Reproduction Flashcards
menstrual cycle
- only in primates; estrous cycle in other animals
- refers to changes in the uterus as it prepares for pregnancy
- menstruate in each cycle that does not result in pregnancy (menstruation long after ovulation)
estrous cycle
- go into estrus (heat) in synchrony with ovulation
- use behaviors/signals (pheromones) to indicate they’re sexually receptive
- estrus lasts from a few hours to a few days
ovarian cycle
- development of primordial follicles into mature ova
- female mammals produce all the egg cells they will ever have prior to birth
- at birth about 5 million primordial follicles and only about 4-5 hundred develop into mature ova
- oogenesis in lower verts occurs throughout life
- meiotic events begin during embryogenesis and are then halted until puberty
gemtogenesis
- oogonium divide by mitosis to produce many oogonia
- become primary oocyte when they undergo first stage of meiosis (chromosomes replicate)
- remain primary oocytes until ovulated following puberty
- completes first meiotic division at ovulation (only completes second meotic division if fertilized)
signal for germinal vesicle breakdown
- occurs after vitellogenesis is complete
- signal for this is hormonal (hypothalamus and anterior pituitary, GnRH, FSH, and LLH for follicle development, estrogen production, and vitellogenesis, and progesterone production)
hypothalamus
secretes GnRH (gonadotrophic releasing hormone)-> affects ant pit-> secretes gonadotrophins (FSH and LH)-> affects gonads-> secrete sex steroids (estrogen and progesterone)
- these have feedback at ant pit and hypothalamus (mostly neg)
- LH and FSH regulated by GnRH and estrogen and progesterone
oogenesis in humans
- post-puberty when ovarian cycle begins
- humans- occurring periodically- cyclic
periodic ovulators
season (spring/summer)
- have period of heat/estrus
reflex ovulators
- ex: cats, rabbits
- require copulation for ovulation (but also have a cycle of estrus)
spontaneous ovulators
LH surge produced endogenously in female (independent of copulation) by a series of events throughout menstrual/estrus cycle
cycle of oogenesis regulated by
- GnRH (from hypothalamus)
- LH(ant pit hormone)
- FSH(ant pit hormone)
- estrogen (steroid)
- progesterone(steroid)
LH and FSH
controlled by ovarian hormones and small set of neuroendocrine cells in hypothalamus of brain that secrete GnRH
LH
ovulation of a mature ova is triggered by LH (GnRH causes release of LH)
FSH
causes growth phase of the follicle (GnRH causing release of FSH)
GnRH
causes release of LH and FSH
- released in pulses
- pulses of GnRH are carried by blood flow into hypothalamo-hypophysial portal system to ant pit gland-> stimulates secretion of LH and FSH
granulosa cells
- surround oocyte
- early in follicular phase, somatic cells enclosing primordial follicle become more cuboidal-> granulosa cells-> becomes primary follicle
thecal cells
- steroid producing cells
- connective tissue on outside of granulosa differentiates into this
primordial follicle
soon after female is born, each primary oocyte in her ovaries becomes enclosed by a single layer of somatic cells
follicular growth phase
- part of menstrual/estrus cycle when follicles mature
ovarian cycle
primordial follicle-> surrounded by granulosa cells-> differentiate into thecal cells
- then some periodically enter follicular growth phase_> inc granulosa cells, inc concentric layers around oocyte
- fully grown follicle cell with large oocyte, still arrested
how many follicles mature fully per estrus/menstrual cycle
- one dominant follcle matures fully in most menstrual/estrus cycles-> grows large through mitosis of granulosa and thecal cells-> when follicular phase ends with LH surge, the oocyte of the dom follicle completes the first meiotic division-> one daughter cell becomes secondary oocyte that will be fertilized if mating is successful
- Graafian Follicle
antrum cavity
filled with fluid, certain proteins, cAMP, hormones, etc.
GnRH->
FSH-> follicle growth (inc estrogen from cells around ova)
- inc estrogen-> initially pos feedback to inc FSH
- with higher estrogen= neg feedback to dec FSH but a pos feedback to inc LH
- inc LH-> pre-ovulatory surge of LH in response to high estrogen-> ovulation
estrogen
inc slowly in follicular phase, dramatic inc before ovulation
- estrogen causes pos feedback tof further FSH
- higher estrogen causes negative feedback and shut off of FSH and stimulation of LH
- estrogen also inc uterine mucosa to proliferate
- inc the blood vessels
- high estrogen- pre-ovulatory
during follicular phase…
LH and FSH levels remain flat until a few days before ovulation-> peak at ovulation-> LH acts on theca cells, FSH acts on granulosa cells-> lead to secretion of estrogen
pre-ovulatory surge of LH
- in response to high estrogen
- causes: ovulation, also inc progesterone production by corpora luteum (tissue left behind)
LH binding to theca cells
cells are stimulated to produce androgens-> diffuse to granulosa cells
binding of FSH to granulosa cells
stimulates aromatase which converts androgens to estrogen
- estrogen stimulates proliferation of granulosa cells-> pos feedback
increased progesterone
- causes germinal vesicle breakdown
- resumption of meiosis
0 high levels will have negative feedback on LH and FSH - as LH dec, so does progesterone
- dec in progesterone-> menstruation
- causes FSH to be released for a new cycle
menses
bleeding (day 0-5)
follicular phase
around day 5-15 (aka proliferative phase)
- endometrium undergoes rapid thickening and redevelops glands and circulatory vascularization
- proliferation and growth due to FSH release-> FSH causes estrogen to be produced (stimulates follicle cells to grow)
corpus luteum
essential to establishing conditions that permit implantation and pregnancy
- progesterone secreted in luteal phase prepares uterus for implantation, thickening of endometrium supports implantation and nourishment of embryo if fertilization occurs
luteal phase hormones
- day 15-29 (follows ovulation)
- LH surge-> ovary begins to produce progesterone from corpora luteum
- meiotic arrest is broken and germinal vesicle breakdown–> both are progesterone dependent
- leads to one large duaghter cell and one polar body- both still encased by zona pellicida
ovulation
- about 10-12 hours after LH surge
- physical mechanism to expel ovum
LH induces:
- inc collagenase, inc plasminogen activation, inc prostaglandin intensity (allows for smooth muscle contraction), can prevent ovulation by prohibiting prostaglandins (and hormones) at this stage
- LH causes oocyte to complete its first meiotic division, causes granulosa cells to secrete progesterone, dec estrogen
- initiates changes in granulosa cells and theca cells to form corpu luteum
luteal phase
- follows ovulation
- from remaining follicle tissue
- tissue fills with blood and becomes corpus luteum
- CL produces primarily progesterone (and some estrogen)
- CL maintained by LH
progesterone
- further stimulates uterine tissue growth and growth of additional blood vessels (progesterone at this point blocks implantation)
- inhibits FSH (and so prevents maturation of additional follicles at this time)
- lower progesterone has a positive feedback on LH (higher progesterone has a negative feedback on LH)
- neg feedback results in degeneration of CL-> turns into corpa albican (stops producing progesterone)
- progesterone is a good birth control pill because it prevents follicle maturation and pre-ovulatory LH surge
- dec in progesterone-> menstruation, ability of FSH to start inc (for growth of another follicle)
HCG
human chorionic gonadotropin hormone
- would maintain the CL following implantation
effects of estrogens
- affects ovulation by dec FSH and inc LH
- inc growth and development of follicles
- develops uterine mucosa (both in proliferative and secretory phase)
- stimulates uterine smooth muscle (at birthing)
- protein anabolic
- behavioral effects-> makes females receptive to mating at ovulation
- dec serum cholesterol
- estrogen stimulates endometrial cells to produce receptor molecule for progesterone
secretory phase
- endometrium matures to point that it is fully ready to accept implantation of an embryo and provide the embryo with nutritive support during early post implantation development
effects of progesterone
- inhibits contraction of uterus
- development of breasts
- prevents midcycle burst of LH (pill)
- maintains blood supply to myometrium
- inhibits FSH
- high progesterone during pregnancy, drops right before birth
