65 Spermatogenesis

Question 1

What are the two major compartments of the testes?

Answer 1

1. Seminiferous tubules
2. Interstitial spaces

• Both compartments separate: “blood-testis barrier”

Question 2

What are the seminiferous tubules in testes?

Answer 2

• ~ 250 m total length
• Developing germ cells
• Sertoli (sustentacular) cells

Question 3

What are the interstitial spaces in testes?

Answer 3

• Leydig cells (synthesise androgens

* Blood and lymph vessels

Question 4

Role of blood-testis barrie?

Answer 4

• Prevents immune reaction to spermatozoa

* Separates fluids of different composition

Question 5

What is spermatogenesis?

Answer 5

Production of mature spermatozoa from undifferentiated germ cells (primordial germ cell)

Question 6

What are the 3 stages of spermatogenesis?

Answer 6

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

Question 7

How long is the spermatogenic cycle?

Answer 7

~74 days (from 1st mitotic division to release of spermatozoa)

Question 8

Spermatogenesis occurs in waves, how often is its initiated?

Answer 8

Every 16 days

Question 9

Spermatogenic cycle stages (length of time)

Answer 9

• Spermatogonium —> 1 ̊ spermatocytes = 25 days
• Meiotic division 1 —> 2 ̊ spermatocytes = 9 days
• Development —> spermatids = 19 days
• Differentiation –> spermatozoa = 21 days

= ~ 74 days

Question 10

Structure of sperm

Answer 10

• Flagella: End piece, principal piece, middle piece

* Head (nucleus covered by acrosome)

Question 11

How much sperm produced a day?

Answer 11

200 million/ day (~ 2300/sec)

Question 12

What happens in spermiation at the end of differentiation?

Answer 12

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

Question 13

Role of Sertoli cells in spermiation?

Answer 13

Fluid secreted by Sertoli cells flushes 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
• Instead movement through reproductive tract is aided by peristaltic muscle contractions

Question 14

What is capacitation?

Answer 14

• If ejaculated spermatozoa are placed with oocytes in vitro fertilisation doesn’t occur immediately
• Need to undergo capacitation - occurs in female reproductive tract (2-6 h)
• Glycoprotein coat gained in the epididymis is stripped
• Results in 2 changes:

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

Question 15

Human sperm quality?

Answer 15

• Relatively poor

* ~ 30% show morphological abnormalities or abnormal function

Question 16

Normal sperm count?

Answer 16

50-150 million/ml

Question 17

Sub fertility sperm count?

Answer 17

< 15 million/ml

Question 18

What is oligozoospermia?

Answer 18

Low sperm count (<15 million/ml)

Question 19

What is azoospermia?

Answer 19

Absence of sperm in the ejaculate

Question 20

What is asthenozoospermia?

Answer 20

Low sperm motility (< 50% moving)

Question 21

What is teratozoospermia?

Answer 21

High proportion of abnormally-shaped sperm

Question 22

What is antiserum antibodies?

Answer 22

Abnormal immune response to semen

Question 23

What stimulates the anterior pituitary gonadotrophs?

Answer 23

Pulsatile secretion of Gonadotrophin-releasing hormone (GnRH) from the hypothalamus

Question 24

What pituitary hormones control testicular functions?

Answer 24

1. Gonadotrophins
2. Luteinizing hormone (LH)
3. Follicle stimulating hormone (FSH)

Question 25

Blood supply between hypothalamus and pituitary gland

Answer 25

Hypothalamo-hypophysial portal system - allows the hypothalamus to communicate with the anterior pituitary via the release of neurotransmitters into the bloodstream

Question 26

Control of gonadotrophin secretion

Answer 26

* LH and FSH secretion is controlled by GnRH secreted by the hypothalamus * GnRH is released into the portal blood in pulses every hour * GnRH must be pulsatile or it's 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 27

Hormone production in the anterior pituitary gland

Answer 27

1. Gonadotrophs • Secrete LH and FSH (glycoproteins) • Most cells secrete one or other, but some secrete both 2. Lactotrophs • Secrete prolactin (protein)

Question 28

Hormone production in the posterior pituitary gland

Answer 28

Neurosecretory neurones | • Secrete arginine vasopressin (AVP) and oxytocin (peptides)

Question 29

Functions of LH and FSH

Answer 29

* Leydig cells in the testes have receptors for LH - stimulates synthesis and secretion of testosterone * If LH secretion is too low, testosterone is low - spermatogenesis halts * However, LH and testosterone cannot maintain spermatogenesis at its normal level without FSH * FSH is required for maximum sperm production - acts on Sertoli cells

Question 30

Functions of FSH on Sertoli cells

Answer 30

* ↑ RNA and protein synthesis * ↑ Energy metabolism * ↑ cAMP * ↑ Inhibit secretion * ↑ ABP secretion * ↑ Fluid secretion * ↑ Androgen receptors ---> ↑ FSH receptors

Question 31

What hormones are produced by the testes?

Answer 31

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

Question 32

Steroid hormone biosynthesis

Answer 32

Acetate --> Cholesterol --> (Progesterone ---> Testosterone) OR (Testosterone) ---> Oestogens

Question 33

Role of testosterone

Answer 33

• Essential for spermatogenesis – If production prevented 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 34

What does inhibin do?

Answer 34

Hormone secreted by Sertoli cells that inhibit the production of follicle-stimulating hormone (FSH) by anterior pituitary