MM

19 TSH _ Human Reproductive System: Male Reproductive System

Learning Outcomes

  • ALO1: Discuss embryological origins of gonads and development of Mullerian and Wolffian ducts in mammals.
  • ALO2: Describe structure of male reproductive system, including ducts and accessory glands.
  • ALO3: Illustrate histology of testes, highlighting seminiferous tubules and interstitial cells.
  • ALO4: Discuss spermiogenesis and structure of spermatozoan.

Reproduction Basics

  • Types of Reproduction:
    • Asexual Reproduction: One parent, genetically identical offspring except for mutations.
    • Parthenogenesis: Unfertilized egg develops into haploid adult.
    • Sexual Reproduction: Fusion of sperm and egg, genetic variation in offspring.
  • Importance: Essential for species survival and adaptation, removes harmful mutations efficiently.

Sexual Reproduction

  • Gametes produced: Sperm (male) and Eggs (female).
  • Fertilization forms Zygote.
  • Types of fertilization:
    • External: Common in aquatic animals, occurs outside female body.
    • Internal: Sperm delivered into female body, occurs in most mammals.
  • Involves two parent organisms leading to genetically diverse offspring.

Gonads and Genital Organs

  • Gonads:
    • Males: Testes produce spermatozoa.
    • Females: Ovaries produce ova.
  • Both gonads develop from mesodermal genital ridge near mesonephros.
  • Embryonic structures initially sexually indifferent; undergo differentiation:
    • Wolffian Ducts (males): Develop, Mullerian ducts degenerate.
    • Mullerian Ducts (females): Develop, Wolffian ducts degenerate.

Male Reproductive System Anatomy

  • Testes Location: Primarily in upper lumbar region; descend into scrotum through inguinal canal.
    • Scrotal Sacs: Paired pouches for testes, maintain temperature regulation for sperm production (thermoregulation).

Testes Structure

  • Equipped with Seminiferous Tubules:
    • Highly coiled, produce spermatozoa; lined with basement membrane, supported by connective tissue.
  • Histology:
    • Composed of Sertoli cells, Leydig cells, and germ cells at various developmental stages.
    • Blood-Testis Barrier: Formed by tight junctions between Sertoli cells, protects developing sperm from autoimmune reactions.

Spermatogenesis Process

  • Begins at puberty; regulated by FSH and LH (from pituitary gland).
  • Steps in Spermatogenesis:
    1. Spermatogonia (diploid) undergo mitosis and meiosis to form primary and secondary spermatocytes.
    2. Resulting in Spermatids (haploid) that undergo differentiation into spermatozoa (spermiogenesis).
  • Sertoli Cells: Provide nourishment and protection, and assist in sperm maturation process.

Spermiogenesis Understanding

  • Transformation from spermatids to spermatozoa:
    • Nucleus condenses, Golgi forms acrosome, centrioles develop into tail structure.
    • Mitochondria arrange in helix around tail.
    • Finalized structure has distinct head, midpiece, principal piece, and end piece.

Spermatozoon Structure

  • Parts:
    • Head: Contains acrosome and nuclear material.
    • Tail: Divided into middle piece (with mitochondria), principal piece, and end piece.
  • Axoneme: Central filament with typical 9+2 microtubular arrangement.

Hormonal Control of Spermatogenesis

  • Spermatogenesis regulated by:
    • FSH: Stimulates Sertoli cells.
    • Leydig Cells produce Testosterone: Important for male secondary sexual characteristics, regulated by LH.

Male System Ducts and Accessory Glands

  • Duct System:
    • Epididymis: Storage and maturation of sperm before ejaculation.
    • Vas Deferens: Transports sperm from epididymis to urethra.
  • Accessory Glands:
    • Seminal Vesicles: Produce fructose-rich seminal fluid (60% of semen).
    • Prostate Gland: Produces alkaline fluid (30% of semen).
    • Cowper’s Glands: Provide lubricating fluid.

Seminal Fluid Composition

  • Ejaculation Sequence: Cowper’s secretions → prostatic fluid → spermatozoa → seminal vesicle secretions.
  • Initial coagulation followed by liquefaction.
  • Average volume: 3.5 ml per ejaculation, with 120 million spermatozoa/ml being normal for fertility.

Summary and Learning Outcomes Revisited

  • Understanding of embryological origins and development of gonadal structures in mammals.
  • Mastery of male reproductive system structure and function, including histology of testes and spermatogenic processes.