DUODENUM
The duodenum has characteristic long villi mimicking leaf shapes. The Crypts of Lieberkuhn are present which extend down towards the muscularis mucosae.

A unique feature and key ID are the Brunner’s Glands found in the submucosa (the whitish coloured branched tubular glands) just above the connective tissue layer. When distinguishing from the Jejunum, use the shapes of the villi and presence of Brunner’s glands to guide you.

ESOPHAGUS
This is the cross section of the esophagus. In a relaxed state, the esophagus is deeply folded and becomes extended when food is present. The lumen is lined by stratified squamous epithelium.

It is hard to tell what section of the esophagus this is from, try looking at the following picture for a better muscularis externa.

COLON
The colon has the typical histological structure as the digestive tube: mucosa, submucosa, muscularis and serosa/adventitia. The mucosa is lined by simple columnar epithelium (lamina epithelialis) with long microvilli. It is covered by a layer of mucus which aids the transport of the feces.

In the mucosa, goblet cells dominate secreting mucous for faecal lubrication. You can see the closely packed tubular glands which create crypts that sit on the muscularis mucosae. Although not visible here, lymphoid aggregates are also found in the colon, however, they are smaller than the Peyer’s Patches found in the ileum.