins with the true labor, the cervix dilates and the fetus begins to shift toward the cervical canal. The duration of this stage is 4-8 hours. At last the amnion ruptures ("water break").
Secon stage (expulsion stage): contractions reach maximum intensity, expulsion lasts until fetus emerges from the vagina. At last newborn infant is born. This stage lasts less than two hours.
Third stage (placental stage): the uterus endometrium and the placenta are ejected.
Lactation is the process of milk secretion from the mammary glands. Regulation of progesteron and estrogen secretion by the LH and FSH (pitutary gland hormones) promotes the development of the milk duct system. Prolactin is another pitutary gland hormone that stimulates lactation and promotes the mammary gland growth.
External factor that stimulates the lactation is the suckling by the baby. It stimulates the paraventricular nuclei and supraoptic nucleus in the hypothalamus, which signals to the posterior pituitary gland to produce oxytocin. Oxytocin stimulates contraction of the myoepithelial cells and cause the release of milk through the nipple.

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