Adrenal Flashcards
describe the anatomy of the adrenal medulla and cortex
what are 3 substances produced by the adrenal cortex
- glucocorticoids e.g. cortisol
- mineralocorticoids e.g. aldosterone
- androgens e.g. testosterone/dihydrotestosterone
what process does cortisol play a key role in
metabolism
how is the synthesis of cortisol regulated
ACTH
- cortisol exerts negative feedback on hypothalamis to reduce CRH & vasopressin and anterior pituitary to reduce ACTH
what is the pattern of cortisol production
diural
- highest at 8am
- lowest and midnight
in what state can cortisol be found
- mostly bound to cortisol binding globulin and albumin
- small proportion exists in free biologically active state
what do cortisol immunoassays measure
total cortisol both bound and free
- this means that conditions e.g. oestrogen therapy that increase CBG levels can increase measured cortisol levels without affecting biologically active free levels
give 4 places in which androgens might exert their effects
- sebaceous glands
- hair follicles
- prostate gland
- external genitalia
how is aldosterone regulated
RAAS
- in response to low circulating blood volume, hypoNa or hyperK, renin activated
- this catalyses the reaction of Ang I –> Ang II
- stimulates aldosterone release upon binding to angiotensin receptor
where does aldosterone mainly act and what is its effect
renal DCT
- Na retention and K loss
what type of tissue is the adrenal medulla made up of
SNS
what does the adrenal medulla secrete
- adrenaline
- noradrenaline
- dopamine
- metabolites e.g. metanephrines, nor-metanephrine, methoxytyramine
what is Addison’s disease
primary adrenal insufficiency due to autoimmune destruction of the adrenal glands or genetic defect in steroid synthesis
- all 3 zones of cortex usually affected
- reduced cortisol and aldosterone secretion
how might a patient w Addison’s disease present and why
largely non-specific symptoms e.g. fatigue, weakness, anorexia, weight loss
- mineralocorticoid deficiency: dizziness, postural hypotension
- glucorticoid deficiency: hypoglycaemia, increased pigmentation due to ACTH excess
- androgen deficiency: reduced libido and loss of axillary/pubic hair
how is Addison’s crisis treated
- A-E assessment
- IM or IV hydrocortisone 100mg followed by infusion or 6 hourly doses
- IV fluids
- correct hypoglycaemia
- monitor electrolytes and fluid balance
why do patients with Addison’s disease have hyperpigmentation
excessive ACTH stimulates melanocytes to produce melanin
- largely affects skin creases, scars, lips and buccal muscosa
what are key biochemical findings of Addison’s
hyponatremia
- also hyperkalaemia, hypoglycaemia, raised Cr/urea
- low early morning cortisol + raised ACTH
what is the key diagnostic investigation for Addison’s disease
short synacthen test
what are the findings of the short synacthen test in addison’s
- give dose of synacthen
- check blood cortisol before then 30 and 60 inutes after
- the synacthen will stimulate healthy adrenal glands to produce cortisol which should double in levels
- failure of this indicates primary adrenal insufficiency
how is adrenal insufficiency treated
lifelong glucocorticoid (hydrocortisone) and mineralocorticoid (fludrocortisone) to replace aldosterone
what advice should be given to patients with adrenal insufficiency
- double glucocorticoid dose at time of illness and continue until resolved
- steroid emergency card
- wear medical alert jewellery
- emergency contact detials for endocrine team
how does secondary adrenal insufficiency arise
inadequate ACTH and lack of stimulation of the adrenal glands –> low cortisol due to loss/damage of the pituitary gland
what are causes of secondary adrenal insufficency
- pituitary adenoma
- surgery
- RT
- sheehan’s
what is tertiary adrenal insuffiency
inadequate CRH release from hypothalamus
- usually as a result of long-term oral steroids > 3 weeks
give examples of disorders that affect the adrenal medulla
- phaeochromocytoma - adrenal medulla
- paraganglioma - extra adrenal chromaffin tissue
these are catecholamine-secreting tumours that occur in 0.1% of patients with HTN
in which genetic disorders can phaeochromocytoma be seen
- MEN II (multiple endocrine neoplasia)
- neuofibromatosis type 1
- von Hippel-Lindau disease
what is the pattern of symptoms in patients with phaeochromocytoma
adrenaline tends to be released in bursts causing intermittent symptoms
what are symptoms as a result of excessive adrenaline in phaeochromocytoma
- anxiety
- sweating
- headache
- tremor
- palps
- HTN
- tachycardia
what are 2 common initial tests used to diagnose phaeochromocytoma
- plasma free metanephrine
- 24hr urinary catecholamines
what radiological imaging is used to localise phaeochromocytoma
CT or MRI of abdomen
why is genetic testing advised in phaeochromocytoma
in pt presenting at a young age or in those with multifocal, malignnat or extra adrenal disease
- if a predisposing mutation is identified, annual screening should commence for new/recurrent disease
what is the definitive treatment of phaeochromocytoma
surgical excision
- lap or open
at diagnosis of phaeochromocytoma, what medication should all patients be commenced on
alpha +/- beta blockade
e.g. phenoxybenzamine or doxazosin
why is alpha blockade often done before beta blockade in phaeochromocytoma
to avoid unopposed a-adrenergic stimulation and risk of hypertensive crisis
why are b-blockers introduced in management of phaeochromocytoma
to control reflex tachycardia
what scan may be used to locate phaeochromocytoma tumours not seen on MRI
I-meta-Iodobenzylguanidine (MIBG)
- useful pre-operatively to exclude multiple tumours or mets
