Menstrual Cycle Flashcards
What mechanisms facilitate the movement of an ovum along the uterine tube?
Cilia (particularly in the ampulla)
Muscle-controlled movements of the fimbria (peristaltic pumping of smooth muscle)
How does the cervical mucus change during the menstrual cycle?
Prior to ovulation: slippery, cloudy to clear mucus (fertile mucus)
After ovulation: thicker, sticky, opaque mucus (plugs cervix, preventing entry of bacteria and sperm)
Pregnancy: thick cervical mucus plug forms, loss of which may indicate labour
How can you calculate when previous ovulation has occurred?
14 days previous to last menstruation
7 days before next menstruation is predicted (7 days before end of cycle)
Serum progesterone
What is the difference between primary and secondary amenorrhoea? Give some examples of causes for each.
PRIMARY = never menstruated
- Turner’s syndrome
SECONDARY = stopped menstruating (3 month cessation)
- pregnancy (hCG, high oestrogen & progesterone)
- menopause (low oestrogen & progesterone, high LH, very high FSH)
- fall in body weight (gonadotrophin levels)
Outline what happens in the follicular phase of the menstrual cycle?
Days 0-12
- ovum develops spontaneously
- reproductive layer prepared for sperm transport & implantation of conceptus (proliferation)
- maximises chance of conception
Rising levels of oestrogen
How does the endometrium change during the menstrual cycle?
PROLIFERATIVE PHASE:
- days 5-7 = rapid regrowth from remaining epithelial cells
- days 7-14 = endometrial regrowth is completed
- glands proliferating
- spiral arteries enlarge & become convoluted, extend from basal layer into the functional layer
SECRETORY PHASE:
- endometrial thickening
- enlargement of glandular cells (become saw-toothed)
- oedema
- proliferation of WBCs
- spiral arteries continue to grow & extend into the stratum functionalis
MENSTRUAL PHASE:
- arteries spasm & retract into deeper layers —> ischaemia of stratum functionalis causes it to be sloughed off
- stratum basalis left intact
What hormone provides evidence of ovulation?
Progesterone (serum)
Measure 7 days prior to predicted menstruation (day 21)
note: progesterone elevates basal temp. (+ circadian rhythm of body temp. will confuse the results if not taken at same time of day)
What is the normal length of the menstrual cycle?
21-35 days
Outline the ovulatory phase in the menstrual cycle.
Days 12-14
- release of resulting ovum
- ~36hrs of fertility (but sperm can enter prior to this phase and survive in the reproductive tract)
- first division of meiosis occurs
LH surge (once rising oestrogen reaches a critical threshold)
Outline the luteal phase of the menstrual cycle.
Days 14-28
- further gamete production suspended until pregnancy is confirmed (by secretion of hCG)
- conceptus too small to signal its presence (initially)
- corpus luteum formed spontaneously
- uterus secretes fluid for potential conceptus
Fall in LH to constant level
FSH low to constant level
Rise in progesterone and inhibin until the corpus luteum dies —> crossover point between progesterone & oestrogen triggers menstrual bleed
What are the stages in follicular development?
Primordial follicle (primary oocyte + granulosa cells)
Spontaneous development of zona pellucida
Formation of pre-antral follicle (internal & external theca formed)
Expansion of pre-antral follicle
FSH & LH stimulate 1 or 2 follicles to grow; theca secrete increasing levels of oestrogen (follicle with most developed theca takes control)
Pre-ovulatory follicle formed (capable of rupture to release ovum)
Oestrogen causes LH surge, which stimulates rupture of pre-ovulatory follicle
Outline the stages of the menstrual cycle.
- PREPARATION: (Days 0-12)
- ovum develops spontaneously (follicular phase)
- reproductive tract prepared for sperm transport and implantation of conceptus (proliferative phase)
- maximises chance of conception - OVULATION: (Days 12-14)
- release of resulting ovum
- ~36hrs of fertility (but sperm can survive in tract for ~5-7 days?)
- 1st division of meiosis occurs - WAITING: (Days 14-28)
- further gamete production suspended until pregnancy is confirmed by secretion of placental hormone
- conceptus too small to signal its presence initially
- luteal and secretory phases occur - MENSTRUATION: endometrium shed at end of unsuccessful cycle
note: ovulation -> menses is “always” 14 days but overall cycle length varies (due to variation in timing of ovulation, pelvic clock)
note: ovulation is spontaneous, therefore there is an optimum period of fertility, unlike other species
Outline the stages of follicular development.
PRIMORDIAL FOLLICLE (primary oocyte + granulosa cells) spontaneouslyw develops zona pellucida and an internal and external theca —> PRE-ANTRAL FOLLICLE
—> antrum develops in follicle
+ FSH & LH stimulates 1 or 2 follicles to grow to ~20mm and the theca to begin to secrete increasing amounts of oestrogen (one follicle takes precedence once it has developed a theca and increased inhibin)
—> PRE-OVULATORY FOLLICLE (majority made of antrum, capable of rupture to release ovum)
Presence of oestrogen increases LH secretion, which stimulates rupture of the pre-ovulation follicle
Outline the relationship between oogenesis and ovulation. What environmental factors affect ovulation?
PRIMARY OOCYTE
/ \
SECONDARY OOCYTE POLAR BODY
Fertilisation: / \ / \
MATURE OVUM POLAR BODY POLAR BODY POLAR BODY
note: asymmetric division
- stress delays ovulation —> longer menses
- occurs more often at night (circadian rhythm)
- when intercourse occurs during a certain window of time
Is the oocyte fertile by the time it has reached the uterus?
No - therefore fertilisation must occur prior to this (in the oviduct, in the 2nd meiotic division)
