L28 - Spermatogenesis Flashcards
Define the duration and number of spermatozoa formed in 1 spermatogenesis cycle?
60 -70 days
1 spermatogonium»_space;64 spermatozoa (4 mitosis + 1 meiosis)
Give differences between Meiosis in spermatogenesis and oogenesis?
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
Compare the end products of spetmatogenesis and oogenesis?
Spermatogenesis = 4 functional spermatid
Oogenesis = one functional oocyte + polar bodies
List the stages of sperm maturation? Define the number of pairs of chromosomes?
Spermatogonium = 2c
Primary spermatocyte = 4c
Secondary spermatocyte = 2c
Spermatid = 1c
Speratozoan (with tail) = 1c
How do spermatogonia retain lifelong capacity to produce spermatocyte?
Number of spermatogonia always remain in stem cell pool and self-renew»_space; unlimited spermatocytes production
Anatomical site of sperm production?
Seminiferious tubules in testis
Define the phases of spermatogenesis that occur in the 2 compartments of the seminiferous tubules?
Basal compartment (outside of Blood-testis barrier) = Mitosis of Spermatogonia
Adluminal compartment = Meiosis and Spermiogenesis
Describe the function of sertoli cells as spermatocytes mature?
Maintain blood testis barrier by breaking tight junctions in front of moving spermatocyte + reforming tight junctions behind
How is testicular temperature regulated?
Testis temp = 2 degrees lower
1) Contraction of scrotum muscle
2) Countercurrent heat exchange between arteries and veins cool arterial blood
Which cell type divide seminiferous tubules into compartments?
Sertoli cells:
Form tight junctions that separate pre- and post-meiotic germ cells
List the 4 main structural changes in spermiogenesis. exam
Nuclear condensation
Shrinkage of cytoplasm
Formation of an acrosome
Development of a tail
How does temperature affect sperm quality?
High temp = decrease sperm quality, motility and count
Describe the process of spermiogenesis?
- 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
Define spermiation
spermatozoa is extruded into the lumen of the seminiferous tubule
= Ovulation in female
Describe how sperm is transported to the epididymis?
tubular fluid current created by peritubular myoid cells + cilia of epididymis
contraction of the testicular capsule
Describe the change of sperm maturation as it travels through the epididymis?
Sperm gain motility & lose cytoplasm
Define the hormones secreted by Sertoli cells and their functions?
- Anti-Mullerian hormone = regression of paramesonephric ducts before puberty
- Androgen-binding protein (ABP) = high testosterone
- Inhibin/activin:
- Regulate testosterone
- Secreted in different parts of seminiferous tubules to guide spermatogenesis - Plasminogen activator for spermiation
Describe the 2 processes that occur in capacitation of sperm?
- 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
Compare the physiological effects of Inhibin and Activin secreted by Sertoli cells?
Inhibin = Decrease FSH production at Pituitary, Increase Testosterone production from Leydig cells
Activin = Decrease Testosterone production from Leydig cells, Increase FSH from pituitary
Role of peritubular myoid cells in testes?
modulate function of other testicular cells e.g. Sertoli cells
Contraction = Move spermatozoa to rete testis
List the hormone produced by Leydig cells? Location in testis?
In interstitial tissue outside seminiferous tubules
Make Testosterone»_space; converted to estrogen and Dihydrotestosterone (DHT) in target tissue
The ability to synthesize testosterone begins only at puberty. T or F
False
Testosterone production is high during fetal development and after birth
How is Cholesterol turned into estrogen?
Cholesterol»_space; pregnenolone»_space; progesterone (C21)»_space; Androgen (testosterone, Androtenedione)
Androgen turned into estrogen by Aromatase enzyme
Which hormones controls Leydig cell activity?
Growth factor from germ cells, Pituitary LH, Inhibin from Sertoli= stimulate
Estradiol, Activin from Sertoli = Inhibit
Explain how testosterone exerts direct and indirect effect on target cells?
- Directly activate target cell
- Converted to DHT, or Estradiol (E2) before acting on target cell
List some physiological effects mediated by DHT?
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
List some physiological effects mediated by estradiol in male?
Same as DHT:
- Sex drive, behavior
- Spermatogenesis
Different:
- imprint male pattern of gonadotrophins
- inhibit leydig cells
- Regulate bone growth
Summarize all the activating factors of Sertoli cells?
Testosterone from leydig cells
FSH from pituitary
Growth factors from germ cells
Proteins from Peritubular cells
Name the activating factor of peritubular cells?
Testosterone from Leydig cells
Which hormone is an absolute requirement for spermatogenesis?
Testosterone*
> > stimulate androgen receptors at Sertoli cells and peritubular cells
Which hormones regulate Quantitative spermatogenesis?
FSH and LH»_space; controls proliferation of sertoli cells and regulate mitosis of spermatogonia»_space; control spermatogenesis quantitatively
Which hormone is responsible for sexual behavior and male ejaculation?
Testosterone»_space; only hormone to act on preoptic areas & anterior hypothalamus for sexual behavior
3 phases of the male sex act?
Erection of penis
Emission
Ejaculation
Describe the process of penile erection?
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
Describe the process of emission during male sex act?
activate sympathetic*** nervous system
> > contraction of vas deferens, male sex accessory glands
> > semen forms in prostatic urethra
Describe the process of ejaculation during male sex act?
Filling of prostatic urethra
> > rhythmic contraction of genital duct + ischiocavernosus and bulbocavernosus muscle
> > expel sperm
Emission + ejaculation = orgasm
Define the secretion and function of the Bulbourethral gland?
Pre-ejaculate:
5% ejaculate volume
- Alkaline to neutralize vaginal acidity
- Lubricate tip of penis during intercourse
Define the secretion and function of the Seminal vesicles?
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
Define the secretion and function of the prostate gland?
15-30% ejaculate volume:
- Citric acid = antioxidant
- Zinc = antioxidant + stabilize sperm chromatin
- Prostatic acid phosphatase (PAP) for proteolytic cleavage of semenogelins
