Ileum
This cross section through the ileum shows less dramatic plicae circularis compared to the jejunum. The villi remain quite prominent, but are shorter than those in the previous portions of the tract. The submucosal layer contains Peyer’s patches, diffuse lymphoid tissue that play an important immunological role in sampling the contents of the tract. Peyer’s patches are unique to the ileum. The muscularis externa is visible most externally.

Jejunum
This cross section through the jejunum shows very prominent plicae circulares lined by numerous villi. Plicae circulares are more extensive in the jejunum compared to the duodenum and ileum. Plicae circulares are out foldings of both the mucosa and submucosa. Projecting from these folds are numerous villi that are outfoldings of the mucosa. Note that while the submucosa and mucosa extend into the plicae circulares, the muscularis externa does not.

Gastric Glands
Gastric glands are structured as a gastric pit that opens into the lumen, followed by an isthmus, neck, and base. The mucosal layer appears here with its columnar epithelial cells, narrow lamina propria, and pink-staining muscularis mucosa