Male Reproductive Endocrinology

Question 1

In addition to germ cells (developing spermatozoa), testis contains two important somatic cell types…

Answer 1

• Sertoli cells (nurse cells)
• Leydig cells

Question 2

Leydig cells (vascularized interstitial cells)

Answer 2

• Express LH factors: LH stimulates androgen biosynthesis by stimulating conversion of cholesterol into pregnenolone
• Synthesized androgens can diffuse across the Leydig cell membrane into interstitial space, sertoli cells, and systemic circulation

Question 3

Androgens

Answer 3

• Testosterone
• Dehydroepiandrosterone (DHEA)
• Androstenedione (andro)
• Dihydrotesterone (DHT)

Question 4

Where is 95% of circulating testosterone synthesized?

Answer 4

Testes

Question 5

Where is 5% of circulating testosterone synthesized?

Answer 5

Adrenal cortex

Question 6

Steroid hormones are…

Answer 6

hydrophobic

Question 7

Carrier proteins increase…

Answer 7

the solubility of steroid hormones in aqueous solutions and decrease clearance rate

Question 8

Where is sex hormone binding globulin produced?

Answer 8

Liver

Question 9

Two carrier proteins

Answer 9

• Sex hormone binding globulin
• Albumin

Question 10

60% of testosterone is bound to which carrier protein?

Answer 10

Sex hormone binding globulin

Question 11

25% of testosterone is bound to which carrier protein?

Answer 11

Albumin

Question 12

Where is albumin produced?

Answer 12

Liver

Question 13

Which percent of testosterone is not bound to a carrier protein?

Answer 13

15%

Question 14

Which form of testosterone is biologically active and able to enter the cell to activate its receptor?

Answer 14

Free unbound testosterone

Question 15

FSH Stimulates

Answer 15

• Mitosis of spermatogonia
• Spermiation (release of sperm into lumen)
• Production of androgen binding protein
• Synthesis and secretion of inhibin

Question 16

Androgen binding protein

Answer 16

• Maintains high testosterone levels in the vicinity of developing germ cells
• Same amino acid sequence as SHBG but is produced by testes and has different sugar moieties

Question 17

Inhibin

Answer 17

• Member of the TGFB hormone family
• Inhibits anterior pituitary gonadotrope secretion of FSH but not LH

Question 18

Responsibilities of Sertoli cells

Answer 18

1. Express FSH receptors
2. Maintain the blood-testis barrier
3. Phagocytize abnormal sperm and excess cytoplasm
4. Secrete fluid that nourishes sperm and provides transport medium

Question 19

Blood-testis barrier

Answer 19

Tight junctions between cells to create immune barrier

Question 20

Testosterone concentration in the tubule is…

Answer 20

200x higher than in extracellular fluid/systemic circulation due to high androgen binding protein

Question 21

Testosterone in systemic circulation is carried by…

Answer 21

A carrier protein (mostly sex hormone binding globulin)

Question 22

Reproductive effects of testosterone

Answer 22

• Maintenance of internal reproductive tract
• Required for spermatogenesis

Question 23

Anabolic effects of testosterone

Answer 23

• Increased skeletal muscle mass
• Increased red blood cell production

Question 24

Androgenic effects of testosterone

Answer 24

• Increased libido
• Deepening of voice
• Sebum formation by sebaceous gland (acne)
• Facial hair growth
• Male pattern baldness
• Growth of prostate

Question 25

Endogenous

Answer 25

Made by the body

Question 26

Exogenous

Answer 26

Made outside the body

Question 27

Genetic sex

Answer 27

- XX - XY

Question 28

Gonadal sex

Answer 28

- Testes - Ovaries

Question 29

Phenotypic sex

Answer 29

- Male - Female

Question 30

Mullerian ducts

Answer 30

Female reproductive tract

Question 31

Wolffian ducts

Answer 31

Male reproductive tracts

Question 32

Fetal development of internal reproductive tract is directly affected by...

Answer 32

testosterone

Question 33

Fetal development of external genitalia and prostate requires...

Answer 33

conversion of testosterone to DHT by 5 alpha reductase in target tissues

Question 34

SRY gene products contribute to:

Answer 34

1. Differentiation of gonads into testes 2. Production of anti-mullerian hormone by sertoli cells 3. Production of testosterone by leydig cells

Question 35

Sertoli cells are located in the __________ and they synthesize _______________.

Answer 35

seminiferous tubules; androgen binding protein

Question 36

If the amount of testosterone in a patient's blood serum decreases, their kisspeptin secretion will ________.

Answer 36

Increase

Question 37

If you administer exogenous testosterone to a patient, their LH and FSH production will _________.

Answer 37

Decrease

Question 38

If you administer exogenous testosterone to a patient, the testosterone concentration in the seminiferous tubule will _________.

Answer 38

Decrease (FSH decreases --> ABP decreases --> decreased testosterone concentration)

Question 39

Who is 5 alpha reductase deficiency primarily a concern for?

Answer 39

XY genotype (males)

Question 40

5 alpha reductase deficiency

Answer 40

Deficiency in enzyme required for conversion of testosterone to DHT

Question 41

How does 5 alpha reductase deficiency impact a developing fetus?

Answer 41

- DHT is required for fetal development of external genitalia and prostate - Normal testes but incomplete masculinization of external genitalia - Increased testosterone production at puberty results in masculinization

Question 42

Who is androgen insensitivity primarily a concern for?

Answer 42

XY genotype (males)

Question 43

Androgen insensitivity

Answer 43

- Deficiency in androgen receptors on target cells - Defect in gene controlling the androgen receptor expression - Affects actions of T and DHT

Question 44

What is the most likely diagnosis for Caster Semenya?

Answer 44

- XY genotype with 5 alpha reductase deficiency - Increased testosterone and able to respond to it