PH1124 - Reproductive Hormones 3 Flashcards
what is oogenesis and what does it start with? (2)
- oogenesis is the formation of the female gameteovum (egg) cell from precursor cells in the ovaries
- oogenesis actually begins in ovaries prior to birth where precursor germ cells (oogonia) are found in foetal ovary
when does production of egg cells span?
- production of egg cells spans pre-reproductive & reproductive life
what happens in oogenesis? (3)
- initial mitosis of the germ cells (oogonia) occurs in the foetal ovary
- early meiosis of primary oocyte that completes after puberty (before ovulation)
- late meiosis of secondary oocyte that completes after ovulation if there is fertilization, giving the mature ovum
what does the reproductive cycle consist of? (2)- ovarian cycles
- ovarian cycles
- uterine cycles
what is the ovarian cycle? (2)
- controls stages of oogenesis in the ovary
- comprises events in the ovary that precede and follow oocyte maturation and ovulation
what is the uterine cycle?
- the preparation of the uterus to receive the ovum
what are the reproductive cycles regulated by?
- hormonally regulated by the HPG axis and reproductive hormones
how does the HPG axis help the hormonal control of the female reproductive cycle?
- synthesis and secretion of LH and FSH
- LH promotes follicle development, androgen production and triggers ovulation and development of corpus luteum
- FSH initiates follicle development and growth, conversion of androgens to oestrogens
what is the corpus luteum?
- the corpus luteum develops from a ruptured follicle in the ovary and secretes estrogen and progesterone
how does the reproductive hormone oestrogen help the hormonal control of the female reproductive cycle? (2)
- controls ovarian/follicular function
- feeds back onto hypothal/pit to control GnRH, FSH and LH
how does the reproductive hormone progesterone help the hormonal control of the female reproductive cycle? (2)
- regulates preparation of uterine endometrium for potential implantation
- feeds back onto hypothal/pit to control GnRH, FSH and LH
how does the reproductive hormone inhibin help the hormonal control of the female reproductive cycle? (2)
- protein hormones made by ovarian granulosa cells in response to high FSH/oestrogen
- feeds back to inhibit FSH release from pituitary
what are the phases of the ovarian cycle? (3)
- follicular phase up to day 14; development of graafian follicle and its oocyte
- ovulatory phase at day 14; release of secondary oocyte from follicle
- luteal phase after day 14 to day 28; formation of corpus luteum
what happens in the follicular phase over the first 14 days? (3)
- primary follicle growth
- secondary follicle growth
- graafian follicle stage
what happens in the primary follicle growth stage of (the follicular phase)?
- involves thickening of follicular epithelium (granulosa cells) round the primary oocyte by proliferation
what happens in the secondary follicle stage of (the follicular phase)? (3)
- theca cells round the follicles develop and secrete androgens which granulosa cells use to make oestrogen
- granulosa also secretes nutrient fluid into cavity (antrum)
- one follicle and its oocyte becomes dominant
what happens in the graafian follicle stage of (the follicular phase)? (2)
- early meiotic division to produce secondary oocyte completes just before ovulation at day 14
- the mature graafian follicle has large antrum with this secondary oocyte
what happens in the ovulatory phase at day 14? (3)
- mature graafian follicle bulges from the wall of ovary
- ovarian wall ruptures and expels the secondary oocyte into uterine tube
- wound healing of ovarian surface epithelium after rupture
what happens in the luteal phase after day 14 to day 28? (2)
- granulosa cells of empty graafian follicle proliferate forming the corpus luteum which secretes progesterone
- progesterone prepares uterus endometrium for implantation
what happens in the uterine (menstrual) cycle?
- cyclical changes also occur in the endometrium of the uterus over the 28 day cycle
- occur in response to the changing levels of ovarian reproductive hormones (oestrogen and progesterone) during the ovarian cycle
- comprised of three phases that correlate with the ovarian cycle - uterine changes ensure endometrium is most receptive to potential implantation of a fertilised ovum after ovulation
- the ovarian cycle thus not only promotes oogenesis but also helps prepare the endometrium for pregnancy
what are the phases of the urterine (menstrual) cycle? (3)
- menstrural phase (days 1 to 5)
- proliferative phase (days 6 to 14)
- secretory phase (days 15 to 28)
what happens in the menstrual phase of the uterine (menstrual) cycle?
- muscular layer of endometrium is detached from uterine wall and expelled
what happens in the proliferative phase of the uterine (menstrual) cycle? (3)
- endometrium proliferates and thickens
- synthesis of progesterone receptor (PR) in the endometrial cells
- ovulation occurs at the end of this phase at day 14
what happens in the secretory phase of the uterine (menstrual) cycle? (3)
- progesterone (from corpus luteum) stimulates endometrial lining via PR
- in absence of fertilisation endometrium progressively degenerates
- cycle starts again with day 1 of the next menstrual cycle
what is the luteal phase?
- after ovulation LH promotes transformation of the ruptured graafian follicle into the corpus luteum which contains luteal cells
what does LH stimulate the luteal cells to secrete?
- substantial progesterone and some oestrogen; progesterone maintains and stimulates the thickened endometrium in its secretory phase
what is oestrogen and progesterone secreted by?
- corpus luteum negatively feedback onto the anterior pituitary inhibiting FSH and LH production in order to prevent development of any new follicles
