The Rectum and Anal Canal

Question 1

At what level does the rectum begin?

Answer 1

S3

Question 2

How can the start of the rectum be easily identified (visually)?

Answer 2

By the ending of the sigmoid mesocolon

Question 3

What anatomical differences does the rectum have compared to the rest of the large intestine?

Answer 3

The teniae coli, epiploic appendages and haustra all disappear

Question 4

What replaces the teniae coli in the rectum?

Answer 4

A full layer of longitudinal muscle once again

Question 5

What are the X3 divisions of the rectum and what are the anatomical landmarks that denote each of these divisions?

Answer 5

The divisions are in relation to the peritoneum:

1) superior rectum = upper 1/3
= peritoneum is found anteriorly and laterally (not posteriorly as it is retroperitoneal)

2) middle rectum = middle 1/3
= peritoneum is anterior only

3) inferior rectum = loser 1/3
= devoid of peritoneum

Question 6

What are the different peritoneal pouches in males and females?

Answer 6

Males = X1 pouch only
= rectovescicle

Females = X2 pouches
= rectouterine
= vesicouterine

Question 7

Which pouch is referred to as the pouch of Douglas?

Answer 7

The rectouterine pouch in females

Question 8

What is the difference in terms of location with regards to the rectum and anal canal?

Answer 8

The rectum lies above the pelvic floor within the pelvis

The anal canal lies below the pelvic floor within the perineum

Question 9

What are the boundaries or the anal triangle?

Answer 9

A horizontal line drawn between the two ischeal tuberosiries which both join to the coccyx

Question 10

What is the name of the triangular space between the skin and the pelvic diaphragm, which occurs bilaterally either side of the anal canal?

Answer 10

The ischioanal fossa

Question 11

What are the boundaries or the ischioanal fossa:

• superiorly
• medially
• laterally

Answer 11

Superiorly = levator ani muscle

Medically = levator ani, anal canal and external anal sphincter

Laterally = obturator internus muscle

Question 12

What is the name of the neruovascular bundle containing canal which sits within the fascial sheath of obturator internus around the area of the ischeal tuberosity?

What does it house?

Answer 12

The pudendal canal

1) internal pudendal artery
2) internal pudendal vein
3) pudendal nerve

Question 13

Which nerve supplies the external anal sphincter and which nerve is it a branch of?

Answer 13

The inferior rectal nerve

A branch of the pudendal nerve

Question 14

What is the name of the muscular sling attached to the pubis bone which marks the end of the rectum?

Answer 14

Puborectalis

Question 15

What does puborectalis do to the rectum?

Answer 15

It pulls it forward?

Question 16

What happens in defection to puborectalis?

Answer 16

It relaxes (is usually under constant tonal control) so the rectum can align with the anal canal instead of being at 90 degrees.

Question 17

What is the name of the rectal expansion just before where it meets the anal canal?

Answer 17

The rectal ampulla

Question 18

What does the rectal ampulla contain?

How many of these are there?

What are they?

Answer 18

X3 rectal valves of Houston

These are semicircular infoldings of the rectal wall

Question 19

How are the rectal valves of Houston named and to which side do each lie?

Answer 19

They are named:

Superior = left
Middle = right 
Inferior = left

Question 20

How many sections is the anal canal divided into?

What is the name of the line which separates them?

Answer 20

X2

Pectinate line / dentate line

Question 21

What is the name of the line just below the pectinate line at which the anal canal’s circular layering of muscle stops?

Answer 21

Hilton’s line

Question 22

Where does the transverse muscle of the anal canal stop?

Answer 22

It blends into the skin or the anus (puckering)

Question 23

What are the folds of anal canal called above the pectinate line?

Answer 23

Anal columns with valves between

Question 24

What are the folds of anal canal called below the pectinate line?

Answer 24

Pecten

Question 25

Where does the internal anal sphincter end?

Answer 25

At the pectinate line

Question 26

What is the arterial supply to the hindgut above the pectinate line?

Which branch travels to the rectum specifically?

Answer 26

The inferior mesenteric artery

The superior rectal artery

Question 27

What is the venous drainage of the hindgut above the pectinate line?

Answer 27

Via the inferior mesenteric vein into the hepatic portal system

Question 28

What is the arterial supply to the hindgut below the pectinate line?

Answer 28

Via the inferior rental arteries which are branches of the internal pudendal arteries (themselves arising from the internal iliac)

Question 29

What is the venous drainage of the hindgut below the pectinate line?

Answer 29

The inferior rectal veins —> internal pudendal nerve —> internal iliac veins

NB: same name system as the arteries supplying this area

Question 30

What is the lymphatic drainage above the pectinate line?

Answer 30

Inferior mesenteric nodes (pre-aortic) —> cysterna chyli —> thoracic duct —> left lymphovenous-venous portal

Question 31

What is the lymphatic drainage below the pectinate line?

Answer 31

Internal iliac nodes —> common iliac nodes —> para-aortic nodes —> cysterna chyli —> thoracic duct —> left lymphovenous-venous portal

Question 32

What are the stages of neuronal control of defeacation?

Answer 32

1) parasympathetic afferent set off by stretch receptors (S2-S4)
2) the ascending sacral nerve fibres from step 1 inhibit lumbar sympathetics (L1+L2) which therefore involuntarily relax.
3) somatic nerves inhibited via the pudendal nerve (under our control)
4) parasympathetic efferent trigger peristalsis (S2-S4)