PROGESTINS-THE HORMONES OF PREGNANCY
Progestins are a group of steroidal female sex hormones mostly synthetic.The only naturally occuring progestin is the Progesterone which is the base for these synthetic progestins.Unlike estrogens this progesterone is secreted during the gestational periods only that means the period from which a fully developed ovum detached from the overy and waiting for a sperm to fertilize it and upto the end of either the menstural cycle if no fertilization happen or upto the end of the pregnancy period if fertilization happened.The hormone progesterone is secreted from the yellow gland Corpus Luteum the gland which is temporarily formed at the gap from which the matured ovum detached from the ovary.
Progesterone the hormone of the pregnancy is controlling both the anterior pituitary-ovary axis and as well as the hypothalamus- anterior pituitary axis during the gestational period by a feed back mechanism to protect the fetus by preventing further maturing of the ovarian follicles.At the domination of progesterone at the set plasma limit during the gestational period there are no further secretions of FSH but, increases the LH pulsative sectretions from the anterior pituitary.The GRH secretions from the hypothalamus also decreased similar to FSH by progesterone While estradiol the main estrogen is controlling only the hypothalamus- anterior pituitary- axis and thus prevent the secretions of FSH and not of LH from the anterior pituitary by feed backchanism for all the times if its plasma level is raised to certain limits.
Once the ovum is fertilized the implantation takes place in one week.A hormone called human chorionic gonadotropin (HCG) is secreted from the a special layer within the uterus known as trophoblast to keep the carpus luteum to be sustained and functional for some time upto the trophoblast itself becomes a fully developed placenta..This hormone is largely excreted by the kidneys mostly in the morning hours.Detection of this hormone in the urine by a specialised home kit test can confirm Pregnancy.
After several weeks of implantation placenta begins to develop.As a fully developed placenta can sufficiently produce progesteron and estrogen with collaberation of fetal adrenal glands and thereafter the corpus luteum begins to fade as its function is not further required and the secretion of CGH too will fade to be secreted further.
The amount of secretions of progesterone is varying as a few milligram per day at the beginning of follicular phase of the cycle followed by increasing upto 10 to 20 milligram during the luteal phase and further increases to several hundred milligrams during the later parts of the pregnancy period.
In the luteal phase progesterone act on the endometrium produced by the estrogens and decrease its further proliferation by estrogen,and develop a secondary endometrium as a luxury cusion for the convenience of the fertilized egg.
In case if there is no fertilization happened the secretions of progesterone and its domination decreased and the corpus luteum begins to fade at the end of the cycle and the domination of estrogen cause shedding of the secondary endometrium as a waste and excreted as menses at the end of the cycle.
At normal pregnancy period progesterone also act on the cervix and make it into thick and secretions to be more viscid inorder to prevent further entry of sperms through.This mechanism is more beneficiary for the use of synthetic progesterone like Norgestrel as a best oral contraceptives used alone or in combinations with estrogens.This we will discuss later in detail by the following posts.
Progeserone also modify the estrogen controlled matured vaginal epithelium in order to make it convenient and more elastic for delivering the baby
Progeserone is very important in maintaining pregnancy.During pregnancy it protect the fetus by preventing contractions of the uterus and further mensturation.
During the pregnancy period progesterone along with estrogen acting on the mammary glands and proliferate it for milk production.But at the beginning of the lactating period the actions and secretions of progesterone and estrogen becomes nill.