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GI > The microbiota of the GI tract > Flashcards

The microbiota of the GI tract Flashcards

1
Q

How does the quantity of bacteria change along the GI tract?

A

Bacterial density increases
Stomach ~10^4
Colon ~10^11

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2
Q

What is a facultative anaerobic bacteria?

An obligate anaerobe?

A

FAB - can grow in the presence of oxygen AND in the absence of oxygen

OA - cannot grow in the presence of oxygen

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3
Q

What factors influence the type of bacteria that grow in the gut tube?

A

Oxygen concentrations
pH levels
Transit time (off food through structure)

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4
Q

How many bacterial cells are in the average human gut?

A

Up to 100 trillion

More bacteria than human cells in the body

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5
Q

What is an OTU? What does it indicate?

A

OTU - operational taxonomic unit

Indicates diversity of bacteria in the gut flora, indicates health

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6
Q

Functions of the bacterial microbiota?

A
  • Metabolism of some dietary components
  • Defence against pathogens
  • Produce metabolites
  • Develop immune system (immune priming)
  • Host signalling (gut-brain axis)
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7
Q

Digestion of junk food vs fibre with regard to gut microbiota?

A

Junk food digested in stomach/small intestine - doesn’t feed gut microbes

Fibre feeds gut microbes, energy absorbed in the colon after their action

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8
Q

Benefits of including fibre in your diet?

A
  • Improves faecal bulking, eases passage, shorter transit time
  • Contains phytochemicals, anti-oxidants and vitamins
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9
Q

Benefits of bacterial fermentation of fibre in the gut?

A
  • Additional phytochemicals
  • Maintains slightly acidic pH
  • Increased commensal population and maintenance of pH protects against pathogens
  • Essential supply of short chain FA’s
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10
Q

Three main short chain fatty acids provided by microbial fermentation and their functions?

A
  • Butyrate: epithelial cell regrowth and regeneration
  • Propionate: gluconeogenesis & satiety signalling
  • Acetate: supplies peripheral tissues, lipogenesis
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11
Q

Main products of bacterial carbohydrate metabolism?

A
  • Short chain fatty acids

- Gases (CO2, H2, CH4)

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12
Q

Main products of microbiota protein metabolism? When is this type of metabolism high?

A
  • Branched short chain fatty acids
  • Gases (NH3, H2S)
  • Phenols, indoles, amines

High at pH’s above 6 - non healthy microbiota

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13
Q

How does what we eat influence gut microbiota? What sort of diet does this encourage?

A

Certain bacteria are primed to digest certain foods - these thrive if your diet focuses on a few tings

Want to be eating a diverse, balanced diet

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14
Q

Ways in which microbiota contributes to colonization resistance?

A
  1. Barrier effect

2. Active competitive exclusion

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15
Q

How does the lowering of gut pH by bacterial fermentation help?

A
  • Higher fermentation rates, more short chain FA production/absorption
  • Pathogen exclusion: typically pathogens grow at pH’s over 6
  • Quicker transit & high epithelial cell turnover
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16
Q

What is the barrier effect?

A

Commensal bacteria lie within the lumen and outer mucous layer of the gut - prevents adhesion/colonization by pathogens

17
Q

What happens when a bacteria from the gut microbiota penetrates the inner mucous layer and gets past epithelial cells?

A

IgA mediated immune response leads to the bacteria being killed off

More bacteria constantly entering gut, more being killed off - homeostasis

18
Q

What happens when the immune response to a penetrating gut bacteria is not regulated?

A

Inflammation - results in destruction of the mucous layer and conflict between immune system and newly exposed bacteria

19
Q

Why do the gut microbiota and immune system need to co-evolve? What happens if they don’t?

A

Evolve together so that the immune system is tolerant of the gut microbiota and can regulate it so that it doesn’t grow out of control

Autoimmune diseases

20
Q

How does the gut microbiota influence host signalling?

A

By producing short chain FA’s - important signalling molecules. Act on receptors on gut epithelial cells

21
Q

Some of the short chain fatty acid receptors and their functions?

A
  • GPR43/FFAR2: activated by acetate/propionate. Results in GLP-1 secretion, inhibits fat accumulation
  • GPR/FFAR3: activated by acetate/propionate. Results in PPY secretion - improves insulin sensitivity and signals satiety
  • GPR109A: activated by butyrate, suppresses colonic inflammation and carcinogenesis
22
Q

Is the gut microbiota the same throughout life?

A

No - changes constantly depending on age and diet

23
Q

How does microbial diversity change throughout life?

A

Infant - low diversity, good

Healthy adult - high diversity, good

Elderly - declines a bit, want it to stay as high as possible

GI (46 decks)

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