The adrenal gland (13) Flashcards
What is the blood supply to the adrenal glands?
right adrenal gland has many arteries (57) but only 1 vein (right adrenal vein)- all hormones come out here
right adrenal vein drains into IVC, but left adrenal vein drains into renal vein
inferior vena cava and abdomina aorta supply
What is the microanatomy of the adrenal glands?
adrenal medulla and adrenal cortex: zona reticularis, zona fasciculata, zona glomerulosa, capsule
Where are the different adrenal hormones secreted?
- adrenal medulla–> secretes catecholamines: adrenaline (80%), noradrenaline (20%)
- adrenal cortex–> secretes corticosteroids: aldosterone (z.g.), cortisol (z.f. +z.r.), androgens, oestrogens
What is a steroid?
any molecule that comes from cholesterol e.g. cortisol
What are the steps/enzymes that differ between aldosterone and cortisol synthesis?
both start with cholesterol–> pregnenolone–> progesterone
21 hydroxylase–> 11-deoxycorticosterone, 11 hydroxylase–> corticosterone, 18 hydroxylase–> ALDOSTERONE
17 hydroxylase–> 17-OH progesterone, 21 hydroxylase–> 11-deoxycortisol, 11 hydroxylase–> CORTISOL
What is the mechanism of action of aldosterone?
very important role in BLOOD PRESSURE control
if BP falls, aldosterone turns on synthesis of proteins that pump sodium from urine into cell then back into blood using ATP
- stimulates Na+ reabsorption in distal convoluted tubule + collecting duct–> therefore inc. water reabsorption–> raising blood volume and so BP
- also stimulates K+ and H+ secretion in kidney
How is aldosterone secretion regulated?
decreased BP passing through renal system–> more renin made by juxtaglomerular apparatus–> renin exits kidney- enzyme that converts angiotensinogen to angiotensin 1- converted to angiotensin 2 by ACE–> stimulates vasoconstriction and directly stimulates adrenal gland (z.g.) to make aldosterone (via enzyme rxns)
What are the physiological effects of cortisol?
- normal stress response
- metabolic effects: hepatic gluconeogenesis, peripheral protein catabolism, inc. blood glucose conc., fat metabolism (lipolysis in adipose tissue)
- weak mineralocorticoid effects
- renal and cardiovascular effects: excretion of water load, inc. vascular permeability
How is cortisol secretion regulated?
HPA axis
hypothalamus secretes CRH
- ->promotes pituitary to secrete ACTH
- -> stimulates adrenal to produce cortisol
cortisol feeds back negatively to pituitary AND hypothalamus
How can we describe the pattern of cortisol production throughout the day/night?
diurnal rhythm
circadian rhythm
e.g. increase starts at 5am
peak at 8.32 am
What is Addison’s disease?
primary adrenal failure
- autoimmune disease where immune system destroys adrenal cortex
- can be caused by TB
- high levels of ACTH–> also high levels of MSH (bc share large precursor protein POMC)–> look tanned
- increased pigmentation
- no cortisol or aldosterone, so low blood pressure
- autoimmune vitiligo
- lose salt, so eventual death
How can we urgently treat Addison’s?
- rehydrate with normal saline
- give dextrose to prevent hypoglycaemia
- give hydrocortisone or another glucocorticoid
What is Cushing’s syndrome?
excess cortisol
put on weight
- can be caused by a tumour of adrenal (excess cortisol) or pituitary (excess ACTH)
- can be caused by taking steroids by mouth
- ectopic ACTH (wrong place)
- high dose of synthetic glucocorticoid
What are the clinical signs of Cushing’s syndrome?
- thin skin
- proximal myopathy- weak muscles (hard to climb stairs)
- centripetal obesity
- diabetes, hypertension and osteoporosis
- immunosuppression (reactivation of TB)
- moon face
- striae (stretch marks)
What is the role of catecholamines?
fight or flight response
e.g. tachycardia, sweating, inc. blood glucose, alertness, vasoconstriction
NA+ A circulate bound to albumin…
broken down by monoamine oxidases + catechol-O-methyl transferase in liver
