4) The Menstrual Cycle Flashcards
What cycle prepares the gamete?
Ovarian
What cycle prepares the endometrium?
Uterine
Why is the waiting phase required?
Maintaining the endometrium until a signal form conceptus is received. Conceptus needs to have many cells to produce a signal (14 days)
What is the effect of gonadotropins on the ovary?
Promote follicular development and cause production of ovarian hormones
What is the effect of gonadal steroids in the menstrual cycle?
Affect tissues of the reproductive tract and control the cycle through positive and negative feedback
What occurs in the early stages on the menstrual cycle?
LH and FSH can rise as no inhibition
Follicular development so follicle can secret oestrogen and inhibin
What causes the LH surge?
Follicular oestrogen now at concentration where it can exert positive feedback causing rise in LH
Why doesn’t FSH rise as much in the LH surge?
Follicular inhibin also rising
What effect does high oestrogen have on anterior pituitary itself?
Enhances sensitivity of gonadotropes to GnRH so more LH release
What promotes secretion of gonadal steroids from the corpus luteum?
Granulosa cells become responsive to LH
What effect does inhibin have on the gonadal steroids?
Promotes production of progesterone
Why does the corpus luteum regress and what does this lead to?
No further rise in LH
Oestrogen and progesterone production fall, no negative feedback and menstrual bleeding
What prevents corpus luteum regression?
Synctiotrophoblast of embryo produces human chorionic gonadotropin, which exerts a luteinising effect and prevent CL regression
What are the stages of the uterine cycle?
Menses, proliferative and secretory
What are the stage of the ovarian cycle?
Follicular and luteal
What happens to basal body temperature during the menstrual cycle?
Increases after ovulation and until menstruation
When does the corpus luteum stop producing progesterone, if fertilisation occurs?
Until placenta is capable of producing sufficient quantities of progesterone
What effect does oestrogen have on cervical mucus and why?
Thin, alkaline to conduct sperm
What effect does oestrogen have on the endometrium and myometrium?
Thickening of endometrium
Growth and motility of myometrium
What other effects does oestrogen have in the follicular phase?
(not on endometrium, myometrium or cervical mucus)
Fallopian tube function
Vaginal changes
Change in skin, hair and metabolism
What effect does progesterone have on cervical mucus and why?
Thick, acidic so no sperm can get through
What effect does progesterone have on the endometrium and myometrium?
Further thickening of endometrium into secretory form
Thickening of myometrium but less motility
What other effects does progesterone have in the luteal phase?
(not on endometrium, myometrium or cervical mucus)
Changes in mammary tissue
Increased body temp
Metabolic and electrolyte changes
What is the length of the menstrual cycle and what allows variation?
21-35 days, variable follicular phase length
What factors can affect the menstrual cycle?
Pregnancy and lactation
Emotional stress
Low body weight
