Endocrine disorders

Question 1

What is the HPG axis?

Answer 1

If T4 and T3 levels decrease - so produce more TRH and less negative feedback

Question 2

What are the disorders of the HPG axis?

Answer 2

Hypothyroidism - low levels of T3/T4

• Primary = problem with the thyroid gland so there is high levels of TSH
• Secondary = not to do with thyroid gland - so there is low levels of TSH

Hyperthyroidism - high levels of T3/T4

• Primary = problem with the thyroid gland so there is low levels of TSH
• Secondary = not to do with thyroid gland - so there is potentially high TSH levels or normal range

Question 3

What is the structure of adrenocortical?

Answer 3

Question 4

What are the different disorders of adrenal hyperfunction?

Answer 4

Excess cortisol - Cushing’s syndrome (primary or secondary)

Excess aldosterone - Conn’s syndrome/primary hyperaldosteronism

Question 5

What is cushing’s syndrome?

Answer 5

Too much cortisol

Cause:

• where exogenous glucocorticoids activate cortisol receptors but at high dose it will shut down HPA
• Adrenal cortex will waste away with lack of ACTH stimulation and it could be several days before the adrenal may become responsive to ACTH again
• Due to ACTH-secreting pituitary adenoma
• Due to ectopic ACTH source

Question 6

What is Conn’s syndrome?

Answer 6

Overproduction of aldosterone

Aldosterone secretion if activated by RAAS and increased plasma K+

Question 7

What are the different disorders of adrenal insufficiency?

Answer 7

Hypercortisolism

Lack of aldosterone and cortisol (Addison’s)

Question 8

What is Addison’s disease?

Answer 8

Lack of aldosterone and cortisol

Primary

• Hypotension
• Plasma Na+ - low
• Plasma K+ - high
• High ACTH
• Elevated plasma renin

Progressive, can eventually lead to adrenal crisis

Hallmark = high ACTH, low cortisol

Question 9

How can you diagnose Addison’s?

Answer 9

Dynamic test can aid diagnosis - assesses the ability of adrenal to produce cortisol in response to ACTH= ACTH stimulation test

Short synacthen test

• Measure baseline cortisol (9am) and 30 min after 250 µg synacthen (synthetic ACTH) i.m.
• Adrenal insufficiency is excluded by an increase in cortisol of >200 nmol/L and/or a 30 min value >550

Long synacthen test

• Adrenal cortex ‘shuts down’ in absence of stimulation by ACTH – time needed to regain responsiveness
• 3-day stimulation with synacthen
• In secondary (but not primary) adrenal insufficiency cortisol increases by >200 nmol/L over baseline
• Long test not often necessary since ACTH assay can distinguish