8. Spermatogenesis

Question 1

What are the two major compartments of the testes?

Answer 1

Seminiferous tubules

• Developing germ cells
• Sertoli cells

Interstitial spaces

• Leydig cells (synthesise androgens)
• Blood and lymph vessels

Both compartments are separate, “blood-testis barrier”

Question 2

Role of “blood-testis barrier”?

Answer 2

Prevents immune reaction to spermatozoa

Separates fluids of different composition

Question 3

What is spermatogenesis?

Answer 3

Production fo mature spermatozoa from undifferentiated germ cells (primordial germ cell) occurs in three stages;

1. Mitotic proliferation
2. Meiotic (reduction) division
3. Cell modelling (spermatogenesis)

Question 4

First mitotic division to release spermatozoa…

Answer 4

after 74 days

Question 5

Spermatogenesis occurs in waves, initiated every ___ days…

Answer 5

16 days

Question 6

Structure of sperm

Answer 6

Flagella: End piece, principal piece, middle piece and head (covered by acrosome)

Question 7

Sperm maturation at the end of differentiation, what happens?

Answer 7

• Cytoplasmic links are broken
• Spermatozoa released into tubule lumen
• Sperm virtually immobile

Question 8

Role of Sertoli cells at sperm maturation stage>

Answer 8

Fluid secreted by Sertoli cells flushes developing spermatozoa from seminiferous tubules, through the rete testis into the epididymis:
– Capacity for motility by the time they reach the tail of the epididymis
– Motility is suppressed by epididymal fluid

Question 9

What is capacitation?

Answer 9

If ejaculated spermatozoa are placed with oocytes in vitro fertilization does not occur immediately.
They need to undergo the process known as capacitation:
- Normally occurs in the female reproductive tract (2-6h)

Process: Glycoprotein coat gained in epididymis is stripped. Results in two changes:

1. Hyperactivation (increased flagellar beats)
2. Head acquires the capacity to initiate the acrosome reaction

Question 10

Sperm quality?

Answer 10

Poor

30% show morphological abnormalities

Question 11

Normal and sub fertile sperm count?

Answer 11

Normal: 50-150 x 10^6/ml

Sub-fertile: Less than 20 x 10^6/ml

Question 12

What is oligozoospermia?

Answer 12

Less than 20 x 10^6/ml sperm count

Question 13

What is azoospermia?

Answer 13

Absence of sperm in ejaculate

Question 14

What is asthenozoospermia?

Answer 14

Low sperm motility (<50% moving)

Question 15

What is teratozoospermia?

Answer 15

High proportion of abnormally-shaped sperm

Question 16

What is antiserum antibodies?

Answer 16

Abnormal immune response to sperm

Question 17

What hormones are produced by the testes?

Answer 17

1. Testosterone (steroid) by Leydig cells
   • In some tissues do not exert direct effects, but are converted to dihydrotestoterone or oestrogens
2. Oestrogens (steroid) by Sertoli and Leydig cells
3. Inhibits (polypeptides) by Sertoli cells
   - Feedback loop to control hormone levels
4. Oxytocin (polypeptide) by Leydig cells
   - Contraction of smooth muscle of the genital tract

Question 18

Role of testosterone in spermatogenesis?

Answer 18

– If production prevented spermatogenesis ceases
– Blocked when primary spermatocytes enter meiotic prophase

if blood levels are low then fewer stem cells will begin division but whole process will still take 74 days

Question 19

Role of pituitary glands and hypothalamus in spermatogenesis?

Answer 19

Ant pituitary controls testicular function by secreting the gonadotrophin from the gonadotroph cells
Pituitary gonadotrophs in turn are controlled by the hypothalamus, which secretes gonadotrophin-releasing hormone (GnRH)
Secretion of hormones by the hypothalamus, anterior pituitary and testes are regulated by complex feedback loops

Question 20

Blood supply between hypothalamus and pituitary glands

Answer 20

The hypophyseal portal system is a system of blood vessels in the brain that connects the hypothalamus with the anterior pituitary. Its main function is the transport and exchange of hormones to allow a fast communication between both glands.

Question 21

Hormone production in the pituitary gland that influence spermatogenesis?

Answer 21

1. Ant pituitary
   -Gonadotrophs
   Basophili cells secrete LH and FSH
   Most cells secrete one or there, or both
   -Lactotrophs
   Acidphilic cells secrete prolactin

Post pituitary
-Neurosecretory neurones
Secrete arginine vasopressin and oxytocin

Question 22

Control of gonadotrophin secretion

Answer 22

LH and FSH secretions controlled by GnRH secreted by the hypothalamus
GnRH is released into the portal blood in pulses every hour
GnRH must be pulsatile or it is ineffective
High GnRH pulse amplitude and frequency preferentially stimulates LH synthesis and secretion
Low GnRH pulse amplitude and frequency stimulates FSH synthesis and secretion

Question 23

Functions of LH and FSH in spermatogenesis

Answer 23

Leydig cells in the tests have receptors for LH. Stimulates synthesis and secretion of testosterone

If LH secretion is too low, testosterone is low and spermatogenesis helps.

All 3 hormones essential for process to resumes

FSH is required for max sperm production, acts on Sertoli cells

Question 24

Function of FSH on Sertoli cells

Answer 24

1. Increase RNA and protein synthesis
2. Increase energy metabolism
3. Increase inhibin secretion (reduces FSH secretion from ant pituitary)
4. Increase cyclic AMP
5. Increase ABP secretion
6. Increase fluid secretion
7. Increased androgen receptor expression –> Increase FSH receptors