Male Reproductive System Anatomy

• The male reproductive system produces, maintains, and transports sperm cells, the male gametes, to the female reproductive tract.

Anatomy

• The major organs include the testes, epididymis, vas deferens, seminal vesicles, prostate gland, bulbourethral glands, and penis.
• Testes: Located within the scrotum, the testes are responsible for producing sperm and testosterone.
  • They contain tightly coiled seminiferous tubules, the site of spermatogenesis.
  • Interstitial cells (Leydig cells) between the tubules produce testosterone.
• Epididymis: A coiled tube connected to the testis where sperm mature and are stored.
  • Sperm spend about two to four weeks in the epididymis, where they gain motility and the ability to fertilize an egg.
• Vas Deferens: A muscular tube that transports sperm from the epididymis to the ejaculatory duct.
  • It ascends within the spermatic cord, which also contains blood vessels and nerves.
• Seminal Vesicles: Glands that produce a fluid rich in fructose, prostaglandins, and other substances that nourish and protect sperm.
  • This fluid constitutes a significant portion of semen volume.
• Prostate Gland: Surrounds the urethra and produces a milky fluid containing enzymes and zinc that enhance sperm motility and fertilization.
• Bulbourethral Glands (Cowper's Glands): Small glands located near the urethra that secrete a clear, alkaline mucus that lubricates the urethra and neutralizes acidic residues.
• Penis: The external organ that delivers sperm to the female reproductive tract during sexual intercourse.
  • It consists of the root, the shaft or body, and the glans penis.
  • The glans is covered by the foreskin, or prepuce, which may be removed during circumcision.
  • The penis contains three cylindrical masses of erectile tissue: two corpora cavernosa and one corpus spongiosum, which surrounds the urethra.

Hormonal Control

• The hypothalamus, pituitary gland, and testes form a hormonal axis that regulates male reproductive functions.
• Gonadotropin-Releasing Hormone (GnRH): Released by the hypothalamus.
  • Stimulates the anterior pituitary to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
• Luteinizing Hormone (LH): Stimulates Leydig cells in the testes to produce testosterone.
• Follicle-Stimulating Hormone (FSH): Acts on Sertoli cells in the seminiferous tubules to support spermatogenesis.
  • Sertoli cells also produce inhibin, which inhibits FSH secretion.
• Testosterone: The primary male sex hormone, responsible for the development of male secondary sexual characteristics, muscle growth, and maintenance of libido.
  • It also has a negative feedback effect on the hypothalamus and anterior pituitary, reducing GnRH, LH, and FSH secretion.

Spermatogenesis

• Spermatogenesis is the process of sperm production that occurs in the seminiferous tubules of the testes.
• It involves three main phases:
  • Mitosis: Spermatogonia (diploid stem cells) undergo mitosis to produce more spermatogonia.
  • Meiosis: Primary spermatocytes undergo meiosis I to form secondary spermatocytes, which then undergo meiosis II to produce spermatids (haploid cells).
  • Spermiogenesis: Spermatids differentiate into mature spermatozoa (sperm cells). This involves the formation of a flagellum (tail) and condensation of the nucleus.
• Each sperm cell consists of a head (containing the nucleus and acrosome), a midpiece (containing mitochondria), and a tail (flagellum) for motility.
• The entire process of spermatogenesis takes approximately 64 to 72 days in humans.

Erection and Ejaculation

• Erection: The enlargement and stiffening of the penis, caused by vasodilation of blood vessels in the erectile tissues (corpora cavernosa and corpus spongiosum).
  • Parasympathetic nerves trigger the release of nitric oxide (NO), which relaxes smooth muscle in the penile arteries, allowing increased blood flow.
  • The engorgement of erectile tissues compresses the veins, preventing blood from leaving the penis.
• Ejaculation: The expulsion of semen from the male urethra, involving two phases:
  • Emission: Sympathetic nerves stimulate peristaltic contractions of the vas deferens, seminal vesicles, and prostate gland, which move semen into the urethra.
  • Expulsion: Semen is forcefully expelled from the urethra by contractions of skeletal muscles at the base of the penis.
• After ejaculation, sympathetic stimulation causes vasoconstriction in the penile arteries, reducing blood flow and leading to detumescence (loss of erection).

Semen

• Semen is a mixture of sperm cells and seminal fluid.
• Seminal fluid is produced by the seminal vesicles, prostate gland, and bulbourethral glands.
  • It provides nutrients, buffers, and other substances that support sperm viability and motility.
• A typical ejaculate contains 2 to 5 ml of semen, with 20 to 150 million sperm cells per milliliter.
• Semen is slightly alkaline, which helps neutralize the acidic environment of the female reproductive tract.

Male Fertility

• Male fertility depends on several factors, including sperm count, sperm motility, and sperm morphology (shape).
• Low sperm count (oligospermia) or the absence of sperm (azoospermia) can lead to infertility.
• Impaired sperm motility (asthenozoospermia) or abnormal sperm morphology (teratozoospermia) can also reduce fertility.
• Other factors that can affect male fertility include hormonal imbalances, genetic disorders, infections, and environmental toxins.