The Male Reproductive System 1

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What is the point?

The male reproductive system, although significantly less complex than the female equivalent, has two critical functions:
  1. To produce haploid spermatozoa
  2. To deliver spermatozoa into the uterus and fallopian tubes, enabling fertilisation and production of an embryo

Components of the system

Below is a summary of each structure in the male reproductive system:

Testes: have an endocrine function and produce spermatozoa

Epididymus: spermatozoa are matured (18 hours to 10 days) and stored in the epididymus

Ductus (vas) deferens: spermatozoa are stored and passed through here from the testes to the ejaculatory duct

Urethra: passageway for urine from the bladder, receive spermatozoa/semen from the ejaculatory duct

Seminal glands (vesicles): secrete most of the fluid that makes up semen, drains into the ductus deferens

Prostate gland: produces prostatic fluids which mix with seminal fluids in the urethra

Bulbourethral glands: small mucous secreting glands located at the base of the penis

External genitalia: scrotum (contains testes) and penis (release of urine and semen during sexual intercourse)

Spermatogenesis

The testes are housed in the scrotum, a skin sac divided into two chambers. The scrotum allows temperature regulation below normal body temperature, which is critical to the production of sperm which survive in a temperature 1 to 2 degrees less than normal body temperature. The testes are comprised of lobules with seminiferous tubules, where sperm production occurs. These tubules empty into the mediastinum via an interconnected passageway called rete testis. This then empties into the efferent ductules that connect to the epididymus. There are interstitial cells (Leydig cells) present in the space around the seminiferous tubules. They produce the male sex hormones, e.g. androgens such as testosterone.

Spermatogenesis occurs in the seminiferous tubules.
  1. Spermatogenesis begins in the outermost layer of seminiferous tubules and proceeds down to the lumen
  2. Spermatozoa being as stem cells (spermatogonium) and divide by mitosis to produce daughter cells → one remains a spermatogonium and the other differentiates into a primary spermatocyte
  3. Spermatocytes undergo meiosis to form gametes → primary spermatocytes divide into secondary spermatocytes → secondary spermatocytes divide and differentiate into spermatid (immature gametes)
  4. Spermatid become spermatozoa and are released into the lumen of the seminiferous tubules
Meiosis is the production of haploid cells from diploid cells. Diploid human cells contain 23 pairs of chromosomes (total of 46), whereas haploid cells contain 23 chromosomes in total.

Finalisation of semen

Sperm reside in the epididymus for 2-3 weeks after production and release into the lumen. The epididymus has several functions:
  • Stores and finalises the maturation of spermatozoa
  • Monitors and adjusts fluid composition
  • Acts as a recycling centre
The spermatozoa then empty into the ductus deferens, where they are inactive for several months. Accessory glands aid with the creation of semen when spermatozoa are moved into the ejaculatory duct. The ejaculatory duct then empties into the urethra, with a dual purpose of urine and semen transport.

The seminal vesicles produce 60% of the volume of semen, an alkaline fluid which neutralises the prostate secretions and vaginal acids. It is a viscous fluid containing prostaglandins for smooth muscle contractions, fructose for sperm metabolism and fibrinogen for forming a semen clot in the vagina.

The prostate gland makes up 20-30% of the semen volume. It is the size of a chestnut and secretes an acidic, thin, milky fluid. The fluid contains seminal plasmin, with antibiotic properties. The prostatic fluid contributes to sperm motility and viability.

Semen is a thick, whitish fluid containing sperm, seminal fluid and enzymes. 2-5mL of semen is released per ejaculation and there are about 20-100 million sperm per millilitre of semen. The pH of semen is 7.2-7.6.

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