Rectal and anal anatomy

Question 1

Which vertebral level does the rectum begin at?

Answer 1

S2-S3

Question 2

Where is the pubococcygeus in relation to the rectum?

Answer 2

It slings around the ano-rectal junction to aid in faecal continence under voluntary control

Question 3

Describe the peritoneal coverings of the rectum?

Answer 3

Superior third = intraperitoneal
Middle third = retroperitoneal
Inferior third = external to peritoneum

Question 4

Where is the dentate/pectinate line found?

Answer 4

It divides the superior third (columnar) with the middle third (intermediate) of the anal canal

Question 5

Where is the internal anal sphincter located in relation to the anal canal?

Answer 5

The internal anal sphincter covers the upper two thirds of the anal canal (columnar and intermediate zones)

Question 6

How does the autonomic nervous system control internal anal sphincter tone?

Answer 6

The internal anal sphincter is constantly contracted by sympathetic nervous system and only relaxes with parasympathetic innervation

Question 7

Where is the external anal sphincter located in relation to the anal canal?

Answer 7

The external anal sphincter covers the lower two thirds of the anal canal (intermediate and cutaneous zones)

Question 8

Where does the superior rectal artery arise from?

Answer 8

The superior mesenteric artery

Question 9

Where does the middle rectal artery arise from?

Answer 9

The internal iliac artery

Question 10

Where does the inferior rectal artery arise from?

Answer 10

The internal pudendal artery

Question 11

What does the superior rectal artery supply?

Answer 11

Rectum and anal canal up to the dentate line(columnar zone)

Question 12

What does the middle rectal artery supply?

Answer 12

Middle rectum and anal canal

Question 13

What does the inferior rectal artery supply?

Answer 13

Distal rectum and anal canal below the dentate line

Question 14

What drains the blood from the muscular wall of the rectum?

Answer 14

The perimuscular rectal venous plexus - superior to superior rectal vein to inferior mesenteric vein, middle rectal vein to internal iliac, inferior rectal vein to internal pudendal

Question 15

What is the difference between the perimuscular and external venous plexi of the rectum?

Answer 15

The perimuscular venous plexus drains the rectal muscles to the superior, middle and inferior rectal veins. Whereas the external venous plexus, like the internal plexus lies internal to the muscle and drains into the perimuscular venous plexus

Question 16

What is the sympathetic supply to the rectum?

Answer 16

Lumbar splanchnic, superior and inferior hypogastric plexi

Question 17

What is the parasympathetic supply to the rectum?

Answer 17

Pelvic splanchnic and inferior hypogastric

Question 18

What is the nervous supply to the anal canal?

Answer 18

inferior hypogastric above the dentate line

Inferior rectal nerve below the dentate line

Question 19

What are the boundaries of the ischioanal fossa?

Answer 19

Superior = levator ani
Inferior= deep perineal facia
Medial = external anal sphincter
Lateral = obturator internus

Question 20

Where does the pudendal canal run?

Answer 20

In the obturator internus fascia (lateral wall of the ischioanal fossa)

Question 21

Which structures are found in the pudendal canal?

Answer 21

pudendal nerve, artery, vein
perineal nerve (branch of the pudendal nerve)