Male Reproductive System: Structure, Function, and Histology

Male Reproductive System

General Function of the Reproductive System

The reproductive system is responsible for producing, storing, and delivering gametes (sperm in males) and for the secretion of sex hormones. In males, this system ensures the continuation of the species through sexual reproduction.

• Primary function: Production and delivery of sperm cells.

• Secondary function: Secretion of male sex hormones (primarily testosterone).

Semen: Definition, Composition, and Producing Organs

Semen is the fluid that is ejaculated from the male reproductive tract and contains sperm and secretions from accessory glands.

• Composition: Spermatozoa, seminal fluid (from seminal vesicles), prostatic fluid (from prostate gland), and mucus (from bulbourethral glands).

• Organs/Glands involved:

  • Testes: Produce sperm cells.

  • Seminal vesicles: Contribute fructose-rich fluid (energy source for sperm).

  • Prostate gland: Adds enzymes and nutrients, enhances sperm motility.

  • Bulbourethral glands: Secrete mucus for lubrication and neutralization of acidic urine in urethra.

Pathway of Sperm from Formation to External Environment

Sperm travel through a series of ducts and structures before being expelled from the body.

1. Seminiferous tubules (in testes): Site of sperm production.

2. Rete testis: Network collecting sperm from seminiferous tubules.

3. Epididymis: Sperm mature and are stored here.

4. Vas deferens (ductus deferens): Transports sperm during ejaculation.

5. Ampulla of vas deferens: Expanded region near the prostate.

6. Ejaculatory duct: Formed by the union of vas deferens and seminal vesicle duct.

7. Urethra: Prostatic, membranous, and penile (spongy) segments; conducts semen to the exterior.

Exocrine and Endocrine Products of the Gonads

• Exocrine product: Spermatozoa (sperm cells).

• Endocrine product: Testosterone and other androgens (hormones).

Homologous Structures in Male and Female Systems

Some reproductive structures in males and females are derived from the same embryonic tissues and are considered homologous.

• Testes (male) — Ovaries (female)

• Penis (male) — Clitoris (female)

• Scrotum (male) — Labia majora (female)

Meiosis, Spermatogenesis, and Comparison with Oogenesis

Meiosis is a specialized type of cell division that reduces the chromosome number by half, producing haploid gametes.

• Spermatogenesis: The process of sperm cell development in the seminiferous tubules of the testes.

• Oogenesis: The process of egg cell development in the ovaries (female).

• Comparison:

  • Spermatogenesis produces four viable sperm from each precursor cell; oogenesis produces one viable ovum and polar bodies.

  • Spermatogenesis occurs continuously after puberty; oogenesis has long resting phases and is completed only if fertilization occurs.

Key equation for chromosome number reduction in meiosis:

$2n \rightarrow n$

where $n$ is the haploid number of chromosomes.

Testes and Associated Structures

Testes: Anatomy and Histology

• Seminiferous tubules: Coiled tubes where spermatogenesis occurs.

• Septa: Connective tissue partitions dividing the testis into lobules.

• Tunica vaginalis: Outer serous membrane covering the testis.

• Tunica albuginea: Dense fibrous capsule surrounding the testis.

• Rete testis: Network of tubules collecting sperm from seminiferous tubules.

• Epididymis: Site of sperm maturation and storage.

• Cremaster muscle: Raises and lowers the testes to regulate temperature.

• Dartos muscle: Wrinkles the scrotal skin to reduce heat loss.

Vas Deferens and Ejaculatory Duct

• Vas deferens (ductus deferens): Muscular tube transporting sperm from epididymis to ejaculatory duct.

• Ampulla: Expanded distal end of the vas deferens.

• Spermatic cord: Contains vas deferens, blood vessels, nerves, and lymphatics.

• Ejaculatory duct: Short duct passing through the prostate, merging with the urethra.

Accessory Glands

• Seminal vesicle/gland: Produces alkaline, fructose-rich fluid (about 60% of semen volume).

• Prostate gland: Secretes milky, slightly acidic fluid with enzymes and nutrients.

• Bulbourethral gland: Secretes clear mucus for lubrication and pH neutralization.

Penis: Structure and Erectile Tissue

• Glans: Enlarged tip of the penis.

• Prepuce: Foreskin covering the glans (may be removed by circumcision).

• Erectile tissue:

  • Corpus spongiosum: Surrounds the urethra, prevents compression during erection.

  • Corpora cavernosa: Paired columns of erectile tissue responsible for erection.

Urethra: Segments

• Prostatic urethra: Passes through the prostate gland.

• Membranous urethra: Short segment passing through the urogenital diaphragm.

• Penile (spongy) urethra: Runs through the corpus spongiosum to the external urethral orifice.

Histology of the Testis

Microscopic Structures

• Seminiferous tubules: Lined with spermatogenic cells at various stages of development.

• Interstitial cells (Leydig cells): Located between tubules; secrete testosterone.

• Spermatogonia: Stem cells at the periphery of the tubules; divide to produce sperm.

• Lumen: Central cavity of the tubule where mature sperm are released.

• Spermatozoa: Mature sperm cells with distinct head, midpiece, and tail.

Spermatozoon Structure

• Head: Contains nucleus and acrosome (enzymes for penetrating the egg).

• Midpiece: Packed with mitochondria for energy production.

• Tail (flagellum): Provides motility.

Example: During ejaculation, sperm produced in the seminiferous tubules travel through the epididymis, vas deferens, and urethra, mixing with fluids from the seminal vesicles, prostate, and bulbourethral glands to form semen.

Additional info: The temperature regulation of the testes by the cremaster and dartos muscles is essential for optimal spermatogenesis, which occurs best at temperatures slightly below core body temperature.