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SGUL - Physiology 1 > Steroids of the Adrenal Cortex > Flashcards

Steroids of the Adrenal Cortex Flashcards

1
Q

Describe adrenal blood flow.

A

Flows from outer cortex to inner medulla.

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2
Q

Describe adrenal functional zonation of steroid synthesis.

A
  • Layer-specific enzymes
  • Steroid synthesis in one layer can inhibit different enzymes in subsequent layers.
  • Different hormones being made in each layer.
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3
Q

Describe mineralocorticoid function.

A

SODIUM RETENTION:
- active reabsorption of sodium (with the associated passive reabsorption of water)
- active secretion of potassium
VOLUME REGULATION (part of RAAS)

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4
Q

Describe the actions of aldosterone that aid in retaining water.

A
  • Increase expression of specific membrane transporters for Na+, K+ and Cl-.
  • Stimulates Na+/K+ ATPase
  • Strong Na+ gradient for Na+ enter through an ENaC where water will also follow.
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5
Q

Cortisol and aldosterone have a similar affinity for the aldosterone receptor.
Circulating concentrations of cortisol are much higher than aldosterone, so why doesn’t cortisol stimulate salt and water retention?

A
  • Cortisol rapidly metabolised to inactive cortisone in kidney
  • Requires an enzyme - 11 β-hydroxysteroid dehydrogenase type 2 - to be converted back to cortisol
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6
Q

Describe the glucocorticoid receptor. PART 1

A

Member of the nuclear receptor superfamily. It has a characteristic 3-domain structure:
- ligand-binding area
- DNA-binding (binds to HRE on genomic DNA)
- N-terminal transcription cofactor-binding

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7
Q

Describe the glucocorticoid receptor. PART 2

A
  • Receptors dimerise on ligand binding and translocate to the nucleus.
  • Only one gene for the glucocorticoid receptor
  • 2 different variants due to alternate splicing of the 9th exon, giving rise to two major isoforms of GR - α and β.
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8
Q

Describe the glucocorticoid receptor. PART 3

A
  • Response elements can be positive or negative.
  • Positive GREs result in transactivation, when GR enhances transcription of target gene.
  • Negative GREs result in transrepression, when the GR represses transcription
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9
Q

List the functions of glucocorticoids on glucose utilisation.

A

DECREASED GLUCOSE UTILISATION:
- proteolysis, gluconeogenesis, lipolysis

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10
Q

List the functions of glucocorticoids on the CVS.

A
  • Required for vascular integrity and maintenance of blood pressure
  • Hypocortisolism: inappropriate vasodilation, hypotension
  • Hypercortisolism: hypertension
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11
Q

List the pharmaceutical functions of glucocorticoids.

A
  • Highly profitable industry
  • SIDE EFFECTS: hyperglycaemia, insulin resistance
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12
Q

How are the anti-inflammatory effects of cortisol mediated?

A
  • Inhibit inflammatory response
  • Induces Annexin-1, which inhibits Phospholipase A2 (PLA2) and inhibits the induction of COX-2.
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13
Q

What are the different types of adrenal insufficiencies?

A
  • PRIMARY ADRENAL INSUFFICIENCY: Addison’s Disease
  • SECONDARY ADRENAL INSUFFICIENCY: Hypopituitarism and RAAS defect
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14
Q

What are the clinical features of Addison’s Disease?

A
  • Low circulating adrenal steroids but high ACTH
  • Hyponatremia
  • Hyperkalaemia
  • Hypotension, volume depletion (adrenal crisis).
  • Skin pigmentation
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15
Q

Describe the ACTH receptor.

A
  • Member of melanocortin group of receptors.
  • Different forms of melanocyte-stimulating hormones bind to melanocortin receptors.
  • ACTH can also bind to other melanocortin receptors.
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16
Q

Describe hypercortisolism

A

Cushing’s Syndrome - excess glucocorticoid.

17
Q

Describe the ACTH-dependent causes of hypercortisolism

A
  • Cushing’s Disease: due to an increased ACTH secretion (due to pituitary adenoma)
  • Ectopic ACTH-secreting tumour
18
Q

Describe the ACTH-independent causes of hypercortisolism.

A
  • Adrenal oedema or carcinoma
  • Iatrogenic causes - effect of GC therapy
19
Q

Describe the clinical features of hypercortisolism.

A
  • Hypertension
  • Hyperglycaemia
  • Muscle weakness
  • Depression
20
Q

How would you diagnose hypercortisolism?

A

Confirm the hypersecretion of cortisol:
- 24-hour urinary cortisol
- cortisol at nadir of secretion (around midnight)

Determine the cause:
- dexamethosome suppression test

21
Q

Summarise what the different results of the dexamethasone suppression test mean.

A
  • Low doses will suppress ACTH secretion via negative feedback
  • Low dose fails to suppress ACTH secretion with pituitary disease (Cushing’s)
  • Higher dose will suppress ACTH secretion in Cushing’s
  • No suppression with low or high doses suggests an ectopic source of ACTH (eg. a tumour)
22
Q

Why does Addisons cause hyperpigmentation?

A
  • Lack of negative feedback from cortisol leads to increased production of ACTH.
  • ACTH is derived from pro-opiomelanocortin (POMC), which is cleaved into ACTH and α-MSH, which regulates production of melanin in the skin.
  • Overproduction of α-MSH leads to hyperpigmentation
23
Q

When there is very low cortisol what two hormones are high?

A
  • ADH - plasma dilution so low Na+
  • ACTH
24
Q

What is the pathway for the production of cortisol?

A

→ Hypothalamus makes CRH
→ CRH stimulates anterior pituitary
→ Anterior pituitary makes ACTH
→ ACTH stimulates the adrenal cortex
→ Adrenal cortex makes cortisol

25
Q

What are prostaglandins and leukotrienes derived from?

A

Lipid-derived compounds

26
Q

What is the juxtaglomerular apparatus stimulated by?

A

→ Increased sympathetic activity
→ Decreased perfusion pressure
→ Decreased Na+ and Cl-

27
Q

What is the function of mineralocorticoid?

A

→ Na+ retention
→ Active Na+ reabsorption
→ Active secretion of K+

28
Q

What is the zona fasciculata pathway?

A

Progesterone
↓
17 OH progesterone
↓
Deoxycortisol
↓
Cortisol

29
Q

What is the pathway in the zona glomerulosa?

A

Cholesterol
↓
Pregnenolone
↓
Progesterone
↓
Deoxycorticosterone
↓
Corticosterone
↓
Aldosterone

30
Q

What do the adrenal cortex and medulla secrete?

A

→ Steroid hormones - CORTEX
→ Adrenaline - MEDULLA

31
Q

What does steroid hormone synthesis always start with?

A

Cholesterol

32
Q

What are the steroids of the adrenal cortex?

A
  • Glucocorticoids - cortisol
  • Mineralocorticoids - aldosterone
  • Androgens

SGUL - Physiology 1 (68 decks)

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