9. The adrenal glands Flashcards
Where are the adrenal glands located?
cap upper poles of kidneys and lie against diaphragm in retroperitoneal space
name the 2 regions of the adrenal glands
outer CORTEX
inner MEDULLA
which hormones does the adrenal cortex produce?
The deeper the sweeter:
- zona glomerulosa:
- mineralocorticoids (e.g. ALDOSTERONE)
- regulate body Na+ and K+ levels
- salt - zona fasiculata:
- glucocorticoids (e.g. CORTISOL)
- many important functions inc. regulation of carbohydrate metabolism
- sugar - zona reticularis:
- glucocorticoids and small amount of ANDROGENS
- sex
what happens to the androgens released by the AGs?
converted to testosterone and oestrogens by other tissues
which hormones does the adrenal medulla produce?
chromaffin cells synthesise ADRENALINE (80%) and NORADRENALINE (20%)
what are steroid hormones synthesised from?
cholesterol (in AGs and gonads)
name the 5 major types of steroid hormone
- glucocorticoids
- mineralocorticoids
- androgens
- oestrogen
- progesterone
what is the MOA of steroid hormones?
lipid soluble hormones that bind to receptors of the nuclear receptor family to modulate gene transcription
describe how glucocorticoids modulate gene transcription
i. diffuse across plasma membrane…
ii. bind to and activate glucocorticoid receptors by causing dissociation of chaperone proteins (e.g. heat shock protein 90)…
iii. receptor-ligand complex translocates to nucleus…
iv. dimerisation with other receptors can occur…
v. receptors bind to glucocorticoid response elements (GREs) or other transcription factors
What is the primary mineralocorticoid?
aldosterone
What is the primary glucocorticoid hormone?
cortisol
Which hormones does the zona reticularis secrete?
weak androgens: DHEA and androstenedione
How is adrenal release of androgens controled?
partially regulated by ACTH and CRH
What happens to DHEA in males?
converted to testosterone in testes (after puberty this is insignificant since testes release far more testosterone themselves)
What is the role of adrenal androgens in females?
converted to oestrogen by other tissues (only source after menopause). promotes libido.
promotes axillary and pubic hair growth in both sexes
What type of cells does the adrenal medulla consist of?
adrenal medulla = modified sympathetic ganglion of ANS
- chromaffin cells lack axons but act as post-ganglionic nerve fibres that release hormones into blood
which 2 hormones are released by the adrenal medulla?
ADRENALINE (80%)
NORADRENALINE (20%) - 20% chromaffin cells lack N-methyl transferase enzyme
Name 2 precursors of Ad and NA.
tyrosine and dopamine
Describe the receptor subtypes of Ad and NA.
act at adrenergic receptors = GPCRs
- alphaRs
- alpha1: increase in intracellular Ca2+ via coupling to Galpha q
- alpha2: decrease in intracellular cAMP via coupling to Galpha i
- betaRs
- beta1, 2 and 3: increase in intacellular cAMP via coupling to G alpha s
What are the main actions of adrenaline?
fight or flight
- cardiovascular system
- increase HR and contractility (B1)
- vasoconstriction to skin/gut (a1)
- vasodilation to skeletal muscle (B2)
- lungs
- bronchodilation (B2)
- carbohydrate metabolism
- increase glucagon and decrease insulin secretion from pancreas
- increase glycolysis and glycogenolysis in muscle
- increase glycogenolysis and gluconeogenesis in liver
- lipid metabolism
- increase lipolysis in adipose
- other
- increase mental alertness
- increased renin secretion in kidney
Describe how adrenaline increases HR.
activates B1 GPCR…GDP for GTP exchange at G protein… alpha s-GTP activates AC… conversion of ATP to cAMP… 4 cAMP activate PKA.
- direct activation by cAMP of HCN channels resposible for funny/pacemaker current
- PKA phosphorylation of HCN channels modulates function
- PKA phosphorylation of L-type Ca2+ channels - potentiates opening, increasing slope of upstroke of AP
Compare the 2 main types of hormones released by the adrenal glands: corticosteroids and catcholamines.
CORTICOSTEROIDS (cortisol, aldosterone, androgens)
1) synthesised in cortex
2) derived from cholesterol
3) endocrine
4) lipid soluble
5) nuclear Rs - regulate gene expression
6) slow resp (min-hrs)
CATECHOLAMINES (Ad and NA)
1) synthesised in medulla
2) derived from tyrosine
3) neurocrine
4) water soluble
5) GPCRs - regulate activity of existing enzymes
6) fast resp (secs)
