Hormones Flashcards
(24 cards)
What hormones are released from the posterior pituitary gland?
Oxytocin and ADH
What is the function of the posterior pituitary?
Storage (hormones produced in neurone bodies)
Function of the anterior pituitary
Production of protein hormones
Which hormones are released from the anterior pituitary gland?
Growth hormone, thyroid stimulating hormone, follicle stimulating hormone, luteinising hormone and adrenocorticotropic hormone
Where is gnrh secreted from?
Hypothalamus
What frequency is gnrh secreted?
In pulses
What are four examples of glycoproteins?
FSH, LH, TSH, hCG
Describe glycoproteins
Two non-covalently bonded sub chains - alpha and beta. Alpha is same, beta is different forming ab dimer. hCG and LH show greatest beta chain similarity.
How does GNRH frequency affect secretion of LH and FSH?
Rapid pulses favour LH secretion and slower pulses favour FSH secretion
What are inhibin and activin?
Produced by ovary, testes, pituitary gland and placenta, involved with regulation of gonadotrope production
How do gonadal steroids affect FSH and LH, and are there any exceptions?
All three (oestrogen, progesterone, androgens) exert negative feedback of FSH and LH secretion via receptors in the gonadotropin-secreting cells of the pituitary. Only exception is when oestrogen exerts positive feedback to produce a LH surge midcycle. It requires a sustained elevation (>48hrs) of circulating oestradiol
Describe gonadotropin (protein hormone) mechanism of action
And example
Distinct receptors in gonads
Interaction causes conformational change which activates G protein-coupled signalling system by replacing G subunit with a GTP molecules
G subunit then activates adenyl(ate) cyclase –> increased cAMP –> intracellular protein kinase A pathway –> modulates functions of number of cells by protein phosphorylation.
E.g. in gonads, responsible for for gonadal steriodogenesis and gametogenesis.
What are G proteins and what do they do
Subset of regulatory GTP binding proteins, which activate adenyl cyclase and increase cAMP production.
What is desensitisation and it’s two stages
Binding of a gonadotropin initiates regulatory function. reducing cell’s responsiveness to ongoing stimulation.
- gonadotropin receptor becomes uncoupled so it no longer activating adenyl cyclase
- increased degradation rate of receptors called ‘down-regulation’
Where can FSH and LH receptors be found in gonads?
Sertoli and granulosa = FSH and LH
Leydig and theca = LH
How does cholesterol enter cells?
Carried in the blood in LDLs and are removed using specific cell surface receptors for proteins called apoproteins
Steroid hormone production in OVARIES
Theca cells produce androgens in response to LH (by increasing LDL receptors); diffuse into granulosa cells where converted into oestrogen.
Aromatase converts into oestrogen under influence of FSH.
Steroid hormone production in TESTES
Androgen in Leydig under influence of LH –> either enter bloodstream or diffuse into Sertoli cells. Sertoli converts into oestrogen by aromatase
Steroid hormone production in ADRENALS
Important only during pregnancy (placenta can’t use cholesterol) and after menopause.
Classes of steroid hormone
Sex steroids (androgens, progesterones, oestrogens), glucocorticoids (‘sugar’) and mineralcorticoids (‘salt’)
What do steroid hormones do
Induction of new protein synthesis in target cells
Steroid hormone mechanism of action
Diffuse into cell with specific intracellular receptor.
Conformational change, forming dimer which can enter nucleus and bind to region of DNA called hormone response element.
This activates the hormone-receptor complex, causing increased gene transcription.
All receptors form a superfamily of nuclear receptors.
How is gene expression regulated with steroid hormones
- Promoters
- Steroid-responsiveness enhancers (hormone response elements)
- Silencers
- Hormone-independent enhancers
Tamoxifen - agonist vs antagonist
Acts as an antagonist in breast tissue, agonist in uterus and bone.
Is an antioestrogen drug
