lecture 9 - part 3- Rectum

Question 1

Rectum: Features

Answer 1

• Begins at S3
• Macroscopically distinct from the colon with an absence of taeniae coli, haustra and omental indices
• Pelvic parts of the GIT
• Retroperitoneal and subperitoneal

Question 2

Rectosigmoid junction

Answer 2

• Anterior to S3
• Teniae coli spread to form continuious longitudinal layer of smooth muscle

Question 3

Flexures

Answer 3

• Sacral flexure
• Anorectal flexure – NB for faecal continence
• 3 lateral flexures

Question 4

Question 5

Anal canal: Features

Answer 5

• Final segment of the GIT
• Opens within anal triangle
• Continuation of rectum
• Anal canal is surrounded by internal and external sphincters

Question 6

Anal sphincters:

Answer 6

• – Internal: upper 2/3rds thickening of involuntary smooth m
• – External sphincter: lower 2/3rds (thus overlapping with internal sphincter), voluntary mm, blends with puborectalis

Question 7

Anorectal ring: Muscular ring

Answer 7

• At the junction of the rectum and anal canal
• Formed by the fusion of the Internal anal and External anal sphincter as well as the puborectalis muscle
• – Digital examination

Question 8

• Superior part: same epithelial lining as the rectum (columnar epithelium)
• Mucosa is organised into longitudinal folds, → anal columns
• Joined at their inferior ends by anal valves
• Anal sinuses found above anal valves
• They contain glands that secrete mucus
• Anal valves collectively form an irregular circle → pectinate line
• Which divides it into upper and lower parts

Question 9

• Upper and lower parts differ in both structure and neurovascular supply
• Due to different embryological origins:
• Above the pectinate line: derived from the embryonic hindgut.
• Below the pectinate line: derived from the ectoderm of the proctodeum lined with non-keratinised stratified squamous epithelium (→ anal pecten)
• Pale and smooth surface, then transitions to true skin at the level of the inter-sphinteric groove to true skin (keratinised stratified squamous)

Question 10

Rectum & anal canal: Blood supply

Answer 10

Arterial supply
* Sup rectal (IMA) – proximal rectum and anal canal above pectinate line
* Middle rectal – middle and inferior rectum
* Inf rectal – anorectal jnx and anal canal (inf to pectinate line)

Venous drainage
* Sup (drains into portal system), middle and inf rectal vv (into systemic system)
* Anastomoses – portocaval anastomosis
- Submucosal rectal venous plexus surrounds the rectum
Consists of 2 parts
– internal rectal venous plexus – just deep to the epithelium of rectum
- external rectal venous plexus – external to the muscular rectum

Anus is supplied by the sup rectal artery above the pectinate line

Question 11

Question 12

Rectum & anal canal: Lymphatics

Answer 12

Rectum:
* Upper 1/3rd: Pararectal sup mesenteric lymph nodes, LEFT common iliac nodes
* Middle 1/3rd: Internal iliac nodes
* Lower 1/3rd: Internal iliac nodes

Anal canal (in relation to pectinate line)
* Above: Internal iliac lymph nodes
* Below: Superficial inguinal lymph nodes

Question 13

Anal canal innervation:

Answer 13

• Part of the hindgut, thus sensory and autonomic innervation from lumbar splanchnic and sup and inf hypogastric plexuses
• Parasympathetic: S2-S4 via pelvic splanchnic nerves and inf hypogastric plexus