The Adrenal Gland

Question 1

Where are the adrenal glands located?

Answer 1

On the superior pole of the kidney in the retroperitoneal space

Question 2

What are the characteristics of the adrenal medulla?

Answer 2

The adrenal medulla is a modified sympathetic ganglion derived from neural crest tissue

Question 3

What does the adrenal medulla secrete?

Answer 3

Catecholamines

Mainly epinephrine, norepinephrine and dopamine

Question 4

What are the characteristics of the adrenal cortex?

Answer 4

Adrenal cortex is a true endocrine gland derived from mesoderm

Question 5

What does the adrenal cortex secrete?

Answer 5

The adrenal cortex secretes three classes of steroid hormones:
Mineralocorticoids- involved in regulation of sodium and potassium
Glucocorticoids- involved in regulation of plasma glucose
Sex steroids

Question 6

What are the three layers of the adrenal cortex, from superficial to deep?

Answer 6

Zona glomerulosa
Zona fasciculata
Zona reticularis

Question 7

What does the zona glomerulosa secrete?

Answer 7

Aldosterone

Question 8

What does the zona fasciculata secrete?

Answer 8

Glucocorticoids

Question 9

What does the zona reticularis secrete?

Answer 9

Sex hormones

Question 10

Briefly describe the synthetic pathways of the adrenal cortex

Answer 10

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

Question 11

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

Answer 11

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

Question 12

What kind of hormone is cortisol?

Answer 12

Glucocorticoid hormone

Question 13

How do cortisol receptors react to cortisol?

Answer 13

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

Question 14

Describe how plasma levels of cortisol fluctuate

Answer 14

Plasma levels of cortisol show a characteristic pattern with a marked circadian rhythm, preceded by a similar pattern of ACTH. Cortisol bursts last longer as half-life is much longer. Peak is ~6-9am, lowest level is ~midnight
Other fluctuations occur throughout the day due to effects of other stimuli related to stress

Question 15

How does cortisol act on glucose metabolism?

Answer 15

Gluconeogenesis- cortisol stimulates formation of gluconeogenic enzymes in the liver
Proteolysis- cortisol stimulates the breakdown of muscle protein to provide gluconeogenic substrates for the liver
Lipolysis- cortisol stimulates lipolysis in adipose tissue which increases free fatty acids in the plasma and so creates an alternative fuel supply that allows blood glucose to be protected while also creating a substrate (glycerol) for gluconeogenesis
Decreases insulin sensitivity of muscles and adipose tissue

Question 16

What are the non-glucocorticoid actions of cortisol?

Answer 16

Negative effect on calcium balance- decrease absorption from the gut, increases excretion at kidney resulting in net calcium loss
Impairment of mood and cognition- depression and impaired cognitive function linked to hypercortisolaemia
Permissive effects on norepinephrine- particularly in vascular smooth muscle
Suppression of the immune system- cortisol reduces circulating lymphocyte count, reduces antibody formation and inhibits the inflammatory response

Question 17

What are the side effects of glucocorticoid therapy?

Answer 17

Increased severity and frequency of infection

Loss of percutaneous fat stores gives appearance of thinning skin and makes it more fragile

Question 18

What kind of hormone is aldosterone?

Answer 18

Mineralocorticoid

Question 19

What is the function of aldosterone?

Answer 19

Aldosterone acts on the distal tubule of the kidney to determine the levels of minerals reabsorbed/secreted.
Aldosterone increases the reabsorption of sodium ions and promotes the excretion of potassium ions

Question 20

What are the effects of aldosterone secretion?

Answer 20

Increased aldosterone release stimulates sodium and water retention and potassium depletion, resulting in increased blood volume and pressure
The opposite is true of decreased aldosterone

Question 21

What type of tissue is the adrenal medulla?

Answer 21

Modified sympathetic ganglia rather than true endocrine tissue. Preganglionic sympathetic fibres terminate on specialised postganglionic cells in the adrenal medulla, which do not have axons and instead release their neurohormones directly into the blood