Lips - Three zones (outer skin, vermilion border, inner mucosa) with the vermilion's rich capillary papillae explaining the red color; labial salivary glands in submucosa.

Cheeks - Non-keratinized stratified squamous lining with buccal glands; buccinator as core muscle; parotid duct opening opposite upper 2nd molar.

Palate - Hard palate = keratinized masticatory mucosa fused to bone; soft palate = non-keratinized oral surface / respiratory epithelium on nasal surface; skeletal muscle core; taste buds possible.

Tongue - Unique triplanar interwoven skeletal muscle; 4 papilla types (filiform = keratinized, no taste buds; fungiform/foliate/circumvallate = non-keratinized, carry taste buds); von Ebner serous glands flush circumvallate trenches; lingual tonsil at base.

Teeth - Enamel (96% mineral, ameloblast-derived, irreversible); dentin (odontoblast processes in tubules, predentin precursor); cementum (acellular + cellular types); pulp (loose CT, odontoblasts lining, nerve supply).

Gums - Masticatory mucosa; mucoperiosteum adherent to bone; junctional epithelium attaches to enamel via hemidesmosomes.

Oropharynx - Non-keratinized SS; palatine tonsils with deep crypts + secondary follicles; Waldeyer's ring; skeletal muscle wall.

Tubular GI tract - Shared 4-layer plan (mucosa/submucosa/muscularis externa/serosa-adventitia) with regional specializations: esophagus = non-keratinized SS with submucosal mucous glands; stomach = simple columnar with oxyntic glands (parietal + chief cells); small intestine = villi + crypts + Paneth cells + Brunner glands (duodenum) + Peyer's patches (ileum); large intestine = no villi, long straight crypts, predominantly goblet cells, taeniae coli.

ENS - Two plexuses: Meissner (submucosa, controls secretion) and Auerbach (between muscle layers, controls peristalsis); IPANs, interneurons, motor neurons, enteric glia; 100-500 million neurons; semi-autonomous gut-brain.