- The sex cells also known as spermatogonia are divided by mitosis to produce a primary spermatocyte. One cell remains as such while other divides further.This primary spermatocyte divides by MIEOSIS-1 in to two secondary spermatocytes.
- The two secondary spermatocytes separately divide by MIEOSIS-2 into two spermatids.
- Spermatids differentiate into sperms.
- Proliferative/follicular stage:This cycle starts on the onset of puberty. In our hypothalamus are certain areas that influence glands to release hormones, hence are called hypothalamic factors. The GONADOTROPHIN RELEASING FACTOR in the hypothalamus affects the pituitary gland to release a hormone named FSH (follicle stimulating hormone). FSH acts on the ovaries to produce follicles/eggs.In competition to pituitary comes the ovary and releases estrogen. Estrogen comes into play making sure that no more FSH is released and also thickening the uterus.
- Ovulatory phase:Pituitary gland making a comeback secreting LH (luteinizing hormone) and as a result releases an ovum.
- Secretory phase:After ovulation the left over follicle cells differentiate rapidly forming a yellow spongy structure corpus luteum. From this structure is secreted a hormone called progesterone which aids the uterus in zygote implantation after fertilization.
- Menstruation:If fertilization has not occurred, the corpus luteum starts degenerating. Progesterone is no more secreted. The spongy corpus luteum with the walls of uterus and blood vessels is ejected out of the body so that the process can repeat itself for the next cycle. This stage lasts for about 3-4 days.
NOTE: the period of menstrual cycle before ovulation is variable while the phase after ovulation is constant i.e. 14 days.
Q: another question may be, in osteoporosis, estrogen replacement therapy (ENT) is given to aged women. This may again start the menstrual cycle after menopause has taken place. ANS: after the above given description of menstrual cycle it is clear that only estrogen is not responsible for the cycle but it is the gonadotrophin releasing factor in the hypothalamus which induces changes in the reproductive structures of the female.