Page 126 - The Miracle of Hormones

THE MIRACLE OF HORMONES

Degenerating
corpus luteum Primary follicle
Corpus
luteum

Blood
vessels

Growing
follicles

Corona
radiata

Mature vesicular
(Graafian) follicle
0
2 oocyte
Germinal epithelium
Ovulation
Ruptured follicle
Antrum

The structure of an ovary where female sex hormones are produced...

How does progesterone know that, after fertilization has occurred, a
second fertilization must not happen and that it is necessary to stop the
activity of the ovary to prevent it? Who gave this ability to progesterone,
which is only a molecule?
Another special function of progesterone is to diminish the influ-
ence of the oxytocin hormone secreted by the pituitary gland. As we saw
earlier, oxytocin is a hormone that goes into effect as the time of birth
approaches and ensures that the uterine muscles will contract. As a result
of these contractions, the baby comes out of the mother's womb more
easily.
If oxytocin affected the uterus during the first days of fertilization,
these muscles would eject the fertilized egg as it attached itself to the
uterine wall, and pregnancy would never occur. Progesterone goes into

124