11 - Gonads 2 Flashcards
What is the main oestrogen in pregnancy?
Oestriol
What is the local positive feedback loop in the ovaries?
- FSH stimulates aromatase and increases conversion of androgens to 17β oestradiol
- Oestrogen leaves granulosa cell and binds to oestrogen receptors on same cell
- further stimulation of oestrogen production
- rising oestrogen levels have negative feedback on FSH
If fertilisation occurs, high levels of oestrogen and progesterone is needed. What molecule is produced to mimic LH and stimulate further oestrogen and progesterone production?
Human Chorionic Gonadotrophin
What are the features of testosterone?
- bound to androgen binding globulin (ABG) in seminiferous tubules
- in blood: 60% bound to sex hormone binding globulin, 38% bound to albumin and 2% free
- aromatised to 17β-oestradiol (aromatase)
- reduced to dihydrotestosterone (5α-reductase)
What is significant about dihydrotestosterone?
it’s a more potent androgen
What is testosterone used for?
- development of male genitalia
- foetal growth
- spermatogenesis
- protein and bone anabolism
- male sexual behaviour
- pubertal growth spurt
What is an oestrogen and its main form?
- any substance (natural or synthetic) which induces mitosis in the endometrium
- 17β-oestradiol
What is an oestrogen used for?
- stimulates mitosis
- stimulates womb thickening
- triggers LH surge (ovulation)
- positive and negative feedback on GnRH
- stimulates osteoblasts
- simulates metabolic actions
- stimulates behavioural effects
What is a progestogen and its main form?
- any substance (natural or synthetic) inducing secretory changes in the endometrium
- progesterone
What is a progestogen used for?
- stimulates secretory activity in endometrium and cervix
- increases basal body temperature
What is the hypothalamo-pituitary gonadal axis of the testes?
- leydig cells: stimulated by LH and reduced by testosterone (negative feedback to reduce LH and GnRH)
- sertoli cells: stimulated by FSH, limited by inhibin negative feedback (direct and indirect)
What are the phases of the menstrual cycle?
- early follicular phase
- early-mid follicular phase
- mid-follicular phase
- late follicular phase
- luteal phase
What are the 2 phases of the ovarian cycle?
- follicular phase
- luteal phase
What are the 2 phases of the endometrial cycle?
- proliferative phase
- secretory phase
What happens in the early follicular phase of the menstrual cycle?
- menstruation occurs
- follicles develop from FSH and LH stimulus
What happens in the early-mid follicular phase of the menstrual cycle?
- primary follicle produces more oestrogen as it gets larger
- oestrogen has negative feedback on FSH
- oestrogen has positive feedback on granulosa cells
What happens in the mid-follicular phase of the menstrual cycle?
- graafian follicle develops
- negative feedback from oestrogen and inhibin
- all follicles regress apart from graafian follicle
What happens in the late follicular phase of the menstrual cycle?
- high levels of E2 from graafian follicle causes positive feedback on GnRH/LH secretion
- LH surge triggers ovulation
What happens in the luteal phase of the menstrual cycle?
- progesterone prepares endometrium for implantation
- if no fertilisation then E2 and inhibin exert negative feedback on LH and FSH
- luteolysis and menstruation occur
- corpus luteum stimulated to produce oestrogen and progesterone
What is amenorrhoea?
the absence of menstrual cycle
What are the 2 types of amenorrhoea?
- primary: if women never had single period
- secondary: if woman has had periods which then stop
What is oligomenorrhoea?
infrequent cycles (less severe than ammenorrhoea)
What is infertility?
when a couple can’t get pregnant following 12 months of regular unprotected sex
What are the causes of infertility?
- pituitary failure
- prolactinoma (tumour on pituitary gland)
- testicular failure (mumps/klinefelter syndrome)
- ovarian failure (turner syndrome)
- polycystic ovarian syndrome (PCOS)
What are the 2 types of cells in an ovarian follicle and their features?
- thecal cell: outer layer, stimulated by LH, produce androgens
- granulosa cell: inner layer, stimulated by FSH, produces oestrogen and inhibin, converts androgens to oestradiol
What are the different follicles produced in the ovaries?
- pre-antral follicle (pre-pubescent)
- early antral follicle (when exposed to sufficient FSH)
- late antral follicle
- graafian follicle (leads to LH surge)
- ovulation and corpus luteum
What is the proliferative phase of the endometrial cycle and what is its main influence?
- days 6-14
- endometrium thickens
- glands enlarge and coil
- gain blood supply
- dominant oestrogen influence
What is the secretory phase of the endometrial cycle and what are its influences?
- days 15-28
- endometrium becomes secretory
- glycogen and mucopolysaccharides secreted
- mucosa engorged with blood
- dominant progesterone influence
- oestrogen influence
