Interactions of Gut Microbiota, Endotoxemia, Immune Function, and Diet in Exertional Heatstroke

Table 2

Human intestinal microbiota: phyla, metabolism, and potential biological functions.

Intestinal segment	Predominant bacterial	Bacterial metabolism		Potential biological functions of bacteria metabolites
		Biochemical	Metabolic intermediates &
Small intestine	Firmicutes; Bacteroidetes; Actinobacteria	Resistant starches, dietary fiber (cellulose, pectin, inulin), carbohydrates, amino acids, lipids, triglycerides, carboxylic acids, creatine, pancreatic/gastrointestinal secretions, and mucus.	Complex carbohydrates, amino acids, lactic acid, ethanol, succinic acid, and formate produce short-chain fatty acids (SCFA; acetate, propionate, butyrate), branched-chain fatty acids (BCFA), CO2, H2, NH3, H2S, amines, phenols, biotin, and vitamins K, B1, B2, B6, B12.	Absorb fats and lipid-soluble vitamins, stimulate systemic hormones to regulate lipid and glucose homeostasis, energy regulation, modulate pro- and anti-inflammatory genes, strengthen epithelial permeability, regulate colon pH, inhibit pathogen growth, provide energy to luminal epithelium.
Large intestine	Bacteroidetes, Firmicutes, Proteobacteria

Notes. Inter-individual differences are great; composition of substrates, intermediates and products change along the course of the intestinal tract; the outer membrane of Proteobacteria is composed mostly of LPS; most SCFA exist in higher concentrations in the proximal (versus distal) colon; phyla differ markedly in proximal versus distal colon, in part due to differences in oxygen tension. Abbreviations: IM, intestinal microbiota; LPS, lipopolysaccharide. Sources: [135, 152, 154, 253, 319, 323–327].