2.1 hypothalamic-pituitary-gonadal axis: lecture Flashcards
what do the output of the hypothalamus-pituitary unit regulate the function of? (axis)
thyroid (hypothalamic-pituitary-thyroid) - HPT
adrenal (hypothalamic-pituitary-adrenal) - HPA
reproductive glands - HPG
what else does the output of the hypothalamus-pituitary unit regulate (non-axis)?
somatic growth
lactation
milk secretion
water metabolism
how is hypothalamic releasing hormones secreted? controlled by?
in pulse tied to internal biological clock
synchronised external signals e.g. light
where do hypothalamic releasing hormones act?
on specific membrane receptors
how do hypothalamic releasing hormones transduce signals?
via second messengers e.g. GPCR (Gs) - G alpha s
what does hypothalamic releasing hormone stimulate?
release of stored pituitary hormones
synthesis of pituitary hormones
how does hypothalamic releasing hormone affect target cells?
stimulate hyperplasia and hypertrophy of target cells
how is hypothalamic releasing hormone regulated?
regulates its own receptor
what does corticotropin releasing hormone (CRH)’s effect on pituitary?
stimulates ACTH secretion
what is thyrotropin releasing hormone (TRH)’s effect on pituitary?
stimulates TSH and prolactin secretion
what is growth hormone releasing hormone (GHRH)’s effect on pituitary?
stimulates GH secretion
what is somatostatin’s effect on pituitary?
inhibits GH (& other hormone) secretion
what is gonadotropin releasing hormone (GnRH)’s effect on pituitary?
stimulates LH and FSH secretion
what is prolactin releasing hormone (PRH)’s effect on pituitary?
stimulates PRL secretion
what is prolactin inhibiting hormone also known as?
dopamine
what is the effect of prolactin inhibiting hormone (PLH) on pituitary?
inhibits PRL secretion
where is the pituitary gland located?
immediately beneath the hypothalamus
in a depression of the base of the skull called the pituitary fossa (Turkish saddle / sella turcica)
sits at the base of brain and is roughly size and shape of a bean
what is the pituitary gland also known as?
hypophysis
what is the anterior pituitary gland also known as?
pars distalis
adenohypophysis
what is the posterior pituitary gland also known as?
pars nervosa
how is the anterior pituitary gland connected to the hypothalamus?
by the superior hypophyseal artery
what is the anterior pituitary gland?
an amalgam of hormone producing glandular cells
NOT nervous tissue
which hormones are produced by the anterior pituitary?
6 peptide hormones: prolactin growth hormone (GH) thyroid stimulating hormone (TSH) adrenocorticotropic hormone (ACTH) follicle stimulating hormone (FSH) leutinising hormone (LH)
which are the most significant hormones in reproduction from the anterior pituitary gland?
FSH
LH
prolactin
what does the HPG axis comprise of? (interactions)
the interaction between hypothalamus, pituitary gland and the gonads
what does the HPG axis work together to regulate?
development
reproduction
ageing and many other body processes
what does the HPG axis regulation rely upon?
a number of complex negative feedback loops, which when lost results in disease
describe the organs involved in the HPG axis
hypothalamus –> anterior pituitary –> gonads –> reproductive tract
what does a major share of the control of sexual functions in both male and female begin with?
secretion of gonadotropin-releasing hormone (GnRH) by the hypothalamus
what does GnRH do?
stimulate anterior pituitary gonadatrophs to secrete 2 gonadotropic hormones: LH + FSH
(little / no FSH, LH without GnRH)
5-10% anterior pituitary cells = gonadatrophs
what is GnRH?
10 amino acid peptide
how is GnRH released?
pulsatile
every 1-3 hours, lasting 5-25 mins
where does GnRH travel to?
anterior lobe of pituitary in hypophyseal portal systen
what is intensity of GnRH stimulus affected by?
frequency of release (how often)
intensity of release (how strong)
what does GnRH control?
synthesis and secretion of FSH and LH by gonadotroph cells in AP
what controls the gonadotroph synthesis (hypothalamus) and release (AP)?
under positive and negative feedback by gonadal steroids (act on repro tract) and gonadal peptides
how do gonadal hormones decrease gonadaotrophin release?
by decreasing GnRH release from hypothalamus and by affecting ability of GnRH to stimulate gonadotrophin secretion from anterior pituitary
how do gonadal hormones decrease gonadotrophin release?
by decreasing GnRH release from hypothalamus
and by affecting ability of GnRH to stimulate gonadotrophin secretion from AP
(neg feedback on hypothalamus and AP)
