Splanchnic circulation in animals
- The splanchnic circulation consists of three parts:
- The mesenteric bed, supplying the gastrointestinal tract;
- The splenic bed and
- The hepatic bed.
A unique feature of this circulatory system is that the combined outflow from the mesenteric and splenic constitutes the major portion of the inflow of the hepatic through the portal vein.
All of the splanchnic flow reaches the liver, 70 per cent arrives there via the portal vein from the stomach, intestine, spleen, and pancreas and the remaining 30 per cent comes via the hepatic artery. Together these fractions constitute the splanchnic flow, the hepatic blood flow, and the total through the hepatic veins.
- Three mechanisms operate to regulate blood flow at the local level.
- Enhanced metabolism of parenchymal cells of the villi which lowers tissue PO2 and increases vasodilator metabolites, relaxing arteriolar smooth muscle and precapillary sphincters to increase mucosal blood flow,
- Increased muscle activity metabolically produces active hyperemia of the muscularis mucosae and
- Intrinsic myogenic response to stretch autoregulates blood flow, when blood pressure fluctuates.