S8.2 Pathology Of The Distal GI Tract Flashcards
Outline the pathophysiology of diarrhoea?
Unwanted substance in gut stimulates secretion to remove it, colon unable to absorb the increasing amount of water
What is osmotic diarrhoea and what causes it?
Gut lumen contains too much osmotic material
Can be from ingesting poorly absorbed materials or from the inability to absorb nutrients
Can stop with fasting
What is secretory diarrhoea and what causes it?
Too much ion secretion due to toxins affecting ion transport messengers
Also too little Na absorption
Therefore net effect is water movement into lumen
Cannot stop with fasting
What is the pathophysiology of constipation?
Caused by slow colonic transport (e.g megacolon, Parkinson’s) or defecation problems (e.g cannot coordinate muscles of defecation).
What are the risk factors and treatment of constipation?
Risk factors: female, old age, low exercise
Treatment: increased fluid/activity/fibre, laxatives
Describe where appendicitis pain originally presents, and then where this pain moves to and why?
Initially has periumbilical pain as visceral (non-specific) peritoneum affected
Then later touches parietal peritoneum which has somatic origin and produces specific RIF pain
What are the two causes of appendicitis?
Blockage of appendices lumen
Infection
How does blockage cause appendicitis?
Blockage of appendiceal lumen (e.g foreign body/faecolith) causes venous pressure to rise.
This prevents arterial blood supply from ileocolic artery leading to ischaemia of appendix walls and bacterial invasion
How does infection cause appendicitis?
An infection can cause mucosal changes that allow bacterial invasion of appendiceal walls
What are the symptoms of appendicitis?
Periumbilical pain, anorexia, vomiting, RIF pain 12h later (unless appendix is in retro-caecal or pelvic position)
What signs will you find on a patient with appendicitis?
Rebound tenderness
Fever
How do you diagnose and treat appendicitis?
Diagnosis: bloods, examination, pregnancy test to rule out
Treatment: appendicectomy
What is diverticulosis?
Outpouchings of mucosa and submucosa in the colon which herniate through muscularis layers
Caused by raised intra-luminal pressure.
What is acute diverticulitis?
When the diverticula become inflamed or perforate.
Occurs in diverticulosis
Outline the pathophysiology of acute diverticulitis
Faeces block entrance to diverticula, inflammation allows bacterial invasion of diverticula walls
What is the difference between uncomplicated and complicated diverticulitis?
Uncomplicated diverticulitis – small abscess confined to colon wall
Complicated diverticulitis – large abscess that perforates
What are the symptoms of acute diverticulitis?
LIF pain
Haematochezia (anal blood loss)
Constipation
What is the diagnosis and treatment of acute diverticulitis?
Diagnosis: blood tests (raised WBC), pregnancy test to rule out ectopic, USS, CT
Treatment: antibiotics, analgesia, surgery for large abscess in complicated
What is the functions of the rectum?
Rectum allows temporary storage of faeces prior to defecation.
Describe the arteries of the rectum
Superior rectal artery; continuation of IMA
Middle RA from internal iliac
Inferior RA from pudendal artery
Describe the veins of the rectum
Portal drainage through superior rectal vein
Systemic drainage through internal iliac vein
Describe the the effect of the pubo-rectalis sling on the anal canal
Pubo-rectalis sling makes rectum point anteriorly and anal canal posteriorly
Describe the features of the anal canal above and below the dentate line
Above: IMA, pelvic nerve, columnar epithelia
Below: pudendal artery, pudendal nerve, stratified squamous epithelia
What features does the anal canal need for defecation to occur?
A distensible rectum
Anal cushions
Normal anorectal angle
Outline the 4 stages of defecation
Mass movement
Defecation reflex
Increased pressure in rectum
Defecation - relaxed anal sphincter
What are haemorrhoids?
These are anal cushions which tell us the composition of faecal matter and aid continence.
Describe the pathology of internal haemorrhoids
Can enlarge and prolapse through anal canal.
Occur above dentate line so are painless.
Treatment: increased hydration and avoid straining
Describe the pathology of external haemorrhoids
Swelling of anal cushions which can then thrombose. Occur below pectinate line so feel pain.
Treatment: surgery
What is an anal fissure?
Linear tear in anoderm.
Results in pain on defecation and haematochezia.
What are some causes of anal fissures?
High internal anal sphincter tone
Reduced blood flow to anal mucosa
What is the treatment for anal fissures?
Hydration
Warm bath
Medication to relax anal sphincter
Name some conditions which result in haematochezia (blood through rectum)
Diverticulitis, angiodysplasia, colitis, colorectal cancer, haemorrhoids, anal fissure, upper GI bleed.
What is melaena?
Black tarry stools, due to Hb being altered by digestive enzymes and gut bacteria.
Name some conditions which result in melaena
Peptic ulcer disease, variceal bleeds, gastric cancer.
