Physiology of Hyperadrenocorticism

Question 1

• What is hyperadrenocorticism characterised by?

Answer 1

Excessive production of steroid hormones from the adrenal cortex

Question 2

• What are the four main possible causes of HAC?

Answer 2

Tumour of the pars distalis, tumour of the pars intermedia, tumour of one (or both) adrenal gland, iatrogenic (drug induced)

Question 3

• What is the most common cause of HAC in dogs and horses?

Answer 3

Dogs – tumour of the pars distalis, horses – tumour of the pars intermedia

Question 4

• Where is CRH released from?

Answer 4

Paraventricular nuclei within the hypothalamus

Question 5

• What happens to the CRH on release?

Answer 5

Travels via hypothalamohypophyseal portal blood vessels to the pars distalis in the anterior pituitary

Question 6

• What cell type produces ACTH?

Answer 6

Corticotrophin cells

Question 7

• What is the alternative hormone that can also stimulate ACTH release from the pars distalis?

Answer 7

ADH (arginine vasopressin)

Question 8

• How else might ACTH be stimulated?

Answer 8

Neurones from the arcuate nucleus of the hypothalamus, release dopamine

Question 9

• What are the two main cell types of the pars intermedia?

Answer 9

A cells make αMSH, B cells make ACTH (both from POMC)

Question 10

• How do glucocorticoids initiate a response?

Answer 10

Bind to specific cell membrane or cytosolic receptors, receptor-steroid complex moves into nucleus, binds to glucocorticoid response elements, causing altered gene expression

Question 11

• What are glucocorticoids metabolised?

Answer 11

In the liver

Question 12

• What are some of the clinical signs of HAC?

Answer 12

Thinning of the skin, muscle weakness, pyoderma, liver enlargement, polyuria with dilute urine