Microbiota of the Gastrointestinal Tract Flashcards
What factors caused the variation of bacteria going down the GI tract
Transit time vs growth rate of bacteria
Different pH
Exposire to toxins
Different oxygen concentrations
Define obligate anerobes
bacteria that cannot grow in the presence of oxygen
Define facultative anaerobes
Bacteria grow in the presence or absence oxygen
Where does the vast majority of bacteria live
Large intestine
What is functions of the GIT Microbiota
Metabolism of dietary components
Production of essential metabolites to maintain health
Development of the immune system
host signalling
modifications of host secretions
Defence against pathogens
What do the gut microbes grow upon
The fibre that we eat
Where is the energy absorbed from the breakdown of dietary fibre by gut microbes
Large intestine
What else can GIT microbes use for growth
endogenous (host derved) substrates
What is the benefit of GIT bacteria breaking down dietary fibre
Improves faecal bulking, eases passage, results in shorter transit time
releases additional phytochemicals
Maintains slightly acidic pH
produces essential supply of short chain fatty acids
What are the three short chain fatty acids released
Butyrate
Propionate
Acetate
What is the function of butyrate
Epithelia cell growth and regeneration
What is the function of propionate
Glucogeness in the liver
satiety signalling
What is the fate and the function of acetate
Transported in the blood to peripheral tissue for lipogenesis
Where does majority of fermentation occur in the large intestine
The right side - Ascending colon
its carbohydrate rich
What is the varying pH of the large intestine
Ascending -Right side is slightly acidic
desending -Left side is pH neutral (has higher pH than ascending)
What has the greatest influence on gut bacterial growth and activity
diet and age
What does a diverse balanced diet give you
A diverse balanced microbiota
and a diverse balanced products
What is the ways bacterial defend you against pathogens
Barrier effect
Active competitive exclusion
produce active compounds that kill incoming pathogen s
How does active competitive exclusion work in defence of pathogens
large number
Commensal bacteria close to epithelium
block and prevent adhesion/colonisation
by pathogens
How does the barrier effect work in defence against pathogens
The inner mucus layer forms barrier between the luminal bacterial poplation and the epithelial cells and prevents pathogen penetration
What happens if bacteria penetrate the epithelium
Normal immune response = homeostasis
What occurs if there is a dysregulated immune response
Inflammation
Why is there a higher risk of disease in the distal colon
Due to higher pH, so there is less pathogen fermentation
and its slower transit time mens there is a higher exposure to harmful compounds
Where is protein fermentation most likely to occur
distal colon (descending)
What is produced in protein fermentation
Branched short chain fatty acids
Gases - NH3 H2S
Phenols
indoles
Amines
What is produced in carbohydrate fermentation
Short chain fatty acids
Gases - CO2, H2, CH4
How does the immune system and the gut microbiota exist
In co-evoloution
As the microbiota shapes the development go the immune system, and the immune system shapes the gut microbiota - basically priming each other
What are Toll like receptors
Receptors that specifically recognise bacterial components in the innate immune system
That determine self from foreign pathogens
What is the major function f the short chain fatty acids produced in bacterial fermentation
Important signalling molecules
What is FFAR2 receptor activated by and what its result
activated by acetate, propionate > butyrate, results in GLP-1 secretion
(inhibits fat accumulation)
What is FFAR receptor activated against and what is the result
activated by propionate and butyrate, results in PYY secretion
(improves insulin resistance and satiety signalling to brain)
What is GPR109A receptor activated by and what is the result
- activated by butyrate
suppresses colonic inflammation and carcinogenesis
(anti-inflammatory cytokines eg. IL-10)
What occurs when the immune system can no longer distinguish between harmful detrimental pathogens and the commensal bacteria
Auto-Immune disease
What can dysbiosis (microbial imbalance) of gut microbiota lead to
can disrupt the homeostasis
and can lead to gut inflammation
