Disorders of Adrenal Cortex Flashcards
what are the two parts of the adrenal gland?
cortex and medulla
what are the three layers of the adrenal cortex?
zona glomerulosa - aldosterone
zone fasiculata - cortisol
zona reticularis - testosterone
what does the medulla release?
adrenaline and noradrenaline
what do glucocorticoids respond to?
stress
how do glucocorticoids increase plasma glucose levels?
- increase gluconeogenesis
- decrease GLUT 4 expression so less glucose utilisation
- increase glycogenesis
- increase glycogen storage
what is the effect of cortisol on lipolysis?
increases so provides energy
effect of cortisol on protein catabolism?
increases in muscle which releases amino acids that can be made available to the liver for use in gluconeogenesis
other effects of cortisol?
- Na+/H20 retention to maintain BP
- anti-inflammatory effect
- increased gastric acid production to prevent infection
what is cushings syndrome?
clinical features of chronic exposure to excessive cortisol levels
incidence of cushings syndrome
2 in 1 million, higher in females. onset of 20-40 years of age
signs and symptoms of cushings syndrome?
changes in body shape, central obesity, moon face, buffalo hump, thin skin, diabetes and osteoporosis.
changes in sex hormones, excessive hair growth, irregular periods, problems conceiving. salt and water retention so high BP and fluid retention
how is cushings disease tested?
- screening via urinary test for free cortisol
- test urine at midnight when cortisol should be lowest but also doa 24 hour test
how many stages in confirming Cushing’s disease?
three (screening, confirmation, differentiation of the cause)
how is the cushings diagnosis confirmed?
overnight dexamethasone suppression test
how is the cushings cause differentiated?
find out if exogenous or if its from ectopic source
what does it mean if cortisol is on circadian rhythm pattern?
24-25 hour cycle so is lowest at night.
what is the normal axis in the negative feedback loop?
cortisol decreases both CRH release from the hypothalamus and ACTH from the anterior pituitary
what is dexamethasone?
drug version of cortisol
how does the dexamethasone test work?
given to normal and healthy person as dexamethasone should inhibit release of CRH and ACTH. ACTH should fall as should cortisol
what is the overnight low dose dexamethasone suppression test?
- cortisol measured at 8am
- 1mg of dexamethasone given at 11pm, person sleeps and then cortisol measured next morning at 8am
- if cortisol suppressed to less than 50nmol/L = normal
- if cortisol is still detectable = cushings
what are the three causes of cortisol levels being high after the low dost dexamethasone test?
1 - patient has Cushings, would be pituitary adenoma releasing high levels of ACTH resulting in high cortisol
2 - patient has adrenal tumour secreting cortisol, could be a benign tumour or a malignant one
3 - patient has an ectopic source of ACTH production meaning tumour is somewhere outside the normal glandular tissue secreting ACTH
what is the high dose dexamethasone test?
- 2 mg of dexamethasone every 6 hours for 48 hours
- if cortisol suppresses to less than 50% of the baseline patient has Cushings disease
why does this result determine if patient has cushings?
shows that -ve feedback loop is in tact and working at greater baseline level so with high dose it should turn down ACTH production but if cortisol still high, patient must have ectopic ACTH production or adrenal tumour
how do we distinguish between ectopic ACTH production and adrenal tumour?
- adrenal tumour secretes high levels of cortisol completely unregulated by ACTH
- high levels of cortisol = decreased CRH and ACTH release into blood
- so in adrenal tumour, ACTH will be low
adrenal tumour
ACTH low
ectopic tumour
ACTH high
what are some laboratory features of someone with cushings?
- hypokalaemia (low K+)
- metabolic alkalosis
- hyperglycemia (caused by effects of cortisol on increasing gluconeogenesis)
why does someone with cushings have hypokalaemia and metabolic alkalosis
at high levels, cortisol can bind to mineralcorticoid receptor in the kidneys. usually enzyme 11-beta hydroxysteroid dehydrogenase converts cortisol to inactive cortisone so cant do this. at high level, enzyme gets overwhelmed and cortisol will bind and the effects of aldosterone will increase
what will aldosterone cause?
increases transcription so there is increased Na+ absorption from the tubule into tubular cells so actively pumps out into the blood via Na+/K+/ATPase pump
how will aldosterone affect?
lots of ATPase pump activity due to aldoestrone so lots of K+ removal from blood and H+ removal leading to alkalosis.
what is ACTH derived from?
POMC
What is a CRH test
test for Cushings. Small dose of CRH given and blood is assayed for ACTH and cortisol at intervals over 2 hours
what would exaggerated response in CRH test mean?
suggests pituitary cushings disease
what would flat response in CRH test mean?
ectopic ACTH production as ectopic source is producing high ACTH at a set level that isn’t being up-regulated by CRH or down regulated by anything. So its levels wont increase by giving CRH