Endocrine disorders

Question 1

adrenal cortex

Answer 1

CRH from the hypothalamus acts on the anterior pituitary
ant pituitary secretes ACTH, which causes the adrenal glands to produce cortisol and androgens

cortisol is secreted as urinary free cortisol

Question 2

cushing’s disease

Answer 2

pituitary adenoma causing elevated ACTH, leading to high cortisol levels

Question 3

Cushing’s syndrome

Answer 3

chronic glucocorticoid excess and the loss of normal feedback mechanisms
chief cause is oral steroids

Question 4

ACTH dependent causes of cushings

Answer 4

1. bilateral adrenal hyperplasia from an ACTH-secreting pituitary adenoma
   low level dexamethasone test leads to no change in plasma cortisol, but a high level test may be enough to halves morning cortisol

*dexamethasone acts as cortisol, causing negative feedback on ACTH secretion in a healthy individual, and a subsequent drop in cortisol

2. Ectopic ACTH production
   especially small cell lung cancer and carcinoid tumours
   specific features: pigmentation, hypokalaemic metabolic alkalosis, weight loss, hyperglycaemia. even in high doses, dexamethasone fails to suppress cortisol levels. classical features of cushing’s usually absent

Question 5

hypokalaemic metabolic acidosis

Answer 5

increased cortisol increases mineralocorticoid activity
This produces a state of hyperaldosteronism
aldosterone increases H+ secretion in the collecting tubule - leading to metabolic alkalosis, reduces K+ in the blood and increases Na+ reabsorption in the kidneys

Question 6

RAS system

Answer 6

renin released from juxtaglomerular apparatus in the kidney in response to low BP or low blood volume and increased sympathetic tone
renin converts angiotensinogen into angiotensin 1
ACE released from the lungs converts angiotensin 1 to angiotensin 2
angiotensin causes vasoconstriction
it also causes release of aldosterone from the zona glomerulosa in the adrenal gland
this retains Na+ at the expense of K+ in order to increase water retention, and raise blood volume

glucose spills over into the urine when plasma concentration is greater than the renal threshold for reabsorption in the distal tubule

Question 7

Addison’s

Answer 7

primary adrenocortical insufficiency
destruction of the adrenal cortex leading to cortisol and aldosterone insufficiency
H+ increased in Addison’s
? decreased aldosterone, increasing H+ secretion in collecting tubule
usually low Na+ and high K+