L28 - Spermatogenesis

Question 1

Define the duration and number of spermatozoa formed in 1 spermatogenesis cycle?

Answer 1

60 -70 days

1 spermatogonium&raquo_space;64 spermatozoa (4 mitosis + 1 meiosis)

Question 2

Give differences between Meiosis in spermatogenesis and oogenesis?

Answer 2

Spermatogenesis = Uninterrupted, Starts at puberty, Equal cell divisions, Constant stem cell pool for lifelong production

Oogenesis = Interrupted twice, unequal division with polar bodies, All oogonia undergo meiosis before birth = limited number

Question 3

Compare the end products of spetmatogenesis and oogenesis?

Answer 3

Spermatogenesis = 4 functional spermatid

Oogenesis = one functional oocyte + polar bodies

Question 4

List the stages of sperm maturation? Define the number of pairs of chromosomes?

Answer 4

Spermatogonium = 2c

Primary spermatocyte = 4c

Secondary spermatocyte = 2c

Spermatid = 1c

Speratozoan (with tail) = 1c

Question 5

How do spermatogonia retain lifelong capacity to produce spermatocyte?

Answer 5

Number of spermatogonia always remain in stem cell pool and self-renew&raquo_space; unlimited spermatocytes production

Question 6

Anatomical site of sperm production?

Answer 6

Seminiferious tubules in testis

Question 7

Define the phases of spermatogenesis that occur in the 2 compartments of the seminiferous tubules?

Answer 7

Basal compartment (outside of Blood-testis barrier) = Mitosis of Spermatogonia

Adluminal compartment = Meiosis and Spermiogenesis

Question 8

Describe the function of sertoli cells as spermatocytes mature?

Answer 8

Maintain blood testis barrier by breaking tight junctions in front of moving spermatocyte + reforming tight junctions behind

Question 9

How is testicular temperature regulated?

Answer 9

Testis temp = 2 degrees lower

1) Contraction of scrotum muscle
2) Countercurrent heat exchange between arteries and veins cool arterial blood

Question 10

Which cell type divide seminiferous tubules into compartments?

Answer 10

Sertoli cells:

Form tight junctions that separate pre- and post-meiotic germ cells

Question 11

List the 4 main structural changes in spermiogenesis. exam

Answer 11

Nuclear condensation

Shrinkage of cytoplasm

Formation of an acrosome

Development of a tail

Question 12

How does temperature affect sperm quality?

Answer 12

High temp = decrease sperm quality, motility and count

Question 13

Describe the process of spermiogenesis?

Answer 13

• Formation of acrosome granules at head of sperm for penetration of egg
• Alignment of mitochondria along tail: store Ca for acrosomal reaction + energy for tail
• form sperm tail for motility
• Nucleus of spermatid become condensed: replace Histone with Protamine

Question 14

Define spermiation

Answer 14

spermatozoa is extruded into the lumen of the seminiferous tubule

= Ovulation in female

Question 15

Describe how sperm is transported to the epididymis?

Answer 15

tubular fluid current created by peritubular myoid cells + cilia of epididymis

contraction of the testicular capsule

Question 16

Describe the change of sperm maturation as it travels through the epididymis?

Answer 16

Sperm gain motility & lose cytoplasm

Question 17

Define the hormones secreted by Sertoli cells and their functions?

Answer 17

1. Anti-Mullerian hormone = regression of paramesonephric ducts before puberty
2. Androgen-binding protein (ABP) = high testosterone
3. Inhibin/activin:
   - Regulate testosterone
   - Secreted in different parts of seminiferous tubules to guide spermatogenesis
4. Plasminogen activator for spermiation

Question 18

Describe the 2 processes that occur in capacitation of sperm?

Answer 18

• Hyperactive motility
• Acrosome reaction: binding of sperm to ZP3 of zona pellucida causes massive Ca2+ influx at head of sperm
  » fusion of sperm and egg membrane
  » release proteolytic enzymes for penetration

Question 19

Compare the physiological effects of Inhibin and Activin secreted by Sertoli cells?

Answer 19

Inhibin = Decrease FSH production at Pituitary, Increase Testosterone production from Leydig cells

Activin = Decrease Testosterone production from Leydig cells, Increase FSH from pituitary

Question 20

Role of peritubular myoid cells in testes?

Answer 20

modulate function of other testicular cells e.g. Sertoli cells

Contraction = Move spermatozoa to rete testis

Question 21

List the hormone produced by Leydig cells? Location in testis?

Answer 21

In interstitial tissue outside seminiferous tubules

Make Testosterone&raquo_space; converted to estrogen and Dihydrotestosterone (DHT) in target tissue

Question 22

The ability to synthesize testosterone begins only at puberty. T or F

Answer 22

False

Testosterone production is high during fetal development and after birth

Question 23

How is Cholesterol turned into estrogen?

Answer 23

Cholesterol&raquo_space; pregnenolone&raquo_space; progesterone (C21)&raquo_space; Androgen (testosterone, Androtenedione)

Androgen turned into estrogen by Aromatase enzyme

Question 24

Which hormones controls Leydig cell activity?

Answer 24

Growth factor from germ cells, Pituitary LH, Inhibin from Sertoli= stimulate

Estradiol, Activin from Sertoli = Inhibit

Question 25

Explain how testosterone exerts direct and indirect effect on target cells?

Answer 25

• Directly activate target cell

- Converted to DHT, or Estradiol (E2) before acting on target cell

Question 26

List some physiological effects mediated by DHT?

Answer 26

Same as E2:
Sex drive and behavior
Spermatogenesis

Different:
Intrauterine development of male reproductive tract
FSH, LH secretion
Pubertal development of beard, penis, seminal vesicle

Question 27

List some physiological effects mediated by estradiol in male?

Answer 27

Same as DHT:

• Sex drive, behavior
• Spermatogenesis

Different:

• imprint male pattern of gonadotrophins
• inhibit leydig cells
• Regulate bone growth

Question 28

Summarize all the activating factors of Sertoli cells?

Answer 28

Testosterone from leydig cells

FSH from pituitary

Growth factors from germ cells

Proteins from Peritubular cells

Question 29

Name the activating factor of peritubular cells?

Answer 29

Testosterone from Leydig cells

Question 30

Which hormone is an absolute requirement for spermatogenesis?

Answer 30

Testosterone*

> > stimulate androgen receptors at Sertoli cells and peritubular cells

Question 31

Which hormones regulate Quantitative spermatogenesis?

Answer 31

FSH and LH&raquo_space; controls proliferation of sertoli cells and regulate mitosis of spermatogonia&raquo_space; control spermatogenesis quantitatively

Question 32

Which hormone is responsible for sexual behavior and male ejaculation?

Answer 32

Testosterone&raquo_space; only hormone to act on preoptic areas & anterior hypothalamus for sexual behavior

Question 33

3 phases of the male sex act?

Answer 33

Erection of penis
Emission
Ejaculation

Question 34

Describe the process of penile erection?

Answer 34

Activate parasympathetic nervous system

1) Vasodilation to fill erectile tissue with blood (corpus cavernosum, spongiosum)
2) Contraction of Ischiocavernosus muscle and Bulbocavernosus muscle for erection

Question 35

Describe the process of emission during male sex act?

Answer 35

activate sympathetic*** nervous system

> > contraction of vas deferens, male sex accessory glands

> > semen forms in prostatic urethra

Question 36

Describe the process of ejaculation during male sex act?

Answer 36

Filling of prostatic urethra

> > rhythmic contraction of genital duct + ischiocavernosus and bulbocavernosus muscle

> > expel sperm

Emission + ejaculation = orgasm

Question 37

Define the secretion and function of the Bulbourethral gland?

Answer 37

Pre-ejaculate:

5% ejaculate volume

• Alkaline to neutralize vaginal acidity
• Lubricate tip of penis during intercourse

Question 38

Define the secretion and function of the Seminal vesicles?

Answer 38

50-80% ejaculate volume:

• Fructose (energy) + Ascorbic acid (antioxidant) for sperm
• Stimulators of sperm motility: Potassium, bicarbonate…
• Semenogelin: form coagulum = inhibit sperm capacitation and motility

Question 39

Define the secretion and function of the prostate gland?

Answer 39

15-30% ejaculate volume:

• Citric acid = antioxidant
• Zinc = antioxidant + stabilize sperm chromatin
• Prostatic acid phosphatase (PAP) for proteolytic cleavage of semenogelins