Gametogenesis
🧬 Gametogenesis is the process by which haploid gametes (sperm in males 🧑🦱➡️🧬 and ova in females 👩🦰➡️🧬) are formed from diploid precursor cells.
It involves mitosis, meiosis, and differentiation, ensuring gametes carry half the genetic material ready for fertilisation.
♂️ Male Gametogenesis: Spermatogenesis
- Occurs in the seminiferous tubules of testes.
- Onset: Begins at puberty and continues lifelong.
- Duration: ⏳ ~64–72 days from start to mature sperm.
🌀 Mitotic Proliferation (Spermatocytogenesis)
- Spermatogonia: Diploid stem cells undergo mitosis in basal compartment.
- Differentiate into primary spermatocytes → move to adluminal compartment.
🔀 Meiosis
- Primary Spermatocytes: Undergo meiosis I → 2 haploid secondary spermatocytes.
- Secondary Spermatocytes: Complete meiosis II → haploid spermatids.
⚙️ Spermiogenesis (Differentiation)
- Spermatids mature into spermatozoa through:
- 🎯 Acrosome formation (enzymes to penetrate ovum).
- 📦 Nuclear condensation + flagellum development.
- 🪶 Cytoplasm shed → streamlined shape.
📊 Hormonal Regulation (Male)
- FSH: Stimulates Sertoli cells → support spermatogenesis.
- LH: Acts on Leydig cells → testosterone production.
- Testosterone: Essential for maturation and maintenance.
🧩 Sperm Structure
- Head: DNA + acrosome (enzymes).
- Midpiece: ⚡ Packed with mitochondria for motility energy.
- Tail: 🚀 Flagellum propels sperm toward ovum.
♀️ Female Gametogenesis: Oogenesis
- Occurs in the ovaries.
- Onset: Begins in fetal life 👶 → pauses → resumes at puberty.
- Completes only if fertilisation occurs.
🌀 Stages of Oogenesis
A. 👶 Fetal Stage
- Oogonia: Diploid → mitosis → primary oocytes.
- Primary oocytes enter meiosis I → arrested in prophase I within primordial follicles.
B. 🌙 Puberty to Menopause
- Hormonal signals restart meiosis during cycles.
- Primary oocyte: Completes meiosis I → secondary oocyte + polar body.
- Secondary oocyte: Arrested in metaphase II → ovulated.
C. 🌟 Completion Upon Fertilisation
- If sperm penetrates, meiosis II completes → mature ovum + second polar body.
📊 Hormonal Regulation (Female)
- FSH: Follicular growth + oocyte development.
- LH: Ovulation trigger.
- Estrogen & Progesterone: Cycle regulation + endometrial preparation.
🍃 Follicular Development
- Primordial Follicle: Primary oocyte inside.
- Graafian Follicle: Mature follicle ready for ovulation.
- Ovulation: Secondary oocyte released, captured by fallopian tube.
⚖️ Comparative Summary: Spermatogenesis vs. Oogenesis
| Feature |
♂️ Spermatogenesis |
♀️ Oogenesis |
| Location |
Testes (seminiferous tubules) |
Ovaries |
| Onset |
Puberty |
Fetal life |
| Duration |
Lifelong |
Until menopause |
| Gametes |
Millions daily |
1 ovum per cycle (if fertilised) |
🏥 Clinical Implications
- Infertility:
♂️ Low sperm count/motility or
♀️ Oocyte maturation/hormonal issues.
- Assisted Reproduction (IVF): Knowledge of gametogenesis guides egg retrieval & fertilisation.
- Genetic Risks: Abnormal meiosis → aneuploidy (e.g. Down syndrome, Turner’s).
