HPG axis Flashcards
what does the HPG axis consist of?
hypothalamus, anterior pituitary, testes/ovaries
what does the hypothalamus regulate?
metabolism, growth reproduction, stress
what does the hypothalamus secrete?
gonadotrophic releasing hormone
what are the different groups of cells that make up the anterior pituitary?
thyrotropes, somatotropes, gonadotrophs, cortiotrpes, cactotropes
how does GnRH influence the gondatrophs?
causes proliferation and FSH and LH hormone production
3 main types of sex steroid hormones
progestagens,androgens, oestrogens
what precursor are all steroids derived from?
cholesterol
what hormones exert a depressant effect on gonadotrophin output?
oestrogens and progestogens, inhbins
what hormones positive regulate gonadotrophins?
activin and oestrodiol at high concentrations
what does oestrogen do at low levels?
negatively regulates LH expression
where do oestrogens and progestagens act?
on the hypothalamus or directly on the pituitary
what are the two types of cells present in developing follicles?
granulosa and thecal cells
what is absent in male HPG regulation?
positive feedback
what cells secrete androgens?
leydig
what cell types do males have in the developing follicles?
sertoli and leydig cells
how often is GnRH released?
once per hour
when do the pulses begin?
after puberty
how can alterations in the LH and FSH output be achieved?
increasing/decreasing amplitude or frequency of GnRH pulses. modulating the response of the gonadotrophs to the pulses
what is kisspeptin?
a 54aa neuropeptide
what does kisspeptin bind to?
GPR54 receptor in GnRH neurons.
what does binding of oestrgens to kisspeptin do?
negative feedback resulting decreased GnRH expression
how may leptin activate the HPG axis?
via kisspeptin, via intermediate neurons or a kisspeptin independent route
