The prostate is a fibromuscular and glandular organ shaped like an inverted
cone with its base in contact with the urinary bladder neck and the apex in
contact with the superior fascia of the urogenital diaphragm. The organ completely
surrounds the prostatic urethra. A fibrous capsule surrounds
it. Enclosing the capsule is a dense fascial sheath, the prostatic sheath,
which is part of the pelvic fascia. The fascial sheath contains the prostatic
venous plexus, lymphatics and nerves. Behind the urethra, the two ejaculatory
ducts traverse the prostate obliquely and antero-medially from its postero-superior
margin to enter the prostatic urethra on either side of the prostatic utricle.
Question: What is the prostatic utricle?
Although no definite lobes are evident either externally or internally, the
prostate is divided into several lobes:
The anterior lobe: This is used to describe the anterior portion of
the organ lying in front of the urethra. It is devoid of glandular tissue
being formed completely of fibromuscular tissue.
The median lobe: A cone-shaped portion of the organ situated between
the two ejaculatory ducts and the urethra.
The lateral lobes: The right and left lateral lobes
form the main mass of the organ and are continuous posteriorly. They are separated
by the prostatic urethra.
The posterior lobe: This is used by some to describe the postero-medial
part of the lateral lobes that can be palpated through the rectum.
The prostate contains glands that open into the prostatic urethra. The glands
are embedded in a stroma composed of smooth muscle fibers and fibrous connective
tissue. Incomplete septa extend from the fibrocollagenous prostatic capsule
into the organ to divide it into about 50 ill-defined lobules. The organ contains
three separate groups of compound tubulo-alveolar glands arranged concentrically
around the urethra:
Mucosal (inner periurethral) glands: These open directly into the
urethra over its entire surface. The layer is the smallest of the three.
Submucosal (outer periurethral) glands: Glands from this layer, which
is larger than the mucosal glandular layer, drain through short ducts into
the urethra sinuses.
Main prostatic glands: This layer constitutes the bulk of the organ
occupying two-thirds of the gland. The glands drain into the urethra via long
The mucosal and submucosal layers form the central glandular zone
while the main prostatic glands form the peripheral glandular zone.
Question: What is the clinical importance of the dividing the prostatic
glandular layers into zones?
An inner layer of tall columnar cells and an outer layer of cuboidal cells
line prostatic glands. The lumen may contain ovoid or spherical, eosinophilic,
lamellated bodies called corpora amylacea (starchy bodies) or prostatic concretions.
These may calcify and form prostatic calculi, which when large may mimic carcinoma
by producing the hard irregular consistency of carcinoma on digital rectal
examination. In some cases the calculi are relatively mobile and give the
palpating finger the impression of a beanbag.
Low magnification view of the prostate showing glandular units surrounded
by stroma rich in smooth muscle.
Portion of prostate showing glands and surrounding fibromuscular stroma. Two
corpora amylacea are present.
Higher magnification of prostatic glands showing the two-layer epithelium
and a good example of a corpus amylaceum.