7. Rectum And Anal Canal Anatomy Flashcards
How long is the rectum?
12-15cm
What is the blood supply to the rectum?
Superior rectal artery - continuation of inferior mesenteric artery
Middle rectal artery - branch of internal iliac
Inferior rectal - branch of pudendal artery
What is the venous drainage of the rectum?
Portal drainage through superior rectal vein
Systemic drainage through internal iliac vein - potential for Porto-systemic anastomoses
Where does the anal canal start?
Proximal border of anal sphincter complex
What are the factors required in anal canal continence?
Distensible rectum Firm bulky faeces Normal anorectal angle Anal cushions - network of venous vessels Normal anal sphincters
What are the 2 parts of the anal sphincter complex?
Internal involuntary sphincter
External anal sphincter
What is the internal involuntary sphincter?
Thickening of circular smooth muscle
Under autonomic control
What is the external anal sphincter?
Striated muscle
Deep section - upper anal canal, mixes with fibres from levator ani, joins with pubs-rectalis to form sling
Superficial and subcutaneous sections
What is the nerve supply of the external anal sphincter?
Pudendal nerve
Describe the process of defaecation?
- Mass movement
- Defaecation reflex - stimulus (distension in rectum), responses (contraction in rectum, sigmoid colon, relaxation of internal anal sphincter, contraction of external anal sphincter)
- Increased pressure in rectum
- Delay or defaecation
What is the dentate line?
Junction of hindgut and proctodaeum (ectoderm) in anal canal
What is above the dentate line?
Visceral pain receptors
Columnar epithelium
What is below the dentate line?
Somatic pain receptors
Stratified squamous epithelia
What are anal cushions?
Anus contains complex venous plexus
Divided into 3+ areas of tissues called anal cushions
Play a role in anal continence
There are connections between the vein and some arteries
Present from birth and a normal finding
What’s are haemorrhoids generally?
Symptomatic anal cushions
What are internal haemorrhoids?
Caused by loss of connective tissue support Above dentate line Relatively painless Enlarge and prolapse through anal canal Bleed bright red blood/pruritus
What is the treatment for internal haemorrhoids?
Increased hydration/high fibres diet
Avoid straining
Rubber band ligation
Surgery
What are external haemorrhoids?
Below dentate line
Swelling of the anal cushions which may then thrombosis
Very painful
Surgery has good outcomes
What are anal fissures?
Linear tear in anoderm
What causes anal fissures?
Passing of hard stool
Pain on defaecation
Haematochezia
What is the underlying causation of anal fissures?
High internal anal sphincter tone
Reduced blood flow to anal mucosa
What is the treatment for anal fissures?
Hydration, dietary fibre, analgesia
Warm baths
Medication trying to relax internal anal sphincter
What are the causes of haematochezia?
Diverticulitis Angiodysplasia Colitis Colorectal cancer Anorectal disease Upper GI bleeding
What is malaena?
Black tarry stools
Offensive smelling
Due to haemoglobin being altered by digestive enzymes and gut bacteria
What are the common causes of malaena?
Upper GI bleeding - peptic ulcer disease, variceal bleeds, upper GI malignancy, oesophageal/gastric cancer
What are the uncommon causes of malaena?
Gastritis
Meckel’s diverticulum
Iron supplements
