The male reproductive system in humans is a complex network of organs designed for the production, storage, and delivery of male gametes (sperm) and the secretion of sex hormones. It comprises primary sex organs, accessory ducts, and glands, functioning under tight hormonal regulation.
Primary Sex Organ: The Testes
The testes are the primary reproductive organs, responsible for spermatogenesis and the secretion of testosterone.
- Location: Situated outside the abdominal cavity within a pouch called the scrotum.
- Thermoregulation: The scrotum maintains a temperature 2–2.5°C lower than the internal body temperature, which is essential for sperm production.
- Internal Structure: Each testis contains approximately 250 compartments called testicular lobules.
- Seminiferous Tubules: Each lobule contains 1–3 highly coiled tubules where sperm are produced.
- Cellular Composition:
- Male Germ Cells (Spermatogonia): Undergo meiotic division to form sperm.
- Sertoli Cells: Provide nutrition to the germ cells; often called “nurse cells.”
- Leydig Cells (Interstitial Cells): Located in the regions outside the tubules; they synthesize and secrete testicular hormones called androgens (primarily testosterone).
System of Accessory Ducts
The duct system is responsible for the maturation and transport of sperm from the testes to the exterior.
- Rete Testis: A network of tubules that receives sperm from the seminiferous tubules.
- Vasa Efferentia: Carries sperm from the rete testis to the epididymis.
- Epididymis: A long, coiled tube located on the posterior surface of each testis where sperm achieve motility and are stored temporarily.
- Vas Deferens: Ascends into the abdomen and loops over the urinary bladder. It joins the duct from the seminal vesicle to form the ejaculatory duct.
- Urethra: Originates from the urinary bladder and extends through the penis to its external opening, the urethral meatus.
Accessory Glands and Semen Composition
The secretions of the accessory glands constitute the seminal plasma, which is rich in fructose, calcium, and specific enzymes.
| Gland | Quantity | Function/Contribution |
| Seminal Vesicles | Paired | Secretes alkaline fluid, fructose (energy for sperm), and prostaglandins. |
| Prostate Gland | Single | Secretes a milky, slightly alkaline fluid that enhances sperm motility. |
| Bulbourethral Glands | Paired | Also known as Cowper’s glands; secrete mucus for lubrication of the penis. |
Semen is the combination of sperm cells and seminal plasma. A single ejaculation typically contains 200–300 million sperm.
External Genitalia: The Penis
The penis is the male external genitalia, composed of specialized erectile tissue (corpora cavernosa and corpus spongiosum) that facilitates erection for insemination.
- Glans Penis: The enlarged distal end of the penis.
- Foreskin (Prepuce): A loose fold of skin covering the glans penis.
Process of Spermatogenesis
Spermatogenesis begins at puberty due to a significant increase in the secretion of Gonadotropin-Releasing Hormone (GnRH) from the hypothalamus.
- Phase 1: Spermatogonia (diploid, 46 chromosomes) multiply by mitosis.
- Phase 2: Primary spermatocytes undergo the first meiotic division to form two equal haploid secondary spermatocytes (23 chromosomes).
- Phase 3: Secondary spermatocytes undergo the second meiotic division to produce four haploid spermatids.
- Phase 4 (Spermiogenesis): Spermatids are transformed into mature spermatozoa (sperm).
- Spermiation: The release of mature sperm from the seminiferous tubules.
Structure of a Mature Spermatozoon
A mature human sperm is a microscopic, motile structure composed of four distinct parts:
- Head: Contains an elongated haploid nucleus. The anterior portion is covered by a cap-like structure called the acrosome, filled with enzymes (hyaluronidase) that help in fertilizing the ovum.
- Neck: Connects the head to the middle piece.
- Middle Piece: Contains numerous mitochondria, which produce energy (ATP) for the movement of the tail.
- Tail: Facilitates sperm motility essential for reaching the ovum.
Hormonal Regulation
The male reproductive system is governed by the Hypothalamic-Pituitary-Gonadal (HPG) axis.
- GnRH: Stimulates the anterior pituitary to secrete two gonadotropins: LH and FSH.
- Luteinizing Hormone (LH): Acts on the Leydig cells to stimulate the synthesis and secretion of androgens.
- Follicle Stimulating Hormone (FSH): Acts on the Sertoli cells and stimulates the process of spermiogenesis and the secretion of factors required for sperm maturation.
Fact File for UPSC Prelims
- Cryptorchidism: A clinical condition where the testes fail to descend into the scrotum, which can lead to sterility due to high internal body temperatures.
- Andropause: Unlike the distinct menopause in females, males experience a gradual decline in testosterone levels and sperm quality with age, though sperm production can continue into old age.
- Semen pH: Semen is slightly alkaline (pH 7.2–7.7) to neutralize the acidic environment of the male urethra and the female vaginal tract.
- Sperm Requirement for Fertility: For normal fertility, at least 60% of sperm must have normal shape and size, and at least 40% must show vigorous motility.