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