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Flashcards in GI S7 (Done) Deck (79)
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1

List the categories of toxins that may be encoutered in the GI tract

Chemical

Bacteria

Viruses

Protozoa

Nematodes, Cestodes, Trematodes

2

What methods of defense are used aginst these toxins?

Innate:

Physical

Celullar

Adaptive

3

What are the innate phyiscal defenses protecting the GI tract?

Sight

Smell

Memory

Saliva

Gastric Acid

Small intestine secretions

Colonic mucus peristalsis/Segmentation

4

What is the effect of slowed peristalsis on a gut infection?

Course of disease is prolonged (E.g. Shigellosis)

5

How is saliva protective against infection?

Contains Lysosyme, lactoperoxidase, complement, IgA and polymorphs

Washes toxins into the stomach (acid)

6

What effect can severe dehydration have on salivary defense?

Xerostomia:

Lead to microbial overgrowth in the mouth and dental caries

Parotitis:

Caused by staph aureus

7

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

8

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

9

Give examples of bacteria and viruses resistant to stomach acid

Mycobacterium tuberculosis

Enteroviruses:

Hep A, Polio, Coxsackie

10

List the protective mechanisms of the small intestine

 

Bile

Proteolytic enzymes

Lack of nutrients

Anaerobic environment

Shedding of epithelial cells

Rapid transit (Peristalsis)

11

What is the normal bacterial load in the small intestine?

Normally sterile

12

What are the main protective mechanisms of the colon

Why are the important?

Mechanism:

Mucus layer covering epithelium

Anaerobic environment

Importance:

Faeces are 40% bacteria by weight and so the colon wall must be isolated from this

13

What are the cells involved in the innate cellular defense of the GI tract?

Neutrophils

Macrophages

NK cells

Tissue mast cells

Eosinophils

14

What is the role of eosinophils in the gut and their clinical importance?

Act against worms

Eosinophilia may indicate parasiste infection

15

What conditions may also produce eosinophilia?

Asthma and Hayfever

16

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

17

What are two clinical signs of cholera?

Washerwomans hands:

Severe dehydration

Ricewater stool:

Rapid fluid loss

 

18

What is the definition of a 'portal system'?

Give an example

Definition:

Two capillary systems in series

Example:

Hepatic portal system

19

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

20

List some examples of causes of liver failure

Viral Hepatitis

Alcohol

Drugs (Paracetamol, halothane)

Industrial solvents

Mushroom poisoning

21

Describe the effects of liver failure on the GI tract

Infection:

Increased susceptiblity to infection

Toxins, drugs, hormones:

Increased susceptibility

Ammonia:

Ammonia produced by colonic bacteria may not be cleared due to failure of the urea cycle

Hepatic encephalopathy may result

22

Describe the effects of cirrhosis

Hepatic fibrosis:

Leads to reductions in liver function (liver failure)

Also portal hypertension (>20mmHg)

Porto-systemic shunting:

Portal hypertension leads to shunting of blood into systemic circulation (therefore toxins are also shunted)

Can cause:

- Oesophageal varices

- Haemorrhoids

- Caput medusae

23

Describe fully the symptoms of Porto-systemic shunting in liver cirrhosis

Haemorrhoids:

Highly vascular 'cushions' in the anal canal become swollen due to increased venous pressure

Oesophageal varices:

Venous dilation in the lower third of the oesophagus due to increased venous pressure

Caput medusae:

Engorged para-umbilical veins visible on the peri- umbilical skin due to increased venous pressure

Ascites:

Portal anstomoses with retroperitoneal veins cused capillary leakage into peritoneum

Splenomegaly:

Congestion due to portal hypertension

Spider naevi:

Small spiderwebs of swollen veins on the skin surface, found in the areas drained by the SVC only

 

24

What are the cellular adaptive defenses releavant to the GI tract?

B lymphocytes:

Production of antibodies (IgE, IgA) for defense against extracellular microbes

T Lymphocytes:

Defense against intracellular organisms

25

Describe the distribution of lymphatic tissue in the GI tract

GALT:

Gut associated lymphoid tissue is diffusely distributed throughout the gut and surrounding tissues (E.g. Mesentery)

Also nodular in 3 locations:

- Tonsils

- Peyer's Patches

- Appendix

 

26

Describe the drainage of the tonsils and the clincial relevance of this

Drainage:

Drain into cervical lymph nodes in the neck

Clincal:

Sore throats and cervical lymphadenopathy are a common presentation due to bacteria/viruses entering the body through the mouth

27

What are Peyer's patches?

Major clincal relevance?

Peyer's Patches:

Nodular GALT in the mucosa of the terminal ileum

Clinical:

Infection and subsequent inflammation of Peyer's patches in typhoid fever can cause perforation of the terminal ileum, which can be rapidly fatal

28

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

29

What is Appendicitis?

Appendix obstruction leads to fluid stasis within the lumen

Infection results and the appendix becomes inflammed

 

30

What are the common causes of appendicitis?

Obstruction:

Faecoliths

Lymphoid hyperplasia

Lymphoid infection/inflammation