GI Pathology Flashcards
What is hereditary haemochromatosis?
An autosomal recessive disorder of iron metabolism leading to iron overload.
What causes hereditary haemochromatosis?
Mutation in the HFE gene - often a homozygous C282Y mutation.
What are the complications of hereditary haemochromatosis?
Liver - cirrhosis Skin - bronzing Pancreas - diabetes Heart - restrictive cardiomyopathy Joints - arthritis
What causes iron deficiency anaemia (IDA)?
In young women - menstruation +/- pregnancy
In men and post-menopausal women - GI bleed until proven otherwise.
What is sideroblastic anaemia?
Disorder in which Eb take in iron but don’t convert it to haem (can be caused by an ALA-S2 mutation) hence there are large stores of iron bound to haemosiderin in mitochondria.
What are the causes and risk factors of peptic ulcer disease?
Causes
- H. Pylori
- NSAIDs
- Zollinger-Ellison syndrome (gastrin secreting tumour)
Risk factors
- Smoking
- Alcohol excess
- Radiation therapy
- Stomach cancer
What are the effects of H. Pylori infection in the different parts of the stomach?
In the antrum - increased risk of peptic ulcers.
- G cells are most abundant here.
- H. Pylori produces urease which converts urea to ammonia.
- The ammonia neutralises the environment, both allowing the bacteria to survive and also the G cells to detect a high pH, therefore gastrin production is stimulated.
- This increases HCl volume –> increased ulcer risk.
In the body/pylorus - increased risk of gastric cancer.
- Parietal cells are abundant here.
- HCl is being neutralised and so can’t act on parietal cells are effectively.
- This causes parietal cell atrophy and so increased risk of gastric cancer.
How do NSAIDs cause peptic ulcers?
Inhibit COX pathway, therefore inhibiting the production of PGs and so there is a decreased protection of the gastric mucosa.
How can H. Pylori be diagnosed?
- C urea breath test
- Stool test (H. Pylori antigen)
- Serum test (blood, urine, saliva for antibody)
- Biopsy (with histology or CLO test)
What is the C urea breath test?
Usually C14 isotope used to prevent radiation exposure.
- Patient drinks a solution containing urea.
- The urease in the stomach will break down the urea to ammonia and CO2.
- They then breath out and C02 levels are measured.
HIGH CO2 - signifies H. Pylori infection
What is the CLO test?
Endoscopy is done and a biopsy is taken.
The biopsy tissue is then placed in a solution/gel of urease and pH indicator
- If H. Pylori is present, ammonia will be formed and the pH will increase.
When is a biopsy carried out to diagnose H. Pylori?
In patients over 55 or those with red flag signs.
- dysphagia
- signs of GI bleed (such as maleena)
- persistent vomiting
- weight loss
- IDA
What does maleena suggest?
Upper GI tract bleed
How is peptic ulcer disease treated?
Lifestyle changes
- stop NSAIDs and smoking, increase exercise.
Pharmacology
- Triple therapy - PPI/H2R antagonist plus 2 antibiotics - amoxycillin, clarithromycin or metroniazadole.
What is the mechanism of action of PPIs, and an example of one?
Omeprazole
- Inhibits the proton pump on parietal cells therefore decreasing the amount of H+ pumped into the lumen.
What is the mechanism of action of H2R antagonists, and examples of them?
Cimetidine and ranitidine.
Block the H2 receptor on parietal cells, therefore decreasing the amount of HCl.
How is the oesophagus normally protected from reflux?
- UOS and LOS sphincters.
- Intra-abdominal oesophagus (diaphragm helps close it)
- Angle of His/flap valve (angle the oesophagus enters the stomach, forms a flap)
- Secondary peristalsis
What can cause gastro-oesophageal reflux disease?
Impaired defences
- Low LOS pressure
- Hiatus hernia
- Impaired peristalsis (and therefore clearance)
- Transient lower oesophageal spasm
Increased offences
- Increased intra-abdominal pressure (pregnancy/obesity)
- Reduced gastric emptying
What is a hiatus hernia and their types?
Protrusion of the stomach through the diaphragmatic hiatus, into the chest.
Sliding - gastro-oesophageal junction slides through hiatus.
Rolling - fundus of stomach protrudes alongside GOJ through hiatus
How does the stomach protect itself from gastric acid?
Pre-epithelial
- Mucous-HCO3 barrier
- Surfactant - prevent water solue tble materials entering the epithelium
- Rapid cell turnover.
Sub-epithelial
- Good mucosal blood flow removing waste and supplying nutrients
- PGs protect mucosa and help maintain blood flow.
What are the symptoms of GORD?
Most common - heartburn and acid regurgitation
Other - night wakening, dysphagia, chest pain
What are the complications of GORD?
Initially, oesophagitis - may cause strictures.
May progress to Barrett’s oesophagus - premalignant change of mucous from simple squamous to simple columnar.
This may then progress to an adenocarcinoma.
How can GORD be treated?
Prevention - lose weight, avoid smoking and alcohol, prop head up at night.
Pharmacotherapy
- antacids
- alginates
- prokinetics
- PPIs
- H2R antagonists
- surgery
What are the side effects of H2R antagonists?
- Diarrhoea
- Headache
- Dizziness
- Fatigue
- Rash
- Cimetidine may cause gynaecomastia and constipation.
- Tachyphylaxis can also occur.