The Adrenal gland

Question 1

Where are the adrenal (suprarenal) glands situated?

Answer 1

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

Question 2

What are the 2 separate endocrine glands within the adrenal gland?

Answer 2

Adrenal medulla

Adrenal cortex

Question 3

What is the adrenal medulla and what does it secrete?

Answer 3

a modified sympathetic ganglion derived from neural crest tissue (makes up 25%)

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

Question 4

What is the adrenal cortex and what does it secrete

Answer 4

a true endocrine gland derived from mesoderm

secretes 3 classes of steroid hormones

Question 5

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

Answer 5

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

Question 6

Which 2 steroid hormones are essential for survival

Answer 6

cortisol and aldosterone

Question 7

What are the 3 zones of the adrenal cortex

Answer 7

Zona glomerulosa

Zona fasciculata

Zona reticularis

Question 8

Which hormone is secreted from the Zona glomerulosa

Answer 8

aldosterone

enzymes needed to make aldosterone are found only in the zona glomerulosa

Question 9

Which hormone is secreted from the Zona fasciculata

Answer 9

glucocorticoids

Question 10

Which hormone is secreted from the zona reticularis

Answer 10

sex hormones

Question 11

What are all steroid hormones derived from

Answer 11

cholesterol

Question 12

What is a common cause of congenital adrenal hyperplasia? and what is the effect of this

Answer 12

defects in the 21-hydroxylase enzyme

results in deficiency of aldosterone and cortisol associated disruption of salt and glucose balance

androgen biosynthesis is unaffected - accumulating steroid precursors are channeled into excessive adrenal androgen production

babies become very ill within a few days of birth

Question 13

What % of plasma cortisol is bound to a carrier protein called cortisol binding globulin (CBG)?

Answer 13

95%

Question 14

What is ACTH

Answer 14

Adrenocorticotropic hormone (ACTH) regulates levels of cortisol

Question 15

Describe cortisol release

Answer 15

Marked circadian rhythm (same daily)

preceded by a similar pattern of release of ACTH. Cortisol burst persists longer than ACTH due to longer half-life

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

Other fluctuations during the day are due to effects of other stimuli which are related to stress.

Question 16

Why is cortisol so essential for life?

Answer 16

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.

Question 17

Actions of cortisol on glucose metabolism (4)

Answer 17

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

Proteolysis: cortisol stimulates the breakdown of muscle protein to provide gluconeogenic substrates for the liver.

Lipolysis: 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.

Decreases insulin sensitivity of muscles and adipose tissue.

Question 18

How is excess cortisol diabetogenic?

Answer 18

Cortisol acts to oppose insulin

Question 19

What other actions does cortisol have that are non-glucocorticoid

Answer 19

Negative effect on Ca2+ balance

impairment of mood and cognition - depression + impaired cognitive functioning links with hypercortisolaemia

permissive effects on norepinephrine

suppression of the immune system

Question 20

How does cortisol suppress the immune system

Answer 20

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

Question 21

Side effects of glucocorticoid therapy

Answer 21

Increases severity and frequency of infection (immune suppression

muscle wastage

loss of percutaneous fat stores gives appearance of ‘thinning skin’ making it more fragile

Question 22

What is Aldosterone and what is it’s function

Answer 22

Aldosterone is 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.

Question 23

What controls the release of aldosterone by the adrenal cortex

Answer 23

a complex reflex pathway originating in the kidney - the RAAS system

Question 24

What is the end effect of aldosterone

Answer 24

Mainly on CVS

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

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

Question 25

Which disease is associated with hypersecretion of cortisol

Answer 25

Cushing’s syndrome

Hypersecretion is most commonly due to a tumour in either the adrenal cortex or the pituitary gland

Question 26

Which disease is associated with hyposecretion of cortisol

Answer 26

Addison’s disease

Hyposecretion of all adrenal steroid hormones

Due to autoimmune destruction of adrenal cortex

Question 27

What is cushing’s disease characterised by?

Answer 27

wasting of the extremities (due to catabolic action of cortisol) but for unknown reasons fat is redistributed to the face (“moon face”) and trunk.

Question 28

What things disinhibit the hypothalamo-pituitary-adrenal axis?

Answer 28

alcohol

caffeine

lack of sleep

Question 29

Adrenal medulla

Answer 29

Modified sympathetic ganglion, not true endocrine tissue.

Similar to posterior pituitary in having neuroendocrine role.

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.

Question 30

What is Pheochromocytoma

Answer 30

A rare neuroendocrine tumour, found in adrenal medulla which results in excess catecholamines: increased HR => increased CO => big increase in BP

Diabetogenic due to adrenergic effect on glucose metabolism.

Responds well to surgery.

Question 31

Name 3 sites of pathology in hypothalamic-pituitary-adrenal axis

Answer 31

In the hypothalamus

In the anterior pituitary

In the adrenal cortex

Question 32

Why is care required when withdrawing glucocorticoid treatment

Answer 32

Due to enhanced negative feedback effects of exogenous cortisol

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.