Microbiota of the GI tract Flashcards
(46 cards)
how does trinity time change along the GI tract
increases: mouth - 1 min oesphagus - 4-8 secs stomach - 2-4 hr small intestine - 3-5 hr colon/large intestine - 10 hr to severla days
what does transit time effect
Bacterial populations due to different bacterial growth rates
Intestinal cell exposure to toxins
- Consumed with food or produced by bacteria
what happens to bacterial populations as you travel along the GI tract from mouth to rectum
increasingly anaerobic (due to anaerobic conditions)
increasing bacterial density (stomach = 10(3)-10(4)/ml)
(small intestine = 10(8)/ml)
(colon/large intestine = 10(10)-10(11)ml)
increasing dominance of obligate anaerobes
define anaerobic
living in the absence of air
define aerobic
living in the presence of air
define facultative anaerobic bacteria
can go in the presence of oxygen AND in the absence of oxygen
(although some may prow poorly)
define obligate anaerobic bacteria
cannot grow in the presence of oxygen - many rapidly killed in the presence of oxygen (i.e. would therefore not be found in the mouth)
give some factors that can affect what bacteria is dominant at different points in the GIT
oxygen concentration
different pH
different transit time
eg stomach - pH1.5-4 and mixed O2 = facultative anaerobes
eg colon - pH 5.5-6.5 and no O2 = obligate anaerobes
at what level of classification are meaningful comparisons done between bacteria types
at the genus level
what are some of the functions of GIT microbiota
metabolism of dietary components
production of essential metabolites to maintain health
development of immune system - immune priming
host signalling - gut-brain axis
defence against pathogens - competition, barrier function, pH inhibition
modifications of host secretions (mucin, bile, gut receptors, etc)
what components of our diet do GIT microbes grow on
fibre from fruit, vegetables, pulses, whole grains - microbes convert it into thousands of different products
can also use endogenous (host derived) substrates for growth
what are the benefits of having fibre in your diet
health protection - improves faecal bulking, eases passage, results in shorter transit times
contains important phytochemicals, antioxidants and vitamins
bacterial fermentation
what does bacterial fermentation of fibre result in
Releases additional phytochemicals
Maintains slightly acidic pH
Increased commensal bacterial population and pH improves resistance to pathogens
Essential supply of short chain fatty acids
converts non-ingestible carbohydrates and residual proteins into short/branched chain fatty acids, gases, phytochemical, minerals, other metabolites
what are the three main short chain fatty acids and what are their functions
ratio 1:1:3 (depends in substrate availability AND bacterial composition)
butyrate - epithelial cell growth and regeneration
propionate - gluconeogenesis in the liver and satiety signalling
acetate - transported in blood to peripheral tissues for lipogenesis
what are the major products of carbohydrate metabolism by the GIT microbiota
- short chain fatty acids - acetate, propionate, butyrate
2. gases - CO2, H2, CH4
what are the major products of protein metabolism by the GIT microbiota
- branched short chain fatty acids - iso-butyrate, isovalerate
- gases - NH3, H2S
- phenols, indoles, amines
different bacteria produce different metabolites - give some examples
firmicutes - polysaccharide utilisation = butyrate production
actinomycetes - utilise prebiotics = lactate production
how does the GIT bacteria defend against pathogens
- colonisation resistance
- pH inhibition
- gut mucosal immune system
what are the 2 methods of colonisation resistance and describe briefly how they work
- barrier effect - uses mucous layers and large number of indigenous bacteria prevent colonisation by ingested proteins AND inhibit overgrowth of potentially pathogenic bacteria normally resident at low levels
- active competition exclusion - conferred by both microbe-microbe and microbe-host interactions
how does the mucous layer help keep the gut healthy
2 mucous layers - outer and inner
outer - contains bacteria, barrier affect
inner - normally only few bacteria, prevents bacterial penetration
forms barrier between luminal bacterial populations and epithelial cells
commensal bacteria close to epithelium block and prevent adhesion/colonisation by pathogens
the few bacterial cells that penetrate through the epithelium are dealt with by the immune system
what can happen if the mucus layer barrier is disrupted
bacterial cells penetrate the mucus layer and the epithelial barrier - causes a dysregulated immune response and inflammation
at what pH do pathogens generally go best at
pH >6
where is more likely to get disease from pathogens - the proximal or distal colon
distal colon more prone to disease that proximal colon
why is the distal colon more prone to disease from pathogens
- high pH so less pathogen exclusion
- more protein fermentation - slower transit therefore higher exposure to harmful compounds
