A girl approaching puberty around 10-12 years of age begin to show a cyclicity in her reproductive organs called menstrual cycle. Each cycle is of about 28 day’s duration with day of start being first day of menstruation. Ovulation occurs about day 14 of the cycle that is in the middle of cycle around which fertilization is possible. Each period of menstruation is 1-5 days which is characterized by loss of about 30-40 ml blood tinged with uterine cells. After menstruation period, FSH hormone is discharged from anterior pituitary causing development of ovum and follicles on the ovaries. Developed follicle releases high quantity of estrogen around mid cycle (14 days) that stimulates release of LH from anterior pituitary. Within hours of LH release, the ovum is shed from the ovaries and ruptured follicle grows into corpus luteum. Two pituitary hormone functions during menstrual cycle could be summarized as below:
Hormone
Stage of Cycle
Action
FSH
5-14 days
Growth of follicles Estrogen release
LH
14-15 days
Ovulation Corpus luteum formation
During later half of the cycle both LH and FSH remains at low levels but progesterone is secreted from corpus luteum (Fig 28a). At the end of cycle, corpus luteum undergoes degeneration and progesterone secretion declines and menstruation starts. Thus every 28 days, the cycle is repeated with consistent changes in FSH, LH, Estrogen and progesterone hormones and changes in reproductive organs specially ovaries and uterus. In non pregnant female, the cyclicity continues uninterruptedly until the age of menopause (about 50 years).
When fertilization occurs, pregnancy ensues and menstruation is completely stopped. Pregnancy is characterized by continuation of corpus luteum growth, secretion of progesterone beyond day 28 and the hormone causes growth of uterus to accommodate growing embryo/fetus.
Participants