In females, gonadotropin output is regulated by the ovary.
Low circulating levels of estradiol exert a negative feedback control on LH and FSH secretion, and high-maintained levels of estradiol exert a positive feedback effect.
High plasma levels of progesterone enhance the negative feedback effects of estradiol and keep FSH and LH secretion down to a low level.
The secretion of FSH, but not LH, is also regulated by nonsteroidal high-molecular-weight proteins called inhibins found in follicular fluid: inhibins are found at high levels in late follicular phase plasma of fertile women, and although they have been used as a relative marker of ovarian reserve, the direct correlation is not clear.
Neuroendocrine mechanisms that regulate testicular function are basically similar to those that regulate ovarian activity. The male hypothalamic-pituitary unit is responsible for the secretion of gonadotropins, which regulate the endocrine and spermatogenic activity of the testis, and this secretion of gonadotropin is subject to regulation with feedback. Read more
Although the embryo is well protected in the uterus, some environmental substances – teratogens – can cause developmental disorders after maternal exposure to them. Teratogen is any agent, which can cause congenital defect, or increase the frequency of defect occurrence in a population. Environmental factors, such as infections and drugs, can simulate genetic conditions, for example, when two or more children of normal parents are affected. It is important to remember that not everything that is familial is genetic. Read more
Multiple pregnancies (gestations) are associated with a higher risk of chromosomal abnormalities, fetal morbidity and fetal mortality than a single pregnancy. The risk gradually increases with the number of fetuses. Globally, twins naturally occur approximately once in every 85 pregnancies, triplets approximately once in every 902 pregnancies, quadruplets approximately once in every 903 pregnancies, and quintuplets approximately once in every 904 pregnancies. Read more
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