Steroid Biosynthesis

Question 1

What regulates cholesterol desmolase activity?

Answer 1

ACTH

Question 2

What does cholesterol desmolase do?

Answer 2

converts cholesterol to pregnenolone (committed step)

Question 3

What tissues is cholesterol desmolase found in? (4)

Answer 3

• adrenals
• testes
• ovary
• placenta

All steroid-producing tissues!

Question 4

What is the most important biochemical intermediate?

Answer 4

pregnenolone

Question 5

What role does progesterone play in pregnancy? (correlation box)

Answer 5

• It regulates voltage-gated Ca2+ channels on spermatozoa
• prepares uterus for implantation
• causes smooth muscle relaxation
• decreases maternal immune response

basically supports pregnancy, and decreases prior to menstruation, labor, and lactation

Question 6

How are glucocorticoids and infant respiratory distress syndrome related (IRDS)? (correlation box)

Answer 6

• normally burst of glucocorticoids prior to birth causes production of surfactant
• preemie’s don’t have this, get IRDS unless glucocorticoids given to mother before birth

Question 7

Metabolic modulation of steroid hormones is important for what? (correlation box)

Answer 7

• Not OD’ing yourself on mineralocorticoids or glucocorticoids
• changes affinity of hormone for receptor so you don’t get overeffect (like too much Na/H20 retention)

Question 8

What globulin is progesterone carried on? (correlation box)

Answer 8

CBG (corticosteroid-binding globulin)

Question 9

How does cortisol suppress the immune system? (correlation box)

Answer 9

It inhibits the transcription factor that activates NF-KB, inhibiting B cell response and apoptosing T cells.

Question 10

What disorders are associated with vitamin D? Why? (correlation box)

Answer 10

• brittle bones/ rickets in kids

- osteomalacia / several fx’s in adults

Question 11

What can adrenal hyperplasia cause in women? (3)

Answer 11

• hirsutism
• general oligomenorrhea
• infertility

Question 12

What is adrenal hyperplasia caused by? (2)

Answer 12

• deficiencies in the adrenal enzymes used to synthesize corticosteroids
• increased production from adrenal gland of both cortisol precursors and androgens

Question 13

What two enzyme deficiencies can cause adrenal hyperplasia?

Answer 13

• 21 hydroxylase

- 11-beta hydroxylase

Question 14

What does a 21 - hydroxylase deficiency result in a buildup of? (2)

Answer 14

• progesterone

- 17-hydroxyprogesterone

Question 15

What is another name for 21 - hydroxylase?

Answer 15

CYP21A2

Question 16

What does a 11-beta hydroxylase deficiency result in a buildup of? (2)

Answer 16

• deoxycorticosterone

- 11-deoxycortisol

Question 17

What is another name for 11-beta hydroxylase?

Answer 17

CYP11B1

Question 18

What can a deficiency of CYP11B1 result in, physiology-wise?

Answer 18

• hypertension and high testosterone, because 11-deoxycorticosterone can act as a ligand in the aldosterone pathway

Question 19

What can a deficiency of CYP21A2 result in, physiology-wise?

Answer 19

• low blood pressure and high testosterone, because progesterone CAN’T act as a ligand, and you get no aldosterone effect

Question 20

What is primary aldosteronism also known as?

Answer 20

Conn’s syndrome

Question 21

What does aldosterone do?

Answer 21

Promotes excretion of H+ and K+

Question 22

What are the symptoms of Conn Syndrome? (4)

Answer 22

• excessive aldosterone secretion
• retention of sodium
• loss of potassium
• hypertension

Question 23

What hormones increase sodium retention? (5)

Answer 23

• aldosterone
• 11-deoxycorticosterone
• testosterone
• cortisol
• cortisone

Question 24

What is the physical manifestation of 11 - beta hydroxylase deficiency?

Answer 24

• virilization

Question 25

How do tumor cells affect cortisol production?

Answer 25

- they cause its release in the absence of any ACTH stimulation

Question 26

What is another name for 17, 20-lyase?

Answer 26

CYP17A1

Question 27

What do mutations in 17, 20-lyase cause?

Answer 27

deficiency in androgens and estrogens

Question 28

What two ways is vitamin D3 obtained?

Answer 28

- absorbed through intestine as ergocalciferol | - converted from 7-dehydrocholesterol in the skin

Question 29

Where is 25-hydroxycholecalciferol found?

Answer 29

in the liver exclusively

Question 30

What is the pathway of Vitamin D3 synthesis?

Answer 30

cholecalciferol → 25-hydroxycholecalciferol → 1,25-dihydroxycholecalciferol

Question 31

What enzyme converts cholecalciferol to 25-hydroxycholecalciferol?

Answer 31

25-hydroxylase

Question 32

What enzyme converts 25-hydroxycholecalciferol to 1,25-dihydrocholecalciferol?

Answer 32

1-alpha-hydroxylase

Question 33

Where does the final step of Vit D3 synthesis occur?

Answer 33

kidney