Alimentary System 8 - Infection & Immunology Flashcards
What is restrained activation?
Seen in the gut, this is the balance between tolerance of food and commensal bacteria and the immunoreactivity with pathogens
List the 4 major phyla of bacteria in the gut microbiota
- Bacteroidetes
- Firmicutes
- Acinobacteria
- Proteobacteria
Define dysbiosis
Altered microbiota composition
List the causes of dysbiosis
- Infection/ inflammation
- Diet
- Xenobiotics
- Hygiene
- Genetics
List the defences the mucosa has
Physical barrier
- Chemical (enzymes/acidic pH)
- Anatomical (epithelial barrier/peristalsis)
Commensal bacteria
Immunological (following invasion)
- MALT (mucosa associated)
- GALT (gut associated)
List the mucosal defence in the epithelial barrier
- Goblet cells + mucus layer
- Epithelial monolayer with tight junctions
- Paneth cells (secrete peptides and lysozyme in the SI)
What is MALT?
- Found in submucosa below the epithelium
- Contains lymphoid follicles surrounded by high endothelial venules (postcapillary venules) allowing easy passage of lymphocytes
List not organised GALT
- Intra-epithelial lymphocytes
- Lamina propria lymphocytes
List organised GALT
- Peyers patches (SI)
- Caecal patches (LI)
- Isolated lymphoid follicles
- Mesenteric lymph nodes (encapsulated)
What is the function of GALT?
Both adaptive and innate immune responses through generation of lymphoid cells and antibodies
Describe the structure of peyers patches
- Mainly in the distal ileum
- Covered with follicle associated epithelium (FAE)
- FAE contains no goblet cells, secretory IgA and has a lack of microvilli
- Organised collection of naive T and B cells
What is the function of M cells?
- Uptake antigens, and make IgA
- Facilitates transfer of the IgA-bacteria complex into peyers patches
- Found in the FAE
How do peyers patches develop?
Following exposure to bacterial microbiota
What is the full name of M cells?
Microfold cells
How do transepithelial dendritic cells sample antigens?
- The foot of the dendritic cell extends and samples antigens from the mucosa
- They then take these antigens to the lymph nodes
Briefly summarise the B cell adaptive response
- Mature B cells express IgM in peyers patches
- Upon antigen presention there is a class switch to IgA
- T-cells and epithelial cells influence B cells maturation by cytokine production
- B cells become IgA secreting plasma cells and populate the lamina propria
What percentage of gut B-cells secrete IgA?
90%
Compare the immune system in the small intestine and the large intestine
- SI has deep folds, with peyers patches and paneth cells at the bottom of the crypt. LI has shorter crypts with no paneth cells
- Resident macrophages under the epithelium in both
- One layer of mucous. LI has two layers
Describe the process of lymphocyte circulation
- Made in primary lymphoid organs
- Stored in secondary
- Released into lymph nodes and enter circulation
- There they may meet their antigen, or enter the lamina propria, skin or BALT
Describe the process of gut homing
- Lymphocyte rolls along the epithelium and is activated by binding of a4B7 integrin to MAdCAM1 on the membrane
- This causes transmigration and chemotaxis
Describe the mechanism of cholera
- Bacteria disease caused by vibrio cholerae
- Reach the small intestine and releases cholera toxin
- Cholera toxin enters the epithelial cell and causes water and ions to leave the cell
Describe the diagnosis and treatment of cholera
- Diagnosed by growing bacterial culture on agar
- Treated by rehydration
- Vaccines can be used before going on holiday
Describe the transmission of cholera
- Feco-oral route
- Spreads through contaminated water and food
List the symptoms of cholera
- Severe dehydration
- Watery diarrhoea
- Vomiting
- Nausea
- Abdominal pain
Describe the epidemiology of rotavirus
Most common cause of diarrhoea in infants and young children world wide
What is the vaccination for rotavirus?
Rotarix
How is campylobacter transmitted?
Undercooked meat, untrated waer, and unpasturised milk
What antibiotic is used to treat campylobacter and why?
- Azithromycin
- Due to ressitance to flouroquinolones
How many pathotypes of E coli are there?
6
How is C difficile managed?
- Isolate patient
- Stop antibiotics
- Can use faecal microbiota transplantation
List the infectious causes of diarrhoea
- Cholera
- E coli
- C difficile
- Rotavirus
- Norovirus
- Campylobacter
Describe the mechanism of coeliac disease
- Gliadin is not broken down in the stomach
- It reaches the small intestine, binds to sIgA and is transferred to the lamina propria
- Results in immune response
List the symptoms of coeliac disease
- Abdominal distention
- Diarrhoea
List the methods used to diagnose and treat coeliac disease
- Diagnosed by anti-gliadin blood tests and biopsy tests
- Treated by diet management
Describe the mechanism of IBS
- Visceral hypersensitivity
- Triggered by diet and stress
List the symptoms of IBS
- Recurrent abdominal pain
- Abnormal bowel motility
- Constipation and/or diarrhoea
List the treatments of IBS
- Modify diet (avoid apples, beans, cauliflowers)
- Treat constipation (soluble fibre, stool softeners/laxatives)
- Treat spasms and pain (anti-diarrheals, anti muscarinic)
- Manage stress, anxiety and depression
How can crohns and ulcerative colitis be differentiated?
- Crohns affects the distal ileum and colon, while ulcerative colitis affects only the colon
- Ulcerative collitis causes continuous inflammation, while crohns occurs in patches (cobblestone)
- Ulcerative colitis can be cured by surgery
Describe the mechanism of inflammatory bowel disease
- Impaired barrier function due to diet, stress, smoking, and genetic factors
- Leads to chronic inflammation and resulting destruction of tissue
List the two inflammatory bowel diseases
- Crohns
- Ulcerative colitis
List the symptoms of inflammatory bowel disease
- Bloody diarrhoea
- Abdominal cramping
- Anaemia
- Weight loss
- Fatigue
How can inflammatory bowel disease be diagnosed?
- Antibody tests
- Endoscopy
- Barium x-ray
List the treatments for inflammatory bowel disease
- Anti-inflammatory drugs
- Immunosuppressants
- Surgery (curative in ulcerative colitis but not in crohns)
