Rectum + Anal Canal Flashcards
Describe the rectum
- 12-15cm long
- passes through pelvic floor
- continuous band of outer longitudinal muscles (unlike taeniae coli of rest of colon)
- cured shape anterior to sacrum
- temporary storage for faeces
What stimulates the urge to defaecate?
Stretching of rectum
Function of rectum
Temporary storage of faeces prior to defaecation
Blood supply to the rectum
Superior rectal artery
Middle rectal artery
Inferior rectal artery
What does the continuous longitudinal muscles of the rectum aid?
Distension + contraction of the rectum before defecation
What is the middle rectal artery a branch of?
Internal iliac
What is the inferior rectal artery a branch of?
Pudendal artery
Venous drainage of the rectum
Portal drainage - superior rectal vein
Systemic drainage - internal iliac vein
Where is the start of the anal canal?
Proximal border of the anal sphincter complex
What is the puborectalis sling?
puborectalis muscle forms a sling around the lower rectum when it meets the fibers from the opposite side
Function of the puborectal sling
Maintains faecal continence by angling the anal canal posteriorly
What are the parts of the anal sphincter complex?
Internal involuntary sphincter
External anal sphincter
Factors required for continence
- distensible rectum
- firm bulky faeces
- normal anorectal angle
- anal cushions
- normal anal sphincters
What is the normal anorectal angle?
Rectum points anteriorly
Anal canal points posterity
Describe the internal involntary sphincter of the anal sphincter complex
- thickening of circular smooth muscle
- under autonomical control
- 80% of resting anal pressure
Describe the external anal sphincter?
- striated muscle
- under conscious control + allows for voluntary control of defaecation
- innervated by pudenal nerve
- 20% of resting anal pressure
Nerve supply to the external anal sphincter
Pudendal nerve
How much the parts of the anal sphincter complex contribute to resting anal pressure?
Internal involuntary sphincter 80%
External anal sphincter 20%
What is the defecation reflex?
- stimulus: distension in rectum
- response: contraction in rectum + sigmoid colon, relaxation of internal anal sphincter + contraction of external anal sphincter
What happens to the anal sphincter complex during defecation reflex?
Relaxation of internal anal sphincter
Contraction of external anal sphincter
What happens in defecation?
- relaxation of external anal sphincter
- relaxation of puborectalis muscle
- forward peristalsis in rectum + sigmoid colon
- Valsalva maneuver: increased abdominal pressure
What is valsalva maneuver?
- Forced expiation against a closed glottis
- Increases abdominal pressure
- Helps for defecation
What is the dentate/pectinate line?
Junction of hindgut and proctodaeum (ectoderm)
Epithelium above and below pectinate line
Above: columnar epithelium
Below: stratified squamous epithelia
Pain receptors above and below pectinate line
Above: visceral pain receptors
Below: somatic pain receptors
What are haemorrhoids?
Abnormal (symptomatic) anal cushions
What are anal cushions?
3+ areas of tissues divided from a complex of venous plexus in the anus
Two classifications of haemorrhoids
Internal (most common)
External
Describe internal haemorrhoids
- caused by loss of connective tissue support
- above pectinate line
- painless
- enlarge and prolapse through anal canal
- bleed bright red blood + itchy skin
Treatment of internal haemorrhoids
- increased hydration
- high fibre diet
- avoid straining
- rubber band ligation (tie around base > fall off)
- surgery if grade 4
What are the grades of internal haemorrhoids?
- Grade 1: no prolapse, prominent blood vessles
- Gade 2-4: increasing degrees of prolapse
Describe external haemorrhoids
- below pectinate line
- painful
Treatment of external haemorrhoids
Surgical removal
What is an anal fissure
Linear tear in anoderm
(epithelial lining of anal canal)
Presentation of an anal fissure
- pain of defecation (passing glass/razor blades)
- haematochezia
- passing of hard stool
Treatment of anal fissure
- hydration
- dietary fibre
- analgesia
- warm baths
- medications to relax internal anal sphincter
Cause of anal fissure
High internal anal sphincter tone
Reduced blood flow to anal mucosa
What does haematochezia indicate?
Lower GI bleeding
Causes of haematochezia
- diverticulitis
- ulcerative colitis
- colorectal cancer
- anorectal disease: haemorrhoids, anal fissure
- angiodysplasia
What is angiodysplasia?
Small vascular malformation in bowel wall
What is melaena?
Black tarry offensive smelling stool
Due to upper GI bleed > haemoglobin being altered by digestive enzymes + gut bacteria
Causes of melaena
Upper GI bleed
- peptic ulcer disease
- variceal bleeds
- upper GI malignancy
- oesophageal/gastric cance
What does the term ‘mass movement’ describe?
The rapid movement of colonic content
Why are internal haemorrhoids initially painless?
They arise from above the dentate line in the anal canal
A patient complains that it feels like they are passing razor blades when they defacate, what is a likely diagnosis?
Anal fissure
