Physiology: Adrenal Glands Flashcards
Primarily steroids in circulation are bound to what protein?
Corticosteroid-binding protein (CBP)
And/or other plasma proteins (albumin)
3 cellular layers of the adrenal cortex?
glomerulosa
fasiculata
reticularis
glomerulosa creates what steroids? what do they do?
mineralcorticoids (aldosterone)
promotes salt and water retention by the kidney
fasiculata makes what steroids? what do they do?
glucocorticoids (cortisol)
increase plasma glucose levels
reticularis makes what steroids?
androgens/ sex steroids
The adrenal medulla makes what steroids?
catecholamines (Epinephrine, Norepinephrine)
chromaffin cells?
produce epinephrine or adrenaline (catecholamine)
Amino acid needed to synthesize epinephrine?
tyrosine
definiceny in cortisol can lead to?
hypoglycemia
3 major classes of steroid hormones?
glucocorticoids
mineralcorticoids
sex steroids
how does cortisol increase plasma glucose?
enhances mobilization of amino acids from proteins in many tissues and to enhance the ability of the liver to convert these amino acids into glucose and glycogen by activating gluconeogenesis
Other actions of glucocorticoids
potent immunosupressive and anti-inflammatory activity, effects on protein and fat metabolism, behavioral effects on the CNS, and important effects on calcium and bone metabolism
Excess glucocorticoid secretion
Cushing syndrome
glucocorticoid deficiency
Addison disease
glucocorticoid excess is commonly seen because of?
individuals receiving treatment for a chronic inflammatory or neoplastic disorder
less common glucocorticoid excess?
cortisol producing adrenal tumor, secondary to a pituitary tumor
Symptoms of overproduction of glucocorticoid? aka?
truncal adiposity, hypertenstion, loss of subcutaneous adipose and CT in the extremities associated easy brusing, loss of bone mineral, muscle weakness and wasting and hyperglycemia
Cushing Syndrome
If pituitary gland is responsible for cushing syndrome it’s called?
Cushing disease
Common cause of glucocorticoid deficiency?
autoimmune adrenal disease
Etiology of glucocorticoid deficiency?
increase ACTH and other products of POMC
Cause hyperpigmentation of skin?
alpha MSH and gama MSH
lack of glucocorticoid predisposes patient to?
hypoglycemia
combined glucocorticoid and mineralcorticoid leads to?
hypotension
Aldosterone deficiency leads to?
hyperkalemia
2 sources of cholesterol for steroid hormone synthesis?
- LDL receptor-mediated endocytosis
2. synthesize cholesterol de novo from acetate
Which pathway for cholesterol to synthesize hormone is more important?
LDL cholesterol circulating
Except for 3B-HSD all enzymes are found where for steroid synthesis?
mitochondria or smooth endoplasmic reticulum
Adrenal adnrogens?
dehyroepiandrosterone and androstenedione
21alpha Hydroxylase deficiency?
inadequate production of glucocorticoid and mineralcorticoid
hypotension, dehydration, hypoglycemia
excess ACTH
Excess ACTH will cause? (21alpha Hydroxylase deficiency?)
enhanced growth of adrenal gland
excessive production of androgens
females- ambiguous genitalia at birth
effect of glucocorticoid use on the body?
Moon facies- increase in supraclvaicular and dorsal interscapular fat, rounding of the face
wasting of fat in extremities produces thining of skin and fragility of cutaneous blood vessels
osteopenia, osteoporosis
glucose intolerant
CRH?
corticotropin-releasing hormone
travels via hypophyseal portal venous plexus to the anterior pituitary
CRH receptor
G protein coupled receprot on corticotroph cells
Galphas- adenylyl cyclase,cAMP, protein kinase A, increase Ca2+
arginine vasopressin
role in cortisol production under stress
ACTH
secreted by corticotroph cells of the anterior pituitary
melanocortin (as well as a, b, gamma MSH)
ACTH receptor
ACTH binds to MC2R in the fasculata cells of the adrenal cortex
Only source of CYP11b2
glomerulosa layer of cortex
Neg feedback for ACTH?
glucocorticoids neg regulate corticotrophs (release ACTH) and hypothalamus (release CRH)
stAR?
steroidogenic acute regulatory protein
mediates the transfer of cholesterol into the mitochondria for steroidogenesis
cortisol at the pituitary?
decrease synthesis of CRH receptor
decrease synthesis of ACTH
cortisol at the hypothalamus?
decrease synthesis and release of CRH
Glucorticoid receptors?
intracellular, nuclear receptors
heat shock proteins, influence gene transcription
Inhibited by ANP?
stAR
stop cholesterol from making steroids
Congential adrenal hyperplasia
hyposecretion of glucocorticoids
defect/ deletion in genes encoding stAR or steroidogenic enzymes
defects include
CYP21A1, CYP11B1, CYP17, stAR
Overall effect of glucocorticoids?
increase appetite increase fetal maturation through synthesis of surfactant in the lung omental adipose exrpession of GR decrease osteoblast function increase renal Ca expression decrease intestinal Ca uptake decrease Ca absorption increase secretion into aqueous humor decrease GnRH release decrease TSH, deiodinase conversion of T4 to T3
Most common defect with congenital adrenal hyperplasia?
CYP21A2
defect of CYP21A2 causes?
build up of precursors and a shunting to make androgens
Defect of CYP11B1?
not as common, reduce final conversions
again shunt to androgens
defect of CYP17?
very rare, no glucocorticoids and androgens
still make mineralcorticoids
defect of stAR?
no steroids made
Primary cause of hyposecretion of glucocorticoids?
adrenal disease, addison’s disease
Addison’s disease?
autoimmune
infectious (TB)
congenital adrenal hyperplasia
Can adrenal disease also affect mineralcorticoids and androgen production?
yes (congential adrenal hyperplasia for ex)
hirsuitism?
abnormal hair growth in women
Simulate mineralcorticoid release?
Angiotensin II
extracellular K
ACTH
angiotensin II?
AT1 receptor, Gq, activation of calmodulin kinases, increase of CYP11B2
extracellular k?
depolarize plasma membrane, open Ca channels, activate calmodulin kinases, increase CYP11B2
renin-angiotensin-aldosteone and potassium-aldosterone negative feedback loops?
Decreased Na activates the acis, angiotensin II promotes renal retention of Na
decrease renal perfusion, aldosterone increases the expression of Na channel in apical membrane of cells in the the distal tubule of the kidneyand also a NA/K ATPase in the BM (promote Na reabsorption)
Aldosterone increases membrane permeabilty to K in the kidney tubule, facilitating the secretion of K into the tubule lumen
Aldosterone elicits effects via
mineralcorticoid receptor (type 1 GR) conservation of sodium, secretion of potassium, increased water retention, and increased blood pressure.
11bHSD on mineralcorticoids?
limits cortisol in kidney thereby reserving activation of type 1 GR for mineralcorticoids aka aldosterone
why aldosterone works in kidney vs cortisol
Role of mineralcorticoids?
salt and water retention maintain K blood pressure elicit effects via mineralcorticoids receptor (type 1 GR) excess aldosterone leads to hypertension
Adrenal Androgens?
stimulated by ACTH
important contributor of circulating androgens in women, not in men (testes)
reticularis layer
Catecholamines?
chromaffin cells in the adrenal medulla
Epi primary product, NE secondary
stored bound to granular proteins, chromogranins
rate limit step in catecholamine production?
tyrosine hydroxylase
catecholamines?
epi, ne, dopamine, L-DOPA
Stim release of Epi?
preganglionic sympathetic axons terminate on chromaffin cells
Catecholamine regulation: ACTH?
increase tyrosine hydroxylase, N-methyltransferase
Catecholamine regulation: Cortisol?
increase N-methyltransferase
Catecholamine regulation: Sympathetic stimulation?
increase tyrosine hydroxylase
chronic: increase N-methyltransferase
Catecholamine regulation: Chromogranins?
vasostatin- vasoinhibitory effects on bv
catestatin- inhibit nicotinic actylcholine receptor, limit catecholamine secretion, suppressive on cardiomyocytes
used to eval tumors, hypertension, organ failure
receptors for catecholamines: alpha 1?
Gq
vasconstriction, gluconeogenesis, glycogenolysis
receptors for catecholamines: alpha 2?
Gi
vasoconstriction, decrease sympathetic outflow, simulate vagal outflow, decrease insulin secreation
receptors for catecholamines: beta 1?
Gs
increase hear rate, myocardial contractilility, lipolysis, increase renin secretion
receptors for catecholamines: beta 2?
Gs
vasodilate, bronchial relax, GI relax, stim renin secretion, gluyconenolysis, gluconeogeneis
receptors for catecholamines: beta 3?
Gs
lipolysis