Fig. 1

Schematic of gut oxygen gradient. The intestine faces daily fluctuations in blood flow and a steep oxygen gradient is present, extending from the highly vascularized and oxygenated subepithelial mucosa (4–8 %), across the epithelial and mucous layer (2–4 %), and into the severely oxygen-deficient lumen (<2 %). Arterial blood oxygen content is approximated as 80–100 % while venal blood oxygen content is approximated as 20 % [1, 4, 5]