EXTERNAL GENITALIA

EXTERNAL MALE GENITALIA:

Superficial (Dartos) Fascia: Goes all the way down into the penis.

Deep Fascia: Directly overlies the penis, deepest layer.

PENIS CROSS SECTION:

Corpus Cavernosa: The two more dorsal bodies of the penile shaft. They fill with blood from the deep artery when erect.

Tunica Albuginea: The very dense fascia that surrounds the corpus cavernosa.

Corpus Spongiosum: The most ventral of the three erectile tubes.

Urethra: Travels through the corpus spongiosum.

Glans Penis: Extension of the corpus spongiosum, and it overlies (caps) the two corpora spongiosa.

The Root of the Penis: The three bodies (corpora spongiosa and cavernosa) converge on the penis. Conversely, the corpus cavernosa divert as you move

down the shaft of the penis, toward the ischiopubic rami.

When they get down to the bottom, they are then called the left crus and right crus of the penis.

Left and right crura attach to both the ischiopubic rami and the fascia of the UG diaphragm.

As you move down the shaft, the corpus spongiosum becomes thicker until it called the bulb of the penis at the base. It also attaches to the fascia of

the UG diaphragm.

Communication between Corpora: The corpus bodies do communicate with each other. They are not strictly isolated.

Penile Stimulation:

Afferent fibers are carried back through the Pudendal Nerve as GSA somatic fibers.

At the same time, parasympathetic fibers of the ANS travel along the Pudendal Nerve, specifically the Pelvic Splanchnic Nerves -- S2, S3, S4.

PATHWAY OF THE PELVIC SPLANCHNICS INTO THE PENIS:

They travel down through the prostatic plexus, which is deep to the UG diaphragm.

Then they pass under the sub-pubic arch.

Then they pass through a hiatus in the UG Diaphragm, where they join the fibers of the pudendal nerve.

The job of the parasympathetic pelvic splanchnics is to induce vasodilation, causing corpus cavernosa to fill with blood from the deep artery.

Sympathetic Stimulation gets rid of an erection.

Muscles: There are muscles along the root of the penis that aid in erection, by preventing the backflow of blood back out of the shaft.

Investing Fascia (Gallaudet's Fascia) is the penile fascia that surrounds the muscles.

Bulbospongiosus Muscle: Penile muscle surrounds the corpus spongiosum and urethra. Aids in the last part of urination and ejaculation.

Forms a herringbone pattern, V-shape on either side of the urethra. Hence when it contracts it compresses the urethra to aid in expulsion of

fluids.

It inserts on the central tendon of the perineum.

Ischiocavernosus Muscle: Penile muscles surround the corpora cavernosa.

Upon contraction they restrict the return flow of blood, to maintain erection.

They insert on the Ischiopubic Rami bones -- they do not insert on the Central Tendon of the Perineum.

Ejaculation:

Emission: Peristaltic wave of contractions through the ductus deferens, along with contraction of seminal vesicles and prostate gland, causes fluid to

move to the Ejaculatory Duct which leads into the urethra.

Emission is a sympathetic response.

Seminal Vesicle add fluid to the urethra at the ejaculatory duct, most distally. The ejaculatory duct is where the seminal vesicle joins the ductus

deferens.

Prostate gland adds fluid to the urethra at the prostatic utricle, more proximally.

Expulsion: Spastic contraction of the muscles that overlie the corpora cavernosa. and spongiosa. The same type of muscular contraction (though not

spastic) will expel the last bit of urine during urination.

Expulsion is a parasympathetic response.

MALE URETHRA:

Prostatic Portion of Urethra: The part that passes through the prostate gland. Directly inferior to the bladder.

The prostate sits directly superior to UG diaphragm.

Membranous Portion of Urethra: The part of the urethra that passes through the urogenital diaphragm.

Spongy (Penile) Urethra: The part of the urethra that goes up the shaft of the penis, starting from the bulb of the penis at its base.

Bulbourethral Gland: Supplies lubrication to the urethra. It is located in the urogenital diaphragm.

Ducts open into spongy portion of urethra.

Greater Vestibular Gland (Bartholin's Gland) is homologous structure in female.

Ductus Deferens: Pathway

It starts at epididymis, passes through the inguinal canal, over the pelvic brim and into the pelvis.

It passes medial to the ureters on the posterior aspect of the bladder.

It joins with the seminal vesicles to form the ejaculatory duct.

Seminal Vesicles: Located posterosuperior to the prostate gland. They go into the prostate gland anteriorly and empty into the ejaculatory duct.

FEMALE EXTERNAL GENITALIA:

Mons Pubis: Overlies the pubic bone.

Labium Majus: Outermost region, covered with hair. Composed of skin and elongated tubes of fat.

The distal end of the ROUND LIGAMENT of the uterus inserts into the labia majora.

Anterior Labial Commissure: Just anterior to the prepuce (hood) of the clitoris. The area where the labia majora meet anteriorly. There is no true

posterior labial commissure.

Pudendal Cleft: All structures in between the left and right labia majora. It contains the following:

Labia Minora: Fat-free folds between the labia majora. All structures in between the labia minor are contained in the vestibule.

The labia minora enclose the vestibule.

Anteriorly, the labia minora come together to form the prepuce of the clitoris.

Frenulum of Labia Minora: The posterior junction of the labia minora. This is also known as the Fourchette.

Vestibule = the space + all structures located between the labia minora.

Clitoris: Homologous to the penis in the male.

The corpora and crura of the clitoris originate in the labia minora.

Prepuce = the anterior convergence of the two labia minora.

Frenulum: The posterior aspect of the clitoris, where the labia minora also converge.

Glans Clitoris: Distal end. Proximal to it is the body, or, shaft of the clitoris.

Angle of the Clitoris: Still more distal to the body.

Then the two corpora divert into a left and right crus, that insert into ischiopubic rami, just as in the male.

Suspensory Ligament of Clitoris: An extension of deep fascia, which attaches at the symphysis pubic. Just anterior to the clitoris.

Vestibular Bulbs: Homologous to the corpus cavernosa in the male.

They are erectile tissue, one on each side.

They are not officially part of the clitoris.

Development: Unlike the male, the development of the urethra is independent to that of the external genitalia, since the urethra does not travel through

the clitoris.

Greater Vestibular (Bartholin's) Gland: Inferior fascia of the UG diaphragm, just posterolateral to the vaginal wall.

Unlike the male counterpart, these glands are superficial to the inferior surface of the UG diaphragm, in the superficial perineal space.

Glands empty into the posterolateral wall of the vaginal orifice, providing lubrication.

CLINICAL: Because of close proximity to outside, vestibular glands are susceptible to infection.