50-STEROID HORMONE METABOLISM – Dr. Venk

Question 1

Name a few androgens.

Answer 1

Testosterone, dehydroepiandrosterone (DHEA), dihydrotestosterone.

Question 2

Name a few estrogens.

Answer 2

17-beta-estradiol, progesterone.

Question 3

Name the hormone that is required for embryo implantation.

Answer 3

Progesterone

Question 4

What are the functions of DHEA?

Answer 4

DHEA is a precursor of estrogen and inhibits glucose-6-phosphate dehydrogenase.

Question 5

What are the functions of aldosterone and cortisol?

Answer 5

Cortisol functions to increase blood glucose through stimulating gluconeogenesis in liver, protein degradation in muscle and mobilization of fatty acids from adipose tissue).

Aldosterone raises blood pressure and fluid volume by retaining Na+ and excreting K+.

Question 6

What is the role of StAR?

Answer 6

StAR (steroidogenic acute regulatory protein) is a hormone-induced transport protein factor that mediates acute regulation of steroid hormone biosynthesis.

Question 7

What is the rate-limiting step in steroid biosynthesis?

Answer 7

The side chain cleavage of cholesterol (C-27) into pregnenolone (C-21) and C-6 isocaproaldehyde.

Question 8

What is the role of 5alpha-reductase?

Answer 8

5 -reductase is the enzyme that converts testosterone into DHT.

Question 9

Name the enzyme that converts testosterone into estradiol.

Answer 9

Testosterone is converted into estradiol from aromatase in leydig cells or via DHEA in follicular cells and mammary glands.

Question 10

Name the organ in which aldosterone and cortisol are produced.

Answer 10

The adrenal gland.

Question 11

Name the most common enzyme in steroid biosynthesis (generic is OK).

Answer 11

P450-hydroxylases are the most common enzyme in steroid biosynthesis.

Question 12

Conversion of cholesterol into pregnenolone occurs in ________________.

Answer 12

Mitochondria

Question 13

Describe the signaling relay for the synthesis and secretion of cortisol.

Answer 13

When the Hypothalamus is stimulated, it releases corticotropin releasing factor, which stimulates the anterior pituitary to release adrenocorticotropic hormone (ACTH). ATCH stimulates the adrenal cortex to release Cortisol. The presence of Cortisol acts as a feedback inhibition to the Hypothalamus.

Question 14

Describe the signaling relay for the synthesis and secretion of aldosterone.

Answer 14

The effect of angiotensin II and III on the zona glomerulosa causes the release/secretion of aldosterone.

Question 15

Describe the signaling relay for the synthesis and secretion of estradiol and progesterone.

Answer 15

The hypothalamus secretes Gonadotropin Releasing Hormone (GnRH), which stimulates the anterior pituitary to secret FSH and LH. In females, FSH and LH target the ovary to release estradiol and progesterone. In males, there is no FSH, and LH stimulates the testis to release testosterone.

Question 16

Describe the role of cholesterol as a precursor for various metabolisms.

Answer 16

Cholesterol is a precursor for several steroid hormones that affect several different types of metabolism.
Cortisol stimulates gluconeogenesis in the liver and protein degradation in muscle.

CHolesterol is also a precursor for Bile acid (cholic acid), Vitamin D3, Membrane biosynthesis, and Cholsterol 3-O-sulfate.

Question 17

Describe the signaling relay for the synthesis and secretion of angiotension II and III.

Answer 17

Kidney’s juxtaglomerulosa cells secrete renin that convert Angitensinogen (inactive) to Angiotensin I (active). Angiotensin converting enzyme ,ACE, then converts Angiotensin I (active) to Angiotensin II, and then to Angiotensin III. (II and III which can cause release of Aldosterone).