Estrogen continues being produced throughout childhood.It is this that inhibits the production of gonadotropin releasing hormone until hypothalamatic changes override the oestrogen signals.
- MENSTRUAL PHASE: (DAY 1-5)
UTERINE CHANGES:
The shedding of the endometrium causes the blood vessels to rupture ,thereby starting the bleeding which marks the onset of the menstrual phase.
OVARIAN CHANGES:
At this stage ,follicles are developing in the ovaries from the aggregate of germinal epithelial cells of that organ.These follicles later house the egg cells.
- FOLLICULAR PHASE:(DAY 6-12)
At the onset of puberty or just before it the release of GNRH into the brain positively effects the anterior pituitary gland to commence the production and secretion of the human gonadotropins, LH and FSH.OVARIAN CHANGES:
FUNCTION OF FSH :
Since the follicular cells are responsible for the output of estrogen, LH and FSH, in turn, promote maturation of follicle.A single primary oocyte is targeted to resume the halted stages of meiosis and develop into a mature follicle.
Maturation of the follicle means increased production of estrogen.
FUNCTION OF ESTROGEN:
This increase in estrogen serum levels exhibits a negative feedback on the anterior pituitary inhibiting the release, but stimulating the production and storage of the gonadotropins.
UTERINE CHANGES:
FUNCTION OF ESTROGEN:
Initiates thickening of uterine wall ,endometrium by formation of mucous and blood capillaries.
- OVULATORY PHASE:(DAY 13-15)
The phase during which the egg cells rupture out from the follicles and enter the fallopian tube.
FUNCTION OF ESTROGEN:
With the cessation of gonadotropin output, estrogen levels continue to rise; and, while the initial small rise in estrogen inhibits gonadotropin release, high estrogen levels have the opposite effect. By the time the ovarian estrogen production reaches its maximum before day 14, the negative feedback effect on the anterior pituitary is reversed to a dramatically positive one and a burst-like surge of stored LH is released .
FUNCTION OF LUTEINIZING HORMONE:
The LH surge is actually responsible for affecting the final development, and subsequent rupture of the mature follicle
ESTROGEN INHIBITION :
The cells responsible for estrogen secretion -- are damaged by the rough contact with the ovary wall. Estrogen output is then halted and serum levels drop slowly for a short period immediately following the ovulatory process.
- CORPUS LUTEAL PHASE:(DAY 16-28)
OVARIAN CHANGES:FUNCTION OF LUTEINIZING HORMONE:
The extraordinarily high levels of LH now have another function.
Once the ovum and its remaining surrounding cells are swept into the fallopian tube, luteinizing hormone works to establish the corpus luteum from the remnants of the ruptured mature follicle inside the ovary.The remaining follicular cells then enlarge .Under the influence of LH, these enlarged cells become the corpus luteum.
FUNCTION OF PROGESTERONE AND ESTROGEN:
The corpus luteum is a gland which maintains the responsibility of both the production and secretion of estrogen and progesterone.
As estrogen and progesterone levels again rise, their combined effect on the anterior pituitary's production of the gonadotropins is extremely negative and LH levels decline significantly.
LUTEINIZING HORMONE INHIBITION:
Since it is LH that is responsible for the maintenance of the corpus luteum, the marked decline in LH levels heralds the degeneration of the corpus luteum into a scar called the corpus albicans.
PROGESTERONE INHIBITION:
With the corpus luteum no longer producing progesterone and estrogen, the serum levels of the ovarian hormones decline sharply and the menstrual phase may then begin.
UTERINE CHANGES:
FUNCTION OF PROGESTERONE:
It makes the endometrium thicker and more blood vessel rich to ready it for the product of fertilization,if there is any.
Low levels initiates shedding of endometrium.
