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Systems: Endocrine AB > Adrenal Gland > Flashcards

Adrenal Gland Flashcards

1
Q

Where are the adrenal glands situated?

A

Adrenal glands are situated on the superior pole of the kidney in the retroperitoneal space

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2
Q

How much do the adrenal glands weigh?

A

~4g each

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3
Q

How does the anatomy of the left and right adrenal glands differ?

A

Left adrenal vein drains into left renal vein, while R adrenal drains directly into the inferior vena cava. Implications for surgery.

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4
Q

What are the 2 endocrine glands that make up the adrenals?

A
  • Adrenal medulla

- Adrenal cortex

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5
Q

What is the adrenal medulla?

A

A modified sympathetic ganglion derived from neural crest tissue.

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6
Q

What does the adrenal medulla secrete?

A

Secretes catecholamines, mainly epinephrine (adrenaline), also norepinephrine and dopamine

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7
Q

What is the adrenal cortex?

A

A true endocrine gland derived from mesoderm

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8
Q

What does the adrenal cortex secrete?

A
  • Mineralocorticoids e.g. aldosterone: involved in the regulation of Na+ and K+
  • Glucocorticoids e.g. cortisol: involved in maintaining plasma glucose
  • Sex steroids e.g. testosterone
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9
Q

What 2 hormones are essential for life?

A
  • Cortisol

- Aldosterone

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10
Q

Describe the structure of the adrenal glands.

A

Cortex surrounds the medulla and is arranged in 3 concentric zones:

  • Zona glomerulosa
  • Zona fasciculate
  • Zona reticularis
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11
Q

What does the zona glomerulosa secrete?

A

Aldosterone

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12
Q

What does the zona fasciculate secrete?

A

Glucocorticoids

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13
Q

What does the zona reticularis secrete?

A

Sex hormones

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14
Q

How are different products produced in the different adrenal zones?

A

All steroid hormones are derived from cholesterol, but different enzymes are found in different adrenal zones, resulting in different end products

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15
Q

What are the main products of the adrenal cortex?

A
  • Cortisol

- Aldosterone

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16
Q

What is the prehormone of testosterone and oestrogen?

A

DHEA

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17
Q

What happens to DHEA with age?

A

Marked decline

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18
Q

What is a common cause of congenital adrenal hyperplasia?

A

Defects in 21-hydroxylase

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19
Q

What does congenital adrenal hyperplasia result in?

A

Deficiency of aldosterone and cortisol and associated disruption of salt and glucose balance.

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20
Q

Why is there excessive adrenal androgen production in congenital adrenal hyperplasia?

A

Androgen biosynthesis is unaffected so accumulating steroid precursors are channelled into excessive adrenal androgen production

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21
Q

What effect does an increase in cortisol have on CRH?

A

Negative feedback effect> decrease

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22
Q

Why does a deficit in 21-hydroxylase cause adrenal hyperplasia?

A
  • Lack of 21-hydroxylase inhibits synthesis of cortisol.
  • This removes the negative feedback on ACTH and CRH release.
  • Increased ACTH secretion is responsible for enlargement of adrenal glands.
  • Negative feedback of ACTH on CRH synthesis remains.
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23
Q

What type of hormone is cortisol?

A

Glucocorticoid hormone

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24
Q

What do glucocorticoid hormones influence?

A

Glucose metabolism

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25
Q

What do ALL nucleated cells have?

A

Cytoplasmic glucocorticoid receptors

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26
Q

What is ~95% of cortisol bound to?

A

A carrier protein, cortisol binding globulin (CBG)

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27
Q

Briefly describe how cortisol binding to its receptor leads to translation

A

The hormone receptor complex migrates to the nucleus, binding to DNA via a hormone-response element to alter gene expression, transcription and translation

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28
Q

Describe the characteristic pattern shown by plasma levels of cortisol.

A

There is a marked circadian rhythm, preceded by a similar pattern of release of ACTH. Cortisol “burst” persists longer than ACTH burst because half-life is much longer.

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29
Q

When do cortisol plasma levels peak?

A

~6-9am

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30
Q

When is the nadir of cortisol plasma levels?

A

~midnight

31
Q

Why are there fluctuations of cortisol plasma levels during the day?

A

Due to effects of other stimuli which are related to stress

32
Q

Why does removal of the adrenal glands result in death?

A
  • Loss of cortisol means animals cannot deal with stress, particularly in terms of maintaining blood glucose levels. Cortisol as a glucocorticoid is crucial in helping to protect the brain from hypoglycaemia.
  • Removal of adrenal glands also renders animals incapable of maintaining their extracellular fluid volume, an effect mediated by aldosterone
33
Q

Why is the permissive action of cortisol on glucagon vital?

A

It has a permissive action on glucagon, which is vitals as glucagon alone is inadequate in responding to a hypoglycaemic challenge

34
Q

What are the 4 actions of cortisol on glucose metabolism (glucocorticoid actions)?

A
  • Gluconeogenesis
  • Proteolysis
  • Lipolysis
  • Decreases insulin sensitivity of muscles and adipose tissue
35
Q

How is cortisol involved in gluconeogenesis?

A

Cortisol stimulates formation of gluconeogenic enzymes in the liver thus enhancing gluconeogenesis and glucose production. This is aided by cortisol’s action on muscle

36
Q

How is cortisol involved in proteolysis?

A

Cortisol stimulates the breakdown of muscle protein to provide gluconeogenic substrates for the liver

37
Q

How is cortisol involved in lipolysis?

A

Cortisol stimulates lipolysis in adipose tissue which increases [FFA] plasma creating an alternative fuel supply that allows [BG] to be protected while also creating a substrate (glycerol) for gluconeogenesis

38
Q

Why is cortisol said to be diabetogenic?

A

Cortisol acts to oppose insulin

39
Q

What are the 4 non-glucocorticoid actions of cortisol?

A
  • Negative feedback on Ca balance
  • Impairment of mood and cognition
  • Permissive effects on norepinephrine
  • Suppression of the immune system
40
Q

How does cortisol have a negative effect on Ca balance?

A

Decrease absorption from gut, increases excretion at kidney resulting in net Ca2+ loss. Also increase bone resorption leads to osteoporosis

41
Q

What changes in mood are associated with excess cortisol?

A

Depression and impaired cognitive function

42
Q

Describe the permissive effects that cortisol has on norepinephrine.

A
  • Particularly in vascular smooth muscle (a-receptor effect = vasoconstrictive).
  • Cushings Disease (hypercortisolaemia) is strongly associated with hypertension. Likewise, low levels of cortisol are associated with hypotension.
43
Q

Describe the part cortisol plays in suppression of the immune system

A

Cortisol reduces the circulating lymphocyte count, reduces antibody formation and inhibits the inflammatory response. Latter effect can be useful clinically e.g. asthma/ulcerative colitis/organ transplant.

44
Q

What action does cortisol have on adipose tissue?

A

Lipolysis

45
Q

What action does cortisol have on muscle?

A

Protein catabolism

46
Q

What action does cortisol have on liver?

A

Gluconeogenesis

47
Q

What action does cortisol have on the immune system?

A

Function suppressed

48
Q

Why does excess cortisol lead to thinning of the skin?

A

Loss of percutaneous fat stored and protein muscle wastage gives fragile appearance

49
Q

What type of hormone is aldosterone?

A

Mineralcorticoid

50
Q

What is the function of aldosterone?

A
  • Acts on the distal tubule of the kidney to determine the levels of minerals reabsorbed/excreted.
  • Aldosterone increases the reabsorption of Na+ ions and promotes the excretion of K+ ions.
51
Q

How is the secretion of aldosterone from the adrenal cortex controlled?

A

The secretion of aldosterone by the adrenal cortex is primarily controlled by a complex reflex pathway originating in the kidney, the renin-angiotensin-aldosterone system (RAAS).

52
Q

How does increased aldosterone increase BP?

A

Increased aldosterone release stimulates Na+ (and H2O) retention and K+ depletion, resulting increased blood volume and increased blood pressure

53
Q

How does decreased aldosterone decrease BP?

A

Decreased aldosterone leads to Na+ (and H2O) loss and increase in [K+]plasma, resulting in diminished blood volume and decreased blood pressure

54
Q

What condition is associated with hypersecretion of cortisol?

A

Cushing’s syndrome/Disease

55
Q

What is hypersecretion of cortisol most commonly due to?

A

Due to a tumour in either adrenal cortex or pituitary

56
Q

What causes primary hypercortisolism?

A

Tumour in adrenal cortex causing Cushing’s syndrome

57
Q

What causes secondary hypercortisolism?

A

Tumour in pituitary gland causing excess ACTH leading to Cushing’s disease.

58
Q

What is the main cause of iatrogenic hypercortisolism?

A

Too much cortisol being administered therapeutically

59
Q

What condition is associated with hyposecretion of cortisol?

A

Addison’s disease

60
Q

What is Addison’s disease?

A

Hyposecretion of all adrenal steroid hormones due to autoimmune destruction of adrenal cortex

61
Q

What is Cushing’s disease characterised by?

A

Cushing’s Disease is characterised by wasting of the extremities (due to catabolic action of cortisol) but for unknown reasons fat is redistributed to the face (“moon face”) and trunk

62
Q

What is CRH and ACTH release promoted by?

A

Stress

63
Q

What can disinhibit the hypothalam-pituitary-adrenal axis?

A
  • Alcohol
  • Caffeine
  • Lack of sleep
64
Q

What effect does alcohol have on the hypothalamo-pituitary-adrenal axis?

A

Alcohol depresses the neurons involved in negative feedback further enhancing stress effect and increasing levels of CRH and ACTH.

65
Q

How does elevation of cortisol increase vulnerability to infection?

A

Turns down the immune system

66
Q

Describe how the adrenal medulla secretes hormones.

A

Preganglionic sympathetic fibres terminate on specialised postganglionic cells in the adrenal medulla. These postganglionic fibres do not have axons – instead they release their neurohormones (adrenaline) directly into the blood.

67
Q

What rare neuroendocrine tumour is associated with the adrenal medulla?

A

Pheochromocytoma

68
Q

What does a pheochromocytoma result in?

A

Excess catecholamines which:

  • Increase Hr
  • Increase CO
  • Increase BP
69
Q

What do pheochromocytomas respond well to?

A

Surgery

70
Q

Describe CRH, ACTH and Cortisol levels in: secondary hypersecretion due to hypothalamic problem

A
  • CRH: high
  • ACTH: high
  • Cortisol: high
71
Q

Describe CRH, ACTH and Cortisol levels in: Secondary hypersecretion due to pituitary problem

A
  • CRH: low
  • ACTH: high
  • Cortisol: high
72
Q

Describe CRH, ACTH and Cortisol levels in: Primary hypersecretion due to problem with adrenal cortex

A
  • CRH: low
  • ACTH: low
  • Cortisol: high
73
Q

Why is care required when withdrawing glucocorticoid treatment?

A

Enhanced negative feedback effects of exogenous cortisol

74
Q

Why is there risk of adrenal insufficiency if glucocorticoid treatment is withdrawn too fast?

A
  • Additional, therapeutic cortisol enhances the negative feedback on hypothalamus and pituitary reducing release of CRH and ACTH.
  • Loss of trophic action of ACTH on adrenal gland cause atrophy of gland. Risk of adrenal insufficiency if withdrawal is too fast.

Systems: Endocrine AB (25 decks)

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