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The Alimentary Canal > Microbiota of the GIT > Flashcards

Microbiota of the GIT Flashcards

1
Q

Describe transit time in relation to section of GIT

A

Transit time gets longer from mouth to large intestine
In large intestine for 10hrs to several days
Stomach 2-4hrs and small intestine 3-5hrs

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2
Q

How does transit time affect the microbiota?

A

Bacterial population effected due to different bacterial growth rates
Also intestinal cell exposure to toxins

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3
Q

Describe the bacterial populations along the GIT

A

Increasing anaerobic conditions
Increasing bacteria density
Increasing dominance of obligate anaerobes

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4
Q

What is the total number of bacteria in the human gut?

A

Up to 100 trillion
Everyone’s microbia is different - unique

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5
Q

Why is there a dominant bacteria change along the GIT?

A

Different oxygen conc., different pH and different transit times

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6
Q

What are the pH changes of the GIT?

A

Mouth - 6.5-7.5
Stomach - 1.5-4
Duodenum - 7-8.5
Ileum - 4-7
Large Colon - 5.5-6.5

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7
Q

Why does microbial composition change throughout life?

A

Anatomy is the same but food is different
Our food is microbiota’s food

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8
Q

What is the role of the GIT microbiota?

A

Metabolism of dietary components
Production of metabolites
Modification to host secretions
Defence against pathogens
Development of immune system
Host signalling

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9
Q

What does healthy gut microbiota equal?

A

Healthy person

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10
Q

Is junk food good for microbes?

A

Junk food provides a lot of calories but does not feed gut microbes as does not reach large colon
Most absorbed in small intestine/stomach - 70% energy uptake

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11
Q

What food does GIT microbes grow on?

A

Fibre - fruit, veg, pulses and whole grains
Converts to different products
Energy absorbed in large intestine

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12
Q

What are the benefits of including dietary fibre in our diet?

A

Improves faecal bulking, eases passage and results in shorter transit time
Contains phytochemicals, antioxidants and vitamins
Bacterial fermentation

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13
Q

What does bacterial fermentation do?

A

Releases additional phytochemicals
Maintains slightly acidic pH
Increased commensal bacterial population
Essential supply of short chain fatty acids

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14
Q

What is the right side of the colon responsible for?

A

Site of most bacterial fermentation
Carbohydrate metabolism
Gives SCFA and gases

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14
Q

What does a diverse balanced diet do microbes?

A

A diverse balanced microbiota and diverse balanced products
What we eat affects amount and type of microbial metabolites produced

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14
Q

What does SCFA give?

A

Acetate, propionate and butyrate

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15
Q

What is the left side of the colon responsible for?

A

Site of most intestinal disease
Protein metabolism
Major products
Branched SCFA, gases, phenols, indoles and amines

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16
Q

What are the 3 main short chain fatty acids?

A

Butyrate, propionate and acetate

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17
Q

What is the function of butryrate?

A

Epithelial cell growth and regeneration

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18
Q

What is the function of propionate?

A

Gluconeogenesis in the liver
Satiety signalling

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19
Q

What is the function of acetate?

A

Transported in blood and to peripheral tissues
Lipogenesis

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20
Q

What does pH lowering help?

A

Pathogen inhibition
Increased Ca absorption

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21
Q

What is the optimum pH for growth of pathogens?

A

Over 6

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22
Q

Describe pH and proximal colon

A

Low pH so pathogen exclusion - Less disease
Quicker transit
High epithelium turnover
High fermentation rates
High SCFA production

23
Q

Describe pH and distal colon

A

Higher pH - less pathogen exclusion and more protein fermentation - more disease
Low substrate concentrations
Slower transit so higher exposure to harmful compounds

24
Q

What are the 2 defences which help colonisation resistance?

A

Barrier effect
Active competitive exclusion

25
Q

What is barrier effect?

A

Large numbers of indigenous microbiota prevent colonisation by ingested pathogen and inhibit overgrowth of pathogenic bacteria
This bacteria could be normally at low levels

26
Q

What is active competitive exclusion?

A

Both microbe to microbe and microbe to host interactions

27
Q

What happens to the products of the bacteria?

A

transported in blood to liver, peripheral tissues, brain and signalling molecules

28
Q

Why are short chain fatty acids important?

A

Important signalling molecules

29
Q

How are SCFA detected?

A

By receptors which secrete gut hormones

30
Q

What are the GPR43/FFAR2 receptors activated by?

A

Acetate, propionate more than butyrate

31
Q

What are GPR41/FFAR3 receptors activated by?

A

Propionate and butyrate

32
Q

What are GPR109A receptors activated by and what do they do?

A

Butyrate
Suppress colonic inflammation and carcinogenesis

33
Q

Describe gut microbiota in the development of he immune system

A

Commensal bacteria close to epithelium block adhesion by pathogens
Inner mucus layer prevents bacterial penetration
Immune system deals with few bacteria cells leaving epithelium

34
Q

Are microbiota species pro or anti-inflammatory?

A

Can be either

35
Q

What does bacterial composition and metabolite conc. also effect?

A

Gut-brain axis

36
Q

What are some non-gut conditions associated with changing of gut microbiota?

A

CNS - Multiple sclerosis
GI - IBD, IBS
Metabolism - Insulin resistance, obesity
Immunity - allergies, autoimmune disease

37
Q

What are the 2 diseases in inflammatory bowel disease?

A

Chron’s Disease and Ulcerative Colitis

38
Q

What can dysregulation of immune response lead to?

A

Chronic gut inflammation
Autoimmune disease

39
Q

What does inflammation in IBD likely result from?

A

Dysregulated host immune response to gut microbiota

40
Q

What do CD patients have a lower number of?

A

F. prausnitizil - anti-inflammatory bacteria
Instead an increase in pro-inflammatory

41
Q

What is the effect of antibiotic use and gut microbiota?

A

Reduces bacterial diversity and increases enterobacteria

42
Q

Explain the vicious cycle in IBD

A

Decrease in mucus barrier then increase in O2 pressure
Then alters microbial composition
Which increases inflammation then continues again

43
Q

What are some causes for change in gut microbial composition?

A

Antibiotic use
Inflammation
Diarrhoea - decreased transit time
Host diet - less fibre
Host genotype

44
Q

What decreases diversity of bacteria when antibiotics used?

A

Selective pressure
There is increase in resistant community
Gradual recovery but never bac to normal

45
Q

What antibiotics have more effect on intestinal microbiota?

A

Vancomycin > clindamycin > ciprofloxacin

46
Q

What are the consequences of exposure to antibiotics?

A

Decreased microbial diversity
Opportunity fir pathogen colonisation so results in pathogen dominant community
Can end up with recurrent C. difficile infections

47
Q

What can reduce incidence of CDAD?

A

Probiotics

48
Q

Explain a FMT

A

Faecal sample from screened healthy donor transplants into patient
This displaces C. difficile and prevents reinfection

49
Q

What are the factors which affect gut microbiota?

A

Environment, diet, life stage, antibiotics, prebiotics, faecal transplant, disease

50
Q

How does decreased dietary carbohydrate content effect faecal short chain fatty acid production?

A

Decreased production of SCFA
Significant decrease un numbers of E.rectale group

51
Q

What are probiotics?

A

Live microorganisms that when administered in adequate amounts, confer health benefit on host

52
Q

What are prebiotics?

A

Substrate that is selectively utilised by host microorganisms conferring health benefit
Prebiotics are food for resident bacteria

53
Q

What are some widespread mechanisms carried out by prebiotics?

A

Competition
Competitive exclusion
Barrier function
Reduce inflammation

54
Q

What are some frequent mechanisms carried out by prebiotics?

A

Bioconversions
Direct antagonism
Immune stimulation

55
Q

How does prebiotics help satiety signalling?

A

Stimulate SCFA production by gut microbiota
Interact directly with immune cell receptors

56
Q

What are the systemic effects of prebiotics?

A

Increased health benefit as metabolic effects, satiety an immunomodulatory effects
There is decreased inflammation

The Alimentary Canal (33 decks)

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