Makindo Medical Notes

Gametogenesis is the process through which haploid gametes (sperm in males and ova in females) are produced from diploid cells. This process includes stages such as mitosis, meiosis, and differentiation to ensure that the resultant gametes carry half the genetic material, ready for fertilization.

Male Gametogenesis: Spermatogenesis

• Spermatogenesis is the process of sperm formation in males, occurring in the seminiferous tubules of the testes.
• Begins at puberty and continues throughout life.
• Duration: Approximately 64-72 days from start to finish.

Mitotic Proliferation (Spermatocytogenesis)

• Spermatogonia: Diploid cells undergo mitotic divisions in the basal compartment of seminiferous tubules.
• Differentiate into primary spermatocytes, which move to the adluminal compartment.

Meiosis

• Primary Spermatocytes: Each undergoes meiosis I to produce two haploid secondary spermatocytes.
• Secondary Spermatocytes: Undergo meiosis II, forming haploid spermatids.

Spermiogenesis (Differentiation)

• Spermatids undergo morphological changes to mature into spermatozoa (sperm).
• Key changes:
  • Formation of the acrosome (enzymes to penetrate egg).
  • Condensation of the nucleus and formation of the flagellum.
  • Shedding of excess cytoplasm for a streamlined structure.

Hormonal Regulation of Spermatogenesis

• FSH: Stimulates spermatogenesis by acting on Sertoli cells.
• LH: Stimulates testosterone production by Leydig cells.
• Testosterone: Essential for maturation and maintenance of spermatogenesis.

Sperm Structure and Function

• Sperm cells have a head, midpiece, and tail:
  • Head: Contains genetic material and acrosome.
  • Midpiece: Packed with mitochondria for energy.
  • Tail (Flagellum): Propels sperm toward the egg.

Female Gametogenesis: Oogenesis

• Oogenesis is the process of egg (ova) formation in females, occurring in the ovaries.
• Begins during fetal development and resumes at puberty, completing only upon fertilization.

Stages of Oogenesis

A. Fetal Stage (Oocyte Arrest in Prophase I)

• Oogonia: Diploid cells that undergo mitosis to form primary oocytes.
• Primary oocytes enter meiosis I and are arrested in prophase I, forming primordial follicles.

B. Puberty to Menopause (Resumption of Meiosis)

• At puberty, hormonal signals cause primary oocytes to resume meiosis in each menstrual cycle.
• Primary Oocyte: Completes meiosis I to form a secondary oocyte and a polar body.
• Secondary Oocyte: Arrested at metaphase II, released during ovulation.

C. Completion of Meiosis (Upon Fertilization)

• If fertilized by sperm, the secondary oocyte completes meiosis II, forming a mature ovum and second polar body.

Hormonal Regulation of Oogenesis

• FSH: Stimulates follicular development and oocyte growth.
• LH: Triggers ovulation.
• Estrogen & Progesterone: Regulate menstrual cycle and prepare uterus for implantation.

Follicular Development and Ovulation

• Stages:
  • Primordial Follicle: Contains primary oocyte.
  • Graafian (Mature) Follicle: Follicle that undergoes ovulation.
  • Ovulation: Release of secondary oocyte, captured by fallopian tube.

Comparative Summary: Spermatogenesis vs. Oogenesis

Process	Spermatogenesis	Oogenesis
Location	Testes (seminiferous tubules)	Ovaries
Onset	Puberty	Begins in fetal development
Duration	Continues throughout life	Ends at menopause
Gametes Produced	Millions daily	1 mature ovum per cycle (if fertilized)

Clinical Implications

1. Infertility

• Male Infertility: Issues in spermatogenesis (e.g., low sperm count, poor motility).
• Female Infertility: Issues in oogenesis or hormonal imbalances.

2. Assisted Reproductive Technologies (ART)

• IVF techniques utilize knowledge of gametogenesis for egg retrieval and fertilization.

3. Genetic Counseling

• Meiosis abnormalities can result in chromosomal disorders (e.g., Down syndrome).