Lymphatic pathways and role of valves in lymph propulsion from small intestine

The pathways through which lymph is propelled from the mucosal, submucosal, and muscle layer lymphatics of the small intestine, the interconnections between these layers, and the location of lymphatic valves within these layers were studied. Injections of fluid into a single lacteal or submucosal lymphatic of rats, rabbits, dogs, and cats spread in all directions through the submucosal lymphatics and into laceteals but did not enter the lymphatics of the muscle layer. Injections into muscle layer lymphatics also spread in all directions but in no case entered the submucosal lymphatics. The submucosal and muscle layer lymphatics join within the bowel wall near the mesenteric border to form collecting lymphatics characterized by valves and spontaneous contractions. These data indicate that lymphatics of the mucosa and submucosa form a syncytium independent of the muscle layer lymphatics and that few if any valves exist within these lymphatic networks. Cycling lacteal pressures were measured when intestinal motility was present but not when motility was abolished, suggesting that intestinal motility might have a role in lymph propulsion.