SDL - Perineum and External Genitalia Flashcards
What is the perineum bounded by superiorly and inferiorly?
The perineum is the area inferior to the pelvic floor, bounded by the pelvic outlet and limited inferiorly by the skin.
Where does the rectum become the anal canal?
At the U-shaped sling created by puborectalis (anorectal angle)
How is the anal canal divided into 2 separate parts?
By the pectinate line
What is the upper 2/3 of the anal canal derived from?
Derived from the embryonic hindgut (endoderm)
Where is lower 1/3 of the anal canal derived from?
Derived from the ectoderm of the proctodeum.
Describe the epithelial lining of the upper 2/3 of the anal canal?
Columnar epithelium (same as rectum) but mucosa organised into longitudinal folds, known as anal canals which are joined together at their inferior ends by anal valves. Above the anal valves are anal sinuses (pouches that contain glands which secrete mucus)
Describe the epithelial lining of the lower 1/3 of the anal canal?
Non-keratinised stratified squamous epithelium (anal pecten).
Transitions to true skin (keratinised stratified squamous) at level of sphincteric groove
Describe the arterial supply of the upper 2/3 of the anal canal?
Superior rectal artery (branch of IMA), anastomosing branches from the middle rectal artery
Describe the arterial supply of the lower 1/3 of the anal canal?
Inferior rectal artery (branch of internal pudendal artery). Anastomosing branches from middle rectal artery
Describe the venous drainage of the upper 2/3 of the anal canal?
Superior rectal vein which empties into inferior mesenteric vein (portal venous system)
Describe the venous drainage of the lower 1/3 of the anal canal?
Inferior rectal vein which empties into internal pudendal vein (systemic venous system)
Describe the lymphatic drainage of the upper 2/3 of the anal canal?
Internal iliac lymph nodes
Describe the lymphatic drainage of the lower 1/3 of the anal canal?
Superficial inguinal lymph nodes
Describe the nerve supply of the upper 2/3 of the anal canal?
Visceral innervation via the inferior hypogastric plexus. Sensitive to stretch.
Describe the nerve supply of the lower 1/3 of the anal canal?
Somatic innervation via the inferior rectal nerves (branches of the pudendal nerves). Sensitive to pain, temperature, touch and pressure.
What is the mucosa of the upper anal canal arranged into?
Longitudinal folds called anal columns
What are the inferior ends of the anal columns linked by?
Ridges called anal valves
What is the pectinate line formed by?
The ring formed by the anal valves is termed the pectinate line
What does the pectinate line mark?
marks the approximate boundary between the embryologically different regions of the anal canal
What surrounds the anal canal?
internal and external anal sphincters
Describe the internal anal sphincter
around the upper two-thirds of the canal, is the thickened lower end of the circular smooth muscle of the rectum.
Describe the external anal sphincter
striated muscle surrounds the lower two-thirds of the canal. It comprises subcutaneous, superficial and deep parts
What type of muscle is the internal anal sphincter?
Circular smooth
What type of muscle is the external anal sphincter?
Striated
What is the deep part of the external anal sphincter closely related to?
related posteriorly to the fibres of puborectalis
What is the nerve supply to the internal anal sphincter?
Autonomic –> Visceral innervation via the inferior hypogastric plexus.
What is the nerve supply to the external anal sphincter?
Somatic –> via the inferior rectal nerves (branches of the pudendal nerves).
What are haemorrhoids?
swellings containing enlarged blood vessels that are found inside or around the bottom
What are ischioanal fossae?
These are wedge shaped spaces in the lateral parts of the anal triangle.
They unite posteriorly, behind the anal canal, and anteriorly they extend into the urogenital triangle, above the urogenital diaphragm
The ischioanal fossae are largely filled with fat and are a common site for infection. What can this result in?
Abscesses which may rupture to produce a fistula between the anal canal and ischioanal fossae
Where do the internal pudendal vessels and nerve travel as they supply the perineum?
What branches come off as the structures traverse the ischioanal fossa?
In the pudendal canal in the lateral wall of each ischioanal fossa as they pass anteriorly to supply the structures of the perineum.
Inferior rectal artery, nerve and vein
How and why would you carry out a pudendal nerve block?
To anaesthetise the perineum – childbirth during an episiotomy.
What is the UG triangle in males and females subdivided into and by what?
Into deep and superficial parts by the urogenital diaphragm
What is the urogenital diaphragm?
a triangular layer of muscle and dense fascia that extends between the inferior ischiopubic rami and merges with the perineal body posteriorly.
What is the fascial component of the urogenital diaphragm called?
The perineal membrane
What does the UG diaphragm merge with posteriorly?
Perineal body
How are the external urethral sphincters formed?
By muscles within the UG diaphragm (deep pouch)
What is the deep artery of the clitoris/penis a branch of?
Internal pudendal artery
What is the dorsal artery of the penis/clitoris a branch of?
Internal pudendal artery
Describe full course of internal pudendal artery
It pierces the parietal pelvic fascia to exit the pelvis. It passes through the greater sciatic foramen inferior to the piriformis muscle to enter the gluteal region. It then curves around the ischial spine and sacrospinous ligament to re-enter the pelvis by passing through the lesser sciatic foramen. It then re-exits the pelvis through the pudendal canal with the internal pudendal veins and the pudendal nerve. It then runs in the lateral wall of the ischioanal fossa and the perineal region.
What are the branches of the internal pudendal artery?
inferior rectal artery, deep artery of the penis/clitoris, dorsal artery of the penis/clitoris, perineal artery, posterior scrotal/labial artery, transverse perineal artery, artery to the bulb
What does the deep artery of the penis/clitoris supply?
Corpus cavernosum
What is the nerve supply to the external urethral sphincter?
Deep perineal branch of pudendal nerve
Which vessel does external pudendal artery branch off? What does it supply?
Femoral artery
Skin of scrotum and labia
What are the branches of the internal pudendal artery?
Inferior rectal artery, perineal artery, posterior scrotal/labial artery, artery to bulb, deep artery of penis/clitoris, dorsal artery of penis/clitoris
What does the superficial perineal pouch in males contain?
Testis, vas, root of penis
What would a why rupture of the urethra in the bulb of the penis lead to?
Swelling of scrotum, penis and lower abdominal wall
Which structures do the bulb of the penis and the crura of the corpora cavernosa attach to?
Perineal membrane and ischiopubic ramus
What are the actions of bulbospongiosus and ischiocavernosus muscles?
What is their nerve supply?
Contraction of these muscle prevents venous return, thereby allowing engorgement of the erectile tissues.
Deep branch of perineal nerve
What is the sensory nerve supply to the skin of the scrotum?
Ilioinguinal nerves, genital branch of genitofemoral nerves = anterior
Branches of pudendal nerve, posterior scrotal nerve = posterior
From what is the tunica vaginalis derived? How?
Processus vaginalis
During descent of the testis, the testis pushes through a serous pouch of the peritoneum
What is the cremasteric reflex?
a superficial reflex found in human males that is elicited when the inner part of the thigh is stroked. Stroking of the skin causes the cremaster muscle to contract and pull up the ipsilateral testicle toward the inguinal canal.
What lies deep to the skin and fat of the labia majora?
a mass of erectile tissue called the bulb of the vestibule
What is the bulb of vestibule attached to?
Perineal membrane
What do the bulbs of vestibule partially overlie?
the greater vestibular glands
What are the bulbs of vestibule covered by?
Bulbospongiosus muscles
Where do the bulbs of vestibule join? What does this form?
Join anterior to the external opening of the urethra and pass forwards to form the glans of the clitoris
Two other masses of erectile tissue also contribute to the formation of the clitoris. What name is given to these masses?
Corpora cavernosa
Which part of the clitoris do the corpora cavernosa form?
Body and contribute to glans
How is the clitoris anchored in the perineum?
Via crus which insert onto the ischiopubic ramus
What is the function of the vestibular glands (also known as Bartholin’s glands)?
Secretion of mucus in to the vaginal during sexual arousal.
What forms during infection of vestibular glands?
a Bartholin’s cyst
To which nodes does lymph from perineal structures drain?
Superficial inguinal lymph nodes, the deep and then internal iliac.
