List the categories of toxins that may be encoutered in the GI tract
Nematodes, Cestodes, Trematodes
What methods of defense are used aginst these toxins?
What are the innate phyiscal defenses protecting the GI tract?
Small intestine secretions
Colonic mucus peristalsis/Segmentation
What is the effect of slowed peristalsis on a gut infection?
Course of disease is prolonged (E.g. Shigellosis)
How is saliva protective against infection?
Contains Lysosyme, lactoperoxidase, complement, IgA and polymorphs
Washes toxins into the stomach (acid)
What effect can severe dehydration have on salivary defense?
Lead to microbial overgrowth in the mouth and dental caries
Caused by staph aureus
Describe the functions of the stomach as they relate to innate protection of the gut
Stomach acid works to digest food, but also to sterilise it
The 2.5L of gastric juice per day can have a pH as low as 0.87, killing all but a few bacteria and viruses
What might reduce the protective effect of stomach acid?
What is the effect of this?
Pts who have achlorhydria (Lack of stomach acid) due to anaemia, H2 antagonists and PPIs
This increases susceptibility to Shigellosis, cholera, salmonella and C. difficle infections
Give examples of bacteria and viruses resistant to stomach acid
Hep A, Polio, Coxsackie
List the protective mechanisms of the small intestine
Lack of nutrients
Shedding of epithelial cells
Rapid transit (Peristalsis)
What is the normal bacterial load in the small intestine?
What are the main protective mechanisms of the colon
Why are the important?
Mucus layer covering epithelium
Faeces are 40% bacteria by weight and so the colon wall must be isolated from this
What are the cells involved in the innate cellular defense of the GI tract?
Tissue mast cells
What is the role of eosinophils in the gut and their clinical importance?
Act against worms
Eosinophilia may indicate parasiste infection
What conditions may also produce eosinophilia?
Asthma and Hayfever
What is the clinical relevance of mast cells in the GI tract?
Gut infections may activate complement, recruiting Mast cells
Mast cells degranulate and release histamine, increasing capillary permeability
This can lead to massive fluid loss
In the case of cholera, up to 1L/hour
60% mortality untreated
What are two clinical signs of cholera?
Rapid fluid loss
What is the definition of a 'portal system'?
Give an example
Two capillary systems in series
Hepatic portal system
What are the two capillary systems linked in the hepatic portal system?
Villus capillaries along the gut wall
System of capillaries suppliying the hepatic lobules
Blood flow is from villus to lobule via the portal vein and other intermediate veins
List some examples of causes of liver failure
Drugs (Paracetamol, halothane)
Describe the effects of liver failure on the GI tract
Increased susceptiblity to infection
Toxins, drugs, hormones:
Ammonia produced by colonic bacteria may not be cleared due to failure of the urea cycle
Hepatic encephalopathy may result
Describe the effects of cirrhosis
Leads to reductions in liver function (liver failure)
Also portal hypertension (>20mmHg)
Portal hypertension leads to shunting of blood into systemic circulation (therefore toxins are also shunted)
- Oesophageal varices
- Caput medusae
Describe fully the symptoms of Porto-systemic shunting in liver cirrhosis
Highly vascular 'cushions' in the anal canal become swollen due to increased venous pressure
Venous dilation in the lower third of the oesophagus due to increased venous pressure
Engorged para-umbilical veins visible on the peri- umbilical skin due to increased venous pressure
Portal anstomoses with retroperitoneal veins cused capillary leakage into peritoneum
Congestion due to portal hypertension
Small spiderwebs of swollen veins on the skin surface, found in the areas drained by the SVC only
What are the cellular adaptive defenses releavant to the GI tract?
Production of antibodies (IgE, IgA) for defense against extracellular microbes
Defense against intracellular organisms
Describe the distribution of lymphatic tissue in the GI tract
Gut associated lymphoid tissue is diffusely distributed throughout the gut and surrounding tissues (E.g. Mesentery)
Also nodular in 3 locations:
- Peyer's Patches
Describe the drainage of the tonsils and the clincial relevance of this
Drain into cervical lymph nodes in the neck
Sore throats and cervical lymphadenopathy are a common presentation due to bacteria/viruses entering the body through the mouth
What are Peyer's patches?
Major clincal relevance?
Nodular GALT in the mucosa of the terminal ileum
Infection and subsequent inflammation of Peyer's patches in typhoid fever can cause perforation of the terminal ileum, which can be rapidly fatal
What is mesenteric adenitis?
Inflammation of lymph nodes along the mesentery
Common cause of right iliac fossa pain in children, can be mistaken for appendicitis
Often caused by adenovirus/coxsackie virus
What is Appendicitis?
Appendix obstruction leads to fluid stasis within the lumen
Infection results and the appendix becomes inflammed
What are the common causes of appendicitis?