Phyiology of hypoadrenocorticism

Question 1

What is the common name for hypoadrenocorticism?

Answer 1

Addisons

Question 2

Which regions of the adrenal gland are involved with addisons disease?

Answer 2

The zona glomerulosa and fasciulata

Question 3

What do the zona glomerulosa and zona fasciulata produce?

Answer 3

ZG=mineralocorticoids

ZF= glucocorticoids

Question 4

Describe the actions of glucocorticoids

Answer 4

• Stimulate gluconeogenesis
• Stimulates glycogenolysis
• Causes proteolysis
• Promotes lipolysis

Question 5

What is the main control of mineralocorticoid release?

Answer 5

• Low blood pressure-> triggers RAAS-> stimulates release of aldosterone.
• Aldosterone also released due to high serum potassium

Question 6

Briefly describe the RAAS

Answer 6

• Renin converts angiotensinogen to Angiotensin 1 (liver)
• Ang 1 to Ang 2 occurs due to ACE enzyme in the lungs
• Ang 2= potent vasoconstrictor-> increases BP
• Ang 2 also stimulates release of aldosterone

Question 7

How is decreased BP detected?

Answer 7

• Baroreceptors in the wall of the afferent arteriole (in kidney)
• Cells of macula densa in early DCT= stimulated by reduction in NaCl
• Cardiac and arterial baroreceptors

Question 8

What is the function of aldosterone?

Answer 8

• Regulation of BP
• Acts on distal tubule/ CD to increase reabsorption of Na, Cl and water
• Stimulates secretion of K+ into lumen
• Stimulates secretion of H+ in exchange for K+ in collecting tubules= regulates acid /base

Question 9

Describe iatrogenic hypoadrenocorticism

Answer 9

-Usually caused by the sudden removal of exogenous steroids. Long course of exogenous steroids cause adrenal atrophy. When suddenly removed animal can’t produce its own sufficiently.

Question 10

What is the signalment for hypoadrenocoricism?

Answer 10

-Usually 4-6 years old
-Mainly females
-Any breed but more common in:
Poodles, bearded collies, graat danes, WHWT
-Very rare in cats

Question 11

Hypoadrenocorticism causes a lack of aldosterone, what affects does this have?

Answer 11

• Loss of Na, Cl and water
• Retention of potassium and hydrogen
• Pre-renal renal failure

Question 12

Hypoadrenocorticism causes a deficiency in glucocorticoid what are the effects of this?

Answer 12

-Decreased stress tolerance, weakness, appetite loss, anaemia

Question 13

What are the two forms of addisons disease?

Answer 13

Chronic= present with a waxing. waning form
Acute= Addisonian crisis, has hypovolaemia and azotaemia

Question 14

Describe the signs of the acute form of hypoadrenocorticism

Answer 14

• May have recent history of V+D
• Signs of hypovolaemic shock
• Collapsed/ weak
• May have bradycardia (this is unusual with shock, it is caused by increased potassium= big clue to Addisonian crisis)

Question 15

What does the biochem profile for a dog with addisons look like?

Answer 15

• Hyperkalaemia
• Hyponatraemia
• Hypochloridaemia
• Na:k ratio low

Question 16

What will urinalysis show up on a dog with addisons?

Answer 16

-Low USG due to increased loss of water.

Question 17

What will show up on the ECG of an addisons dog?

Answer 17

• Bradycardia
• Decreased P waves
• All due to hyperkalaemia

Question 18

How is addisons diagnosed?

Answer 18

ACTH stimulation test

-The animal cannot produce cortisol and so it stays low

Question 19

How is addisons treated?

Answer 19

Mineralocorticoids =DOCP
Glucocorticoids given during acute crisis and times of stress
-Often start treatment with both, then gradually wean off the glucocorticoids whilst leaving them on the mineralocorticoids for maintenance