The role of progestins
Progestins are female sex hormones and are a generic term that encompasses all natural progestins produced by the body, such as progesterone, as well as synthetic progestins.
The first day of monthly bleeding marks the start of a new cycle. While the uterine lining (endometrium) is still being broken down and shed, new follicles are maturing inside the ovary. The messenger substance FSH (follicle-stimulating hormone) stimulates the growth of a follicle in the ovary. As a rule, only one follicle containing an egg reaches full maturity per cycle.
Over the first 14 days of the cycle, this follicle grows to a size of around 2 centimetres. The larger the follicle, the higher the concentration of estradiol in the body.
Increased estradiol secretion signals the brain that ovulation is taking place. This in turn releases large quantities of luteinizing hormone (LH, Latin for "hormone that colors yellow") from the pituitary gland. This increase in LH concentration causes the egg to be expelled from the follicle into the Fallopian tube (ovulation). The remaining follicle then collapses on itself, developing into the corpus luteum and producing the corpus luteum hormone, progesterone.
Together, estrogen and progesterone ensure that the uterine lining is ready for implantation of a fertilized egg. The corpus luteum is preserved for around 14 days. If implantation does not take place, the corpus luteum regresses, hormone production declines and bleeding (menstruation) occurs.
Progestogen Progestin
- synthetic progestins are often used as part of hormone replacement therapy or hormonal contraception
- their effect is similar to that of natural progesterone. However, they last longer in the body, as they are not broken down and eliminated as quickly as natural progestins.