The Microbiota of The Gastrointestinal Tract Flashcards

1
Q

Why does transmit time affect bacterial populations?

A

Different bacterial growth rates

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2
Q

How do the following change as you descend the GIT?

Anaerobic conditions

Bacterial density

Obligate anaerobes

A

Anaerobic conditions - increase

Bacterial density - increase

Obligate anaerobes - increase

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3
Q

What is meant by a facultative anaerobic bacteria?

A

Can grow in the presence and absence of oxygen

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4
Q

What is meant by an obligate anaerobe?

A

Cannot grow in the presence of oxygen

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5
Q

Where are you likely to find facultative and obligate anaerobes?

A

Stomach and Colon respectively

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6
Q

What does the GIT microbiota do?

A
  • Defence against pathogens (pH inhibition, competition, barrier function)
  • Modification of host secretions
  • Metabolism of dietary components
  • Production of essential metabolites to maintain health
  • Development of immune system - immune priming
  • Host signalling
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7
Q

What are the factors that determine the composition of the dominant bacteria along the GIT?

A

different oxygen concentrations, different pH, different transit time

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8
Q

What do the GIT microbes grow on?

A

Fibre we eat in foods like fruit, vegetables, pulses and whole grains to convert it into thousands of different products

•GIT microbes can also use endogenous

(host-derived) substrates for growth

(apparently energy absorbed from these food sources is absorbed in the large intestine)

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9
Q

What is the benefit to our health if we include dietary fibre in our diet?

A

Improves faecal bulking, eases passage, results in shorter transit time

Contains important phytochemicals, anti-oxidants and vitamins

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10
Q

What is the result of bacterial fermentation?

A

Releases additional phytochemicals

Maintains slightly acidic pH

Resistance to pathogens is increased as a result of increased commensal bacterial population and pH

Supplies essential short chain fatty acids and branched chain fatty acids

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11
Q

What are the main short chain fatty acids?

A

Butyrate

Propionate

acetate

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12
Q

What is the function of butyrate, propionate, acetate?

A

Butyrate - Epithelial cell growth and regeneration

Propionate - gluconeogenesis in the liver,

satiety signalling

Acetate - lipogenesis

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13
Q

What are the major products of carbohydrate metabolism?

A

SCFA

Gases (CO2, H2, CH4)

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14
Q

Whar are the major products of protein metabolism?

A

Branched short chain fatty acids

Gases (ammonia) hydrogen sulphide

Phenols, indols, amines

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15
Q

Where are most of the short chain fatty acids produced?

A

In the ascending colon - hence the slightly acidic environment

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16
Q

What is the pH of the descending colon?

A

pH neutral

17
Q

Give examples of utilised materials by bacteria and examples of products

A

Potential substrates: Polysaccharides, prebiotics, mucin

Potential products: SCFA’s, lactate

18
Q

Describe the barrier effect that protects the host against pathogens?

A

Colonisation of pathogens is prevented as a result of large numbers of indigenous microbiota

It also keeps in check potentially pathogenic bacteria that are normally resident at low levels

19
Q

What does the mucus layer form a barrier inbetween?

A

The luminal bacterial population and the produciton of epithelial cells

20
Q

What is the function of the inner mucus layer?

A

Prevents bacterial penetration

21
Q

What is in place to deal with the few bacterial cells that penetrate through the epithelium?

A

The immune system

(Dendritic cells, IgA, macrophages)

22
Q

Which bacteria prevent the adhesion / colonisation of pathogens?

A

Those that are close to the epithelium

23
Q

What might cause a disruption in the structure and or function of the GI tract?

A

IBD - reduces the barrier effect.

24
Q

What is the effect of a disrupted mucus layer barrier?

A

Weakens the protection of the gut epithelium, enables the bacteria to bind to the gut surface and potentially cause inflammation.

25
Describe some of the differences between Proximal colon and distal colon. Relevant Learning intention (Understand why there are differences in bacterial communities through the GIT)
26
What is the immune function of the gut? (No relevant learning intention)
Surface is in constant interaction with the external environment Must be able to: * Respond to pathogens * Inhibit immune response to self proteins, dietary antigens and the commensal microbiota
27
How does the innate immune system detect bacteria that do not penetrate?
Pattern recognition receptors Toll like receptors
28
What is the activity of pattern recognition receptors?
Molecules that are associated with pathogens, microbes or cell components are detected and binded by PRR's Results in the release of pro-inflammatory and anti-inflammatory cytokines, chemokines and co-stimulatory molecules.
29
What is the activity of toll like receptors?
Specifically recognise bacterial components
30
When do autoimmune diseases occur?
When the host immune system can no longer distinguish between detrimental pathogens and commensal bacteria
31
What is meant by dysbiosis?
Microbial imbalance
32
What is the result of dysbiosis of the gut microbiota?
Inflammation
33
What are some of the benefits of SCFA's? Which are detected by receptors in the gut epithelial cells Learning intention (Explain why the presence of/products of bacteria are important for a healthy gut)
Inhibits fat accumulation Improves insulin resistance and satiety signalling to brain Suppresses colonic inflammation and carcinogenesis
34
How does microbial diversity change with age?
35
Summary: How do resident bacteria prevent pathogen colonisation?
lowering pH, creating a physical barrier, prime immune system, produce active compounds that kill incoming pathogens