The microbiota of the GI tract

Question 1

As you move down the gut tube what changes are there in regards to bacteria/environment? (3)

Answer 1

Increasingly anaerobic conditions

Increasing bacterial density

Increasing dominance of obligate anaerobes

Question 2

What are Facultative anaerobic bacteria

Answer 2

Can grow in the presence of oxygen AND in the absence of oxygen

Question 3

Obligate anaerobe

Answer 3

Cannot grow in the presence of oxygen – many rapidly killed in the presence of any oxygen

Question 4

What can impact the activities of microbes/ what directly affects the composition of the gut microbiota?

Answer 4

our diet

Question 5

Function of GI tract microbiota (5)

Answer 5

Modification of host secretions (mucin, bile, gut receptors)

Defence against pathogens - competition

Barrier function

pH inhibition

Development of immune system - immune priming host signalling - gut-brain axis production of essential metabolites too maintain health

Question 6

Why is a high fibre diet good for us? (4)

Answer 6

GIT microbes grow on the fibre we eat in foods like fruit, vegetables, pulses and whole grains, and convert it into thousands of different products

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

Contains important phytochemicals, anti-oxidants and vitamins

Bacterial fermentation:

➢Releases additional phytochemicals

➢Maintains slightly acidic pH

➢Increased commensal bacterial population and pH improves resistance to pathogens

➢Essential supply of short chain fatty acids

Question 7

Where does 70% of energy uptake occur

Answer 7

stomach

Question 8

What are the three main Short Chain Fatty Acids called? what’s the ratio between them?

Answer 8

Butyrate

Propionate

Acetate

In order ^ top to bottom 1:1:3

Question 9

Function of Butyrate

Answer 9

Epithelial cell growth and regeneration

Question 10

Function of Propionate

Answer 10

Gluconeogenesis satiety signalling

Question 11

Function of Acetate

Answer 11

transported in blood to peripheral tissues lipogenesis

Question 12

What mechanisms make microbiota have colonisation resistance (2)

Answer 12

Barrier effect The large numbers of the indigenous microbiota prevent colonisation by ingested pathogens AND inhibit overgrowth of potentially pathogenic bacteria normally resident at low levels Active competitive exclusion conferred by both microbe-microbe and microbe-host interactions

Question 13

In which part of the colon is there:- more disease higher pH slower transit high exposure to harmful compounds low fermentation routes

Answer 13

distal colon

Question 14

What happens when the mucus layer barrier is disrupted?

Answer 14

bacterial cells penetrate the mucus layer and the epithelial barrier

Question 15

Homeostasis between what maintains good health?

Answer 15

between the gut microbiota and the host immune system

Question 16

What are some key receptors on the gut epithelial cells that detect SCFA (subset of fatty acids that are produced by the gut microbiota) and secrete gut hormones? What activates these and what is the outcome? (3)

Answer 16

GPR43/FFAR2 – results in GLP-1 secretion (inhibits fat accumulation) GPR/FFAR3 - activated by propionate and butyrate, results in PYY secretion (improves insulin resistance and satiety signalling to brain) GPR109A - activated by butyrate suppresses colonic inflammation and carcinogenesis (anti-inflammatory cytokines eg. IL-10)