VIVA: Pathology - Gastrointestinal Flashcards
Describe the common causes of bowel obstruction
4/7 to pass:
- Adhesions
- Hernia
- Malignancy
- Volvulus
- Intussusception
- Mesenteric infarct
- Strictures (e.g. due to Crohn’s, radiation, mesenteric ischaemia)
How does a hernia form, and cause a bowel obstruction?
- Weakness/defect in abdominal wall* leading to protrusion of serosa-lined pouch of peritoneum (hernial sac)
- Visceral protrusion* (small bowel, large bowel, or omentum most often involved)
- Entrapment of hernia sac in a narrow neck* causes pain
- Persistent obstruction leads to venous stasis and oedema, which can cause incarceration and strangulation
- Common locations include inguinal, femoral, incisional and umbilical
*needed to pass + 2 others
Describe some important clinical sequelae of bowel obstruction
- Intestinal perforation *
- Intestinal ischaemia *
- Peritonitis
- Sepsis
- Abscess
- Electrolyte disturbance
- Vomiting and aspiration
- Death
*needed to pass
Which bacterial class does Escherichia coli belong to?
E. coli is a Gram negative bacillus which is a facultative anaerobe; it is also a normal GI commensal
What is the difference between an endotoxin and an exotoxin?
Endotoxins:
- Lipopolysaccharides in the outer membrane of the cell wall of Gram negative bacteria which cause injury via the host immune response
Exotoxins:
- Proteins that are secreted by the bacterium and cause direct injury
List some types of infections that can be commonly caused by E. coli
3 to pass:
- UTI
- Prostatitis
- Epididymo-orchitis
- Infectious enterocolitis
- Cholecystitis
- Bacterial peritonitis
What are the infectious causes of gastroenteritis? Give examples
- Viral*:
- Norovirus
- Rotavirus
- Adenovirus - Bacterial*:
- Cholera
- Campylobacter
- Shigella
- Salmonella
- Enteric typhoid fever
- Yersinia
- E. coli
- C. difficile - Parasitic*:
- Ascaris
- Strongyloides
- Necator
- Ancylostoma
- Trichuris
- Enterobius
- Schistosomiasis
- Intestinal cestodes
- Entamoeba
- Giardia
- Cryptosporidium - Mycobacterial*
*2/4 categories with 1 example from each to pass
What are non-infectious causes of enterocolitis?
2 to pass:
- Cystic fibrosis
- Coeliac disease
- Autoimmune enteropathy
- Inflammatory bowel disease
- Irritable bowel syndrome
- Ischaemic gut
- Diverticulitis
- Lactase (disaccharidase) deficiency / lactose intolerance
- Environmental enteric dysfunction
Describe the classification of major categories of diarrhoea
- Secretory*:
- Isotonic stool
- Persists during fasting
- E.g. cholera - Osmotic*:
- Excessive osmotic force exerted by unabsorbed luminal solutes
- Abates with fasting
- E.g. sorbitol - Malabsorptive*:
- Generalised failure of nutrient absorption associated with steatorrhoea
- Abates with fasting
- E.g. chronic pancreatitis - Exudative*:
- Secondary to inflammatory disease
- Characterised by purulent, often bloody stools
- Persists during fasting
- E.g. IBD
*2/4 to pass
What is pseudomembranous colitis?
- Colitis caused by overgrowth of C. difficile* (can also be caused by Salmonella, C. perfringens type A, Staph aureus)
- Associated with antibiotic use
- Forms a pseudomembrane* made up of adherent layer of inflammatory cells and debris
*needed to pass
What are the risk factors for development of pseudomembranous colitis?
2/3 to pass:
- Advanced age
- Hospitalisation
- Antibiotic treatment
What are the clinical features of pseudomembranous colitis?
- 30% of hospitalised patients colonised, but most asymptomatic
- Fever *, leucocytosis, abdominal pain *, cramps, hypoalbuminaemia, watery diarrhoea *, dehydration, rarely gross bloody diarrhoea
- Diagnosis usually via detection of toxin
- Treated with metronidazole, vancomycin
*needed to pass
What conditions can lead to infarction of the bowel?
- Acute arterial obstruction*:
- Atherosclerosis
- Aortic aneurysm
- Hypercoaguable state
- OCP use
- Embolism - Intestinal hypoperfusion*:
- Cardiac failure
- Shock
- Dehydration
- Vasoactive drugs - Systemic vasculitis:
- Henoch Schonlein purpura
- Wegener’s granulomatosis - Mesenteric venous thrombosis:
- Hypercoaguable state
- Invasive neoplasm
- Cirrhosis
- Trauma
- Abdominal masses - Miscellaneous:
- Radiation
- Volvulus
- Stricture
- Amyloid
- Diabetes
*2 from each to pass + 2 total from other categories
What are the clinical features of ischaemic bowel?
- Severe pain* (may be transient)
- Tenderness
- Peritonism
- Nausea and vomiting
- Bloody diarrhoea
- Melaena
- Shock
- Hyper/hypothermia
- Sepsis
- needed to pass + 3 others
What parts of the bowel are most susceptible to ischaemic injury and why?
- Watershed zones*:
- Splenic flexure, sigmoid colon, rectum
- Located at end of arterial supply - Surface epithelium:
- Villi more at risk than crypts (intestinal capillaries run from crypts up villi to surface)
*needed to pass + explanation
What type of bacterium is Salmonella?
Gram negative bacillus
Enterobacteriaceae family
Describe the pathogenesis of typhoid fever
- Caused by Salmonella typhi (endemic) and paratyphi (travellers)
- Endemic in India, Mexico, Phillipines, Pakistan, El Salvador, Haiti
- Taken up by mononuclear cells in the underlying lymphoid tissue in gut and invades M cells* -> reactive hyperplasia in lymph tissue
- Disseminates by blood*
*needed to pass
What are the clinical features of typhoid fever?
- Fever
- Anorexia
- Vomiting
- Bloody diarrhoea
- Flu-like symptoms
- Blood culture positive in 90% of those with fevers
What are the causes of chronic gastritis?
- H. pylori *
- Chronic bile reflux
- NSAIDs
- Autoimmune
- Allergic response
- Infections
- Radiation
- Mechanical
- Psychological stress
- Chronic irritants (coffee, alcohol, caffeine)
- Systemic disease (Crohn’s, amyloid, GVHD)
*needed to pass + 2 others
Describe the features of H. pylori induced chronic gastritis
3/6 to pass:
- Most common cause
- Predominantly antral
- High acid production
- Hypogastrinaemia
- Generates ammonia (specific test)
- Disruption of normal mucosal defence mechanisms
What are the complications of gastric ulcer?
2/4 to pass:
- Bleeding (15-20%; accounts for 25% of ulcer deaths)
- Perforation (5%; accounts for 2/3 of ulcer deaths)
- Obstruction (2%)
- Malignant transformation (gastric adenocarcinoma, MALT lymphoma)
What are the pathological features of Crohn’s disease?
2/3 to pass:
- Transmural inflammation of the bowel with skip lesions
- Non-caseating granulomata
- Fissures and fistulae
What are the extraintestinal manifestations of Crohn’s disease?
3 systems to pass:
- Migrating polyarthritis
- Sacroiliitis
- Ankylosing spondylitis
- Erythema nodosa
- Clubbing
- Sclerosing cholangitis (uncommon)
- Uveitis
- Mild hepatic pericholangitis
- Renal disorders due to trapping of the ureters (uncommon)
- Systemic amyloidosis (rare)
- GIT cancer (less common than in UC)
What is the causative organism of cholera?
Vibrio cholerae
Gram negative comma-shaped
Describe the pathogenesis of cholera
- Non-invasive
- Flagella proteins for attachment and colonisation
- Preformed enterotoxin with B unit that binds to intestinal epithelium, and A unit that activates GPCR to induce adenylyl cyclase and increase cAMP, opening the CFTR and resulting in Cl- release into lumen with secretion of Na+, HCO3- and H2O
- Massive secretory diarrhoea which overwhelms colonic resorption
By what mechanisms may Helicobacter pylori cause peptic ulcer?
- Secretes urease which generates free ammonia
- Secretes proteases which breaks down protective mucosal glycoprotein layer
- Secretes phospholipases which damages surface epithelium
- Enhances gastric secretion and impairs bicarbonate secretion
- Immunogenic proteins causes T and B lymphocyte activation and inflammation
- Thrombotic occlusion of surface capillaries via bacterial platelet-activating factor
- LPS induces further immune response
- Damage to mucosa permits leakage of nutrients which sustain the bacteria
What are the pathological features of ulcerative colitis?
- One of two disorders that compromise inflammatory bowel disease
- Severe ulcerating inflammatory disease
- Limited to colon and rectum
- Continuous distribution (no skip lesions)
- Extends only into mucosa and submucosa (not transmural)
- Superficial broad-based ulcers
- Pseudopolyps
- Complications include malignant transformation and toxic megacolon
What extra-intestinal manifestations occur in ulcerative colitis?
- Migratory polyarthritis
- Sacroiliitis
- Ankylosing spondylitis
- Uveitis
- Skin lesions (erythema nodosum, pyoderma gangrenosum)
- Pericholangitis
- Sclerosing cholangitis
