Lymph pathways associated with Peyer's patches in sheep.

Lymphatic drainage of the ileum associated with Peyer's patches begins with lymph entering a single lacteal of the villus, probably through intercellular flaps, which prevent retrograde flow to the interstitium. These lacteals are continuous with an interconnecting plexus of branching sinuses which surrounds the crypts and follicle domes in the lamina propria. Small vessels emanating from this plexus penetrate the muscularis mucosa, where lymph can either flow within septal vessels to the deep submucosa, or enter the follicular sinuses to move freely around follicles, and through gaps in septal walls. All lymph enters a deep submucosal network where retrograde flow is prevented by valves. Lymph is then conveyed through vessels passing between the fibres of the muscularis externa to other lymphatics, which transport lymph from the ileal surface to the mesenteric nodes.