ERS28 Spermatogenesis Flashcards
Spermatogenesis
- within Seminiferous tubules
- 60-70 days (imply treatment inducing spermatogenesis takes 60-70 days)
- 1 spermatogonium —(4 mitosis + 1 meiosis)—> 64 spermatozoa
(NO unequal cell division)
Direction: Seminiferous tubules —> Rete testis —> Efferent tubules (Vasa efferentia) —> Epididymis (***Caput + ***Corpus + ***Cauda) (coiled tube) —> Vas deferens
Epididymis epithelium: Pseudostratified columnar epithelium with Stereocilia
Cilia越黎越短, Lumen越黎越大
Caput Epididymis:
- ciliated epithelium
- small lumen
- absorption of testicular fluid to concentrate sperm
Corpus Epididymis:
- shorter cilia
- wider lumen
- absorption of testicular fluid to concentrate sperm
Cauda Epididymis:
- cuboidal, poorly ciliated epithelium
- wide lumen
- small muscle cells
- ***store sperm at high density
Time required for sperm to travel through Epididymis —> 2-6 days
- not related to length
Testis
- Reproductive organ (Seminiferous tubule) —> Spermatogenesis
- Endocrine organ (Leydig cells) —> Male sex hormone (Testosterone)
Germ cells in mature testes
Puberty
—> **Spermatogonia (2N, 2C) (periphery of Seminiferous tubules) (Undergo mitosis / **Self-renewal / Proliferating phase)
—> DNA replication
—> **Primary Spermatocyte (2N, 4C)
—> Meiosis 1
—> **Secondary Spermatocyte (1N, 2C)
—> Meiosis 2
—> Spermatids (1N, 1C) (non-motile, without tail) (closer to lumen of Seminiferous tubules)
—> Morphological changes (Spermiogenesis)
—> ***Spermatozoa (1N, 1C)
***Difference between Spermatogenesis and Oogenesis.
- NOT all spermatogonia will undergo meiotic division
—> some will go back to stem cell pool
—> **self-renewal to produce more spermatogonia
—> **“unlimited” number of spermatocytes - Presence of additional step after formation of spermatids: ***Spermiogenesis
—> transformation of spermatids into sperm
—> change in morphology - Meiosis start **before birth in Oogenesis
—> ALL oogonia undergo meiosis
—> Primary oocyte
—> set ceiling of finite number of oocytes in a female
VS
Spermatogonia remain dormant until after puberty, Meiosis start **at puberty -
**Prolonged cell division in Oogenesis (from fetal period to after fertilisation)
- enable external factor to affect division process
—> female Oogenesis **higher aneuploidy rate with age
VS
Spermatogenesis start after puberty, ***once started go to completion (uninterrupted) - Equal cell division in Spermatogenesis
VS
Unequal cell division in Oogenesis - 4 functional spermatozoa in Spermatogenesis (vs 1 functional oocyte each meiosis)
Seminiferous tubule structure
- Myoid cells
- smooth muscles cells
- contraction of tubule, propel content towards Rete testis - Leydig cells
- Testosterone production - Sertoli cells
- Blood-testes barrier
—> separate Seminiferous tubules into Adluminal + Basal compartment
—> Tight junction: important in controlling material going into Seminiferous tubules
- **Spermatogonia outside of tight junction (i.e. in Basal compartment)
—> **Primary spermatocytes move across Blood-testes barrier
—> into Adluminal compartment - Spermatogonia —> Spermatozoa
Basal vs Adluminal compartment
Basal compartment:
—> **Proliferating phase, **Self-renewal
- Spermatogonia
Adluminal compartment:
—> **Meiosis
—> **Spermiogenesis (differentiation into spermatozoa)
- Primary / Secondary Spermatocytes, Spermatids, Spermatozoa
Tight junctions
Dynamic structure
- always assemble / disassemble —> allow germ cells to move across barrier
- form behind moving Preleptotene / Leptotene spermatocytes
—> disassembly of tight junction in front of cells
**Preleptotene (DNA synthesis) / **Leptotene spermatocytes move inwards towards lumen
Spermiogenesis
- Formation of ***Acrosome granule (small vesicle covering one side of spermatid nucleus)
—> contain Enzymes (Acrosin)
—> grow in size
—> cover anterior 1/3 of sperm nucleus - Formation of **Sperm tail
—> Opposite side to Acrosome granule
—> **Mitochondria of spermatid move from periphery of spermatid towards sperm tail
—> within ***Midpiece - Condensation of nucleus of spermatid
—> replacement of Histone protein by ***Protamine - Shrinkage of cytoplasm
—> sperm contains mainly **DNA + **Mitochondria
Structure of mature sperm
- Head
- Nucleus (condensed) covered on one side by Acrosome
- Acrosome
—> covered outside by plasma membrane
—> outer + inner membrane
—> enzyme to help penetrate **Zona pellucida + Cumulus mass (i.e. **Corona radiata) - Midpiece
- Mitochondria
—> **produce energy for sperm movement
—> **Ca storage - Tail
- Active propulsion of sperm
Low temperature is important for spermatogenesis
- Testicular temperature in Scrotum: ***2oC lower than Body temp
- Descent of testis at birth important
- Temperature regulation
- ***Musculature of scrotum (Dartos muscle)
—> contraction in cold temperature to press testes towards body core
—> relax in hot temperature to allow testes to descend
- ***Counter current heat exchange
—> testicular arteries in parallel with veins
—> when hot arterial blood enter testes —> embedded in network of veins (lower temp)
—> cooled down by cold blood in testicular veins
Lifestyle affects sperm quality
Regular hot bath
—> ↓ sperm count
—> ↓ motility
—> poor morphology
Spermiation
Process in which Spermatozoa extruded into lumen of Seminiferous tubule (~ ovulation)
Sperm maturation in Epididymis
Transportation of sperm to Epididymis
- Tubular fluid current created by contraction of peritubular ***Myoid cells (move from Seminiferous tubules towards Rete testis)
- Contraction of ***testicular capsule (Tunica albuginea)
Changes during maturation:
- Marked changes in osmolality
- ***Concentration of osmolytes, molecules in Epididymis - ***Gain motility
- ***Lose cytoplasm
Capacitation
- ***Sperms acquire ability to fertilise ovum
- Occur in female reproductive tract
- Ill-defined process
End point:
- Hyperactivation
- special motility pattern after capacitation —> ↑ amplitude, not necessarily forward (活躍地亂咁走) (Non-hyperactivated: slow, progressive linear forward) - Acrosome reaction
- fusion of Acrosomal + Outer sperm membrane
—> pores on sperm head
—> release of **hydrolytic + **proteolytic enzymes
—> penetration through **Zona pellucida, **Cumulus mass
***Sertoli cells
- Regulate nutrients + environment for Spermatogenesis
- Tight junctions / Blood testes barrier
—> separating pre (Spermatogonia) / post meiotic germ cells (Primary spermatocytes) - Endocrine / Paracrine function
- ***Anti-Mullerian hormone (AMH) —> regression of Müllerian ducts before puberty
- **Androgen binding protein (ABP) —> T becomes less lipophilic —> **concentrate in luminal fluid —> high Testosterone —> enable spermatogenesis + maturation
- ***Plasminogen activator —> Spermiation
- ***Inhibin / Activin —> regulate Testosterone
Inhibin and Activin
Inhibin:
- ↓ FSH production (Testosterone -ve feedback to FSH)
- ***↑ Testosterone production from Leydig cells
Activin:
- ***↑ FSH production
- ↓ Testosterone production from Leydig cells
Peritubular Myoid cells
- Move spermatozoa to Rete testis by contraction
2. Modulate function of other testicular cells e.g. Sertoli cells, Leydig cells
Leydig cells
Testosterone production
Under pituitary LH control
Testosterone
- circulating
- prohormone of DHT (Dihydrotestosterone)
—> T converted to DHT in tissue
Testosterone in male
Ability to produce Testosterone acquired before birth at fetal stage
- **3 peaks:
1. After fertilisation
2. Immediately after birth
3. After puberty
Function:
Note: Precursor in some tissues (need to convert to DHT: more active / E2)
1. Intrauterine development of male reproductive tract
2. Puberty development
3. Spermatogenesis
4. Sex drive
5. Muscle, Skeleton, Body fat
Conversion of Testosterone to Estrogen
Which steroid to produce depends on
- Availability of enzymes
- Activity of enzymes
E.g. High Aromatase activity —> Androgen rapidly converted into Estrogen
Cholesterol
—> Progesterone
—> Corticosteroid (Cortisol, Aldosterone) / Androgen (T, Androstenedione) —> Estrogen (Estradiol, Estrone, Estriol)
***Interaction among Testicular cells (Leydig, Sertoli, Myoid, Germ cells)
Interactions are localised: different position of seminiferous tubule —> different interaction (stimulatory / inhibitory)
LH —(+ve)—> Leydig (~ Theca) —> Testosterone —(+ve)—> Myoid + Sertoli
FSH —(+ve)—> Sertoli (~ Granulosa)
Myoid —(+ve, Proteins)—> Sertoli
- **Sertoli
1. ABP —> ↑ Testosterone
2. Nutrients, Growth factors, ABP —(+ve)—> Germ cell - **3. Activin, Estradiol —(-ve)—> Leydig —> ↓ Testosterone
- **4. Inhibin —(+ve)—> Leydig —> ↑ Testosterone
Germ cell
Growth factors —(+ve)—>
1. Leydig
2. Sertoli
***Gonadotropin and Spermatogenesis
Testosterone: Absolute requirement for spermatogenesis (without T, stop at Preleptotene stage (DNA synthesis))
—> -ve feedback to Gonadotropin
Initially:
- Normal FSH, LH, Testosterone —> High Sperm density
High Testosterone
—> inhibit FSH + LH
—> Sperm density ↓ greatly (太高Testosterone反而令Sperm density ↓ ∵ ↓ FSH, LH)
—> Give FSH, LH
—> Sperm density ↑ slightly but not reach level before
Conclusion:
**Both FSH, LH are also required for **quantitative spermatogenesis
Regulation of spermtogenesis by LH + FSH
- LH
—> Leydig
—> ***Testosterone (absolute requirement for initiation + maintenance of spermatogenesis)
—> Sertoli + Myoid (Androgen receptors) - FSH
- **proliferation of Sertoli in mature testes —> Testicular development
- act on Sertoli cells —> indirectly regulate **Mitosis of Spermatogonia + prevent degeneration
Regulation of spermatogenesis on Hypothalamic-pituitary-gonad axis
LH —> Leydig —> **Testosterone —> -ve feedback on **Gonadotropin + GnRH
FSH —> Sertoli —> **Inhibin —> -ve feedback on **FSH only but +ve to Leydig
Testosterone and Sexual behaviour
T implant into Preoptic areas, Anterior hypothalamus
—> produce similar response to systemic injection of T
Conclusion:
Testosterone act on **Preoptic areas, **Anterior hypothalamus to enhance sexual behaviour
Male sex act
3 stages
1. Erection of penis
- activation of **PNS —> **Vasodilation —> Filling of vascular structure within penis
—> Corpus cavernosum + Corpus spongiosum
—> veins in penis compressed when erectile tissues filled with blood
—> ↓ blood outflow from penis
- Ischiocavernosus muscle + Bulbospongiosus muscle
—> assists in Micturition + Erection
—> compress Bulb of penis
—> pull Root of penis (Crus + Bulb) —> erection
- Emission
- activation of **SNS
—> Contraction of **Vas deferens + **Male sex accessory glands
—> Semen formation in **prostatic urethra - Ejaculation
- filling of prostatic urethra
—> Rhythmical contraction of genital duct + Contraction of Ischiocavernosus muscle / Bulbospongiosus muscle
—> ejaculation
- 40-80 million sperms in 2-4 mL
- Emission + Ejaculation occur during Orgasm
WHO reference ranges for normal Semen
- Volume >= 1.5 mL
- pH >= 7.2 (Alkaline)
- Concentration
- Count
- Motility (<1 hour)
- Morphology
Sperm morphology abnormalities
- Head defects
- Neck and Midpiece defects
- Tail defects
- Cytoplasmic defects
Semen
Seminal plasma + Spermatozoa
Seminal plasma:
- Sex accessory glands
- Alkaline —> neutralise acidity of female tract
- Most spermatozoa expelled with prostatic secretion in first 1/3 of ejaculate —> need to collect whole semen sample (later part of Ejaculate contain less sperm —> not accurate)
Bulbourethral gland (Cowper’s gland)
- 5% ejaculate volume
- clear, **alkaline, mucoid fluid produced on sexual stimulation (pre-ejaculate) into urethra
—> **lubricant for semen
—> lubricant for Glans penis during intercourse
—> ***neutralise acidity of urine residue in urethra + acidity of vagina
Seminal vesicles
- 50-80% of ejaculate volume
- last fraction of ejaculate
- rich in
1. Fructose (energy)
2. Ascorbic acid (antioxidant)
3. **Stimulators of sperm motility: K, HCO3, Mg, Prostaglandin
4. **Semenogelin (protein) —> Coagulum formation, ***inhibit sperm capacitation before passing through cervical canal
—> capacitated sperm have limited lifespan
—> early capacitation not allow enough time for sperm to swim to Fallopian tube
Prostate gland
- 15-30% ejaculate volume
- main source of
1. Citric acid —> antioxidant
2. **Zinc —> antioxidant + **sperm chromatin stabilisation
3. **Prostatic acid phosphatase, **Prostate-specific antigen (PSA)
—> **Semenogelins cleavage
—> allow sperm to **swim and capacitation
