Figure 1-9. Seminal vesicles and other male organs of the genitourinary system.
(6) Prostate gland. This gland is a single doughnut-shaped gland about the
size of a chestnut. The gland lies directly below the urinary bladder and surrounds the
prostatic part of the urethra. The prostate gland secretes a highly alkaline fluid that
protects sperm acidity in the urethra and vagina. Secretion from the prostate gland is
added to the sperm and seminal vesicle fluid. From 13 to 33 percent of the volume of
semen seminal vesicle fluid is prostate gland secretion. Prostate gland secretion also
contributes to sperm motility.
(7) Bulbourethral (Cowper's) glands. These are two small glands, about the
size of peas, located just below the prostate on either side of the urethra. These glands
secrete a mucous-like lubricating fluid into the membranous urethra. The glands also
secrete a substance that neutralizes urine. Ducts of these glands open into the spongy
(8) Urethra. The urethra is a passageway for sperm and urine. The
urethra, measuring about 20 centimeters (8 inches) in length, passes through the
prostate gland, the urogenital diaphragm, and the penis.