The Rectum and Anal Canal Flashcards
At what level does the rectum begin?
S3
How can the start of the rectum be easily identified (visually)?
By the ending of the sigmoid mesocolon
What anatomical differences does the rectum have compared to the rest of the large intestine?
The teniae coli, epiploic appendages and haustra all disappear
What replaces the teniae coli in the rectum?
A full layer of longitudinal muscle once again
What are the X3 divisions of the rectum and what are the anatomical landmarks that denote each of these divisions?
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
What are the different peritoneal pouches in males and females?
Males = X1 pouch only
= rectovescicle
Females = X2 pouches
= rectouterine
= vesicouterine
Which pouch is referred to as the pouch of Douglas?
The rectouterine pouch in females
What is the difference in terms of location with regards to the rectum and anal canal?
The rectum lies above the pelvic floor within the pelvis
The anal canal lies below the pelvic floor within the perineum
What are the boundaries or the anal triangle?
A horizontal line drawn between the two ischeal tuberosiries which both join to the coccyx
What is the name of the triangular space between the skin and the pelvic diaphragm, which occurs bilaterally either side of the anal canal?
The ischioanal fossa
What are the boundaries or the ischioanal fossa:
- superiorly
- medially
- laterally
Superiorly = levator ani muscle
Medically = levator ani, anal canal and external anal sphincter
Laterally = obturator internus muscle
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?
The pudendal canal
1) internal pudendal artery
2) internal pudendal vein
3) pudendal nerve
Which nerve supplies the external anal sphincter and which nerve is it a branch of?
The inferior rectal nerve
A branch of the pudendal nerve
What is the name of the muscular sling attached to the pubis bone which marks the end of the rectum?
Puborectalis
What does puborectalis do to the rectum?
It pulls it forward?
What happens in defection to puborectalis?
It relaxes (is usually under constant tonal control) so the rectum can align with the anal canal instead of being at 90 degrees.
What is the name of the rectal expansion just before where it meets the anal canal?
The rectal ampulla
What does the rectal ampulla contain?
How many of these are there?
What are they?
X3 rectal valves of Houston
These are semicircular infoldings of the rectal wall
How are the rectal valves of Houston named and to which side do each lie?
They are named:
Superior = left Middle = right Inferior = left
How many sections is the anal canal divided into?
What is the name of the line which separates them?
X2
Pectinate line / dentate line
What is the name of the line just below the pectinate line at which the anal canal’s circular layering of muscle stops?
Hilton’s line
Where does the transverse muscle of the anal canal stop?
It blends into the skin or the anus (puckering)
What are the folds of anal canal called above the pectinate line?
Anal columns with valves between
What are the folds of anal canal called below the pectinate line?
Pecten
Where does the internal anal sphincter end?
At the pectinate line
What is the arterial supply to the hindgut above the pectinate line?
Which branch travels to the rectum specifically?
The inferior mesenteric artery
The superior rectal artery
What is the venous drainage of the hindgut above the pectinate line?
Via the inferior mesenteric vein into the hepatic portal system
What is the arterial supply to the hindgut below the pectinate line?
Via the inferior rental arteries which are branches of the internal pudendal arteries (themselves arising from the internal iliac)
What is the venous drainage of the hindgut below the pectinate line?
The inferior rectal veins —> internal pudendal nerve —> internal iliac veins
NB: same name system as the arteries supplying this area
What is the lymphatic drainage above the pectinate line?
Inferior mesenteric nodes (pre-aortic) —> cysterna chyli —> thoracic duct —> left lymphovenous-venous portal
What is the lymphatic drainage below the pectinate line?
Internal iliac nodes —> common iliac nodes —> para-aortic nodes —> cysterna chyli —> thoracic duct —> left lymphovenous-venous portal
What are the stages of neuronal control of defeacation?
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)
