1: Menstruation: Physiology of the menstrual cycle Flashcards
When does menarche start
11-15 years
When does menopause occur
45-55 years
Explain hormone secretion to control the menstrual cycle
GnRH is released from the hypothalamus and stimulates LH and FSH release from anterior pituitary gland.
LH - acts on theca cells
FSH - acts on granulosa cells
What is the role of LH
LH binds to theca cells and stimulates androgen production
What is the role of FSH
FSH binds to granulosa cells: increase conversion of androgens to oestrogen. Enables inhibin secretion
What is the role of oestrogen in negative feedback
Moderate oestrogen - negative feedback
High oestrogen - positive feedback
What is the role of inhibin
Inhibits FSH
What are the 3 phases of the ‘ovarian’ menstrual cycle
- Follicular Phase
- Ovulation
- Luteal Phase
Which part of the menstrual cycle varies
Follicular Phase - varies in length
Explain follicular phase
- Initially follicles can grow steroid independent
- As the follicles grow they produce more oestrogen and progesterone
- This causes negative inhibition of LH and FSH
- Only the follicle with most FSH receptors will survive and continue to grow (this is called the dominant follicle)
- The dominant follicle when growing will produce more oestrogen and inhibin. High levels of oestrogen causes a switch to positive feedback causing a LH surge
What day is ovulation normally
14d
Explain ovulation
- LH Surge causes release of oocyte from the follicle
- Oocyte is available for 24h to be fertilised
- Follicle releases oestrogen and progesterone which causes negative feedback on HPA axis preparing for fertilisation
How long is the luteal phase
14d
Explain the luteal phase
- The corpus luteum forms at the site of the ruptured follicle
- Corpus luteum releases oestrogen and progesterone
- This negatively feedback on HPA axis
- The corpus luteum has a lifespan of 14-days
- When the corpus luteum dies oestrogen and progesterone decreases re-setting the axis
Explain what happens if pregnant
- Syncytiotrophoblasts release bHCG which maintains the corpus luteum
- At 4m the placenta can produce enough steroids to maintain the HPG axis
What are the three phases of the ‘ovarian’ cycle
- Follicular
- Ovulation
- Proliferative
What are the two phases of the ‘uterine cycle’
- Proliferative
2. Secretory
Explain proliferative phase of uterine cycle
Oestrogen causes endometrial proliferation, opening fallopian tube, thinning and alkaline cervical mucus plug to aid sperm transport
Explain secretory phase
Progesterone causes glandular secretory endometrium. And produces a thick acidic cervical mucus plug = preventing sperm entering
What is the proliferative phase equivalent of the ovarian cycle
Follicular phase
What is the secretory phase equivalent of the ovarian cycle
Luteal phase
What is the menopause
End of women’s reproductive life
When does the menopause start
Perimenopause at 45-years
What is the average age of the menopause
51-years
