10.4.11+-+Perineum


 * 1. Define the term perineum and describe its boundaries. Name the perineal triangles and define their borders.**

The perineum is the space of the body bounded inferiorly by the perineal skin and superiorly by the floor/diaphragm of the pelvis. Anteriorly by the mons pubis (fat pad covering pubic symphysis); posteriorly by the intergluteal cleft (butt crack); and laterally by the inner edges of the thighs. The perineum is formed by two equilateral triangles that share a side: the urogenital triangle and the anal triangle. The anal triangle is the more posterior triangle and includes the anal canal and ischioanal fossae. Its anterior border is complex, but it looks like it could be described as the deep transverse perineum muscles meeting at the perineal body. The posterior angle is formed by the coccyx and the lines that connect them are filled by the gluteus maximus and the sacrotuberous ligaments. The urogenital triangle is the more anterior triangle and includes the superficial perineal space and the deep perineal space. Its posterior border is formed by the deep transverse perineum muscles meeting at the perineal body. The anterior angle is formed by the mons pubis. The posterior angles are formed by the ischial tuberosities.


 * 2. Define the perineal fascias, perineal body and perineal membrane.**

Perineal Fascias There are three layers of perineal fascia: Superficial, Deep, and Perineal Membrane


 * Layer Homologue || Perineal || Abdominal || Scrotal || Penis || Lower Limb ||
 * 1 || Skin || Skin || Skin || Skin || Skin ||
 * 2 || Subcutaneous Fat of Perineum || Camper's Fascia || ### || ### ||  ||
 * 3 || Superficial Perineal Fascia || Scarpa's Fascia || Dartos Fascia || Superficial fascia of penis || Fascia Lata ||
 * 4 || Deep Perineal Fascia || EAO (Deep investing fascia of) || External Spermatic Fascia || Suspensory ligament of penis (or Clitoris) + Deep fascia (Buck's) of penis) ||  ||
 * 5 ||  || IAO || Cremasteric Muscle and Fascia ||   ||   ||
 * 6 ||  || TA || ### ||   ||   ||
 * 7 ||  || Transversus Abdominus || Internal Spermatic Fascia ||   ||   ||
 * 8 ||  || Extraperitoneal Fat || ### ||   ||   ||
 * 9 ||  || Parietal Pleura || Tunica Vaginalis ||   ||   ||
 * 10 || Perineal membrane ||  ||   ||   ||   ||

Perineal Body The perineal body is the central tendon of the perineum. It's the fibrous knot lying in the shared border of the UG and anal triangles. The bulbospongiosus and the superficial transverse perineal muscles arise from it. The external anal sphincter also binds to it.

Perineal Membrane A trapezoidal fibrous sheet that spans the ischiopubic rami (the same attachment points for the superficial transverse perineal muscles). Its anterior border thickens as the transverse perineal ligament. The membrane is deep to the superficial transverse perineal muscles and superficial to the deep transverse perineal muscles.


 * 3. Define and describe the anal triangle, ischioanal fossa and its contents, pudendal canal and its contents and anal canal, its blood supply and innervation.**

The anal triangle contains one anus and two fossae. Borders and contents defined elsewhere.

The ischioanal fossae are mirrored on the right and left sides of the anal canal. The sketch is from the posterior side of a right ischioanal fossa. It contains ischioanal fat bodies.

The pudendal canal is a slit in the obturator internus muscle and fascia within the lesser sciatic foramen. The internal pudendal vessels (artery and veins) and the pudendal nerve (S2-S4) pass through the canal. Branches from the pudendal nerve and internal pudendal vessels that head to the inferior anal canal are called inferior rectal nerves and vessels respectively (N4p378/384/391/393).

The anal canal is formed by the terminal end of the embryonic hind gut and the the proctodeum. The line dividing the two tissues is the pectinate line. It is an undulating line marked by alternating anal valves and sinuses. Superior to the pectinate line the anal canal is subserved by superior rectal vessels, innervated by the rectal plexus, and drained by the internal iliac nodes. Inferior to the pectinate line the anal canal is subserved by inferior rectal vessels, innervated by inferior rectal n., and drained by inguinal nodes. The anal canal is controlled by two sphincters. The internal anal sphincter is under tonic control by sympathetics. They're firing all the time that you're not pooping. The external anal sphincter is three parts: subcutaneous, superficial, and deep. They are skeletal muscle and somatic controlled. Anteriorly they are connected the the perineal body; posteriorly they are connected via the anococcygeal liligament to the to the coccyx.


 * 4. Define and describe the UG triangle and its contents.**

The UG triangle is divided into two pouches: The Superficial Perineal Space/Pouch is between the superficial perineal fascia and perineal membrane. It contains the three superficial perineal muscles (bulbospongiosus, ischiocavernosus, and superficial transverse perineal) and the nerves, veins, and arteries that subserve them. Also, the penis in males and the clitoris, vestibular bulbs, vagina, and vestibular glands in females. The Deep Perineal Space/Pouch is the space between the perineal membrane and the pelvic diaphragm. It includes the 2 deep perineal muscles (deep transverse perineal and the two parts of the external urethra: the compressor and sphincter urethrae), the urethra, and the nerves, veins, and arteries that subserve them. Also, the bulbourethral glands in males and the vagina in females.


 * 5. Describe the male perineum: external genitalia and perineal muscles.**

The male perineum can be subdivided into three groups of structures: the external genitalia (scrotum, penis), internal structures (urethra, bulbourethral glands) and the perineal muscles (bulbospongiosus, ischiocavernosus, superficial transverse perineal, deep transverse perineal, external urethra).

Scrotum: Already covered.
 * Penis:** Formed by three columns of erectile tissue: two corpora cavernosa and one corpus spongiosum. Urethra travels through center of corpus spongiosum. Deep penile arteries travel through center of corpora cavernosa. Down dorsal aspect of penis runs neurovascular bundle of deep dorsal vein, 2 dorsal penile arteries, and 2 dorsal penile nerves (parasympathetics) in NAVAN organization. Penis is wrapped deeply by tunica albuginia, then deep penile (Buck's) fascia, then superficial penile fascia, then hairless skin. At the terminal end of the penis the corpus spongiosum expands into the glans penis. At the the base the corpus spongiosum expands into a rounded bulb. The 2 corpi cavernosa split into the crura, anchored to pubic rami. If uncircumcised, glans penis covered by prepuce.
 * Male urethra:** Transmits both sperm and urine to surface through external urethral orifice (expanded into the navicular fossa) at tip of glans penis. Subdivided into 4 regions: pre-prostatic, prostatic, intra-perineal intermediate, and (spongy) penile parts. 90 degree bend at bulb of penis.
 * Bulbourethral glands:** Small, paired glands that produce lubricant during sexual arousal. Located posterior to intermediate urethra with ducts that descend and open into spongy urethra.
 * Bulbospongiosus Muscles:** Arise from perineal body and midline rap he, encircle penile bulb and insert in the perineal membrane and dorsal penile fascia. Support perineal body, empty urethra, augment erection.
 * Ischiocavernosus Muscles:** Arise from ischiopubic ramie and insert onto crural fascia and perineal membrane. Compress crura during erection to force blood into shaft/retard venous drainage
 * Superficial Transversus Perineal Muscles:** Arise from ischiopubic rami and ischial tuberosities. Insert into the perineal body. Provide support to perineal body.
 * Deep Transversus Perineal muscles:** Same as superficial, deep to perineal membrane.
 * External Urethral Sphincter:** Two parts, the compressor urethrae originates from the ischiopubic rami to cover the anterior prostate gland and compress the urethra. The sphincter urethrae circles and closes the urethra.


 * 6. Describe the female perineum: external genitalia and perinieal muscles**

The structures of the female perineum can be subdivided into three categories: External genitalia (mons pubis, labia major, labia minor, clitoris, vestibule of the vagina, vestibular bulbs, vestibular glands), Internal structure (urethra), and Perineal Muscles (bulbospongiosus, ischiocavernosus, superficial transverse perineal muscles, deep transverse perineal muscles, 3 part external urethral sphincter).


 * Mons Pubis:** A mound of fat covering the pubic symphysis.
 * Labia Majora:** Latin for major lips. Meet anteriorly and posteriorly at A and P commissures. Space between is the pudendal cleft. Composed of skin, fibro-fatty tissue, and remnants of round ligament of uterus.
 * Labia minora:** Hairless skin, enclose vestibule of vagina. Anteriorly meet at prepuce of clitoris (superior to clitoris). Posteriorly meet at frenulum of the labia minora.
 * Clitoris:** 3 parts: root, body, glans clitoridis. Composed of corpus cavernosa. The root is composed of paired crura, embedded in perineal pouch and anchored to pubic rami. The glans clitoridis is visible upon exam. Dorsal aspect of clitoris has the deep dorsal vein, 2 dorsal clitoral arteries, and 2 dorsal clitoral nerves (NAVAN).
 * Vestibule of the Vagina:** The antechamber, enclosed by labia minor, that urethra and vaginal orifice open into. The Introitus (vaginal orifice) may be covered by hymen or hymenal caruncles. Vestibule also receives openings of ducts from the greater and lesser vestibular glands.
 * Vestibular Bulbs:** Masses of corpus spongiosum lateral to introitus.
 * Vestibular glands:** Greater are pea-sized glands that along with the diffuse lesser vestibular glands drain into vestibule.
 * Urethra:** 4 cm long. Embedded in anterior vaginal wall. Terminates at external urethral orifice.
 * Bulbospongiosus Muscles:** Perieal body --> pubic arch. Enclose glands and vestibular blub.
 * Ischiocavernosus Muscles:** Ischiopubic rami --> clitoral crura. Compress crura during erection.
 * Superficial Transversus Perineal Muscles:** ischiopubic rami --> perineal body
 * Deep Transversus Perineal Muscles:** ischiopubic rami --> perineal body
 * External Urethral Sphincter:** 3 parts: Sphincter urethrae circles urethra. Compressor urethrae bridges ischiopubic rami anteriorly to urethra and compress it. Urethrovaginal sphincter surrounds and compresses urethra and vagina.


 * 7. Name and describe the arterial supply of the perineum.**


 * Branches of Internal Pudendal Artery Supplying Perineum ||
 * **Branch** || **Structure Supplied** || **Comment** ||
 * Inferior rectal artery || Anal canal ||  ||
 * Perineal Artery || Scrotum (labia in females), perineal skin, subcutaneous fat, and contents of superficial perineal space ||  ||
 * A. to Penis/Vestibular Bulb || Bulb of penis (vestibule in females) ||  ||
 * A. to Urethra || Arises in deep perineal space and supplies the male spongy urethra ||  ||
 * Dorsal artery of penis (clitoris) || Erectile tissue corpus cavernosum || Smaller artery in females ||
 * Deep artery of the penis (clitoris) || Erectile tissue corpus cavernosus || Smaller artery in females ||


 * 8. Name and describe the venous drainage of the perineum.**

With one exception, the venous drainage of the perineum follows the same pattern with the same naming system as the arteries. The exception is the deep dorsal vein of penis or clitoris goes between the transverse perineal and inferior pubic ligaments and ends in the venous plexus. Bypasses internal pudendal v.


 * 9. Name and describe the autonomic and somatic nerves of the perineum.**

Somatic innervation of the perineum shares naming and branching pattern with the perineal arteries with two exceptions: a. Instead of the Pudendal N. (Internal Pudendal A. in sketch) terminating in 4 branches, it just continues as one nerve to the penis or clitoris. b. Instead of the Perineal N. (Perineal A. in sketch) remaining one primary branch, the nerve divides into two branches: the deep and the superficial perineal nerves. The deep perineal branch innervates the superficial and deep perineal muscles. The superficial perineal branch terminates as the posterior scrotal/labial nerves.

Autonomic fibers (both parasympathetic and most of sympathetic) arise from pelvic sub plexuses. Parasympathetic leave prostatic plexus as nervi erigentes, follow deep dorsal vein, innervate helicon arteries of the penile erectile tissues. Sympathetics that innervate the prostate, bulbourethral, and seminal glands also arise from prostatic plexus and head toward target. Sympathetics that innervate the ductus deferens follow testicular vessels from L1,2 sacral nerves. Visceral afferents follow parasympathetic pathways back to spinal cord (below pelvic pain line).


 * 10. Define and describe erection, emission and ejaculation in males and orgasm in females.**

Male Erection (Point): Parasympathetics in nervi erigentes relax helicine arteries in corpora, filling the venous spaces with blood. Emission (Secrete?): lumbar originated Sympathetics contract smooth muscles of ductus deferens to release sperm; prostatic plexus Sympathetics cause prostate, seminal, and bulbourethral glands to secrete Ejaculation (Shoot): prostatic plexus Sympathetics cause internal urethral sphincter to contract to prevent retrograde flow of semen. Parasympathetics cause urethral wall to contract. Somatic fibers (Deep Perineal N.) cause bulbospongiosus muscles to empty the urethra.

Female Presumed identical, sympathetic role is poorly understood. Erection: Parasympathetics in nervi erigentes follow branches of vaginal artery causing erection of clitoris, vagina, labia minor, and vestibular bulbs. And secretion of vestibular glands. Somatic fibers (deep perineal n.) cause bulbospongiosus muscles to clonically contract during orgasm.