Penis, Testes, and Ducts

Penis, Testes, and Ducts

Overview

• The reproductive system facilitates sexual maturation of individuals and sexual reproduction of offspring.
• In the male, this includes the production of semen and its delivery to the outside environment.
• Specific anatomical adaptations, such as the penis, facilitate semen delivery close to the site of conception, within the female reproductive tract.
• Semen comprises sperm cells and seminal plasma, which nourishes and protects the sperm.
• Reproductive structures are classified as either primary or accessory (aka, secondary):
  • The primary structures are referred to as gonads; their function is to produce gametes, aka, sex cells. In males, the primary structures are the testes (aka, testicles), which produce sperm and hormones.
  • The accessory structures are the organs, ducts, and glands that facilitate delivery of the gametes to the external environment.

Ejaculation

• Emission is when semen is ushered into proximal urethra.
• Expulsion is when semen is projected through urethra.

Testes

• Suspended within the scrotum; produce sperm cells and hormones.

Epididymis

• Wraps over posterior-superior aspect of testis.
• Long coiled tube that stores developing sperm.

Ductus deferens

• Continuous with epididymis, ascends to enter the pelvis, then passes over the urinary bladder and ureter.
• It is a muscular tube that actively conducts sperm from the epididymis to the ejaculatory duct; this transport occurs during the emission phase of ejaculation.
• Ampulla is the widened end of the ductus deferens.

Seminal vesicle

• Is adjacent to the ampulla.
• Contributes the majority of the total seminal plasma volume.

Ejaculatory duct

• Drains the ductus deferens and the seminal vesicle into the prostatic urethra.

Prostate gland

• Its secretions enter the prostatic urethra.

Bulbourethral glands (aka, Cowper's glands)

• Lie lateral to the prostate and secrete lubricating mucus into the spongy urethra.
• During the expulsion phase of ejaculation, secretions from the bulbourethral glands precede the rest of the seminal fluid.

Clinical correlations:

• Vasectomy: the paired ductus deferens are surgically sealed shut; sperm is still produced, but cannot be transported to the ejaculatory ducts to join the seminal plasma.
  • Thus, it is a highly effective form of contraception that is sometimes surgically reversed.
• Cryptorchidism, aka, undescended testis, is a common birth abnormality in boys; the testicles usually move into the scrotum on their own, but, if not, surgery may be necessary.
  • Complications of cryptorchidism include increased likelihood of testicular cancer and reduced fertility.