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07. Year 2: Alimentary System > The Microbiota of the GI Tract 1 > Flashcards

The Microbiota of the GI Tract 1 Flashcards

1
Q

What is the transit time in the mouth?

A

1 minute

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2
Q

What is the transit time in the oesophagus?

A

4-8 seconds

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3
Q

What is the transit time in the stomach?

A

2-4 hours

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4
Q

What is the transit time in the small intestine?

A

3-5 hours

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5
Q

What is the transit time in the colon?

A

10 hours to several days

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6
Q

What does transit time affect?

A

Bacterial populations due to different bacterial growth rates

Intestinal cell exposure to toxins, consumed with food or produced by bacteria

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7
Q

How does the amount of bacteria change as you go down the GI tract from the stomach to the colon?

A

Increases

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8
Q

What does anaerobic mean?

A

Living in the absence of oxygen

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9
Q

What does aerobic mean?

A

Living in the presence of oxygen

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10
Q

What are different classes of anaerobic bacteria?

A

Facultative anaerobic bacteria

Obligate anaerobic bacteria

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11
Q

What are facultative anaerobic bacteria?

A

Can grow in the presence of oxygen and in the absence of oxygen (some grow poorly when oxygen is present)

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12
Q

What are obligate anaerobes?

A

Cannot grow in the presence of oxygen (many rapidly killed in the presence of oxygen)

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13
Q

What are examples of bacteria found in the stomach?

A

Lactobacillus

Candia

Streptococcus

Helicobacter pylori

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14
Q

What are examples of bacteria found in the colon?

A

Bacteroides

Clostridium

Bifidpbacterium

Enterobacteriaceae

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15
Q

What class of anaerobes are found in the stomach?

A

Faciltative anaerobes

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16
Q

What class of anaerobes is found in the colon?

A

Obligate anaerobes

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17
Q

Why do different kinds of bacteria dominate different areas of the GI tract?

A

Different oxygen concentrations

Different pH

Different transit times

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18
Q

How does the number of microbial cells compare to human cells?

A

There are more microbial cells

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19
Q

How much bacteria is there in the human gut?

A

100 trillion

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20
Q

What are the different parts of taxonomy?

A

Life

Domain

Kingdom

Phylum

Class

Order

Family

Genus

Species

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21
Q

Why must meaningful comparison between bacteria be done at the genus level?

A

Bacterial comparison at the phylum level is a higher level than grouping all mammals together

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22
Q

What impact does diet have on bacteria?

A

Impacts diversity

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23
Q

What does OTU stand for?

A

Operational taxonomic unit

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24
Q

What does a higher number of OTUs mean?

A

Higher diversity

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25
Q

How are the vast majority of bacteria in the GI tract beneficial for health?

A

Different bacteria perform different functions

Bacteria act together in a population

Bacteria communicate with each other and with the host

A diverse microbiota is important to maintain health

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26
Q

What are some functions of gut microbiota?

A

Modifications of host secretions (mucin, bile, gut receptors etc)

Defence against pathogens

Metabolism of dietary components

Production of essential metabolites to maintain health

Development of the immune system

Host signalling

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27
Q

How does the gut microbiota provide defence against pathogens?

A

Competition

Barrier function

pH inhibition

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28
Q

What host secretions do the gut microbiota modify?

A

Mucin

Bile

Gut receptors

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29
Q

Why is junk food bad although it contains lots of energy (calories)?

A

Does not feed out gut microbes, that grow on fibres

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30
Q

What kinds of food is fibre found in?

A

Fruit

Vegetables

Pulses

Whole grains

31
Q

Where are the products created by bacteria that are derived from fibres absorbed?

A

Large intestine

32
Q

As well as fibre, what else can GIT microbes use for growth?

A

Endogenous (host-derived) substrates

33
Q

What are benefits of including dietary fibre in our diet?

A

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

Contains important phytochemicals, anti-oxidants and vitamins

Bacterial fermentation

34
Q

How does bacterial fermentation impact pH?

A

Maintains slightly acidic pH

35
Q

What are the benefits of bacterial fermentation?

A

Releases additional phytochemicals

Maintains slightly acidic pH that improves resistance to pathogens

Essential supply of short chain fatty acids

36
Q

What are the 3 main fatty acids provided by bacterial fermentation?

A

Butyrate

Propionate

Acetate

(1:1:1 ratio)

37
Q

What are the functions of butyrate?

A

Epithelial cell growth and regeneration

38
Q

What are the functions of propionate?

A

Gluconeogenesis in the liver

Satiety signalling

39
Q

What are the functions of acetate?

A

Transported in the blood to peripheral tissues

Lipogenesis

40
Q

How does the colon change in regards to bacterial fermentation?

A

Proximal is carbohydrate rich, pH midly acidic and transover rapid

Distal has little fermentable carbohydrates, pH neutral and turnover slow

41
Q

How does bile acid concentration change along the bowel?

A

Increases going proximal to distal

42
Q

How much carbohydrates are metabolised by bacteria per day?

A

About 40g/day

43
Q

How much protein is metabolised by bacteria per day?

A

12-18g/day

44
Q

What are important gut microbial activities driven by?

A

What we eat

45
Q

What are the functional importance of firmicutes?

A

Butyrate production

Polysaccharide utlisation

Propionate production

46
Q

What is the functional importance of aminomycetes?

A

Utilise prebiotics

Lactate production

47
Q

What is an example of an actinomycete?

A

Bifidobacteria

48
Q

How does the GI microbiota provide have a barrier effect for defence?

A

Large number of the indigenous microbiota prevent colonisation by ingesting pathogens and inhibit overgrowth of potentially pathogenic bacteria normally resident at low levels

49
Q

How does the GI microbiota provide active competitive exclusion for defence?

A

Conferred by both microbe-microbe and microbe-host interactions

50
Q

How does the GI microbiota protect against pathogens due to pH inhibitions?

A

Generally pathogens grow opimally at pHs over 7

51
Q

Is the pH greater in the proximal or distal colon?

A

Distal

52
Q

What forms a barrier between the luminal bacterial population and the epithelial cells to keep the gut health?

A

Mucus layer

53
Q

What are the different layers of bacteria after the mucus layer?

A

Inner layer and outer layer

54
Q

What happens when the mucus bacterial of the colon disrupted?

A

Bacterial cells penetrate the mucus layer and the epithelial barrier

55
Q

What is the largest lymphoid organ in the body?

A

Gut

56
Q

What must be gut be able to do due to being in constant interaction with the environment?

A

Respond appropriately to foreign/pathogenic agents

Actively down-regulate immune responses to “self” proteins, dietary antigens and the commensal microbiota

Recognise and respond to pathogenic invasions

57
Q

Why do autoimmune diseases occur in relation to the gut?

A

Immune system can no longer distinguish between harmful pathogens and commensal bacteria

58
Q

What does imbalance between the gut microbiota composition lead to?

A

Disrupting homeostasis causing inflammation

59
Q

What are the 2 possible effects that gut bacteria can have on inflammation?

A

Some are pro-inflammatory and some are anti-inflammatory

60
Q

What are important signalling molecules that gut microbiota produce?

A

Short chain fatty acids

61
Q

What impact do short chain fatty acids from bacteria have on the gut epithelial cells?

A

Secretes gut hormones

62
Q

What receptors on the gut epithelium detects short chain fatty acids from bacteria?

A

GRP43/FFAR2

GPR/FFAR3

GPR109A

63
Q

What does SCFA stand for?

A

Short chain fatty acid

64
Q

What are GPR43/FFAR2 receptors activated by?

A

Acetate

Propionate > butyrate

65
Q

What does activation of GPR43/FFAR2 receptors cause?

A

GLP-1 secretions (inhibits fat accumulation)

66
Q

What does GLP-1 do?

A

Inhibits fat secretions

67
Q

What does activation of GPR/FFAR3 receptors do?

A

Results in PYY secretion (improves insulin resistance and satiety signalling to brain)

68
Q

What activates GPR/FFAR3 receptors?

A

Propionate and butyrate

69
Q

What does PYY do?

A

Improves insulin resistance and satiety signalling to brain

70
Q

What activates GPR109A receptors?

A

Butyrate

71
Q

What does activation of GPR109A receptors cause?

A

Suppreses colonic inflammation and carcinomogenesis (anti-inflammatory cytokines such as IL-10)

72
Q

What happens to microbial metabolites that are not utilised by gut epithelial cells?

A

Absorbed into the bloodstream and transported around the body

73
Q

What can be said about microbial composition throughout life?

A

It changes throughout life

74
Q

What are some different factors that influence the microbiota throughout life?

A

Anatomy is the same, food is different

Dietary changes cause the greatest influence

Our food is out microbiotas food

07. Year 2: Alimentary System (41 decks)

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