5.19 Male Urogenital Region

 

2 layers of fascia: superior (354) & inferior fasciae (355) of U-G diaphragm

Enclose sphincter urethrae and deep transverse perineal muscles (357, nb different superficial layer).

-            superior fascia is thin, ill defined, inferior thicker = perineal membrane.

Deep perineal pouch

Lies between superior & inferior fasciae

Transmits membranous urethra, end of internal pudendal vessels (357), dorsal nerve of penis (perineal nerve), bulbourethral glands (of Cowper; each has single duct ¨ seminal fluid to penile urethra). 

-            as well as sphincter urethrae and deep transverse perineal muscles.

Perineal membrane

Inferior fasciae of U-G diaphragm; tough sheet cf loose fascia of superior layer.

-            base to which penis and penile muscles are fixed (Pl 356)

Attached to ischiopubic rami bilaterally; anterior border (= transverse perineal lig) doesnÕt quite reach subpubic angle and resulting space transmits deep vein of penis.

Lies horizontal in upright position. 

Posterior border fuses with perineal body

Above lies the membranous urethra surrounded by urethral sphincter (below prostate; Pl357)

Pierced by urethra, bulbourethral gland ducts and vessels & nerves.

Urethra (357)

Leaves prostate just in front of apex, becoming membranous urethra

-            shortest and least dilatable part of urethra

-            upper wall has smooth muscle fibres continuous with prostatic urethra.

Passes down 1.5cm, pierces perineal membrane 2.5cm behind pubic symphysis ¨ penile urethra

Sphincter urethrae (358)

= external urethral sphincter

Pear shaped: thin upper end and thicker lower part surrounding prostatic urethra

Is above perineal membrane

-            some fibres arise in u-loops in front and behind urethra; some running from transverse perineal ligament to perineal body, some completely encircling the urethra.

-            Striated muscle but small and slow-twitch; supplied by perineal branch of pudendal nerve (S2,3,4 from posterior division sacral plexus).

Deep transverse perineal muscle runs from ischial ramus to perineal body ¨ decussates with collateral muscle and EAS (357) ¨ then merges anteriorly with sphincter urethrae (shares same nerve supply)

Bulbourethral glands (358)

Lie on sides of membranous urethra in deep perineal pouch (above / deep to perineal membrane)

-            covered by urethral sphincter

1cm in diameter, each has a single duct 2.5cm long ¨ pierces perineal membrane ¨ opens into bulb of penile urethra.

Superficial Perineal Fascia (CollesÕ) (357, lower) DIFFERENT FROM ABOVE 2 FASCIA.

Continuation of ScarpaÕs from anterior abdo wall ¨ attaches to ischiopubic rami and posterior margin of perineal membrane enclosing:

Superficial perineal pouch (space) (357, lower, 358) AKA DIFFERENT FROM DEEP POUCH.

Has bulbous scrotal and tubular penile expansions.

Lies between Colles fascia and inferior perineal membrane

Contains root of penis, superficial transverse perinei, branches of pudendal nerve, testes, spermatic cords.

A deep perineal fascia intimately surrounds cavernous bodies of penis / clitoris and associated muscles.

Penis (355-7)

Root and body.

Root attached to inferior surface of perineal membrane = central bulb (¨corpus spongiosum) and crus on each side (¨ corpora cavernosum). 

-            each crus receives deep artery of penis

-            corpus spongiosum transmits penile urethra. 

Body formed as CC bound together beside / dorsal to CS (CS is ventral in erect state)

-            bulge at end of CS = glans penis: overlaps distal ends of the CC

-            urethra enters glans near its front, so most bulge is behind & below the urethra.

-            bulb has slight notch in front; extends back towards perineal body (356)

-            arteries of bulb enter near urethra (receives ducts of bulbourethral glands here also)

CS and CC each surrounded by tough tunica albuginea (¹ TA of testis); sheaths of CC are fused into septum.  Suspensory ligament of penis attaches sheaths to pubic bone. 

-            3 corpora are surrounded by fascia of penis (prolongation of Colles fascia); deep dorsal vein runs beneath it with dorsal artery on each side & dorsal nerves more laterally.

Skin is prolonged forwards as a fold (prepuce) over glans, doubling back to glans neck

-            superficial fascia (BuckÕs) is directly beneath skin, with superficial dorsal vein and lymph

-            on inferior aspect of glans a fold (frenulum) passes prepuce ¨ posterior end of urethral orifice.

Blood supply (376)

3 paired branches (of internal pudendals):

-            artery to bulb (¨ CS including glans)

-            deep artery of penis (¨ CC); end arteries; maintain erection

-            dorsal artery (¨ skin, glans; anastomoses with bulb artery via CS ¨ glans)

Main venous drainage via deep dorsal vein; quite a different course: ¨ pierces suspensory ligament ¨ above perineal membrane (via space anterior to transverse perineal lig) ¨ enters vesicoprostatic venous plexus. (See 376 lower)

-            some drainage passes from corpora by way of veins accompanying arteries.

-            superficial dorsal vein drains skin ¨ superficial external pudendal tributaries of GSV

Lymph drainage (379)

Skin ¨ superficial inguinal nodes

Glans, corpora ¨ deep inguinal nodes

Innervation (381)

Posterior scrotal and dorsal nerves (from pudendals) ¨ skin (S2)

Perineal branch of pudendal (S2,3) ¨ bulbospongiosus, ischiocavernosus

Pelvic splanchnics (S2,3) ¨ parasympathetic supply to corpora ¨ vasodilatation for erection

Sympathetic nerves from superior & inferior hypogastric plexuses ¨ ejaculation

Circumcision

Incise prepuce on dorsum from tip to glans; dissect adhesions; carry incision circumferentially.

-            suture skin edges; control bleeding from a vessel in the frenulum

Superficial perineal muscles (355 top)

Bulbospongiosus (compressor urethrae) ¨ bulb, ischiocavernosus ¨ crura.

i)                         bulbospongiosus from perineal body and a median raphe ¨ dorsal fibrous expansion of penis; more posterior fibres clasp CS; anteriorly extend to CC;

-            empties urethra at end of micturition, assists in erection (compresses deep dorsal vein) and contracts during ejaculation

ii)                       ischiocavernosus: posterior perineal membrane and ischial rami ¨ aponeurosis on CC

-            assists in support of erect penis and can move it slightly.

Superficial transverse perinei run along base of perineal membrane, arising from ischial ramus and inserting into perineal body. 

-            thus triangles formed from these superficial muscles on each side

Innervation: perineal branch of pudendal nerve (S2,3)

Male urethra

Length 20cm; prostatic, membranous and penile parts.

-            prostatic and membranous parts = posterior urethra

Penile urethra (anterior urethra)

15cm long; in corpus spongiosum, in bulbous & pendulous parts

-            pierces perineal membrane, enters bulb ¨ takes a right angle turn forward.

-            Continuous in penis as pendulous part

Dilatation just proximal to external meatus = short dilated region called navicular fossa (359);

-            lined by stratified squamous epithelium cf rest of urinary tract = transitional epithelium.

Urethral mucosa has lacunae (small blind-ending pockets) and mucous urethral glands (Littre)

-            horizontal cross-section, but meatus is a vertical slit ¨ spiral stream of urine, delaying separation into separate droplets

Narrowest at external meatus: dilations in prostatic part, bulb and navicular fossa

-            take account of angle change when passing a catheter.

-            As there is a large lacuna on roof of navicular fossa, pass instruments towards fossa floor (ie towards feet of a supine pt with penis held up over anterior abdo wall.

Blood

Like other tubes: no single supply; adjacent prostate, sphincter urethrae and CS vessels.

Nerves

Branch from perineal nerve to penile part.

Inferior hypogastric plexus reaches more proximal parts.

Remember the sphincters control micturition.

Development

Proximal to openings of ejaculatory ducts = lower ends of mesonephric ducts

Rest = parts of urogenital sinus ventrally supplemented by fusion of urogenital folds

-            epithelium of navicular fossa becomes canalised

-            failure to do so ¨ hypospadias: opening onto ventral surface

Scrotum (361)

Pouch containing testes and cords.

Subcutaneous tissue contains dartos muscle = smooth muscle of panniculus carnosus (innervation = genital branch of GF nerve L2; sympathetic innervation).   Does not contain fat.

-            rugosity due to dartos contraction

Colles fascia lies deep to dartos, attached posteriorly to inferior edge of perineal membrane, at sides to ischiopubic rami and anteriorly continuous with ScarpaÕs fascia. 

Blood supply

Superficial and deep external pudendal arteries (466) (from femoral) + some branches of internal pudendal posteriorly.

Venous drainage ¨ long saphenous vein via superficial and deep external pudendal veins.

Lymphatics

¨ medial group of superficial inguinal nodes. 

Innervation

Anterior axial line crosses scrotum.

Anterior 1/3 = ilioinguinal nerve (L1) and genital branch of GF nerve (L1)

Posterior 2/3 = scrotal branches of perineal nerve (S3) and perineal branch of posterior femoral cut nerve laterally (S2)

Perineal vessels & nerves

Internal pudendal artery (376, 382)

From anterior branch of internal iliac (374 for iliac branches) ¨ along ischiopubic ramus

-            enters deep perineal pouch at anterior end of pudendal canal

¨ inferior rectal branch at posterior end of AlcockÕs canal

¨ perineal branch pierces posterior angle of perineal membrane (runs superficial to perineal membrane)

-            ¨ posterior scrotal & transverse perineal branches; artery to bulb further forward

-            also ¨ branches to CC and passes forward to glans

¨ terminal branches: given off near anterior margin of perineal membrane

-            ¨ deep (¨ CC) and dorsal arteries of penis

-            dorsal ¨ runs into suspensory lig of penis ¨ along with deep dorsal vein

Deep dorsal vein

Drains most of corpora ¨ runs proximally in midline of dorsum of penis ¨ pierces suspensory ligament ¨ passes below subpubic angle, passes up between puboprostatic ligaments ¨ enters vesicoprostatic plexus. 

Pudendal nerve

From sacral plexus (S2,3,4)

Divides within AlcockÕs pudendal canal ¨ terminal branches (both enter deep perineal pouch):

-            dorsal nerve of penis pierces anterior angle of perineal membrane (runs above it then pierces the membrane again anteriorly to meet penis) ¨ runs with the dorsal artery on its lateral side ¨ penile skin, glans and branches to CC

-            perineal nerve (runs superficial to perineal membrane) ¨ muscular branches to superficial & deep perineal muscles and to external  urethral sphincter, also posterior scrotal branches ¨ skin of posterior 2/3 of scrotum

Also ¨ inferior rectal branch at posterior end of AlcockÕs canal

Erection and Ejaculation

See physiology notes

Sympathetic outflow from T11-L2 to epididymis, ductus, seminal vesicle, ejaculatory duct, prostate, superficial trigonal muscle of bladder and circular muscle of bladder neck ¨ emission

-            internal urethral opening becomes constricted to prevent retrograde ejaculation

-            rhythmic contraction of bulbospongiosus ¨ expulsion of fluid

Orgasmic sensations pass in spinothalamic tract, abolished by cord transection.