Gonads 2 Flashcards
What two reactions can testosterone follow and what do they produce?
Testosterone —> Oestrogen (aromatisation: by the action of aromatase)
Testosterone —> Dihydrotestosterone (reduction)
Dihydrotestosterone is a more potent androgen that binds to the same androgen receptors as testosterone.
What is needed for male phenotypic appearance?
Dihydrotestosterone (DHT)
Transport of lipophilic (sex) hormones
Must be bound to carrier protein in the blood
How is testosterone found in the blood?
60% testosterone and DHT are linked to Sex hormone binding globulin (SHBG),
38% testosterone and DHT is bound to Albumin
2% remains “free”
How is testosterone found in seminiferous fluid and semen?
Bound to Androgen binding globulin (ABG)
What are the 2 principal actions of Androgens in a foetus?
Development of male internal and external genitalia Fetal growth (acting with other hormones)
What are the 5 principal actions of Androgens in an adult?
Needed for spermatogenesis
Growth and development of:
Male genitalia
Secondary sex characteristics e.g. facial hair
Protein and bone anabolism i.e. muscle / bone growth
Behavioural: Male sexual behaviour
Pubertal growth spurt (with GH)
Some ‘androgenic’ effects (of testosterone) in men are mediated by conversion to oestrogen: example
Testosterone affects male sexual behaviour in the brain by being converted to oestrogen in the brain
Oestrogens
Any substance (natural or synthetic) which induces mitosis in the endometrium (womb thickening)
Name 3 oestrogens
17 Beta-Oestradiol (main oestrogen in women)
Oestrone (precursor)
Oestriol (main oestrogen produced in pregnancy)
5 reproductive effects of oestrogens
ENDOMETRIUM: Stimulates proliferation (mitosis) i.e. womb thickening
MENSTURAL CYCLE: Triggers LH surge resulting in ovulation
Vagina / Cervix: secretions
Breasts: Stimulates growth of ductile system
Skin: Decreases sebaceous gland secretion
7 non-reproductive effects of oestrogens
Feedback regulation on GnRH (negative and positive)
Stimulates osteoblasts
Metabolic actions (e.g. on lipids)
Behavioural effects
Increases salt (and water) reabsorption
Increases plasma protein synthesis (hepatic effect)
Influences the release of other hormones (e.g. prolactin, thyrotrophin)
Progestogens
Any substance (natural or synthetic) inducing secretory changes in the endometrium (Allowing an embryo to implant)
Name 2 Progestogens
Progesterone
17 Alpha-hydroxyprogesterone
List 5 effects of Progestogens
Stimulates secretory activity in endometrium and cervix (to prepare for implantation of embryo)
Negative feedback regulation on hypothalamic GnRH
Increase in basal body temperature
Decreases renal NaCl re-absorption (competitive inhibition of aldosterone)
Stimulates growth of alveolar system in breast
What hypothalamic hormone stimulates FSH and LH release from the pituitary gland? How often are pulses of it released?
Gonadotrophin Releasing Hormone (GnRH)
Released in pulses~ every hour
Which cells in the testes have receptors for FSH and LH? How do they respond?
FSH: Sertoli Cells; support spermatogenesis and produce inhibin
LH: Leydig Cells; make testosterone (virilises men)
Describe the negative feedback from the testes to hypothalamo-pituitary axis.
Sertoli Cells: produce INHIBIN: negative feedback effect on hypothalamus and pituitary
Leydig Cells: produce TESTOSTERONE: negative feedback effect on hypothalamus and pituitary
What does sperm maturation require?
Testosterone
How do testosterone and inhibin cause negative feedback?
Decreases the AMPLITUDE of the GnRH pulses.
Describe the local positive feedback loop in the ovaries.
FSH stimulate aromatase and increases conversion of androgens to 17 beta oestradiol.
Oestrogen then leaves the granulosa cell and binds to oestrogen receptors on the SAME granulosa cell and further stimulates production of oestrogen.
What are the effects of LH and FSH on the ovaries?
Make ovaries release Oestradiol and Inhibin
Describe the early follicular phase
1st 5 days of cycle
5-10 eggs start to enlarge and grow
Compete with each other (Winner= Graafian follice)
Grow under influence of FSH
Follicles start producing 17 Beta-Oestradiol (+ a tiny bit of progesterone, which is converted to 17 Beta-Oestradriol)
As follicles are very small, relatively small amounts of
17 Beta-Oestradiol is produced
Describe the early-mid follicular phase
17 Beta-Oestradiol starts to increase due to increasing size of follicles (due to stimulation from LH and FSH)
One of the follicles gets bigger than the others
Bigger follicle produces more 17 Beta-Oestradiol
In this follicle you get a local (autocrine) positive feedback loop:
Rising plasma E2 stimulates granulosa cells around it to grow more
Able to make more E2
Describe the mid follicular phase
E2 levels pretty high
Starts to “starve off” supply of LH and FSH from pituitary
This kills off all of the other follicles
Most developing follicles will then undergo atresia and only one follicle remains, the Graffian follicle. What enables this follicle to survive the negative feedback on FSH?
Graffian follicle is no longer FSH-dependent and can survive with it’s own local production of oestrogen.
The other cells are FSH-dependent and so undergo atresia when the FSH is removed.
Describe the late follicular phase
Extremely high E2 from Graafian Follicle triggers positive feedback in hypothalamus and pituitary on GnRH / LH secretion i.e. LH surge / ovulation
Pituitary gets “Activated” = LH Surge
Causes follicle to break open and egg to move down fallopian tube to uterus
What is the difference between the 2 populations of GnRH neurones in the hypothalamus?
1 is negatively fedback (Normal levels)
1 is positively fedback (Under extremely high levels of E2)
Describe the luteal phase
Corpus luteum makes progesterone
Progesterone prepares the endometrium for implantation: converts lining to secretary lining
If fertilisation does not occur, what happens?
Oestradiol, Progesterone and Inhibin have negative feedback effect on FSH and LH leading to luteolysis and menstruation.
What is the difference between primary and secondary amenorrhoea?
Primary: never had a period
Secondary: used to have period but then they stopped
Define infertility.
Couple cannot get pregnant following 12 months of regular unprotected sex
Woman: inability to get pregnant
Man: inability to impregnate
Define amenorrhoea
Absence of menstrual cycles
Define Oligomenorrhoea
Infrequent cycles.
Less severe than amenorrhoea
List 5 causes of infertility
Pituitary failure: won’t make LH and FSH
Prolactinoma: Form of pituitary tumour, make prolactin, inhibits LH and FSH
Testicular failure e.g. mumps, Klinefelter syndrome (XXY)
Ovarian failure e.g. Turner syndrome (XO)
Polycystic ovarian syndrome (PCOS)
List 3 characteristics of Polycystic ovarian syndrome (PCOS)
Infrequent periods
Hyper-androgenaemia e.g. increased male pattern hair, acne
Polycystic ovaries (increased number of enlarging ovarian follicles)
