GI: Dealing with toxins

Question 1

What are the innate physical defences we have against toxins?

Answer 1

Sight, smell, memory, saliva (slightly acidic), gastric acid, small intestine secretions, colonic mucus, anaerobic environment in the small bowel and colon, peristalsis and segmentation to move contents along

Question 2

What microorganisms are resistant to gastric acid?

Answer 2

• mycobacterium tuberculosis is acid and alcohol fast
• h pylori produces urease which forms a protective cloud of ammonia
• enteroviruses eg hep A B, polio and coxsackie

Question 3

What is the main role of the colon?

Answer 3

Water recovery

Question 4

What are the innate cellular defences we have against toxins?

Answer 4

Neutrophils, macrophages, natural killer cells, tissue mast cells, eosinophils

Question 5

What are the 3 causes of eosinophilia? (high eosinophil count)

Answer 5

1. asthma
2. hay fever
3. parasitic infections - eosinophils contain granules with perforins and peroxidases which can puncture holes in worms

Question 6

Where are most of the macrophages located in the body?

Answer 6

80% in liver (specialised, called kupffer cells and sit in gaps in the endothelium), lots in spleen and lungs

Question 7

What are the causes of liver failure?

Answer 7

Viral hepatitis is the most common globally
Alcohol
Drugs such as paracetamol
Industrial solvents
Mushroom poisoning

Question 8

Why can liver failure lead to hepatic encephalopathy?

Answer 8

Ammonia is produced by colonic bacteria and deamination of AA - usually processed to urea in the liver however this is reduced.
Levels of ammonia increase - can cross the BBB and very toxic to the brain

Question 9

What causes portosystemic shunting? and how does this present?

Answer 9

When there is hepatic fibrosis this leads to portal venous hypertension leading to portosystemic shunting (and therefore toxin shunting).
Presents as oesophageal varices, haemorrhoids and caput medusae (varices of gut, butt and caput)

Question 10

What are the adaptive defences we have against toxins?

Answer 10

B lymphocytes - produce antibodies such as IgA and IgE that are effective against extracellular microbes
T lymphocytes - directed against T lymphocytes

Question 11

What is GALT and what 3 locations is it nodular?

Answer 11

GALT is Gut Associated Lymphoid Tissue

It is nodular in 3 location - tonsils, peyers patches (submucosal lymphatics in terminal ileum), appendix

Question 12

What is the potential complication of nodular GALT in the appendix?

Answer 12

Lymphoid hyperplasia in the appendix base leads to obstructive outflow, therefore there is stasis and infection - leading to appendicitis.
(another cause of obstructed appendix is faecolith or a worm blocking the exit)