13. Alimentary Tract Pathology Flashcards
The small and large bowel peristalsis is mediated by what?
Mediated by intrinsic (myenteric plexus) and extrinsic (autonomic innervation) neural control.
Where is myenteric plexus located?
Myenteric plexus:
- Meissener’s plexus: base of the submucosa
- Auerbach plexus: between the inner circular and outer longitudinal layers of the muscularis propria
What are the pathological features of inflammatory bowel disease?
Ulcerative colitis Crohn’s disease Ischaemic colitis Radiation colitis Appendicitis
Ischaemic enteritis:
- What causes ischaemic enteritis?
- Acute occlusion of which major supply vessels leads to infarction?
- Why does gradual occlusion have little effect?
- T/F: Mesenteric venous occlusion less common.
- Inflammation and injury of the large intestine due to inadequate blood supply. Ischaemic lesions can be restricted to either the SI or LI or they can affect both depending on vessel affected.
- Acute occlusion of Coeliac, Inferior or Superior mesenteric arteries may lead to infarction. Major vessel occlusion- transmural injury.
- Little effect due to formation of anastomotic circulation.
- True
What are predisposing conditions for Ischaemia?
- Arterial thrombosis: severe atherosclerosis
- systemic vasculitis eg PAN (Polyarteritis nodose - swollen arteries), HSP (Henoch-Schonlein purpura - inflammation of small vessels), WG (Wegener’s Granulmatosis - inflamed blood vessels)
- dissecting aneurysm
- hypercoagulable states
- oral contraceptives - Arterial embolism: cardiac vegetations
- acute atheroembolism
- cholesterol embolism - Non-occlusive ischaemia: cardiac failure
- shock /dehydration
- vasoconstrictive drugs eg propranolol
What is the pathophysiology of acute ischaemia of bowel?
Sudden interruption of blood flow to small bowel (e.g. due to acute arterial embolism) → intestinal hypoxia → haemorrhagic infarction and necrosis → disruption of mucosal barrier and perforation → release of bacteria, toxins, vasoactive substances → life-threatening sepsis
Which site is more vulnerable to acute ischaemia?
The splenic flexure and the rectosigmoid junction are at high risk for colonic ischemia because they are “watershed areas” (region between two major vessels, which is least perfused and most susceptible to ischemia). These areas receive dual blood supply from the most distal branches of two large arteries (i.e., SMA and IMA). In the case of severe hypoperfusion, blood supply through these end arteries becomes insufficient.
Early-intense congestion due to acute ischaemia. What are the signs of this?
Colour = dusky/purple/blue
Lumen – sanguinous mucin
What are the histological features of Acute Ischaemia?
- Oedema
- Interstitial haemorrhages
- Sloughing necrosis of mucosa-ghost outlines
- Nuclei indistinct
- Initial absence of inflammation
- 1-4 days –bacteria-gangrene and perforation
- Vascular dilatation
What is the pathophysiology of chronic ischaemia of bowel?
Slowly progressing stenosis of two or more main arteries (SMA, IMA, or celiac artery) → postprandial (after eating) mismatch between splanchnic blood flow and intestinal metabolic demand → postprandial pain. Maybe asymptomatic if only one main artery is affected as collateral connections between the arteries can form and compensate for the reduced flow.
What are the features of chronic Ischaemia?
Mucosal inflammation Ulceration Submucosal inflammation Fibrosis Stricture
Radiation colitis:
- What can abdominal irradiation do?
- Which site affected usually?
- T/F: chronic radiation colitis can mimic IBD.
- Abdominal irradiation can impair the normal proliferative activity of the small and large bowel epithelium
- Usually rectum due to pelvic radiotherapy. Damage depends on dose. Targets actively dividing cells esp. blood vessels and crypt epithelium.
- True
What are the symptoms of radiation colitis?
anorexia; abdominal cramps; diarrhoea and malabsorption
What are the histological features of radiation colitis?
- Bizarre cellular changes
- Inflammation-crypt abscesses and eosinophils
- Later: arterial stenosis
- Ulceration
- Necrosis
- Haemorrhage
- perforation
Appendicitis:
- What is it?
- What causes it?
- Obstructed proximal appendiceal lumen can increase intraluminal pressure which can lead to what?
- Acute inflammation of the appendix
- Cause: obstruction e.g. faecalith (hardened faeces) or Enterobius vermicularis (pinworm infection)
- Increased intraluminal pressure → obstruction of veins → oedema of the appendiceal walls → obstruction of capillaries → ischemia → gangrenous appendicitis with/without perforation
