Menstrual Cycle Flashcards
when does the follicular phase occur?
- length can vary
~days 1-14
when does ovulation occur?
day 14
when does the luteal phase occur?
always 14 days before menses
what hormones cause ovulation?
oestrogen-induced LH surge
what hormone causes the luteal phase?
progesterone
what uterine phase(s) occur days 1-14?
- menstrual
- proliferative
what uterine phase(s) occur days 15-28?
secretory
what does FSH bind to?
granulosa cells
what are the actions of FSH?
- stimulates follicle growth
- allows conversion of androgens (from theca cells) → oestrogens
- stimulates inhibin secretion
what does LH bind to?
theca cells
what is the action of LH?
stimulates production & secretion of androgens
what is the difference in GnRH secretion before and after the onset of puberty?
before - released at steady rate
after - released in pulses
what effects does oestrogen have on the HPG axis?
moderate levels - negative feedback
high levels - (in absence of progesterone) positive feedback
in presence of progesterone - negative feedback
what effect does inhibin have on the HPG axis?
inhibits FSH
what are the phases of the ovarian cycle?
- follicular
- ovulation
- luteal
what is a follicle?
primary oocyte surrounded by granulosa and theca cells (stromal cells)
summarise the follicular phase
Follicles begin to mature and prepare to release an oocyte
what controls the maturation of the follicles?
- LH
- FSH
what happens in days 1-10 of the follicular phase?
- Theca cells develop receptors and bind LH
- > Secrete androgen
- Granulosa cells develop receptors and bind FSH
- > Secrete aromatase - converts androgen → oestrogen
what happens in days 10-14 of the follicular phase?1
- follicles grow and oestrogen released in bloodstream
- increased oestrogen acts as negative feedback signal to HPG axis
- less FSH -> some follicles die
- follicle with most FSH receptors continues to grow
- high oestrogen acts as positive feedback signal to HPG axis
- high levels of FSH & LH 1-2 days before ovulation
what happens in ovulation?
- LH surge
- Follicle ruptures
- Mature oocyte assisted to fallopian tube by fimbria
how long does the mature oocyte remain viable in the fallopian tube?
~24 hours
summarise the luteal phase
Remnant of the ovarian follicle becomes the corpus luteum
what is the corpus luteum?
Leutinised theca & granulosa cells
what happens in the luteal phase?
- leutinised theca & granulosa cells continue to secrete androgen/produce oestrogen
- low LH -> granulosa cells produce more progesterone than oestrogen
- Progesterone acts as negative feedback signal on HPG axis
- Leutinised granulosa cells begin secreting inhibin
- Oestrogen levels decline ⇒ progesterone is the dominant hormone
what is the effect of high levels of progesterone and low levels of oestrogen?
- signal ovulation has occurred
- helps to make endometrium receptive to implantation of fertilised gamete
what are the phases of the uterine cycle?
- menstrual
- proliferative
- secretory
when does the menstrual phase occur?
days 1~5
what is menses?
beginning of a new menstrual cycle
summarise the proliferative phase
Changes in endometrium optimise chance of fertilisation
what happens in the proliferative phase?
high oestrogen levels
→ thickening of endometrium
→ growth of endometrial glands
→ emergence of spiral arteries (to feed functional endometrium)
→ change the consistency of the cervical mucus (more hospitable to incoming sperm)
what stimulates the proliferative phase?
high oestrogen levels
when is the highest chance of fertilisation?
days 11-15
when does the secretory phase occur?
days 15-28
what happens on day 15 of the secretory phase?
high progesterone levels
→ spiral arteries coil and grow longer
→ uterine glands secrete more mucus
what happens after day 15 of the secretory phase?
- cervical mucus thickens (less hospitable for sperm)
- corpus luteum -> corpus albicans (levels of progesterone and oestrogen decrease)
lowest progesterone levels
→ spiral arteries collapse
→ functional endometrial layer prepares to shed through menstruation
