A woman's reproductive life spans about 40 years, from puberty with the onset of menstruation to menopause when it ceases. Women are born with all the eggs they will ever need, about 300,000. Of the 100 to 300 that develop each month, only one or two become mature, whilst the remainder are re-absorbed by the body.
The female cycle is dominated by the two main sex hormones, oestrogen and progesterone.
For the first half of a woman's menstrual cycle that is from day 1 to day 13 oestrogen is the dominant hormone. Ovulation usually takes place on day 14, half way through the monthly cycle. About one day before, on day 13, the secretion of oestrogen begins to fall, while at the same time progesterone secretion increases. It continues to rise considerably until day 21 to 23 when it begins to fall, reaching its lowest level at the start of menstruation on about day 28.
Progesterone is made in the body each month by the corpus luteum which is a yellow body which is formed in the ovary after ovulation. It is produced in such quantities by the body that it is measured in milligrams whereas oestrogen is measured in micrograms. Progesterone is a precursor to many other hormones in the body but ensures that the endometrium stays in place, at the same time making the uterus ready for implantation of a fertilised egg. Once this occurs the placenta takes over the production of progesterone, which rises from 25 mg to over 400 mg a day.
The Effects of Progesterone:
Precursor of other sex hormones (oestrogen, testosterone)
Protects against breast fibrocysts
Helps use fat for energy
Helps thyroid hormone action
Normalizes blood clotting
Helps normalize blood sugar levels
Restores proper cell oxygen level
Protects against endometrial cancer
Helps protect against breast cancer
Stimulate osteoblast-mediated bone building
Necessary for survival of embryo and foetus throughout the gestation
Precursor of cortisone synthesis by adrenal cortex