W6 26 gastointestinal tract pathology Flashcards
What is GORD?
Gastro-oesophageal reflux disease is leakage of the gastric contents into the distal oesophagus
What are the aetiological causes of GORD and what do they do?
Alcohol
Cigarettes
Obesity
Pregnancy
Hiatus hernia
These reduce the tone of the lower oesophageal sphincter causing reflux of gastric contents into the distal oesophagus.
What is the pathogenesis of GORD?
- Gastric acid in the distal oesophagus injures the lining squamous epithelium
- Damage associated molecular patterns (DAMPs) produced by the damaged epithelium stimulate an acute inflammatory response
- Squamous epithelium is infiltrated by eosinophils and neutrophils
- Epithelium’s undergoes basal zone hyperplasia
What are the consequences of GORD?
Oesophageal ulceration
Haematemesis and melena (from bleeding)
Oesophageal stricture - caused by excess healing and repair response leading to fibrosis leading to stricture
Barret oesophagus
What is Barret oesophagus?
Intestinal metaplasia within the squamous epithelium of the distal oesophagus.
Metaplastic response of the distal oesophagus to chronic irritation from refluxed acid.
Aetiology of Barret oesophagus
GORD
What is the pathogenesis of Barret oesophagus? (Pg289 img)
New columnar epithelium is generated from re-programmed stem cells, which may arise from:
1. Squamous epithelium (present in the base of normal oesophageal mucosa)
2. Submucosal oesophageal glands (normally present beneath squamous epithelium)
3. Stomach
Why is Barret oesophagus bad?
It is pre-malignant. Majority of oesophageal adenocarcinomas are associated with Barret oesophagus. Associated with accumulation of mutations (dysplasia).
What is gastritis?
Inflammation of the stomach
Why does gastritis occur (pathogenesis)?
Gastritis occurs due to a breakdown in the normal balance between the damaging (acid) and defensive forces acting in the gastric mucosa.
What are the damaging forces of the stomach?
Gastric acidity
Peptic enzymes
What are the defensive forces of the stomach?
Protective layer of mucus
Mucus has neutral pH due to secretion of bicarbonate
Rich blood supply in lamina propria washes away any acid - consequently damage to gastric epithelium bleeds a lot
Prostaglandins synthesis drives bicarbonate secretion and increases vascular perfusion
What is acute gastritis?
Infiltration of gastric mucosa by neutrophils (acute inflammation’
What is the aetiology for acute gastritis, factors causing direct damage to gastric epithelium?
NSAIDs - direct damage and reduces PG synthesis
Alcohol
Radiotherapy and chemotherapy
Splanchnic vasoconstriction during severe physiological stress leading to ischaemia
Gastric acid hypersecretion (from vagal nerve stimulation) - bile reflux
What factors cause impaired defence of the gastric epithelium in acute gastritis?
Reduced PG synthesis
Splanchnic vasoconstriction leading to increased pH of mucosa
Reduced mucin synthesis in the elderly
What is chronic gastritis?
Infiltration of the gastric mucosa by lymphocytes and plasma cells with or without neutrophils
Symptoms less severe but more persistent than acute gastritis
Aetiology of chronic gastritis
Helicobacter-associated gastritis
Autoimmune chronic gastrritis
Reactive gastritis - chronic bile reflux, NSAIDs
What are the virulence factors of Helicobacter pylori that allow it to survive in the hostile stomach?
Flagella - allowing motility in mucus
Urease - generating ammonia from urea, elevating local pH
Adhesins - allows bacteria to adhere to foveolar cells
Toxins - eg cytotoxic-associated gene A (CagA)
What is the pathogenesis of autoimmune gastritis?
- Immune-mediated damage to parietal cells in the gastric body (H+/K+ ATPase is the main autoantigen)
- Reduced gastric acid secretion (achlorhydria)
- Hypergastrinanemia and G-cell hyperplasia in antrum
How is autoimmune gastritis associated with pernicious anaemia?
Parietal cell loss also produces intrinsic factor which binds vitamin B
Parietal cell loss leads to vitamin B deficiency leading to megaloblastic anaemia
Describe the mechanisms behind the pathogenesis of autoimmune gastritis.
- Driven by CD4+ T cells, driving an inflammatory response, (TH1 or TH17) response, releasing IFN-y
- Auto reactive CD8 cells will damage parietal cells either by Fas/FasL interactions or perforin punching holes in membrane allowing granzyme enzymes to come in, causing apoptosis
- Stimulates B cells to make antibodies, including those against intrinsic factor
- The loss of acid production due to damage of parietal cells leads to hyperplasia of the gastrin producing cells (ECL), which could lead to tumour
- Inflammation within the wall of the stomach can alter the healing and repair functions, MMOs degrading the ECM and mediating fibrosis development