This is a placeholder for a description of metabolites produced by bacteria.

SUMMARY Evidence for the occurrence of microbial breakdown of carbohydrate in the human
colon has been sought by measuring short chain fatty acid (SCFA) concentrations in the contents of
all regions of the large intestine and in portal, hepatic and peripheral venous blood obtained at
autopsy of sudden death victims within four hours of death. Total SCFA concentration (mmol/kg)
was low in the terminal ileum at 13±6 but high in all regions of the colon ranging from 131±9 in the
caecum to 80± 11 in the descending colon. The presence of branched chain fatty acids was also
noted. A significant trend from high to low concentrations was found on passing distally from
caecum to descending colon. pH also changed with region from 5-6±0-2 in the caecum to 6-6±0 1
in the descending colon. pH and SCFA concentrations were inversely related. Total SCFA
(~imol/l) in blood was, portal 375±70, hepatic 148±42 and peripheral 79±22. In all samples
acetate was the principal anion but molar ratios of the three principal SCFA changed on going from
colonic contents to portal blood to hepatic vein indicating greater uptake of butyrate by the colonic
epithelium and propionate by the liver. These data indicate that substantial carbohydrate, and
possibly protein, fermentation is occurring in the human large intestine, principally in the caecum
and ascending colon and that the large bowel may have a greater role to play in digestion than has
previously been ascribed to it. Cummings1987

Production of gases

Whilst the bacterial populations of the large bowel are
broadly similar, the rumen is predominantly methanogenic,
producing very little gaseous H, and containing few
sulphate-reducing bacteria (SRB). Cummings1991