Structure and function of adrenal gland and pathophysiology of HAC

Question 1

Label the adrenal glands and associated structures

Answer 1

Question 2

Describe the synthesis of steroid hormones

Answer 2

Begins with cholesterol
Cholesterol converted into pregnenolone by P-450 side-chain cleavage enzyme
Pregnenolone converted into different corticoids according to zone of adrenal cortex

Question 3

Describe the control of glucocorticoid release

Answer 3

CRH from hypothalamus down axons to portal capillary bed
CRH causes corticotrophin cells in ant. pit to make and release ACTH
ACTH travels in circulation to adrenal glands to stimulate synthesis of glucocorticoids

Question 4

How is ACTH formed?

Answer 4

Synthesised from POMC (pro-opiomelanocortin)
POMC undergoes series of post translation modifications before it is cleaves into various polypeptides

Question 5

Describe the physiology of of glucocorticoids

Answer 5

Travel in blood bound to plasma proteins
Bind to specific cell membrane or cytosolic receptors at their target
Receptor-steroid complex is transported to nucleus => altered gene expression

Question 6

What are the actions of glucocorticoids?

Answer 6

‘Stress’ hormone:
- stimulates gluconeogenesis
- stimulates glycogenolysis
- Causes proteolysis
- Promotes lipolysis
- Cortisol in chronic stress - increase in blood glucose

Question 7

What is the action of glucocorticoids on fat?

Answer 7

mobilisation from peripheral stores

Question 8

What is the action of glucocorticoids in muscle?

Answer 8

catabolism

Question 9

What is the action of glucocorticoids in the liver?

Answer 9

gluconeogenesis
antagonise insuline

Question 10

What is the action of glucocorticoids on the kidney?

Answer 10

increased GFR
block ADH action

Question 11

What is action of glucocorticoids on the skin?

Answer 11

Follicular atrophy
Sebaceous gland atrophy
Break down collagen
=> thinner skin

Question 12

What is the action of glucocorticoids on bone?

Answer 12

Reduce calcium levels
Osteopaenia (Reduced bone density)

Question 13

What is the action of glucocorticoids on the brain?

Answer 13

hunger
thirst

Question 14

What is the action of glucocorticoids on the immune system

Answer 14

Release neutrophils from marginated pool
Down regulates immune responses

Question 15

Describe the control of mineralocorticoid release

Answer 15

Main stimulus for aldosterone release = low BP (RAAS)
High serum potassium stimulates release
ACTH has minor role

Question 16

What is the function of aldosterone

Answer 16

Regulation of BP
Acts on distal tubule and collecting duct to increase reabsorption of Na, Cl and water
Stimulates the secretion of K+ into tubular lumen

Question 17

What is the function of androgens

Answer 17

Stimulate or control the development and maintenance of male characteristics by binding to androgen receptors
Precursors for all oestrogens

Question 18

What is HAC?

Answer 18

Hyperadrenocorticism/Cushing’s Disease
Excessive production of steroid hormones, especially glucocorticoids, from the adrenal cortex

Question 19

What is hypoadrenocorticism?

Answer 19

Addison’s disease
under secretion of glucocorticoids and mineralocorticoids from the adrenal cortex

Question 20

What are the 2 forms of HAC?

Answer 20

Pituitary dependent (PDH):
- most common
- excess ACTH secretion => bilateral adrenal hyperplasia
Adrenal dependent (ADH):
- less common
- adenomas or carcinomas

Question 21

What are the 2 forms of PDH (pituitary dependent HAC)

Answer 21

Microadenomas:
- <10mm
- majority of cases
Macroadenomas:
- >10mm
- slow growing
- can produce neurological signs

Question 22

Describe ADH (adrenal dependent HAC)

Answer 22

Unilateral adrenal enlargement and atrophy of contralateral side as compensation
Independent of ACTH control
ACTH conc low or undetectable so normal gland atrophies as it is not stimulated

Question 23

Describe the signalment for PDH and ADH

Answer 23

ADH - more common in larger or older dogs
PDH - more common in middle-aged dogs, poodles, daschunds and small terriers
Females slightly more at risk of ADH
No sex predisposition for PDH

Question 24

What are the clinical signs of HAC?

Answer 24

PU/DP
Abdominal enlargement
Polyphagia
Skin changes
Hepatomegaly
Muscle wasting/weakness
Pot bells
Lethargy
Repro changes - decrease fertility

Question 25

Why does HAC cause abdominal enlargement/pot belly?

Answer 25

• re-distribution of fat into abdomen
• hepatic enlargement
• wasting and weakness of abdominal muscles

Question 26

Why does HAC cause muscle wasting

Answer 26

Caused by protein catabolism
Decreased muscle mass over limbs, spine and temporal region

Question 27

Describe skin changes involved in HAC

Answer 27

Bilaterally symmetrical alopecia:
- inhibitory effect of steroid on anagen phase
Thin skin and reduced elasticity with prominent abdominal veins:
- protein catabolism and loss of subcut fat
Excessive scale and comedones
Slow wound healing:
- inhibition of fibroblast proliferation and collagen synthesis
Firm, slightly elevated plaques surrounded by erythema
Secondary pyoderma

Question 28

Describe the treatment of HAC

Answer 28

Trilostane
Mitotane
Adrenalectomy
Hypophysectomy (pit gland removal)

Question 29

Describe feline HAC

Answer 29

Uncommon
Signalment: middle ages to older cats
Most often PDH

Question 30

Describe the clinical signs of feline HAC

Answer 30

PU/PD
polyphagia
weight loss
extreme skin fragility
pendulous abdomen
UTI’s

Question 31

What colour M&M did Leah eat at 10:55 on 20 April 2024

Answer 31

orange