Session 4 Flashcards
Q. Annotate the menstrual cycle
- Explain the processes involved in and control of ovulation LO
- Explain the pattern of secretion of gonadotrophins and LO
- Explain the hypothalamic and pituitary mechanisms underlying gonadal steroids over the normal menstrual cycle cyclical gonadotrophin secretion LO and the interactions between the ovaries and hypothalamus/pituitary LO
• Explain the changes occurring in the ovary during the ovarian cycle LO
Give a brief explanation of the hisological changes
Decribe histology
Describe the histology
Describe the histology
Explain the hypothalamic and pituitary mechanisms underlying gonadal steroids over the normal menstrual cycle cyclical gonadotrophin secretion LO and the interactions between the ovaries and hypothalamus/pituitary LO
Draw the HPG axis in the female & male
Q. Describe the HPO Axis LO
A. • GnRH produced by the hypothalamus
• Acts on anterior pituitary to release gonadotrophins
– FSH
– LH
• Gonadotrophins act on ovary
– Promoting follicular development
– Production of ovarian hormones
• Steroid hormones
• inhibin
• Controlled by effects of gonadal hormones
– Negative and positive feedback control
Q. 1. How is GnRH released?
- Why is this important?
- Clinical significance?
A. 1. Pulsatile GnRH release
2. Intermittent GnRH receptor is an absolute requirement for fertility
If GnRH receptors are exposed to continuous presence of GnRH they become desensitised
FSH & LH production stops -> Gonadal steroid production stops.
3. Endometriosis -> Treatment with GnRH agonist to relieve symptoms
Sometimes want to switch axis of continuous supply of GnRH which desensitises the receptor
No production of LH and FSH
No positive feedback on the ovaries
No production of oestrogen and progesterone
Endometriosis is when plaques of endometrium grows – irritates peritoneum
As it is endromentrium will grown when there is oestrogen and progesterone
Oestrogen inhibited which inhibits oestrogen induced proliferation of the endometrium
Describe the phases of the menstrual cycle LO
Q. What is the menstrual cycle? (3)
A. • Preparation
– Of the gamete = Ovarian cycle
– Of the endometrium = Uterine cycle
• Ovulation
– Release of the gamete
• Waiting
– Pause, maintaining the endometrium until a signal is received to indicate that fertilisation has happened
Q. The ovarian & uterine cycle is split into what phases?
A. Ovarian: • Follicular • Luteal
Uterine: • Proliferative • Secretory
Q. • Menstruation occurs on a monthly cycle throughout reproductive life unless interrupted by a pregnancy
• Normal duration ? days
• Variations in cycle duration due to variation in the length of the ?
• ? phase strictly controlled ? days
A. 21 – 35
follicular phase
Luteal
14 +/- 2
Q. Factors affecting the menstrual cycle
A. • Physiological factors
– Pregnancy
– Lactation
• Emotional stress
• Low body weight
Q. What phases is the ovarian cycle split in?
A. Menses, proliferative and secretory phase
Q. Explain the levels of hormones at the start of the Ovarian cycle 0-4 days (6)
A. Start of cycle
• No ovarian hormone production -> • Low steroid and inhibin levels
• Early development of follicles begins
• Little inhibition at the hypothalamus / anterior pituitary
• Free from inhibition
• FSH levels rising
(First day of menstraution endometrium has lost its trophic support)
Q. What are the effects of FSH
A. • FSH binds to granulosa cells
• Follicular development continues
• Theca interna appears
• Follicle now capable of oestrogen secretion
• Inhibin secretion begins
(Granulosa cells and theca cells needed to make oestrogen)
Label this image?
Q. Adding subtle control – mid-follicular phase
We need to nominate a dominant follicle & prevent recruitment of any further follicles, how?
A. • Follicular oestrogen now at a conc when it can exert POSITIVE feedback at the hypothalamus & anterior pituitary
• Gonadotophin levels can rise
• Effect seen on LH only
• Follicular inhibin rising
– Selective inhibition on FSH production by anterior pituitary
Q. What changes happen to prepare for ovulation ( I.e. changes in conc)
A. • Circulating oestradiol & inhibin rise rapidly
• Oestradiol production no longer dependent on FSH (theca & granulosa cells?)
• Surge in LH production (positive feedback from oestrogen need surge in oestrogen to create an LH surge)
• Progesterone production begins
– Granulosa cells become responsive to LH
• Modulation of GnRH pulse generator
Q. What is causing the change in the response of GnRH by LH?
A. High [oestradiol] enhances sensitivity of anterior pituitary gondadotrophs to GnRH
Q. What happens in ovulation?
A. • Meiosis I completes & Meiosis II starts
• Mature oocyte extruded through the capsule of the ovary
Q. What are the Effects of LH (5)
A. • After ovulation, the follicle is luteinised -> corpus luteum
• Secretes oestrogen & progesterone in large quantities
• Inhibin continues to be produced (waiting phase prevents further gamete phase?)
• But LH is now also suppressed because of negative feedback due to the presence of progesterone (oestrogen + progesterone = negative feedback on LH or FSH or is it both??)
• Further gamete development suspended
– Waiting phase established
Q. Luteal phase
- The Corpus luteum produces?
- Why does it regress?
- How long does it take to regress?
A. 1. progesterone & oestrogens from androgens • Produces inhibin • Promotes production of progesterone
- Regresses spontaneously in the absence of a further rise in LH
- Stays alive for 14 days then will regress if no LH signal
Q. Uterine cycle
• The lining of the uterus, endometrium, is responsive to hormones produced by the ovary
• The endometrium is a specialised epithelium
• Responds to oestrogen by ?
• Responds to oestrogen and progesterone by ?
A. proliferating, secreting
Q. What two things can happen at the end of the cycle?
A. End of the cycle…..
• In the absence of a further rise in LH, corpus luteum regresses
• Dramatic fall in gonadal hormones
• Relieving negative feedback
• Resets to start again
or not
• If fertilisation has occurred
• Syncytiotrophoblast produces human chorionic gonadotrophin (hCG)
– i.e. made by the embryo to signal its presence
• Exerts a luteinising effect