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7. Endocrinology (Medical Knowledge)a > The Adrenal Gland > Flashcards

The Adrenal Gland Flashcards

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USMLE® Step 1 flashcards
1
Q

Where are the adrenal glands located?

A

Superior pole of kidneys in retroperitoneal space

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2
Q

What does each adrenal gland weigh in an adult?

A

About 4g

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3
Q

What are the two seperate endocrine glands that makes up the adrenal gland?

A

Adrenal medulla

Adrenal cortex

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4
Q

What percentage of the adrenal gland is the adrenal medulla?

A

About 25%

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5
Q

What is the adrenal medulla?

A

Modified sympathetic ganglion derived from neural crest tissue

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6
Q

What does the adrenal medulla secrete?

A

Catecholamines, mainly epinephrine, also norepinephrine and dopamine

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7
Q

What percentage of the adrenal gland is the adrenal cortex?

A

About 75%

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8
Q

What is the adrenal cortex?

A

True endocrine gland derived from mesoderm and secretes 3 classes of steroid hormones

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9
Q

What class of hormones does the adrenal cortex secrete?

A

Steroid

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10
Q

What are the 3 classes of steroid hormones that the adrenal cortex secretes?

A

Mineralocorticoids

Glucocorticoids

Sex steroids

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11
Q

What is an example of a mineralocorticoid?

A

Aldosterone (involved in regulation of Na and K)

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12
Q

What is an example of a glucocorticoid?

A

Cortisol (involved in maintaining plasma glucose)

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13
Q

What is an example of a sex steroid?

A

Testosterone

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14
Q

Is the adrenal cortex or medulla more superficial?

A

Adrenal cortex

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15
Q

What is each layer of the adrenal cortex?

A

Zona glomerulosa (secretes aldosterone)

Zona fasciculate (secretes glucocorticoids)

Zona reticularis (secretes sex hormones)

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16
Q

What does the zona glomerulosa secrete?

A

Aldosterone

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17
Q

What does the zona fasciculate secrete?

A

Glucocorticoids

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18
Q

What does the zona reticularis secrete?

A

Sex hormones

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19
Q

How is it possible for different hormones to be secreted in different layers of the adrenal cortex?

A

All steroid hormones are derived from cholesterol

But different enzymes found in different adrenal zones results in different end products

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20
Q

What is a synthetic pathway?

A

Route taken to build up a specific product

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21
Q

What enzyme is responsible for both the formations of aldosterone and cortisol?

A

21-hydroxylase

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22
Q

What does HPA stand for?

A
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23
Q

What do defects in 21-hydroxylase cause?

A

congenital adrenal hyperplasia resulting in:

  • deficiency of aldosterone and cortisol (so disruption of salt and glucose balance)
  • androgen biosynthesis is unaffected so accumulating steroid precursors are channels into excess adrenal androgen production
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24
Q

What does cortisol provide long loop feedback on?

A

CRH

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25
Q

Cortisol provides long loop feedback on CRH as part of the hypothalamic-pituitary-adrenal pathway, what provides short-loop feedback?

A

ACTH

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26
Q

Explain the process of a deficit in 21-hydroxylase causing adrenal hyperplasia?

A
  1. lack of enzyme inhibits synthesis of cortisol
  2. removal of negative feedback on ACTH and CRH release
  3. increased ACTH secretion = enlargement of adrenal glands
  4. negative feedback of ACTH on CRH synthesis remains balanced
  5. babies become very ill within a few days of birth
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27
Q

What type of hormone is cortisol?

A

Glucocorticoid hormone (influences glucose metabolism)

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28
Q

What percentage of plasma cortisol is bound to carrier protein?

A

About 95%

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29
Q

What plasma protien does most cortisol bind to?

A

Cortisol binding globulin (CBG)

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30
Q

What kind of cells have cytoplasmic glucocorticoid receptors?

A

All nucleated cells

31
Q

What happens when cortisol binds to its cytoplasmic glucocorticoid receptor?

A
  • hormone receptor complex migrates to nucleus
  • binds to DNA via a hormone-receptor element
  • alters gene expression, transcription and translation
32
Q

What kind of rhythm do cortisol plasma levels show, and what are they preceded by?

A

Circadian rhythm, preceded by a similar pattern of release of ACTH

33
Q

Does cortisol or ACTH have a longer half life?

A

Cortisol, so bursts of release persist around longer than ACTH

34
Q

What time of day can the peak and lowest levels of plasma cortisol be obersed?

A

Peak - between 6am and 9am

Lowest - midnight

35
Q

What are fluctations of cortisol levels during the day due to?

A

Effects of stimuli which are related to stress

36
Q

What would a loss of cortisol mean?

A

Animals cannot deal with stress, particularly in terms of maintaining blood glucose levels

37
Q

How does cortisol cause gluconeogenesis?

A

Stimulates formation of gluconeogenic enzymes in liver, enhancing gluconeogenesis and glucose production

38
Q

Does cortisol have permissive action on insulin or glucagon?

A

Glucagon, which is vital as glucagon alone is inadequate in responding to a hypoglycaemia challenge

39
Q

What are the consequences of removing the adrenal glands in animals?

A

Cannot deal with stress, particularly in terms of maintaining blood glucose levels

Incapable of maintaining their ECF volume, an effect mediated by aldosterone

40
Q

What are some actions of cortisol on glucose metabolism?

A

Gluconeogenesis

Proteolysis

Lipolysis

Decreased insulin sensitivity

41
Q

Is excess cortisol diabetogenic or the opposite?

A
  • diabetogenic
  • due to its glucose-counter regulatory effects that oppose insulin
42
Q

Does cortisol have a positive or negative effect on calcium balance, and why?

A
  • negative
  • decreases absorption from gut, increases excretion at kidney resulting in net calcium loss
  • also increase bone resorption, leading to osteoporosis
43
Q

Other than glucose metabolism, what are some additional actions of cortisol?

A
44
Q

How does cortisol cause an impairment on mood and cognition?

A

Depression and impaired cognitive function are strongly associated with hypercortisoaemia

45
Q

Does cortisol have permissive or antagonistic action to norepinephrine?

A
  • permissive
  • particular in smooth muscle (a-receptor effect is vasoconstrictive)

Cushing’s disease (hypercortisolaemia) is strongly associated with hypertension, and low cortisol levels are associated with hypotension)

46
Q

Does cortisol enhance or suppress the immune system, and why?

A
  • suppression
  • reduces the circulating lymphocyte count
  • reduces antibody formation
  • inhibits the inflammatory response
47
Q

What are some side-effects of glucocorticoid therapy?

A
  • increases severity and frequency of infection (due to immune suppresion)
  • muscle wastage (due to proteolysis)
  • loss of percutaneous fat stores gives appearance of thinning skin
48
Q

What kind of hormone is aldosterone?

A

Mineralocorticoid

49
Q

What does aldosterone act on?

A

Distal tubule of kidney to determine to determine levels of minerals reabsorbed/excreted

50
Q

How does aldosterone impact sodium and potassium?

A

Increases reabsorption of sodium and promotes excretion of potassium

51
Q

What is secretion of aldosterone by adrenal cortex primarily controlled by?

A

Renin-angiotensin-aldosterone system (RAAS)

52
Q

What does RAAS stand for?

A

Renin-angiotensin-aldosterone system

53
Q

What system are the effects of aldosterone mainly on?

A

CNS system

54
Q

What does increased aldosterone cause?

A
  • stimulates sodium (and water) retention and potassium depletion
  • resulting in increased blood volume and blood pressure
55
Q

What does decreased aldosterone cause?

A
  • sodium (and water) loss and increased potassium in plasma
  • resulting in decreased blood volume and blood pressure
56
Q

What are some examples of disorders of the HPA?

A

Hypersecretion of cortisol

Hyposecretion of cortisol

57
Q

What are some causes of hypersecretion of cortisol?

A

Cushing’s syndrome/disease

58
Q

What is hypersecretion of cortisol most commonly due to?

A

Tumour in:

  • adrenal cortex (1o hypercortisolism), which is Cushing’s syndrome
  • pituitary gland (2o hypercortisolism), which is Cushing’s disease
59
Q

Does a tumour in the adrenal cortex cause Cushing’s disease or Cushing’s syndrome?

A

Cushing’s syndrome (1o hypercortisolism)

60
Q

Does a tumour in the pituitary cause Cushing’s disease or Cushing’s syndrome?

A

Cushing’s disease (2o hypercortisolism)

61
Q

Is hypersecretion or hyposecretion of cortisol more common?

A

Hypersecretion is much more common

62
Q

What causes hyposecretion of cortisol?

A

Addison’s disease

  • causes hyposecretion of all adrenal steroid hormones
  • due to autoimmune destruction of adrenal cortex
63
Q

What is Cushing’s disease characterised by?

A

Wasting of the extremities (due to catabolic action of cortisol)

Fat redistribution to the face (“moon face”) and trunk

64
Q

What are examples of things that disinhibit the hypothalamic-pituitary-axis (HPA)?

A

alcohol, caffeine and lack of sleep

  • alcohol particularly depresses neurons involved in negative feedback
  • further enhancing stress effect and increasing levels of CRH and ACTH
  • turns down immune system and increases vulnerability to infection
65
Q

What is the adrenal medulla?

A

Modified sympathetic ganglion, not true endocrine tissue

66
Q

What happens to preganglionic fibres to the adrenal medulla?

A
  • terminate on specialised postganglionic cells in adrenal medulla
  • these postganglionic cells do not have axons
  • they releasing neurohormones (adrenaline) into blood
67
Q

What is an example of adrenal medulla pathology?

A

Pheochromocytoma

68
Q

What is pheochromocytoma?

A
  • rare neuroendocrine tumour
  • results in XS catecholamines
  • causes increased heart rate, cardiac output & blood pressure
  • diabetogenic due to adrenergic effects on glucose metabolism
69
Q

What are some different sites of endocrine pathology in HPA?

A
  • secondary hypersecretion due to pathology in hypothalamus
  • secondary hypersecretion due to pathology in anterior pituitary
  • primary hypersecretion due to pathology in adrenal cortex
70
Q

In secondary hypersecretion due to pathology in hypothalamus, what are:

  • CRH levels
  • ACTH levels
  • cortisol levels

(high/low)

A

CRH levels - high

ACTH levels - high

Cortisol levels - high

71
Q

In secondary hypersecretion due to pathology in pituitary, what are:

  • CRH levels
  • ACTH levels
  • cortisol levels

(high/low)

A

CRH levels - low

ACTH levels - high

Cortisol levels - high

72
Q

In primary hypersecretion due to pathology in adrenal cortex, what are:

  • CRH levels
  • ACTH levels
  • cortisol levels

(high/low)

A

CRH levels - low

ACTH levels - low

Cortisol levels - high

73
Q

Why is care required when withdrawing chronic glucocorticoid treatment?

A
  • due to enhanced negative feedback effects of exogenous control
  • therapeutic cortisol also enhances negative feedback on hypothalamus and pituitary, reducing release of CRH and ACTH:
  • loss of trophic action of ACTH on adrenal gland causes atrophy of gland
  • risk of adrenal insufficiency if withdrawal is too fast

7. Endocrinology (Medical Knowledge)a (28 decks)

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