Spermatogenesis

Question 1

What are the two major compartments of testes?

Answer 1

• Seminiferous tubules - 250m total length, developing germ cells, sertoli cells
• Interstitial spaces - leydig cells (synthesise androgens), blood and lymph vessels

Both compartments separate - blood testis barrier, prevents immune reaction to spermatozoa, separates fluids of different composition

Question 2

What is spermatogenesis and what are the stages?

Answer 2

Production of mature spermatozoa from undifferentiated germ cells (primodial germ cell) occurs in three stages:

• Mitotic proliferation
• Meiotic divisions
• Cell modelling (spermiogenesis)

Question 3

Spermatogenic cycle

Answer 3

74 days from first mitotic division to release of spermatozoa
Occurs in waves, initiated every 16 days. Rate of developmental stages is not uniform:
- Spermatogonium - primary spermatocytes - 25 days
- Meiotic division 1 - secondary spermatocytes - 9 days
- Development - spermatids - 19 days
- Differentiation - spermatozoa - 21 days

Question 4

Spermiation

Answer 4

At end of differentiation:

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

Fluid secreted by Sertoli cells flushes spermatozoa from seminiferous tubules through the rete testis into epididymis:

• Capacity for motility by the time they reach the tail of epididymis
• Motility is suppressed by epididymal fluid
• Instead movement through reproductive tract is aided by peristaltic muscle contractions

Question 5

Sperm maturation

Answer 5

If ejaculated spermatozoa are placed with oocytes in vitro fertilisation does not occur immediately
They need to undergo the process known as capacitation - normally occurs in female reproductive tract (2-6h)
Glycoprotein coat gained in epididymis is stripped
This results in two changes:
- head acquires the capacity to initiate the acrosome reaction
- Hyperactivation (inc flaggelar beats)

Question 6

Sub-fertility

Answer 6

Sperm quality is poor - only 4-14% show correct morphology
Infertlity in men is primarily diagnosed by semen analysis comprising of:
- Determination of sperm conc/total count
- Motility
- Morphology

Question 7

Oligozoospermia

Answer 7

Reduced sperm count

Question 8

Azoospermia

Answer 8

Absence of sperm in ejaculate

Question 9

Asthenozoospermia

Answer 9

Reduced sperm motility

Question 10

Teratozoospermia

Answer 10

Reduced percentage of sperm with normal morphology

Question 11

Antisperm antibodies

Answer 11

Abnormal immune response to sperm

Question 12

Role of hypothalamus and pituitary gland

Answer 12

Secretion of hormones - regulated by feedforward and feedback loops

Pulsatile secretion of GnRH from hypothalamus stimulates the anterior pituitary gonadotrophs

The pituitary gonadotrophins, LH and FSH control testicular functions

Question 13

Functions of LH and FSH

Answer 13

Leydig cells in testes have receptors for LH - stimulates synthesis and secretion of testosterone
If LH secretion is low, testosterone is low - spermatogenesis halts

However LH and testosterone cannot maintain spermatogenesis at normal level without FSH

FSH is required for max sperm production - acts on sertoli cells

Question 14

What does low amounts of inhibin mean?

Answer 14

High amounts of gonadotrophins because not getting -ve feedback to reduce amount of gonadotrophins so they are therefore elevated

Question 15

Functions of FSH on sertoli cells

Answer 15

Increase androgen receptors which increase FSH receptors
Inc fluid secretion
Inc ABP secretion
Inc cAMP
Inc inhibin secretion
Inc energy metabolism
Inc RNA and protein synthesis

Question 16

Testicular hormones

Answer 16

Synthesise a number of hormones:
- Testosterone (steroid) by Leydig cells - in some tissues do not exert direct effects but are converted to dihydrotestosterone or estrogens
_ Estrogens (steroid) by Sertoli and Leydig cells

Question 17

Role of testosterone

Answer 17

Essential for spermatogenesis

• If production is prevnted spermatogenesis ceases
• Blocked when primary spermatocytes enter meiotic prophase

If blood (testosterone) is low then fewer stem cells will begin cell division but the whole process will still take 74 days

Question 18

Causal diagnosis of male infertility

Answer 18

Only 28% provided a causal diagnosis
Most consist of previous gondatoxic chemo or radiotherapy for treatment of malignancy, testosterone abuse or other chronic diseases such as diabetes, genetic disorders e.g. Klinefelters

In addition genes involved in migration and function of GnRH neurons or their upstream regulators have been discovered that may be mutated in patients with congenital hypogonadtrophic hypogonadism with or without anosmia