ileum lamina propria

The ileum lamina propria is the connective tissue layer that forms part of the ileal mucosa, lying between the intestinal epithelium above and the muscularis mucosae below. It is a component of the ileum, the final and longest segment of the small intestine.

The lamina propria of the ileum contains blood capillaries, lymphatic lacteals, fibroblasts, smooth muscle cells, and an abundance of immune cells including lymphocytes, plasma cells, macrophages, dendritic cells, and eosinophils. The ileum lamina propria is particularly rich in immune structures due to the presence of Peyer's patches, which are large lymphoid aggregates that are concentrated here.

Peyer's patches are organized lymphoid follicles located predominantly in the distal ileum. They extend through the lamina propria and into the submucosa and are covered by a specialized follicle-associated epithelium containing M cells. Peyer's patches are central to intestinal immune surveillance, sampling luminal antigens to generate secretory IgA responses that protect against pathogens.

The ileum lamina propria supports nutrient absorption by housing the central lymphatic lacteals that absorb dietary fats in the form of chylomicrons from the overlying enterocytes. The lamina propria also contains the capillary network that absorbs amino acids and monosaccharides transported from intestinal epithelial cells, delivering them into the portal circulation.

In Crohn's disease, the ileum lamina propria is a common site of chronic inflammation. Histologically, transmural inflammatory infiltrates, lymphoid aggregates, and granulomas are seen extending through the lamina propria and beyond. In ulcerative colitis, lamina propria inflammation with crypt distortion is prominent throughout the colon but spares the ileum except in backwash ileitis.