Table 9.

Intraluminal physicochemical composition of GI tract.^a) LOD: Limit of Detection.

Location		PH		Dietary nutrients						O2	Gut microbial load [mL]	Electrolyte								Transit [mM]time
				Carbohydrate [mg mL−1]		Protein [mg mL−1]		Lipid (triglyceride) [mm]		PO2 [mmHg]		Osmolality [mOsm kg−1]		Buffer capacity [mmol L−1 pH]		Na+ [mM]	K+ [mM]	Cl− [mM]	HCO3− [mM]
		Fasted	Fed	Fasted	Fed	Fasted	Fed	Fasted	Fed			Fasted	Fed	Fasted	Fed
Esophagus		7[389]	7[389]	–	–	–	–	–	–	150[390]	–	–	–	–	–	40[391]	20[391]	40[391]	0[391]	Few minutes
Stomach		1.4–2.1[235]	3.0–7.0[235]	–	49.1–152.1[392]		11.2–23.3[392]	–	42.7–157.1[393]	77[394]	102–3[395]	83–278[392,396,397]	32–600[398]	4.8–23.8[392,397]	14–28[392]	60[399]	10[399]	90[399]	0[399]	Few minutes–3 hrs[400]
	Duodenum	6.2[235]	5.2[235]	–	62.7–74.3[393]	1.1–2.8[393]	2.9–15.1[393]	1.16–4.7[393]	0.6–63.3[393]	32[394]	105[395]	115–206[398]	215–423[398]	5.7–11.5[398]	20–30[398]	120[399]	15[399]	120[399]	30[399]	3–6 hrs[400]
Small intestine	Jejunum	6.9[235]	6.1[235]	–	62.7–74.3[393]	1.1–2.8[393]	2.9–15.1[393]	1.16–4.7[393]	0.6–63.3[393]	30–45[394]	105[395]	115–206[398]	215–423[398]	5.7–11.5[398]	20–30[398]	120[399]	15[399]	120[399]	30[399]	3–6 hrs[400]
	ileum	8.1[398]	8.1[398]	0.56–2.54[392]	7.4–18.0[392]	1.8–8.4[392]	2.65–4.13[392]	<LOD[392,401]	<LOD[392,401]	33[394]	103–7[395]	60[398]	252[398]	5–10[398]	10–20[398]	120[399]	15[399]	120[399]	30[399]	3–6 hrs[400]
Large intestine	Proximal	7.8[398]	6[398]	0.5–16.7[392,401]	2.8–21.4[392,401]	5.1–14.3[392,401]	3.0–9.4[392,401]	<LOD[392,401]	<LOD[392,401]	11[394]	109–12[395]	100[398]	200[398]	10–20[398]	20–35[398]	120[391]	15[391]	90[391]	50[391]	10–40 hrs[400]
	Distal colon	6.3–7.7[402]	6.3–7.7[402]	–	–	–	–	–		3[394]	109–12[395]	–	–	–	–	–	–	–	–	–