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Second Year Systems > The Microbiota of The Gastrointestinal Tract > Flashcards

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
Q

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)

A
26
Q

What is the immune function of the gut?

(No relevant learning intention)

A

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
Q

How does the innate immune system detect bacteria that do not penetrate?

A

Pattern recognition receptors

Toll like receptors

28
Q

What is the activity of pattern recognition receptors?

A

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
Q

What is the activity of toll like receptors?

A

Specifically recognise bacterial components

30
Q

When do autoimmune diseases occur?

A

When the host immune system can no longer distinguish between detrimental pathogens and commensal bacteria

31
Q

What is meant by dysbiosis?

A

Microbial imbalance

32
Q

What is the result of dysbiosis of the gut microbiota?

A

Inflammation

33
Q

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)

A

Inhibits fat accumulation

Improves insulin resistance and satiety signalling to brain

Suppresses colonic inflammation and carcinogenesis

34
Q

How does microbial diversity change with age?

A
35
Q

Summary:

How do resident bacteria prevent pathogen colonisation?

A

lowering pH, creating a physical barrier, prime immune system,

produce active compounds that kill incoming pathogens

Second Year Systems (21 decks)

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