L24P2_(Asynchronous)

Introduction to Male Reproductive System

  • Preformationism: Historical belief that the sperm carried a miniature version of a person (homunculus) and the egg was merely a vessel.

    • This theory was scientifically promoted but is now dismissed, illustrating how cultural biases influence scientific understanding.

Functions of the Male Reproductive System

  • Three Main Functions:

    • Production of male gametes (sperm).

    • Synthesis of androgens (male hormones).

    • Mechanism for delivering sperm into the female reproductive tract.

  • Note that not everyone with reproductive organs wishes to reproduce; discussion primarily focuses on reproduction.

Anatomy of the Male Reproductive System

  • External Genitalia:

    • Scrotum: Houses the testes.

    • Penis: External structure for mating.

  • Internal Genitalia:

    • Testes: Located in the scrotum, responsible for sperm production.

    • Various ducts involved in sperm transport.

The Testes

  • Composed of approximately 250 lobules separated by connective tissue.

  • Each lobule contains tightly coiled seminiferous tubules (1-4 per lobule).

Cross-section of Seminiferous Tubule

  • Contains various types of cells:

    • Spermatogenic Cells:

      • Spermatogonia: Stem cells that develop into sperm; undergo mitosis and meiosis.

    • Sustentacular Cells (Sertoli Cells):

      • Large supporting cells that provide nourishment and form tight junctions.

    • Interstitial Cells (Leydig Cells): Located outside the seminiferous tubules, produce testosterone.

Spermatogenesis Process

  • Meiosis Overview:

    • Spermatogonia undergo mitosis.

    • Primary Spermatocytes: Diploid; undergo first meiotic division to become haploid Secondary Spermatocytes.

    • Secondary spermatocytes undergo second meiotic division to form haploid spermatids.

  • Result: One primary spermatocyte leads to four spermatids.

Role of Sertoli Cells

  • Nutrient diffusion barrier: Aid in nourishing developing sperm and create the blood-testis barrier to protect sperm from immune recognition.

  • Important to note that developing sperm have different DNA and antigens, which could be recognized as foreign by the immune system.

Maturation of Sperm

  • Epididymis: Location where spermatids mature into motile sperm; connects to seminiferous tubules.

  • Process of Maturation:

    1. Formation of acrosomal vesicle: Contains enzymes essential for fertilization.

    2. Formation of flagellum: Allows for motility, constructed from microtubules.

    3. Recruitment of Mitochondria: Mitochondria cluster in the midpiece to provide energy.

    4. Removal of excess cytoplasm and Golgi apparatus residues for streamlined head.

Sperm Production and Lifespan

  • Sperm production begins at puberty, taking about 64 days to mature.

  • Mature sperm can remain in the epididymis for several months.

  • Unique aspect: Sperm utilize a specific monosaccharide as an energy source, different from glucose.

Age and Fertility in Males

  • Spermatogonia's immortal nature: Can continually divide like other stem cells, but their quality may decline with age.

  • Mutation Rates: Active mitotic cells, including spermatogonia, can accumulate mutations leading to pathologies.

  • Impact of Aging:

    • Sperm count, motility, and morphology may decline with increasing age.

    • There is a potential rise in de novo mutations in sperm with aging.