Steroid Biosynthesis

Question 1

How is sunlight used in steroid biosynthesis?

Answer 1

Converts 7-Dehydrocholesterol into Vitamin D3

Question 2

What enzyme converts cholesterol into pregnenolone?

Answer 2

Desmolase

ACTH regulates desmolase activity

Question 3

What causes adrenal hyperplasia?

Answer 3

Increased production form the adrenal gland of both cortisol repcursors and androgens

Question 4

What is a symptom that women usually develop with adrenal hyperplasia?

Answer 4

Hirsutism-Excessive body hair in men and women

General oligomenorrhea-Infrequent or very light menstruation

Question 5

How to dtermine if fetus is at risk for congenital adrenal hyperplasia?

Answer 5

Using human leukocyte antigen haplotype

Demonstration of excess cortisol precursors in amniotic fluid

Treat with hormone replacement therapy

Question 6

What products would you have a build-up of with a deficiency of 11-B-Hydroxylase (CYP11B1)?

Answer 6

Deoxycorticosterone

11-Deoxycortisol

Question 7

What products would you have a build-up of with a 21-Hydroxylase deficiency?

Answer 7

Progesterone and 170H-Progesterone

Question 8

What does aldosterone bind to?

Answer 8

Binds and activates mineralcorticoid receptor

Question 9

What does the adrenal cortex do?

Answer 9

Promotes retention of Na+ and H2O in the kidneys

Promotes excretion of H+ and K+

Reduced levels: too much salt

Excessive levels: Conn syndrome-increased BV and hypertension

Question 10

What is conn syndrome?

Answer 10

Excessive secretion of aldosterone

Retention of sodium

Loss of potassium

Hypertension

Question 11

List the steroids in decreasing order of efficacy for MR

Answer 11

Aldosterone (highest efficacy)

11-deoxycorticosterone

Testosterone

Hydrocortisone (Cortisol)

Cortisone

Question 12

How do you have hypertension with decreased aldosterone (11-B hydroxylase deficiency)?

Answer 12

Hydrocortisone and cortisone synthesis decreases

11-deoxycorticosterone and 11-deoxycortisol increases

Question 13

How does ACTH act on the adrenal cortex?

Answer 13

Stimulates secretion of glucocorticoids steroid hormones

Acts by binding to cell surface ACTH receptors (GCPR)

Question 14

Once ACTH binds to its receptor what are the effects?

Answer 14

Receptor undergoes conformation changes

Stimulates adenylyl cyclase

Leads to an increase in intracellular cAMP and subsequent activation of Protein Kinase A

Question 15

What happens with a 17,20 Lyase deficiency?

Answer 15

Deficient production of androgens and sex development disoders while the production of glucocorticoids is intact

Question 16

How is Vitamin D obtained?

Answer 16

Through diet Vitamin D2 (Ergocalciferol) absorbed into intestine and converted from 7-dehydrocholesterol in the skin via UV radiation

In the kidney; 1-25-Dihydroxycholecalciferol is synthesized by 1-alpha hydroxylase

25-hydroxychoecalciferol is found exclusively in the liver

Question 17

How is 25-hydroxcholecalciferol converted?

Answer 17

25-hydroxycholecalciferol starts in the liver and is sent to the kidney

it is then converted by 1-alpha-hydroxylase to 1,25-dihydroxycholecalciferol

This conversion is directed by PTH