Rectum and Anal Canal Flashcards
Describe the location of the rectum
- starts at rectosigmoid junction at level S3
- follows curve of sacrum and coccyx
- ends in front of the tip of the coccyx by piercing the pelvic diaphragm and becoming continuous with anal canal
Is the rectum peritoneal?
- upper 1/3: covered in peritoneum anteriorly and laterally in C shape
- middle 1/3: only covered anteriorly
- lower 1/3: no peritoneal covering
- peritoneum reflects off of the surfaces it covers to form pouches/fossae
What do the lateral reflections of peritoneum off of the rectum form?
- pararectal fossa
- lateral curvatures coinciding with rectal folds or valves internally
- important for maintenance of continence
How can you distinguish the rectum from the large intestines?
lacks taenia, haustra or epiploic appendices
How are the lateral flexures of the rectum formed?
- by 3 transverse rectal folds
- forms the 3 lateral flexures:
- superior and inferior on left side
- intermediate on right side
Where is the perineal flexure/anorectal angle and how is it formed?
- it is the junction between the rectum and anal canal
- caused by anterior pull of the rectum by the puborectal muscle
- muscle is important in maintenance of continence by preventing leakage of poop into anus
Describe the anatomical relations of the rectum in males
Posterior:
- S3-5, coccyx and anococcygeal ligament
- pelvic plexus
- rectosacral fascia
- median sacral artery
Anterior:
- rectovesical pouch
- bladder
- prostate and fascia
Lateral:
- pararectal fossae
- pudendal plexus
Describe the anatomical relations of the rectum in females
Posterior:
- S3-5, coccyx and anococcygeal ligament
- pelvic plexus
- rectosacral fascia
Lateral:
- pararectal fossae
- pudendal plexus
Anterior:
- rectourterine pouch
- vagina
- rectovaginal fascia
- bladder (most anterior)
What makes up the anorectal ring, where is it located and what is its purpose?
- puborectalis sling
- upper portions of internal and external sphincters
- located at the junction of the anal canal and rectum
- it stays tonically contracted throughout the day to prevent leakage of faeces into the anus/anal canal
Expand on the internal anal sphincter
- smooth muscle
- autonomic
- derived from circular muscular layer
Expand on the external anal sphincter
- striated muscle
- one functional unit with deep, superficial and subcutaneous parts
- fuses with puborectalis
Describe the anatomy of the anal columns
- anal canal has longitudinal folds called anal columns in upper parts
(house branches of superior rectal vein, artery, lymphatics and nerves) - unite at the bottom to form anal valves
- superior to each valve is an anal sinus (depression)
(location of mucous glands that lubricate faeces)
Describe the anatomical importance of the pectinate/dentate line
- where the anal valves in the anal canal form a circle
- above it is the haemorrhoidal zone
- below is a transition zone called the anal pecten
What is the arterial supply of the rectum and anal canal?
- superior 1/3: superior rectal artery (from IMA)
- middle 1/3: middle rectal artery (from internal iliac)
- below anorectal line: inferior rectal artery (from internal pudendal)
- superior rectal artery
Describe how and where you could see the anal cushions
- patient sitting at an angle with legs spread
- 3 anal cushions:
- 11 o’clock
- 7 o’clock
- 3 o’clock
Describe the pathology you can have in the anal cushions
- haemorrhoids
- dilated veins affecting the submucosal plexus in the rectum/anal canal
- can be internal (above dentate line)
- can be external (below dentate line)
Describe the venous drainage of the rectum and anal canal
- superior 1/3: superior rectal vein to inferior mesenteric to hepatic portal vein
- middle 1/3: middle rectal to internal iliac and internal pudendal veins
- inferior 1/3: inferior rectal to infernal iliac and internal pudendal veins
Describe the lymphatic drainage of the rectum and anal canal
- superior rectum goes to inferior mesenteric nodes
- inferior rectum and proximal anal canal to internal iliac nodes
- distal anal canal goes to superficial inguinal nodes
Describe how the nerve supply of the rectum and anal canal affects the presentation of hemorrhoids
- because above and below the dentate line are innervated differently and have different sensations internal and external haemorrhoids will present differently
- internal will have little to no pain and just feel difficulty in defacating or feeling like they have something to pass, can undergo procedures easily
- external will have a lot of pain and will not be able to go through procedures without pain or LA
Describe the nerve supply of the rectum and anal canal
- parasympathetics S2-4 pelvic splanchnic nerves to pelvic plexus
(increase peristalsis, relax anal sphincter, visceral senses) - upper rectum
- sympathetics from L1-3 by lumbar splanchnic nerves
- somatic nerves from S2-4 pudendal nerve
- below rectum
(external anal sphincter and pelvic floor muscles)
Summarise ways the body maintains faecal continence
- rectosigmoid angle acts as functional sphincter
- levator ani and puborectalis make angle more acute
- anal canal sensation can allow cortex to distinguish between gas, fluid and solid and the stretch receptors can adjust to only allow gas out
- rectal pressure will increase until it forces contents into anal canal but defacation prevented by cortical inhibition and external anal sphincter forces it back into rectum
Describe the conditions which allow for defacation
- cortical inhibition released
- abdo pressure increased
- puborectalis relaxes allowing rectoanal angle to straighten and external anal sphincter to relax (S2-4)
- lower colon and rectum contract and internal anal sphincter relaxes
