Lecture 5 Flashcards
How does the GI tract control the ability of the bacteria which make up the microbiota to access food?
There is a separation of the human and bacterial digestive processes via the one way ileocecal valve which separates the large intestine from the rest of the GI tract
The pH of the two environments is different with the large intestine kept lower to allow bacterial growth while the rest of the digestive tract is kept acidic preventing most bacterial species from growing
Why is it important to seperate the human and bacterial digestive processes?
This allows the human digestive system to have ‘first shot’ at the food ensuring that they get most of the nutrients otherwise the bacteria would starve the human withe their more efficient nutrient uptake due to their surface/volume ratio
What are the factors that prevent bacterial growth in the mouth?
host enzymes such as lipase and amylase in saliva
What are the factors that prevent bacterial growth in the stomach and small intestine?
Low pH
rapid lumenal flow
immunoglobulin A (antibody) triggers bacterial agglutination in mucus
other antimicrobial compounds (e.g. bile salts)
What is the difference between the microbiota and the microbiome?
The microbiota is the collective microbial community inhabiting a specific environment while the microbiome is the colective geentic content of a microbiota
what is an autochthonous bacteria?
endogenously derived and common to a
majority of hosts; form stable populations over long periods
What is a allochthonous bacteria?
derived from outside sources, not found in the
majority of hosts; likely to contribute little to the ecosystem
Why is the large intestine a more hospitable region for bacteria to grow?
less acidic
larger volume / slower peristalsis leading to a longer retention time
lower concentration of bile salts
more permissive immune system
What are the 5 main bacterial phyla in the lower intestine?
Firmicutes and Bacteroidetes are the two largest but there is also Actinobacteria, Verrucomicrobia, Proteobacteria
What do the bacteria do in the lower digestive tract?
They digest the dietary compounds that escape digestion in the small intestine fermenting them to short chain fatty acids
What are the main functions of gut microbes?
They break down dietary compounds into a form that is usable by the host
They aid in pathogen resistence by filling all the available ecological niches with symbionts and commensals
They stimulate and educate the immune system to recognise and respond to later bacterial invasion
How stable is the gut microbiome?
16S rRNA gene sequencing studies have revealed considerable inter-person variation in the composition of the gut microbiota however function appears to be conserved
What factors may have influenced the common makeup of microbiota throughout history?
Cooking which allowed access to a wider range of foods and introduced new toxins
Widespread use of antibiotics
the modern western diet which is low in complex sugars and hig in in simple fats and sugars leading to the reduction in the levels of Bacteroidetes
What is dysbiosis?
a condition in which the normal microbial
community structure is disturbed, often through external pressures such as disease states or medications
What are probiotics?
living microbes thought to confer a benefit to the
host
