368
UNIT 3
Organ Systems
Penis
Dorsal
Dorsal
artery
artery
Dorsal
artery
Helicine artery
Helicine artery
Helicine artery
Superficial
Superficial
dorsal vein
dorsal vein
Superficial
dorsal vein
Deep
Deep
dorsal vein
dorsal vein
Deep
dorsal vein
Corpora
Corpora
cavernosa
cavernosa
Corpora
cavernosa
Corpora
Corpora
cavernosa
cavernosa
Corpora
cavernosa
Urethra
Urethra
Urethra
Urethra
Urethra
Urethra
Skin
Skin
Skin
Corpus
Corpus
spongiosum
spongiosum
Corpus
spongiosum
Tunica
Tunica
albuginea
albuginea
Tunica
albuginea
Erectile
Erectile
tissue
tissue
Erectile
tissue
Sinuses (vein)
Sinuses (vein)
Sinuses (vein)
Urethral glands
Urethral glands
(Littré glands)
(Littré glands)
Urethral glands
(Littré glands)
Figure 18-22.
Overview of the penis.
H&E,
3
13; inset (
upper
)
3
67; inset (
lower
)
3
26
The
penis
is composed of three cylinders of erectile tissue: the two
corpora cavernosa
and the
corpus spongiosum
as shown on the
left
.
Each
cavernosa
is surrounded by a
tunica albuginea
(thick and dense connective tissue); the
corpus spongiosum
is surrounded by a thin
layer of connective tissue with some smooth muscle F bers. The
penile
(
spongy
)
urethra
is enclosed in the center of the corpus spongiosum
and extends into the terminal end (
glans
) of the penis. Each cylinder contains erectile tissue composed of a trabecular network of veins
(
sinuses
) surrounded by collagen, elastic F bers, and smooth muscle cells. The three cylinders, with their tunica albuginea, are surrounded
by hairless
thin skin
containing arteries, veins, nerves, and connective tissue and covered by stratiF ed squamous epithelium. The two
red
circles
indicate the position of the
deep arteries
; the
yellow circles
indicate the position of the
helicine arteries
in the corpora cavernosa.
The penis is supplied by the
dorsal arteries
, and blood drains into the
dorsal veins
. A special blood vessel arrangement called
an
arteriovenous
(
A-V
)
shunt
allows blood to fl ow directly from arteries to veins. In the erect state, the arteriovenous shunt closes,
which results in blood being forced from the
helicine arteries
into the sinuses (cavernous spaces) in the erectile tissue (
right upper
inset
). Dilation of the sinuses produces
penile erection
. Erection is activated by parasympathetic stimulation through the spinal
nerves and the sacral parasympathetic preganglionic motor neurons in the spinal cord (S2–S4). The
right lower
photomicrograph
shows the penile urethra surrounded by
erectile tissue
and
sinuses
(
veins
) F
lled with blood. The
urethral glands
(
Littré glands
) are
mucous glands in the submucosa of the penile urethra, also called
paraurethral
(
periurethral
)
glands
. The secretion of the urethral
glands lubricates the urethra and contributes to the semen during ejaculation.
A clinical condition called
erectile dysfunction
is characterized by the inability to produce or maintain an
erection of the penis. This
happens due to insufF ciency of dilation of the sinuses in the erectile tissue. The causes are varied, including hormonal disorders,
neurological problems, hypertension, psychological factors, smoking, and alcohol use.
SYNOPSIS 18-3
Clinical and Pathological Terms for the Male Reproductive System
IGCN
: Noninvasive intratubular or
in situ
lesions within the seminiferous tubules that give rise to the majority of adult germ
cell tumors of the testis; IGCN is often found adjacent to testicular germ cell tumors on histologic examination (±ig. 18-15C).
Cryptorchidism
: Lack of, or incomplete, descent of a testis, from the abdominal cavity into the scrotum; the testis may
remain intra-abdominal or be found in the inguinal canal; an undescended testis is a risk factor for the development of
testicular tumors (±ig. 18-15C).
Gonadal dysgenesis
: Abnormal development of the gonads with resultant alterations in sexual development; gonadal dys-
genesis is a risk factor for the development of testicular tumors; the underdeveloped gonad is often referred to as a “streak
gonad” (±ig. 18-15C).
PSA
: A protein synthesized by prostatic epithelial cells; elevated serum PSA levels are associated with benign processes such
as benign prostatic hypertrophy as well as adenocarcinoma of the prostate; the PSA test is used as a screening test for prostate
cancer as well as a tumor marker in patients with a history of prostate cancer who have received treatment (±ig. 18-20C).
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