Adrenal Glands and Steroid Hormones

Question 1

What are steroid hormones derived from?

Answer 1

Cholesterol

Question 2

How many carbons does cholesterol have?

Answer 2

27

Question 3

Where does cholesterol come from? (2)

Answer 3

. Mainly derived from plasma LDLs

. Some from cell stores, synthesised from acetyl CoA

Question 4

What is the rate-limiting step of steroidogenesis

Answer 4

Transport of cholesterol from mitochondrial outer membrane to inner membrane

Question 5

Which enzyme is responsible for converting cholesterol to pregnenolone? How does it do this?

Answer 5

Cholesterol-20,22-desmolase
Cleaves between carbon 20 and 22 on the side chain of cholesterol. This removes 6 carbons from cholesterol (C-27) to give pregnenolone (C-21)

Question 6

Name the three zones of steroid hormone synthesis in the adrenal gland. Where are these zones located?

Answer 6

Zona glomerulosa, zona fascicularis, zona reticularis

Located in the cortex of the adrenal gland (zona glomerulosa most outer, zona reticularis closer to medulla)

Question 7

Which important cell types are found in the medulla of the adrenal gland? What do these cells do?

Answer 7

Chromaffin cells
Secrete catecholamines (adrenaline, noradrenaline, dopamine, enkephalins, and somatostatin (GHIH) in to blood)

Question 8

Which type of corticosteroids are produced in each zone of the adrenal cortex?

Answer 8

Zona glomerulosa –> mineralocorticoids (e.g. cortisol)
Zona Fascicularis –> glucocorticoids (e.g. aldosterone)
Zona reticularis –> gonadocorticoids (e.g. androgens)

Question 9

Give the key blood supply of the adrenal cortex and medulla

Answer 9

. Capsular artery gives off cortical arteriole and medullary arteriole
. Cortical arteriole supplies cortex
. Medullary arteriole supplies medulla

Question 10

Which enzyme links the mineralocorticoid and glucocorticoid pathways?

Answer 10

17-alpha-hydroxylase

Question 11

Is the structure of aldosterone and cortisol similar? How so?

Answer 11

Yes they both have a similar structure, but cortisol has an extra hydroxide group

Question 12

How is the release of cortisol, aldosterone, and androgens regulated? How does this affect the endocrine axis?

Answer 12

. Anterior pituitary releases ACTH
. Stimulates adrenal cortex to release cortisol, aldosterone, androgens

. Only cortisol influences endocrine axis (negative feedback etc.) –> aldosterone and androgens don’t affect it

Question 13

What type of steroid hormone is aldosterone? How is its release stimulated and what does it do?

Answer 13

. Mineralocorticoid
. Stimulated by high blood potassium and RAAS system (depends largely on ACTH)
. Acts mainly on DCT and CD to promote sodium and water retention, and potassium elimination

Question 14

What are androgens? What do they do?

Answer 14

. Group of hormones involved in classically ‘male’ and reproductive traits (muscle, body hair, libido)
. DHEA/ DHEAS, androstenedione
. Very like testosterone
. Found in men and women (more effect on women, who don’t have as much testosterone as men)

Question 15

Why do androgens have negligible contribution in men?

Answer 15

Men have lots of testosterone already, so the effects of their testosterone generally override the effects of androgens

Question 16

How are androgens regulated? How does age affect androgen levels?

Answer 16

. Regulated by ACTH released from the anterior pituitary gland
. Androgens increase during childhood and puberty, peak at 20/21, then decreases as you get older

Question 17

What is the diurnal rhythm of cortisol? How is this regulated? How are cortisol levels regulated in stress situations?

Answer 17

. Peak in cortisol in morning, trough at night (sleep wake cycle)
. SCN in hypothalamus determines body clock (endogenous circadian rhythms)
. In stress situations, CRH (from hypothalamus) and AVP act synergistically to increase ACTH by anterior pituitary

Question 18

What is the SCN in the hypothalamus?

Answer 18

Suprachiasmatic nucleus

Question 19

Which general group of hormones are released by the adrenal cortex? How about the adrenal medulla?

Answer 19

Cortex- steroid hormones (glomerulosa gives mineralocorticoids e.g. aldosterone, fasciculata gives glucocorticoids e.g. cortisol, reticularis gives gonadocorticoids e.g. androgens)
Medulla- catecholamines (by chromaffin cells)

Question 20

What effects does cortisol have on the body?

Answer 20

. Increases plasma glucose

. At high levels can be anti-inflammatory and immunosuppressive

Question 21

What effect does cortisol have on catecholamines?

Answer 21

Permissive effect