In-Depth Notes on Male Reproductive System and Spermatogenesis

Introduction to Spermatogenesis

• Chromatogonia Development:
• Undergo mitosis leading to formation of spermatocytes.
• One cell stays as a stem cell; the other becomes a spermatocyte.
• Meiosis Process:
• Primary spermatocytes undergo Meiosis I and II, resulting in four unique haploid cells from one diploid cell.
• Key point: No further DNA replication occurs after mitosis.

Spermatid Development:

• Spermiation:
• Release of spermatids into the lumen of the seminiferous tubule, where Sertoli cells provide nourishment.
• Initially, sperm lack motility; they mature while moving through the epididymis.

Structure of Sperm:

• Components:
• Head: Contains the acrosome, filled with proteolytic enzymes to penetrate the oocyte.
• Tail: Provides propulsion, consists of bulk of the sperm structure;
  • Neck: Narrow part connecting the head to the tail.
  • Middle Piece: Contains mitochondria for ATP production vital for motility.
  • Principal Piece: Longest segment of the tail; essential for swimming.
• Lifespan:
• Sperm can survive up to 48 hours in the female reproductive tract.

Hormonal Regulation of Spermatogenesis:

• Gonadotropin-Releasing Hormone (GnRH):
• Released from hypothalamus; travels through the hypophyseal portal system to the anterior pituitary.
• Anatomical Details:
• Hypophyseal portal system: A network of blood vessels carrying hormones directly to the anterior pituitary.
• Effects of GnRH: Stimulates secretion of Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH).

Luteinizing Hormone (LH) and Testosterone Production:

• Action of LH:
• Binds to Leydig cells in the testes, stimulating testosterone production.
• Role of Testosterone:
• Essential for stimulating spermatogenesis and maintaining male reproductive functions.

Follicle Stimulating Hormone (FSH):

• Role:
• Binds to Sertoli cells, prompting secretion of Androgen Binding Protein (ABP), which facilitates testosterone binding to Sertoli cells, enabling spermatogenesis.

Feedback Mechanisms:

• Inhibin: Produced by Sertoli cells when sperm production levels are sufficient; inhibits FSH secretion from the anterior pituitary, reducing spermatogenesis rate.
• Testosterone Feedback:
• Inhibits LH secretion from the anterior pituitary and GnRH from the hypothalamus, reducing further testosterone production.

Dihydrotestosterone (DHT):

• Formation and Role:
• Conversion of testosterone into DHT; both bind to the same receptors and regulate male development.

Developmental Effects of Androgens:

• Puberty Changes:
• Increased testosterone levels lead to maturation of male sexual characteristics, including increased muscle mass, bone density, body hair and deeper voice.
• Increased libido: Testosterone contributes to sexual drive in both sexes, more prominent in males.

Conditions Affecting Testosterone Levels:

• Cryptorchidism: Undescended testes increase testicular cancer risk.
• Huevesos at 12 (huevedose): Genetic condition where individuals develop female characteristics at birth but may develop male genitalia during puberty due to testosterone surges.

Anatomy of the Testis:

• Seminiferous Tubules: Where sperm production takes place within lobules.
• Epididymis: Site for sperm maturation and storage before ejaculation.
• Vas deferens: Transports sperm from the epididymis to the urethra.

Ejaculation Process:

• Ejaculatory Ducts: Formed by the union of the seminal vesicle ducts and vas deferens, passing through the prostate to the urethra.
• Seminal fluid production: Composed of fluid from seminal vesicles, prostate, and Cowper's gland, with sperm contributing to the total volume.
• Components of Semen:
  • Alkaline nature: Protects sperm against acidic environments of vagina and urethra.
  • Fructose: Provides energy for sperm motility.
  • Clotting proteins and prostaglandins: Assist in sperm mobility and adherence post-ejaculation.

Vasectomy Procedure:

• Overview: Surgical method to prevent sperm passage by ligating the vas deferens; sperm production continues but is prevented from reaching the urethra.