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Endocrying > The adrenal gland > Flashcards

The adrenal gland Flashcards

1
Q

Where are the adrenal glands located?

A

Located on the superior pole of the kidney in the retroperitoneal space, each weighing ~4g in adults.

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2
Q

Identify the labels

A
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3
Q

What is the structure of the adrenal glands?

A

Similar to the pituitary, the adrenal gland is composed of two quite separate endocrine glands rolled into one structure

Adrenal medulla - 25%

Adrenal cortex - 75%

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4
Q

What is the adrenal medulla?

A

Neuroendocrine gland - it a modified sympathetic ganglion

It releases catecholamines from postganglionic cells:

mainly Epinephrine (adrenaline)

Norepinephrine

Dopamine

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5
Q

What is the adrenal cortex?

A

A true endocrine gland - which secretes 3 classes of steroid hormones:

Mineralocorticoids - eg Aldosterone

Glucocorticoids - eg Cortisol

Sex steroids - eg Testosterone

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6
Q

What do the hormones produced by the Adrenal cortex regulate?

A

Mineralocorticoids - eg Aldosterone:

  • Involved in regulation of Na+, K+

Glucocorticoids - eg Cortisol:

  • Involved in maintaining plasma glucose

Sex steroids - eg testosterone:

  • do sex stuff
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7
Q

The adrenal gland produces hormones that play a role in the body’s response to _______

A

The body’s response to stress

Aldosterone and cortisol are essential for survival.

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8
Q

What are the histological regions of the adrenal glands (from out to in)

A

Capsule

Adrenal cortex:

  • Zona Glomerulosa
  • Zona Fasciculata
  • Zona Reticularis

Adrenal Medulla

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9
Q

Identify the histological regions and what they secrete

A
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10
Q

Fill in the blanks about the adrenal cortex

“All steroid hormones are derived from ________, but different _______ are found in different adrenal zones, resulting in different end products e.g. enzymes needed to make aldosterone are found only in the zona _________”

A

All steroid hormones are derived from cholesterol, but different enzymes are found in different adrenal zones, resulting in different end products e.g. enzymes needed to make aldosterone are found only in the zona glomerulosa

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11
Q

Congenital defects in which enzyme are a common cause of adrenal hyperplasia?

What would be the effect of this?

A

21-hydroxylase

Results in the deficiency of cortisol and aldosterone - leading to disruption of salt and glucose balance.

Androgen biosynthesis is only viable pathway - leading to excessive adrenal androgen production

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12
Q

Describe how deficit of 21-hydroxylase causes adrenal hyperplasia?

A
  1. Lack of 21-hydroxylase inhibits synthesis of cortisol.
  2. This removes the negative feedback on ACTH and CRH release.
  3. Increased ACTH secretion is responsible for enlargement of adrenal glands.
  4. Negative feedback of ACTH on CRH synthesis remains.
  5. Babies become very ill within a few days of birth
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13
Q

What is cortisol?

A

A steroid hormone produced by the Zona Fasciculata of the adrenal cortex

It is a Glucocorticoid hormone than influences glucose metabolism

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14
Q

How does cortisol exist in the blood?

A

95% of plasma cortisol exists bound to carrier proteins called Cortisol binding globulin

Only free cortisol can cross into target cells

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15
Q

What cells does cortisol target?

A

Every fkn one of em

Every nucleated cell has cytoplasmic glucocorticoid receptors which bind to cortisol

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16
Q

What is the effect of cortisol binding to cytoplasmic receptors?

A

The cortisol/receptor complex moves to the nucleus

Binds to DNA via Hormone response element

Alters gene expression

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17
Q

Describe the daily release of cortisol

A

Cortisol release initiated by release of ACTH which follows a Circadian rhythm

Cortisol “burst” persists longer than ACTH burst because half-life is much longer

Peak is ~ 6-9am, nadir (lowest level) is ~ midnight

18
Q

What is the effect of a lack of cortisol (ie if the adrenal glands were removed) on the body?

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.

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

19
Q

What is the effect of a lack of aldosterone on the body?

A

Lack of aldosterone would render an individual unable to regulate their extracellular fluid volume

20
Q

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

A

Gluconeogenesis:

  • Cortisol stimulates formation of gluconeogenic enzymes in the liver thus enhancing gluconeogensis and glucose formation
    • This is aided by cortisols action on the muscle…

Proteolysis:

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

Lipolysis:

  • 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

Insulin:

  • Decreases insulin sensitivity of muscles and adipose tissue
21
Q

Why is too much cortisol diabetogenic?

A

Cortisol acts to oppose insulin

22
Q

What are the additional (non-glucocorticoid) actions of cortisol?

A

Negative effect on Ca2+ balance

Impairment of mood and cognition

Permissive effects on norepinephrine

Suppression of the Immune System

23
Q

How does cortisol have a negative effect on Calcium balance?

A

Decreases absorption from gut

Increases excretion from kidney

Increases bone resorption (which is then excreted)

24
Q

How does cortisol affect mood and cognition?

A

depression and impaired cognitive function are strongly associated with hypercortisolaemia.

25
Q

What are the permissive effects of 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.

26
Q

How does cortisol suppress the immune system?

A

Cortisol reduces circulating lymphocyte count, reduces antibody formation and inhibits the inflammatory response

Latter effect can be useful clinically e.g. asthma/ulcerative colitis/organ transplant

27
Q

Complete the diagram hehe

A
28
Q

What are the side effects of glucocorticoid therapy?

A

Muscle wastage

Loss of percutaneous fat (thinning of skin)

Increased frequency of infection - such as thrush etc

29
Q

Why must withdrawal from long-term glucocorticoid treatment be done gradually?

A

Enhanced negative feedback loop from exogenous cortisol may cause ATROPHY of the adrenal gland

This would thus cause adrenal insufficiency

30
Q

What is aldosterone?

A

mineralocorticoid, which 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.

It thus plays a role in governing fluid balance in tissues

31
Q

What controls the release of aldosterone?

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)

32
Q

What are the effects of increased aldosterone release?

A

Increased aldosterone release stimulates Na+ (and H2O) retention and K+ depletion

This results in increased blood volume and increased blood pressure

33
Q

What are the disorders of cortisol secretion?

A

Hypersecretion of cortisol:

  • Cushing’s syndrome/disease
  • Iatrogenic - too much cortisol given

Hyposecretion of cortisol:

  • Addison’s disease
  • much less common
34
Q

What causes Cushing’s disease and Cushing’s syndrome?

A

Hypersecretion of cortisol - caused by a tumour in either:

  • Adrenal cortex - 1o hypercortisolism = Cushing’s syndrome
  • Pituitary gland - 2o hypercortisolism = Cushing’s disease
    • ​Much more common
    • Excess ACTH
35
Q

What causes Addison’s disease?

A

Autoimmune destruction of the Adrenal cortex

Causes Hyposecretion of all adrenal steroid hormones - Cortisol, aldosterone, sex steroids etc

36
Q

What are the effects of Cushing’s disease on body appearance?

A

Moon face and fatty belly

Wasting in extremities and limbs

37
Q

How does stress increase the vulnerability to infection via the HPA?

A

CRH & ACTH release promoted by stress

Alcohol, caffeine and lack of sleep all “disinhibit” the Hypothalamo-Pituitary-Adrenal Axis (HPA).

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

This increases cortisol levels - which turns down the immune system

38
Q

What is the adrenal medulla and how does it secrete into the blood?

A

Modified sympathetic ganglion that serves a neuroendocrine role (similar to posterior pituitary)

In it - pre-ganglionic sympathetic fibres terminate on specialised post-ganglionic cells in the adrenal medulla

These cells have no axons - but instead release their neurohormone (adrenaline) directly into the blood

39
Q

What is Pheochromocytoma?

A

Pheochromocytoma is a rare neuroendocrine tumour of the adrenal medulla

It causes excess release of catecholamines which increases HR, CO and thus causes hypertension (constant symp stimulation)

It also causes Diabetes due to adrenergic action impacting on glucose metabolism

40
Q

How is pheochromocytoma treated?

A

Surgery - responds very well

41
Q

In each pathway - state the impact on the levels of:

CRH

ACTH

Cortisol

A
42
Q
A

Endocrying (21 decks)

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