0.2 Module 3 anatomy and physiology of the male reproductive system  (Page 3/33)

Sperm transport

To fertilize an egg, sperm must be moved from the seminiferous tubules in the testes, through the epididymis, and—later during ejaculation—along the length of the penis and out into the female reproductive tract.

Role of the epididymis

From the seminiferous tubules, the sperm are moved to the epididymis    , a coiled tube attached to the testis where newly formed sperm continue to mature (see [link] ). It takes an average of 12 days for sperm to move through the coils of the epididymis. As they move along the length of the epididymis, the sperm further mature and acquire the ability to move under their own power. Once inside the female reproductive tract, they will use this ability to move independently toward the unfertilized egg. The mature sperm are then stored in epididymis until ejaculation occurs.

Duct system

During ejaculation, sperm exit the tail of the epididymis and are pushed by smooth muscle contraction to the ductus deferens    (also called the vas deferens). The ductus deferens is a thick, muscular tube that is bundled together inside the scrotum with connective tissue, blood vessels, and nerves into a structure called the spermatic cord    . From each epididymis, each ductus deferens extends into the abdominal cavity through the inguinal canal    in the abdominal wall. From here, the ductus deferens continues to the pelvic cavity, ending behind the bladder where it end in a region called the ampulla    . Sperm make up only 5 percent of the final volume of semen    , the thick, milky fluid that the male ejaculates. The bulk of semen is produced by three critical accessory glands of the male reproductive system: the seminal vesicles, the prostate, and the bulbourethral glands.

Seminal vesicles

As sperm pass through the ampulla of the ductus deferens at ejaculation, they mix with fluid from the associated seminal vesicle    (see [link] ). The paired seminal vesicles are glands that contribute approximately 60 percent of the semen volume. Seminal vesicle fluid contains large amounts of sugars, which are used by the sperm to generate ATP to allow movement through the female reproductive tract. The fluid, now containing both sperm and seminal vesicle secretions, next moves into the associated ejaculatory duct    , a short structure formed from the ampulla of the ductus deferens and the duct of the seminal vesicle. The paired ejaculatory ducts transport the seminal fluid into the next structure, the prostate gland.

Prostate gland

As shown in [link] , the centrally located prostate gland    sitsat the base of the bladder surrounding the prostatic urethra (the portion of the urethra that runs within the prostate). About the size of a walnut, it excretes an alkaline, milky fluid to the passing seminal fluid—now called semen—that is critical to to thicken the semen following ejaculation. The temporary thickening of semen helps retain it within the female reproductive tract, providing time for sperm to pass farther into the female reproductive tract.

Bulbourethral glands

The final addition to semen is made by two bulbourethral glands    (or Cowper’s glands) that release a thick, salty fluid that lubricates the end of the urethra and the vagina, and helps to clean urine residues from the penile urethra . The fluid from these accessory glands is released after the male becomes sexually aroused, and shortly before the release of the semen. It is therefore sometimes called pre-ejaculate. It is important to note that, in addition to the lubricating proteins, it is possible for bulbourethral fluid to pick up sperm already present in the urethra, and therefore it may be able to cause pregnancy.