Spermatogenesis and Sperm Development

Spermatogenesis

Spermiogenesis

• Process by which immature spermatozoa (spermatids) develop into mature spermatozoa
• Occurs in the epididymis
• Involves:
  • Removal of excess cytoplasm
  • Formation of the acrosome
  • Development of the tail and flagellum
  • Condensation of the chromatin

Spermatozoa Development

• Spermatogonia (diploid stem cells) undergo mitosis to form primary spermatocytes
• Primary spermatocytes undergo meiosis I to form secondary spermatocytes
• Secondary spermatocytes undergo meiosis II to form haploid spermatids
• Spermatids undergo spermiogenesis to form mature spermatozoa

Meiosis

• Process by which diploid cells (spermatogonia) give rise to haploid cells (spermatozoa)
• Consists of two successive cell divisions: meiosis I and meiosis II
• Meiosis I:
  • Prophase I: homologous chromosomes pair up and exchange genetic material (crossing over)
  • Metaphase I: paired chromosomes align at the center of the cell
  • Anaphase I: paired chromosomes separate
  • Telophase I: nuclear envelope reforms
• Meiosis II:
  • Prophase II: chromosomes condense and become visible
  • Metaphase II: chromosomes align at the center of the cell
  • Anaphase II: sister chromatids separate
  • Telophase II: nuclear envelope reforms, resulting in four haploid cells

Spermatogenesis

• Process by which immature cells develop into mature spermatozoa

Spermiogenesis

• Occurs in the epididymis
• Involves removal of excess cytoplasm
• Involves formation of the acrosome
• Involves development of the tail and flagellum
• Involves condensation of the chromatin
• Results in mature spermatozoa

Spermatozoa Development

• Spermatogonia are diploid stem cells
• Spermatogonia undergo mitosis to form primary spermatocytes
• Primary spermatocytes undergo meiosis I to form secondary spermatocytes
• Secondary spermatocytes undergo meiosis II to form haploid spermatids
• Spermatids undergo spermiogenesis to form mature spermatozoa

Meiosis

• Process by which diploid cells give rise to haploid cells
• Consists of two successive cell divisions: meiosis I and meiosis II
• Meiosis I involves:
  • Homologous chromosomes pairing up and exchanging genetic material (crossing over)
  • Paired chromosomes aligning at the center of the cell
  • Paired chromosomes separating
  • Nuclear envelope reforming
• Meiosis II involves:
  • Chromosomes condensing and becoming visible
  • Chromosomes aligning at the center of the cell
  • Sister chromatids separating
  • Nuclear envelope reforming, resulting in four haploid cells

Oogenesis

Folliculogenesis

• Follicles develop in the ovaries through a process involving growth and maturation from primordial to preovulatory follicles
• Five stages of folliculogenesis: primordial follicle formation, activation of primordial follicles, primary follicle formation, secondary follicle formation, and antral follicle formation

Oocyte Development

• Oocyte development occurs in three stages: oogonia proliferation and differentiation, oocyte growth and maturation, and oocyte maturation and ovulation
• Oocyte growth and maturation involves an increase in oocyte size and acquisition of meiotic competence
• Oocyte maturation involves progression from prophase I to metaphase II of meiosis

Ovarian Reserve

• Ovarian reserve refers to the number and quality of oocytes available in the ovaries
• Determined by the number of primordial follicles present at birth and the rate of follicular atresia
• Ovarian reserve declines with age, leading to decreased fertility
• Factors affecting ovarian reserve: age, genetics, environmental toxins, and medical history

Meiosis

• Meiosis is a specialized form of cell division that occurs in oogenesis
• Involves two successive cell divisions (meiosis I and meiosis II) resulting in four haploid gametes
• Meiosis I: reductional division (diploid to haploid) where homologous chromosomes separate
• Meiosis II: equational division (haploid to haploid) where sister chromatids separate