Hypothalamus - pituitary - adrenal axis

Question 1

Where is the adrenal gland located?

Answer 1

On top of the kidneys.

Question 2

Which area of the adrenal gland is cortisol released fro,?

Answer 2

Zona fasiculata.

Question 3

Describe cortisol’s negative feedback mechanism.

Answer 3

Acts on hypothalamus and ant pituitary to reduce production of CRH and ACTH respectively.

Question 4

What are the functions of mineralocorticoids? E.g. aldosterone.

Answer 4

Increasing blood pressure by increasing reabsorption of reabsorption.

Question 5

What are the functions of glucocorticoids? E.g. cortisol.

Answer 5

Increases gluconeogenesis and drives stress and immune response.
Can also increase reabsorption of sodium.
However it causes poor wound healing and inhibition of bone growth.

Question 6

Define Addison’s disease. What is the world-wide leading cause?

Answer 6

• Adrenal insufficiency.
• Lack of cortisol cortisol.
• Typically present with low blood pressure.
• If due to destruction of adrenal glands, then no mineralocorticoids either.
• Tuberculosis.

Question 7

What blood results would you expect in someone with Addison’s?

Answer 7

• Cortisol low, sodium low and potassium high.

Question 8

What causes hyper-pigmentation in Addison’s?

Answer 8

• ACTH is synthesised by cleaving a precursor complex called pro-opiomelanocortin (POMC).
• In Addisons, the feedback loop will stimulate production of CRH and ACTH.
• A metabolite of the synthesis of ACTH from POMC is melanocyte stimulating hormone (MSH) which causes hyperpigmentation.

Question 9

Why would you give a dose of synthetic ACTH to a patient if they present with low cortisol levels?

Answer 9

Measure patient’s response.
In primary adrenal failure (Addisons) by giving ACTH synthetically, if there is still low cortisol then it is clear they have Addisons.
If it was secondary adrenal failure, giving ACTH will cause cortisol levels to rise as there is a failure in the pituitary/hypothalamus (secondary), not the adrenal glands.

Question 10

How would you manage a patient in acute Addisonian crisis?

Answer 10

Give them hydrocortisone IV.

Question 11

Define Cushing’s syndrome.

Answer 11

This is caused by excess cortisol.

Question 12

Define Cushing’s disease

Answer 12

One specific cause.

Where a tumour of the pituitary causes excess ACTH production, which drives hypercortisolism.

Question 13

Characteristics features of Cushing’s

Answer 13

• moon face.
• thin skin that is easily bruised.
• centripetal obesity.
• lemon on sticks appearance.

Question 14

How do you determine the underlying cause of Cushing’s syndrome?

Answer 14

• need to exclude exogenous cause.
• dexamethasone suppression test.
• measure levels of ACTH in the blood.
• CRH test.