Eventually buildup of local metabolites near areas of active absorption will autoregulate flow to that specific area of the tract. This points to the local vs. general regulation of all processes associated with digestion-absorption. No apparent direct parasympathetic innervation of blood vessels in splanchnic circulation. Parasympathetic nerves can cause significant changes in metabolic activity of gut which then induce changes in blood flow. This arrangement is characteristic of countercurrent exchange systems.
Countercurrent exchange leads to gradients for specific molecules from base to villus tip.
Therefore O2 diffuses from artery to vein, arterial blood O2 content falls as blood approaches villus tip. Countercurrent loss of O2 is thought to be a factor contributing to the high sensitivity of villus cells to ischemic hypoxia. Prolonged ischemia will lead to cell death, sloughing of mucosa and if severe will produce perforation of bowel wall, shock and death. H2O moves from artery to vein along the osmolar gradient and consequently arterial osmolarity is increased as blood approaches villus tip.