Lecture Notes: Spermatogenesis and Genetic Diversity

Key Cell Types

Sertoli Cells (Sustentacular Cells)

• Mediate effects of testosterone and follicle-stimulating hormone (FSH).
• Nourish spermatogenic cells: spermatocytes, spermatids, and spermatozoa.
• Phagocytize excess spermatid cytoplasm.
• Control movement of spermatogenic cells and release them into the lumen.
• Secrete fluid for sperm transport and hormone inhibin.

Leydig Cells (Interstitial Endocrinocytes)

• Located between seminiferous tubules.
• Secrete testosterone.

Spermatogenesis Process

1. Spermatogonium (Diploid) to Primary Spermatocyte
   • Undergo mitosis for stem cell reserve and sperm production.
2. Primary Spermatocyte to Secondary Spermatocyte
   • Meiosis I forms haploid secondary spermatocytes.
3. Secondary Spermatocyte to Spermatid
   • Meiosis II results in spermatids connected by cytoplasmic bridges.
4. Spermiogenesis
   • Maturation of spermatids into sperm.
   • Release of sperm (spermiation).

Chromosome Basics

• Humans have 22 pairs of autosomes and 1 pair of sex chromosomes (X and Y).
• X Chromosome: Contains genes for non-sex traits like clotting factors, color vision.
• Y Chromosome: Contains SRY gene responsible for male development.

Genetic Recombination

• Occurs during Prophase I and Metaphase I of Meiosis I.
• Homologous chromosomes form tetrads (4 chromatids) and undergo crossing over.
• Crossing over results in genetic diversity by swapping genetic material between maternal and paternal chromatids.

Importance of Genetic Diversity

• Crossing over introduces diversity in offspring (e.g., eye and hair color variations).
• Resulting gametes have mixed genetic material from both parents.

Sperm Transport and Storage

• Epididymis: Site of sperm maturation and storage; can store sperm for a month.
• Ductus Deferens (Vas Deferens): Propels sperm towards the urethra via peristalsis.

Hormonal Regulation

• Puberty: Initiates GnRH release, stimulating LH and FSH production.
• LH: Stimulates Leydig cells to produce testosterone.
• FSH: Stimulates spermatogenesis.
• Negative Feedback: Testosterone and inhibin regulate sperm production.

Sperm Viability

• Sperm lifespan: 48 hours in the female reproductive tract.
• Egg lifespan: 24 hours post-ovulation, requiring timing overlap for fertilization.

Conclusion

• The process of spermatogenesis and genetic recombination contributes to genetic diversity and effective reproduction.
• Hormonal regulation ensures the maintenance of consistent sperm production and maturation.