fluid that helps maintain sperm motility. The smooth
muscle of the prostate gland contracts during ejacula-
tionto contribute to the expulsion of semen from the
urethra (see Box 20–3: Prostatic Hypertrophy).
BULBOURETHRAL GLANDS
Also called Cowper’s glands, the bulbourethral
glandsare about the size of peas and are located below
the prostate gland; they empty into the urethra. Their
alkaline secretion coats the interior of the urethra just
before ejaculation, which neutralizes any acidic urine
that might be present.
You have probably noticed that the secretions of
the male reproductive glands are alkaline. This is
important because the cavity of the female vagina has
an acidic pH created by the normal flora, the natural
bacterial population of the vagina. The alkalinity of
seminal fluid helps neutralize the acidic vaginal pH
and permits sperm motility in what might otherwise
be an unfavorable environment.
URETHRA—PENIS
The urethrais the last of the ducts through which
semen travels, and its longest portion is enclosed
within the penis. The penisis an external genital
organ; its distal end is called the glans penis and is cov-
ered with a fold of skin called the prepuce or foreskin.
Circumcisionis the surgical removal of the foreskin.
This is a common procedure performed on male
infants, and though there is considerable medical
debate as to whether circumcision has a useful pur-
pose, some research studies have found fewer cases of
HIV infection among circumcised men, compared
with men who are uncircumcised.
Within the penis are three masses of cavernous
(erectile) tissue (see Fig. 20–3). Each consists of a
framework of smooth muscle and connective tissue
that contains blood sinuses, which are large, irregular
vascular channels.
When blood flow through these sinuses is minimal,
the penis is flaccid. During sexual stimulation, the
arteries to the penis dilate, the sinuses fill with blood,
and the penis becomes erect and firm. The dilation of
penile arteries and the resulting erection are brought
about by the localized release of nitric oxide (NO) and
by parasympathetic impulses. The erect penis is capa-
ble of penetrating the female vagina to deposit sperm.
The culmination of sexual stimulation is ejaculation, a
sympathetic response that is brought about by peristal-
sis of all of the reproductive ducts and contraction of
the prostate gland and the muscles of the pelvic floor.SEMEN
Semenconsists of sperm and the secretions of the
seminal vesicles, prostate gland, and bulbourethral
glands; its average pH is about 7.4. During ejacula-
tion, approximately 2 to 4 mL of semen is expelled.
Each milliliter of semen contains about 100 million
sperm cells.FEMALE REPRODUCTIVE SYSTEM
The female reproductive system consists of the paired
ovaries and fallopian tubes, the single uterus and
vagina, and the external genital structures (Fig. 20–5).
Egg cells (ova) are produced in the ovaries and travel
through the fallopian tubes to the uterus. The uterus
is the site for the growth of the embryo-fetus.OVARIES
The ovariesare a pair of oval structures about 1.5
inches (4 cm) long on either side of the uterus in the
pelvic cavity (Fig. 20–6). The ovarian ligament
extends from the medial side of an ovary to the uter-
ine wall, and the broad ligament is a fold of the peri-462 The Reproductive Systems
BOX20–3 PROSTATIC HYPERTROPHY
Prostatic hypertrophyis enlargement of the
prostate gland. Benign prostatic hypertrophy is a
common occurrence in men over the age of 60
years. The enlarged prostate compresses the ure-
thra within it and may make urination difficult or
result in urinary retention. A prostatectomy is the
surgical removal of part or all of the prostate. A
possible consequence is that ejaculation may be
impaired. Newer surgical procedures may pre-
serve sexual function, however, and medications
are available to shrink enlarged prostate tissue.
Cancer of the prostate is the second most
common cancer among men (lung cancer is
first). Most cases occur in men over the age of 50
years. Treatment may include surgery to remove
the prostate, radiation therapy, or hormone ther-
apy to reduce the patient’s level of testosterone.