Ch 120: Adrenal Glands (Anatomy and Physiology)

Question 1

List then endocrine functions of the arenal cortex

Answer 1

• Regulation of renal fluid and electrolyte balance (aldosterone)
• Chronic stress adaptation
• Carbohydrate metabolism

Question 2

What doe the adrenal medulla arise from?
What does it produce?

Answer 2

• Arising from invasion of the cortical tissue with neural crest ectoderm
• Produces cathcholamines epinephrine and norepinephrine

Question 3

List the zones of the adrenal cortex and what each of them produces

Answer 3

• Zona glomerulosa - mineralocorticoids
• Zona fasciculata - glucocorticoids and sex steroids
• Zona reticularis - Sex steroids and some glucocorticoids

Question 4

What are adrenal corticoids synthesised from?

Answer 4

Cholesterol

Question 5

Describe the synthesis of adrenal corticoids

Answer 5

• Enzymatic cleavage of a carbon side-chain of cholesterol within mitochondria produces C-21 steroid pregnenolone
• In zona fasiculata and reticularis, pregnenolone is hydroxylated at C-17 to form glucocorticoids
• The zona flomerulosa lacks the 17alpha-hydroxylase enzyme, producing the mineralocorticoid aldosterone

Main difference between cortisol and aldosterone is last of hydroxyl group on C-17 of aldosterone

Question 6

What is the main plasma protein which binds cortisol?

Answer 6

Transcortin (75%)
- 15% bound to albumin
- 10% unbound

Question 7

What is the main plasma protein which bind to aldosterone?

Answer 7

Albumin (50%)
- Unbound 40%
- Transcortin 10%

Question 8

What physiologic consitions can effect transcortin?

Answer 8

• Pregnancy - increases synthesis
• Liver dysfunction - decreased synthesis

Question 9

What is the clearance halflife of cortisol and aldosterone?

Answer 9

• Cortisol 60min
• Aldosterone 20min

Question 10

List the primary functions of glucocorticoids

Answer 10

Regulation of metabolism
- Stimulates hepatic gluconeogenesis
- Inhibits glucose uptake
- Stim lipolysis
- Inhibits protein synthesis
- Enhances protein catabolism
- Increased GFR
- Inhibition of vasopressin
- Stim of gastric acid secretion
- Suppression of inflammatory response and immune sys

Control if by NFB of cortisol on hypothalamic corticotrophin releasing hormone, resulting in reduced corticotrophin secretion bu pituitary

Question 11

List the main functions of the mineralocorticoids

Answer 11

Electrolyte balance and blood pressure homeostasis
- RAAS
- Blood K concentrations

Question 12

Describe the RAAS

Answer 12

• Renin is produced by juxtaglomerular apparatus of the kidney
• Splits angiotensinogen into angiotensin I
• Within pulm capillary endothelium, ACE converts angiotensin I into angiotensin II
• Stimulates peripheral vasoconstriction and secretion of aldosterone
• Aldosterone promotes Na, Cl and water reabsorptions and K excretion

Question 13

Where are catecholamines produced and from what substances?
What is the basic biosynthetic pathway of catecholamines?

Answer 13

• Produced by the chromaffin cells of the adrenal medulla from tyrosine and to a lesser extent, phenylalanine
• Tyrosine -> dopa -> dopamine -> norepinephrine -> epinephrine

Question 14

List the receptors which catecholamines work on and their roles

Answer 14

• Alpha-1 and alpha-2
• Beta-1 and beta-2
• Alpha-1 and 2 - Control catecholamine release from presynaptic and postsynaptic synpathetic nerve endings
• Beta-1 - Primarily effects the heart
• Beta-2 - Affects intermediary metabolism and smooth muscle

Epinephrine is approx 10x more potent on Beta-2 receptors than norepinephrine and so is more important in controlling metabolism

Question 15

How does epinephrine effect metabolism?

Answer 15

Action on Beta-2 receptors:
- Promotes hepatic glycogenolysis and gluconeogenesis
- Stimulates glycogenolysis in skeletal muscle
- Inhibits insulin secretion (alpha-2)
- Atimulates pancreatic glucagon secretion
- Promotes lipolysis

Question 16

How do norepinephrine and epinephrine effect the cardiovascular system?

Answer 16

Epinephrine:
- Increases contractility and HR (Beta-1)
- Vasodilation (beta-2)

Norepinephrine:
- Generalised vasoconstriction (alpha)

Question 17

What imaging characterisitics are suggestive of an adrenal mass?

Answer 17

• Invasion of surrounding tissues
• Additional mass lesions
• Masses over 20mm are likely to be malignant (all benign lesions were under 20mm)

Question 18

What is defined as positive suppression on a LDDST?

Answer 18

• 4-hr post dexamethasone serum cortisol below 1.5mcg/dL
• 4-hr post dexamethasone serum cortisol less than 50% of baseline
• 8-hr post dexamethasone serum cortisol less than 50% baseline

Diagnostic for hyperadrenocorticism

Question 19

What diagnostic tests can be used to differentiate a cortisol-secreting tumour from a phaeochromocytoma?

Answer 19

• LDDST
• Urine creatinine:normetanephrine ration
• Serum inhibin assay (dogs with adrenocorticism will have persistantly elevated inhibin, phaeo will have undectable levels)

Question 20

What percentage of adrenal tumours in cats are functional?
What is the most common substance that they produce?

Answer 20

• 76% functional
• Aldosterone most common

Question 21

What is the prognosis for adrenalectomy in cats?

Answer 21

• 77% survive at least 2 weeks
• MST 50wk