Ch 120 - Adrenal Glands (Anatomy and Physiology) Flashcards

1
Q

List then endocrine functions of the arenal cortex

A
  • Regulation of renal fluid and electrolyte balance (aldosterone)
  • Chronic stress adaptation
  • Carbohydrate metabolism
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2
Q

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

A
  • Arising from invasion of the cortical tissue with neural crest ectoderm
  • Produces cathcholamines epinephrine and norepinephrine
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3
Q

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

A
  • Zona glomerulosa - mineralocorticoids
  • Zona fasciculata - glucocorticoids and sex steroids
  • Zona reticularis - Sex steroids and some glucocorticoids
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4
Q

What are adrenal corticoids synthesised from?

A

Cholesterol

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5
Q

Describe the synthesis of adrenal corticoids

A
  • 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

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6
Q

What is the main plasma protein which binds cortisol?

A

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

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7
Q

What is the main plasma protein which bind to aldosterone?

A

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

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8
Q

What physiologic conditions can effect transcortin?

A
  • Pregnancy - increases synthesis
  • Liver dysfunction - decreased synthesis
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9
Q

What is the clearance halflife of cortisol and aldosterone?

A
  • Cortisol 60min
  • Aldosterone 20min
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10
Q

List the primary functions of glucocorticoids

A

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

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11
Q

List the main functions of the mineralocorticoids

A

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

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12
Q

Describe the RAAS

A
  • Renin is produced by juxtaglomerular apparatus of the kidney
  • Splits angiotensinogen into angiotensin I
  • Within pulmonary 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
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13
Q

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

A
  • Produced by the chromaffin cells of the adrenal medulla from tyrosine and to a lesser extent, phenylalanine
  • Tyrosine -> dopa -> dopamine -> norepinephrine -> epinephrine
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14
Q

List the receptors which catecholamines work on and their roles

A
  • 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

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15
Q

How does epinephrine affect metabolism?

A

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

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16
Q

How do norepinephrine and epinephrine effect the cardiovascular system?

A

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

Norepinephrine:
- Generalised vasoconstriction (alpha)

17
Q

What imaging characterisitics are suggestive of an adrenal mass?

A
  • Invasion of surrounding tissues
  • Additional mass lesions
  • Masses over 20mm are likely to be malignant (all benign lesions were under 20mm)
18
Q

What is defined as positive suppression on a LDDST?

A
  • 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

19
Q

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

A
  • LDDST
  • Urine creatinine:normetanephrine ration
  • Serum inhibin assay (dogs with adrenocorticism will have persistantly elevated inhibin, phaeo will have undectable levels)
20
Q

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

A
  • 76% functional
  • Aldosterone most common
21
Q

What is the prognosis for adrenalectomy in cats?

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