The perineum and external genitalia.

Question 1

Define the perineum.

Answer 1

The area inferior to the pelvic floor bounded by the pelvic outlet and limited inferiorly by the skin.

Question 2

What are the vertices of the urogenital triangle?

Answer 2

Anteriorly the pubic symphysis. Posteriorly the ischial tuberosities.

Question 3

What are the vertices of the anal triangle?

Answer 3

Anteriorly the ischial tuberosities. Posteriorly the coccyx.

Question 4

Where does the rectum become the anal canal?

Answer 4

The anorectal junction. Begins where the rectal ampulla narrows at the level of the puborectalis muscle.

Question 5

What landmark divides the two sections of the anal canal and what is its significance?

Answer 5

The pectinate line divides the proximal 2/3 from the distal 1/3. Represents the different embryological origins of the two parts.

Question 6

What is the embryological origin of the proximal anal canal?

Answer 6

The embryonic hindgut.

Question 7

What is the embryological origin of the distal anal canal?

Answer 7

The embryonic proctodeum.

Question 8

Which artery supplies the proximal anal canal and from where is it derived?

Answer 8

Superior rectal - derived from the inferior mesenteric.

Question 9

Which artery supplies the distal anal canal and from where is it derived?

Answer 9

The inferior rectal (x2) - derived from the internal pudendal.

Question 10

Describe venous drainage from the proximal anal canal.

Answer 10

Internal rectal venous plexus -> superior rectal vein -> portal system.

Question 11

Describe venous drainage from the distal anal canal.

Answer 11

Internal rectal venous plexus -> inferior rectal veins -> caval venous system.

Question 12

To where does lymph from the proximal anal canal drain?

Answer 12

Internal iliac lymph nodes.

Question 13

To where does lymph from the distal anal canal drain?

Answer 13

Superficial inguinal lymph nodes.

Question 14

Describe the innervation of the proximal anal canal.

Answer 14

Visceral motor (mixed sympathetic and parasympathetic) and sensory innervation. From inferior hypogastric plexus.

Question 15

Describe the innervation of the distal anal canal.

Answer 15

Somatic motor and sensory innervation. From the inferior anal (rectal) nerves.

Question 16

What are anal valves?

Answer 16

The structures that link the inferior ends of the anal columns.

Question 17

Of what kind of muscle is the internal anal sphincter composed?

Answer 17

Smooth muscle - thickened lower and of the rectum.

Question 18

What portion of the anal canal is enclosed by the internal anal sphincter?

Answer 18

Proximal 2/3.

Question 19

Of what kind of muscle is the external anal sphincter composed?

Answer 19

Striated muscle.

Question 20

What portion of the anal canal is enclosed by the external anal sphincter?

Answer 20

Distal 2/3.

Question 21

What is the nerve supply to the internal anal sphincter and how does it function?

Answer 21

Sympathetic fibres from the inferior hypogastric plexus maintain the tone of the sphincter, while parasympathetic stimulation inhibits the tone and evokes peristalsis.

Question 22

What is the nerve supply to the external anal sphincter and how does it function?

Answer 22

Somatic efferent fibres from the inferior anal nerves stimulate contraction of the voluntary anal sphincter.

Question 23

What are the iscioanal fossae?

Answer 23

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.

Question 24

Which structures form the medial, lateral and inferior borders of the ischioanal fossae?

Answer 24

Medial: External anal sphincter and levator ani. Lateral: obdurator internus (covered by obdurator fascia), pudendal nerve, internal pudendal artery and vein, ischial tuberosity. Inferior: gluteus maximus?

Question 25

Where is the pudendal canal?

Answer 25

In the lateral wall of each ischioanal fossa passing anteriorly.

Question 26

By what route does the pudendal nerve reach the pudendal canal?

Answer 26

Pudendal nerve: originates S3-4, passes out through the greater sciatic foramen between the piriformis and coccygeus, then hooks around the ischial spine and sacrospinous ligament to enter perineum via lesser sciatic foramen.

Question 27

How does the internal pudendal artery reach the pudendal canal?

Answer 27

Passes inferolaterally, anterior to the piriformis and sacral plexus. It leaves the pelvis between the piriformis and coccygeus by passing through the greater sciatic foramen. Then passes round the posterior aspect of the ischial spine or sacrospinous ligament and enters the canal through the lesser foramen.

Question 28

What separates the deep from the superficial urogenital triangle?

Answer 28

Urogenital diaphragm - triangular layer of muscle and fascia (perianal membrane).

Question 29

What are the branches of the pudendal nerve?

Answer 29

Inferior rectal nerve, perianal nerve (gives off posterior scrotal nerves in the male and labial nerves in female), dorsal nerve of penis/clitoris.

Question 30

What is the nerve supply to the external urethral sphincter.

Answer 30

Deep perianal nerve.

Question 31

Which vessel does the pudendal artery branch off and what does it supply?

Answer 31

Internal iliac artery - supplies blood to the external genitalia.

Question 32

What is the action of the bulbospongiosus muscles?

Answer 32

Covers the bulb of the penis. Contributes to erection, ejaculation and orgasm. Innervated by the pudendal nerve. Erects the clitoris in females and contributes to orgasm.

Question 33

What is the function of the ischiocavernosus muscle?

Answer 33

Helps stabilise the erect penis. Helps flex the anus. Tenses the vagina during orgasm.

Question 34

Describe the arterial supply to the penis.

Answer 34

The common penile artery branches into the bulbar artery, the urethral artery, the cavernosal artery and the dorsal artery of the penis.

Question 35

What is the nerve supply to the skin of the scrotum?

Answer 35

Anterolateral: genital branch of genitofemoral nerve. Anterior: anterior scrotal nerves. Posterior: posterior scrotal nerves. Inferior: perineal branches of posterior femoral cutaneous nerve.

Question 36

To which nodes does lymph from perianal structures drain?

Answer 36

Occurs via the superficial inguinal lymph nodes, which receive lymph from the lower abdominal wall, buttocks, penis, scrotum, labium majus, and lower parts of the vagina and anal canal. These nodes have efferent vessels that drain primarily into the external iliac nodes and ultimately to the lumbar (aortic) nodes. Lymph vessels from the glans penis (or clitoris) and labium minus pass to the deep inguinal and external iliac nodes.

Question 37

What is the superficial perineal pouch and what does it contain?

Answer 37

The most inferior division of the perineum. Superior border: perianal membrane, inferior border: Colle's fascia Contains ischiocavernosus, bulbospongiosus, and external genitalia.

Question 38

What is the deep perineal pouch and what does it contain?

Answer 38

the region between the perineal membrane and pelvic diaphragm. Contains external sphincter muscle of urethra, internal sphincter muscle of urethra (males), spongy urethra (males), urethrovaginal sphincter (females), compressor urethrae muscles (females), bulbourethral glands (male), vagina.