The Menstrual Cycle Flashcards
What are the three stages of the menstrual cycle and what occurs in them in basic terms?
Preparation:
- of the gametes (ovarian cycle)
- of the endometrium (uterine cycle)
Ovulation:
Release of gamete
Waiting:
Pause, maintaining endometrium until a signal is received to indicate that fertilisation has happened
What is the importance of GnRH release being pulsatile? How can we use this information to treat a condition?
If GnRH receptors are exposed to continuous presence of GnRH they become desensitised -> FSH + LH production stops -> gonadal steroids stopped
✅endometriosis relieves symptoms rest with agonist for GnRH (stops mensuration)
What happens on days 0-4 of the menstrual cycle?
Day 0- FSH stimulates primary follicles to develop -> FSH increases binds granulosa cells -> theca interna to develop -> follicles can secrete oestrogen and Inhibin
What happens in days 6 -14 of the menstrual cycle?
Oestrogen (oestradiol) increases causes positive feedback on GnRH secretion and LH
Inhibin inhibits FSH secretion so prevent recruitment of more follicles (only dominant follicle gets released)
Around day 14 ovulation occurs, meiosis 2 starts to mature an oocyte and arrests in metaphase (until fertilisation occurs) -> extruded from the ovary by capsule rupturing into peritoneal cavity
What happens on days 14- 28 of the menstrual cycle?
The now leutinised follicle causes release of progesterone, Inhibin and oestrogen from the corpus luteum (temporary gland formed after ovulation)
Progesterone suppresses LH (-ve feedback)
Gamete pauses = waiting phase for 14 days
Day 21/22: Corpus luteum regresses spontaneously in the absence of further rise in LH
Day 25/26: FSH beings to rise due to lack on Inhibin -> cycle starts again day 28
What are the uterine changes from early to late proliferating and secretory?
Early:
Glands spare and straight -> response to oestrogen late: functional layer doubled, glands coiled
Early secretory: endometrium max thickness, v pronounced coiled glands -> response to progesterone late: glands adopt characteristic saw-tooth appearance
What happens if fertilisation occurs?
Syncytiotrophoblast produces human chorionic gonadotropin (LH analogue) -> luteinising effect to support corpus luteum and continue increased production of steroid hormones
(oestrogen causes proliferation of endometrium and progesterone causes growth of blood vessels and stimulates glands to produce nutrients)
Eventually placenta is capable of production of sufficient quantities of steroid hormones to control HPO axis throughout pregnancy
What are the two phases of the ovarian cycle and when do they occur?
Follicular phase 0-14
Ovulation= day 14
Luteal phase (corpus luteum present) 14-28
What are the stages of the endometrial cycle and when do they occur?
Menstrual phase 0-4
Proliferative phase (oestrogen)
Early 4-8
Advanced 8-14
Ovulation
Secretory phase (Progesterone) Early 14-16 Middle 16-25 Late (pre-menstrual) 25-28
What is the function of oestrogen in the follicular stage?
Fallopian tube function
Thickening of endometrium
Growth and motility of myometrium
Thin alkaline cervical mucus
Vaginal changes
Changes in skin, hair, metabolism
What is the function of progesterone in the luteal phase?
Further thickening of endometrium into secretory form
Thickening of myometrium but reduction of motility
Thick, acid cervical mucus
Changes in mammary tissue
Increased body temp
Metabolic changes
Electrolyte changes
What the normal duration of a menstrual cycle? Which phase determines the length?
21-35 days
Due to variation in the length of follicular phase
Luteal phase strictly controlled 14 +/- 2 days
