Male reproductive physiology

Question 1

What are the two main functions of the male testis?

Answer 1

• Male sex steroid production

- Spermatogenesis

Question 2

List the actions of androgen (testosterone, oestradiol and DHT):

Answer 2

• Male fetus embryogenesis
• Negative feedback/regulation of gonadotrophin secretion by the HPA
• Spermtaogenesis
• Male sexual maturation and maintenance
• Male sexual function
• Bone and muscle mass increase and maintenance
• Increasing and maintenance of erythropoiesis and haematocrit

Question 3

Regarding the hypothalamic-pituitary-testicular axis:

What is the actions of
LH and FSH on the testis?

Answer 3

LH:

• Binds to receptors in Leydig cells.
• Stimulates steroid hormone production: testosterone, oestradiol and DHT.

FSH:
- Binds to receptors on Sertoli cells and stimulates spermatogenesis.

Question 4

Regarding the hypothalamic-pituitary-testicular axis:

Describe testicular negative feedback on gonadotrophin secretion:

Answer 4

Negative feedback at hypothalamus level:

• Testosterone is converted to oestradiol through aromatisation (aromatase-enzyme) in the testes (20%).
• Oestradiol suppresses GnRH secretion and therefore LH secretion.

Negative feedback at pituitary level:

• Testosterone directly suppresses LH secretion from the pituitary.
• Inhibin B (Sertoli cell product) and oestradiol inhibit FSH secretion.

Question 5

Regarding the hypothalamic-pituitary-testicular axis:

What other things may suppress this axis?

Answer 5

• Stress/acute illness
• Exogenous corticosteroids
• Hyperprolactinaemia.

Question 6

What are the two compartments of the testis and what do they contain?

Answer 6

1. Interstitial compartment: consists of Leydig cells, peritubular myoid cells, fibroblasts, neurovascular cells and macrophages.
2. Seminiferous tubule compartment consists of Sertoli cells and germ cells in various stages of spermatogenesis.

Question 7

Describe the blood-testis barrier:

Answer 7

• Basal lamina: ECM that forms outer rim of the seminiferous tubules and separates the two compartments.
• BL lined by spermatogonia (undifferentiated germ cells) and Sertoli cells with tight junctions separating the undifferentiated and differentiated germ cells.

Question 8

Describe the flow of sperm from the seminiferous tubules to ejaculation:

Answer 8

Seminiferous tubules –> rete testis –> epididymis –> vas deferens –> seminal vesicle –> ejaculatory duct –> urethra –> out

Question 9

How many mature sperm are made every day?

Answer 9

100 million sperm

Question 10

How long does sperm formation take?

Answer 10

74 days

Question 11

How long does it take to transport sperm through the epididymis to the ejaculatory ducts?

Answer 11

12 to 21 days

Question 12

Describe the process of spermatogenesis:

Answer 12

Spermatogenesis begins after puberty.

1. Mitotic / proliferative phase:
   - Dark spermatogonia undergo mitosis to replenish stem cell pool.
   - Some dark spermatogonia differentiate into pale spermatogonia
2. Meiotic phase:
   - B spermatogonia loses contact with basememnt membrane of seminiferous tubule and passes through blood-testis barrier to become two primary spermatocytes
   - First meiotic division: two primary spermatocytes (46 XY) –> two secondary spermatocytes (23 X or Y).
   - Second meiotic division: two secondary spermatocytes –> 4 spermatids (23 X or Y)
3. Spermiogenesis:
   - Spermatids mature into spermatozoa