Lecture 11 - The rectum and anal canal Flashcards
Rectum: where does it begin, how big is it, what curve does it follow, where does it lie posterior to, where is it relative to the median plane, what happens with the Taenia coli, where does its peritoneum cover, what is in its terminal part, how does it end, what forms a sling around the anorectal junction, and what is it important for?
Begins anterior to S3
15 cm long
Follows the curve of the sacrum and coccyx
Lies posterior to the bladder in men and uterus and vagina in women
Deviates to left but returns to the median plane
Taenia coli merge to form broad longitudinal muscles anteriorly and posteriorly
The peritoneum covers the anterior and lateral surfaces of the upper 1/3, anterior of the middle 1/3, and none of the lower 1/3
An anterior dilation - the rectal ampulla
Ends by piercing the pelvic floor
Puborectalis forms a sling around the anorectal junction
Important for faecal continence
Pararectal fossae
Lateral reflections of the peritoneum that allow
the rectum to distend as it fills
Pelvic floor: what are the components, what is its origin, insertion, and function?
Pelvic floor (diaphragm) = coccygeus + levator ani
Levator ani = puborectalis + pubococcygeus + iliococcygeus
- Levator ani must relax to allow urination and defecation
Origin - Ischial spine
Insertion - lateral margin of the coccyx
Function - support the pelvic viscera
Transverse folds: what are they and what do they do?
Mucous membrane and circular muscle form 2 or 3 transverse folds
Help support faecal mass
Anal canal: where does it begin and end, how long is it, how does it slope, how close are its lateral walls, what does it have, and where are the superior/inferior parts derived from?
Begins at the anorectal junction (i.e. distal to rectal ampulla) and ends at the anus
4cm in length
The canal slopes inferoposteriorly
Its lateral walls are in constant contact (due to levator ani and anal sphincters), except during defaecation
Internal and external anal sphincters
The superior part of the canal derived from the embryonic hindgut
The inferior part of the canal derived from the anal pit
What separates the superior and inferior anal canal?
The pectinate line
The superior part has columnar epithelium and the inferior part has stratified squamous epithelium
Rectum/anal canal blood supply
Superior rectal arteries - inferior mesenteric arteries
Middle rectal arteries - internal iliac arteries
Inferior rectal arteries - internal pudendal arteries
Anastomoses - portocaval in the anal wall
Venous drainage - internal and external venous plexuses (then veins have the same name as the arteries)
Venous plexuses - anal cushions: flutter valves for faecal continence
Haemorrhoids
When the veins or blood vessels in and around your anus and lower rectum become swollen and irritated
Anal columns: what are they, what do they contain, and where do they extend from?
Anal columns - ridges of mucosa
Contain terminal branches of Superior rectal vessels
Extend from the anorectal junction to the anal valves
Anal sinuses above anal valves - produce mucus which helps with movement (?)
Lymphatic drainage of the anal canal
Pectinate line - separates superior and inferior arteries
The nodes around either the superior or inferior arteries are used to drain the anal canal
Large intestines innervation
Above the pectinate line:
- Midgut - sympathetic fibres from the superior mesenteric plexus, parasympathetic fibres from the vagus nerve
- Hindgut: sympathetic fibres from the inferior mesenteric plexus, parasympathetic fibres from pelvic splanchnic nerves
- Visceral afferent fibres: T8 – S4
Below the pectinate line:
- Anal pit: inferior rectal (anal nerves) – pudendal nerve branches (Therefore sensitive to pain, temperature, etc)
Faecal continence: what are the two types
Internal sphincter (involuntary) and external sphincter (voluntary)
Faecal continence - internal sphincter: what is it, where does it surround, what is its innervation, what inhibits its contractions, how is it normally contracted, what is necessary for its voluntary contraction, what happens after peristalsis, and what is its threshold level of distension?
Thickening of the circular muscle
Surrounds superior 2/3 of the anal canal
Innervation (tonus and stimulation) from sympathetic fibres from superior rectal and hypogastric plexuses
Contraction inhibited by parasympathetic innervation due to peristalsis
Tonically contracted most of the time; However will relax temporarily if the rectus is distended by faecal matter or intestinal gas
Therefore voluntary contraction of the puborectalis and external anal sphincter necessary to avoid flatulence or defaecation
Ampulla relaxes after distension and tonus returns until the next peristalsis
Threshold level of distension: inhibition of sphincter continuous until distension relieved
Faecal continence - external sphincter: where is it located, what is its innervation, and what zones are there?
Attached anteriorly to the perineal body and posteriorly to the coccyx via the anococcygeal ligament with a broad band on each side of the inferior 2/3 of the canal, blends superiorly with puborectalis
Supplied by sacral nerve 4 through inferior rectal nerve
Zones (often indistinct):
* Deep (superior) - also receives fibres from nerve to levator ani, and in common with puborectalis, allows synergistic contractions of these
* Superficial part (middle)
* Subcutaneous part (inferior)
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Haemorrhoids
When the veins or blood vessels in and around your anus and lower rectum become swollen and irritated
