Menstrual Cycle Flashcards
1
Q
State what is happening at the start of cycle
A
- 1st day of menstruation
- Endometrium loses trophic hormone support - loss of ovarian hormone support
- FSH levels stimulate early development of follicles
- Low steroid and inhibin levels
- Little inhibition at the hypothalamus or anterior pituitary
- FSH levels rising stimulates further follicle development
2
Q
What does FSH do to follicles
A
- FSH binds to granulosa cells
- Follicular development continues
- Theca interna appears
- Follicle now capable of oestrogen secretion from granulosa cells and theca cells
- Theca cells produce androgens which go to granulosa cells to produce oestrogen
- Oestrogen secretion upregulates FSH receptors on granulosa cells to further increase oestrogen levels - Inhibin secretion begins from granulosa cells
3
Q
Describe the mid-follicular phase
A
- Dominant follicle produced along with second polar body
- Prevent recruitment of further follicles
- Follicular oestrogen exerts positive feedback at the hypothalamus and anterior pituitary
- Gonadotrophin levels rise - especially LH
- Follicular inhibin rising - selective inhibition on FSH production
- FSH low to prevent development of other follicles
4
Q
What happens just before ovulation
A
- Circulating oestrogen and inhibin rise rapidly
- Oestrogen production no longer dependent on FSH
- Surge in LH production
- Progesterone production begins
- Granulosa cells become responsive to LH - express receptors for LH
- Modulation of GnRH pulsatile release
5
Q
What happens just after ovulation
A
- After ovulation, follicle is luteinised
- Secretes oestrogen and progesterone in large quantities
Inhibin continues to be produced - LH is now suppressed because of negative feedback from progesterone
- Oestrogen in presence of progesterone has negative feedback on LH
- Further gamete development suspended - waiting phase established
6
Q
Explain the luteal phase
A
- Corpus luteum - preprogramed life span of ~14 days
- Produces progesterone and oestrogen from androgens
- Produces inhibin
- Promotes production of progesterone
- Regressed spontaneously in the absence of a further rise in LH
7
Q
What happens if no fertilisation happens
A
- In the absence of further rise in LH, corpus luteum regressed
- Dramatic fall in gonadal hormones
- Relieving negative feedback
8
Q
What happens if there is fertilisation
A
- Syncytiotrophoblast produces human chorionic gonadotrophin
- hCG functions as LH and makes the embryo presence known
9
Q
What is the normal menstrual cycle duration
A
- Normal duration 21-35 days
- Variations in cycle duration due to variation in the length of follicular phase
- Luteal phase strictly controlled - 14±2 days
10
Q
What are the stages of ovarian cycle
A
- Follicular phase - FSH stimulates the development of the follicle
- After the LH surge, ovulation occurs where follicle ruptures ovary lining
- Luteal phase - corpus luteum
11
Q
Describe the stages of uterine cycle
A
- Lining of the uterus (endometrium) is responsive to hormones produced by the ovary
- Proliferative phase - responds to oestrogen by proliferating
- Oestrogen is a trophic hormone - cause cells to divide
Secretory phase - responds to oestrogen and progesterone by secreting
- Oestrogen is a trophic hormone - cause cells to divide
12
Q
Describe the structure of the uterine wall
A
- M = myometrium - muscular wall
- Thickens and changes contractility but does not shed
- E = endometrium - epithelial lining
- Functional layer (F) is hormone responsive and is shed if no pregnancy occurs
-
Grows/thickens in menstrual cycle- Secretory
- Basal layer (B) is stem cell layer which provides source from which a new functional layer is developed
- Functional layer (F) is hormone responsive and is shed if no pregnancy occurs
13
Q
Explain the changes to the uterine wall at the different stages of the uterine cycle
A
- Early proliferative - glands sparse, straight
- Late proliferative - functional layer has doubled, glands now coiled
- Early secretory - endometrium max thickness, very pronounced coiled glands
- Late secretory - glands adopt characteristic ‘saw tooth’ appearance
14
Q
What is the role of inhibin in the control of ovulation
A
- Inhibin reduces the release of FSH from the anterior pituitary
- Released by granulosa cell
15
Q
Outline the role of oestrogen in the control of ovulation
A
- Oestrogen has a negative and positive feedback loop to the hypothalamus and anterior pituitary
- At moderate levels of oestrogen (before ovulation), positive feedback initiated causing high LH and FSH
- Oestrogen in the presence of progesterone causes negative feedback and reduces LH
- Released by granulosa cell
