The Microbiota of the GI Tract 1 Flashcards
What is the transit time in the mouth?
1 minute
What is the transit time in the oesophagus?
4-8 seconds
What is the transit time in the stomach?
2-4 hours
What is the transit time in the small intestine?
3-5 hours
What is the transit time in the colon?
10 hours to several days
What does transit time affect?
Bacterial populations due to different bacterial growth rates
Intestinal cell exposure to toxins, consumed with food or produced by bacteria
How does the amount of bacteria change as you go down the GI tract from the stomach to the colon?
Increases
What does anaerobic mean?
Living in the absence of oxygen
What does aerobic mean?
Living in the presence of oxygen
What are different classes of anaerobic bacteria?
Facultative anaerobic bacteria
Obligate anaerobic bacteria
What are facultative anaerobic bacteria?
Can grow in the presence of oxygen and in the absence of oxygen (some grow poorly when oxygen is present)
What are obligate anaerobes?
Cannot grow in the presence of oxygen (many rapidly killed in the presence of oxygen)
What are examples of bacteria found in the stomach?
Lactobacillus
Candia
Streptococcus
Helicobacter pylori
What are examples of bacteria found in the colon?
Bacteroides
Clostridium
Bifidpbacterium
Enterobacteriaceae
What class of anaerobes are found in the stomach?
Faciltative anaerobes
What class of anaerobes is found in the colon?
Obligate anaerobes
Why do different kinds of bacteria dominate different areas of the GI tract?
Different oxygen concentrations
Different pH
Different transit times
How does the number of microbial cells compare to human cells?
There are more microbial cells
How much bacteria is there in the human gut?
100 trillion
What are the different parts of taxonomy?
Life
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Why must meaningful comparison between bacteria be done at the genus level?
Bacterial comparison at the phylum level is a higher level than grouping all mammals together
What impact does diet have on bacteria?
Impacts diversity
What does OTU stand for?
Operational taxonomic unit
What does a higher number of OTUs mean?
Higher diversity
How are the vast majority of bacteria in the GI tract beneficial for health?
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
What are some functions of gut microbiota?
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
How does the gut microbiota provide defence against pathogens?
Competition
Barrier function
pH inhibition
What host secretions do the gut microbiota modify?
Mucin
Bile
Gut receptors
Why is junk food bad although it contains lots of energy (calories)?
Does not feed out gut microbes, that grow on fibres
What kinds of food is fibre found in?
Fruit
Vegetables
Pulses
Whole grains
Where are the products created by bacteria that are derived from fibres absorbed?
Large intestine
As well as fibre, what else can GIT microbes use for growth?
Endogenous (host-derived) substrates
What are benefits of including dietary fibre in our diet?
Improves faecal bulking, eases passage, results in a shorter transit time
Contains important phytochemicals, anti-oxidants and vitamins
Bacterial fermentation
How does bacterial fermentation impact pH?
Maintains slightly acidic pH
What are the benefits of bacterial fermentation?
Releases additional phytochemicals
Maintains slightly acidic pH that improves resistance to pathogens
Essential supply of short chain fatty acids
What are the 3 main fatty acids provided by bacterial fermentation?
Butyrate
Propionate
Acetate
(1:1:1 ratio)
What are the functions of butyrate?
Epithelial cell growth and regeneration
What are the functions of propionate?
Gluconeogenesis in the liver
Satiety signalling
What are the functions of acetate?
Transported in the blood to peripheral tissues
Lipogenesis
How does the colon change in regards to bacterial fermentation?
Proximal is carbohydrate rich, pH midly acidic and transover rapid
Distal has little fermentable carbohydrates, pH neutral and turnover slow
How does bile acid concentration change along the bowel?
Increases going proximal to distal
How much carbohydrates are metabolised by bacteria per day?
About 40g/day
How much protein is metabolised by bacteria per day?
12-18g/day
What are important gut microbial activities driven by?
What we eat
What are the functional importance of firmicutes?
Butyrate production
Polysaccharide utlisation
Propionate production
What is the functional importance of aminomycetes?
Utilise prebiotics
Lactate production
What is an example of an actinomycete?
Bifidobacteria
How does the GI microbiota provide have a barrier effect for defence?
Large number of the indigenous microbiota prevent colonisation by ingesting pathogens and inhibit overgrowth of potentially pathogenic bacteria normally resident at low levels
How does the GI microbiota provide active competitive exclusion for defence?
Conferred by both microbe-microbe and microbe-host interactions
How does the GI microbiota protect against pathogens due to pH inhibitions?
Generally pathogens grow opimally at pHs over 7
Is the pH greater in the proximal or distal colon?
Distal
What forms a barrier between the luminal bacterial population and the epithelial cells to keep the gut health?
Mucus layer
What are the different layers of bacteria after the mucus layer?
Inner layer and outer layer
What happens when the mucus bacterial of the colon disrupted?
Bacterial cells penetrate the mucus layer and the epithelial barrier
What is the largest lymphoid organ in the body?
Gut
What must be gut be able to do due to being in constant interaction with the environment?
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
Why do autoimmune diseases occur in relation to the gut?
Immune system can no longer distinguish between harmful pathogens and commensal bacteria
What does imbalance between the gut microbiota composition lead to?
Disrupting homeostasis causing inflammation
What are the 2 possible effects that gut bacteria can have on inflammation?
Some are pro-inflammatory and some are anti-inflammatory
What are important signalling molecules that gut microbiota produce?
Short chain fatty acids
What impact do short chain fatty acids from bacteria have on the gut epithelial cells?
Secretes gut hormones
What receptors on the gut epithelium detects short chain fatty acids from bacteria?
GRP43/FFAR2
GPR/FFAR3
GPR109A
What does SCFA stand for?
Short chain fatty acid
What are GPR43/FFAR2 receptors activated by?
Acetate
Propionate > butyrate
What does activation of GPR43/FFAR2 receptors cause?
GLP-1 secretions (inhibits fat accumulation)
What does GLP-1 do?
Inhibits fat secretions
What does activation of GPR/FFAR3 receptors do?
Results in PYY secretion (improves insulin resistance and satiety signalling to brain)
What activates GPR/FFAR3 receptors?
Propionate and butyrate
What does PYY do?
Improves insulin resistance and satiety signalling to brain
What activates GPR109A receptors?
Butyrate
What does activation of GPR109A receptors cause?
Suppreses colonic inflammation and carcinomogenesis (anti-inflammatory cytokines such as IL-10)
What happens to microbial metabolites that are not utilised by gut epithelial cells?
Absorbed into the bloodstream and transported around the body
What can be said about microbial composition throughout life?
It changes throughout life
What are some different factors that influence the microbiota throughout life?
Anatomy is the same, food is different
Dietary changes cause the greatest influence
Our food is out microbiotas food
