Rectum and Anal Canal Flashcards
What is the function of the continuous sheet of longitudinal muscle in the rectum?
It aids in distension and contraction during defecation
What role does the puborectalis muscle play in the orientation of the anal canal?
Orientates the anorectal angle
Positions the anal canal posteriorly, important for continence
What are the components of the anal sphincter complex and how does it contribute to faecal continence?
Two components: -internal involuntary sphincter (smooth muscle)
-external voluntary sphincter (striated muscle)
Internal provides 80% of resting anal pressure, external provides other 20% and allows for voluntary control over defaecation
What are haemorrhoids?
Vascular structures found within anal canal
Why can haemorrhoids become symptomatic?
Become symptomatic when they prolapse or bleed.
Prolapsed internal haemorrhoids can cause:
Irritation, itching and bleeding
How are haemorrhoids classified and what are the different grades?
Classified into four grades based on the severity and extend of prolapse.
Grade 1- internal haemorrhoids that dont prolapse
Grades 2-4- varying degrees of prolapse, 4 being most severe
What is an anal fissure?
Tear or ulcer in the lining of the anal canal, typically below the pectinate line
What symptoms are associated with anal fissures?
Severe pain during or after bowel movements, often described as passing glass or razor blades
Conservative treatments for anal fissures?
Preventing constipation:
-increasing fibre intake
-staying hydrated
Medications and ointments that relax the anal sphincter can promote healing.
Function of the rectum?
Acts as a storage area for faeces until it’s ready to eliminated from body
Whats the blood supply to the rectum?
Several arteries form a plexus:
-superior rectal artery - continuation of IMA
-middle rectal artery - continuation of internal iliac
-inferior rectal artery - pudendal artery
Whats the venous drainage of the rectum and anal canal?
-Portal drainage through superior rectal vein
-Systemic drainage through internal iliac veins
Describe the structure and anatomy of the rectum.
-12-15cm long
-passes through pelvic floor
-Has continuous band of outer longitudinal muscles
-Parts are covered in peritoneum, others are extra-peritoneal
-Curved shape, anterior to sacrum
Describe the structure and anatomy of the anal canal.
-Is a narrowed portion of GI tract, continues on from rectum
-Starts at proximal border of anal sphincter complex
-Pubo-rectal is sling changes direction of rectum so the anal canal points posteriorly
What factors are required to aid with faecal continence?
-Distensible rectum
-Firm bulky faeces
-Normal anorectal angle
-Anal cushions
-Normal anal sphincters
Describe the internal involuntary sphincter
-A thickening of circular smooth muscle
-Under autonomic control
-Provides 80% of resting anal pressure
Describe the external anal sphincter
-Striated muscle
-Supplied by pudendal nerve
-Deep in upper anal canal
-Mixes with fibres from levator ani
-Joins with pubo-rectalis to form sling
What is the dentate/pectinate line?
It’s the junction of hindgut and proctodaeum (ectoderm)
Above the dentate line:
-what cells line it?
-What pain receptors are present?
-Columnar epithelium
-Visceral pain receptors
Below the dentate line:
-What cells line it?
-What pain receptors are present?
-Stratified squamous epithelia
-Somatic pain receptors
Describe the processes that lead to defaecation.
1) mass movement
2) defecation reflex:
Stimulus- distension in rectum. Response- contraction in rectum & sigmoid colon, relaxation of internal AS, contraction of external AS
3) increased pressure in rectum
4) delay OR defecation
Describe what happens when delaying defecation
-Contraction of external anal sphincter
-Contraction of puborectalis muscle
-Reverse peristalsis in rectum
Describe what happens during defecation
-Relaxation of external anal sphincter
-Relaxation of puborectalis muscle
-Forward peristalsis in rectum & sigmoid colon
-Valsalva maneuver (increased abdominal pressure)
What can cause internal haemorrhoids?
Loss of connective tissue support
