Digestive System Overview

  • Tongue Epithelium: Comprises stratified squamous epithelium (keratinized in some areas).

  • Papillae Types:

    • Filiform: Most numerous, thread-like, no taste buds. Provides rough surface.
    • Fungiform: Mushroom-shaped, found on anterior tongue, contains taste buds.
    • Foliate: Leaf-like, located on sides, has taste buds.
    • Circumvallate: Large, round, at back, surrounded by trench, contains taste buds.

  • Taste Buds: Located in fungiform and circumvallate papillae; oval shape with central pore.

  • Muscle Layer: Contains skeletal muscle fibers; striated for movement.

  • Connective Tissue: Lamina propria beneath epithelium with blood vessels/nerves; collagen/elastic fibers present.

  • Esophagus:

    • Epithelium: Lined with non-keratinized stratified squamous epithelium (mucosa).
    • Lamina Propria: Less cellular than stomach/intestine, effective barrier.
    • Submucosa: Dense connective tissue with blood/lymphatic vessels; esophageal glands.
    • Muscularis: Thicker longitudinal muscle; mixed skeletal/smooth muscle layers in middle.
    • Adventitia: Outer connective tissue layer anchoring to surrounding tissues.

  • Stomach:

    • Epithelium: Simple columnar with goblet cells secreting mucus.
    • Gastric Glands: Found in various regions (cardiac, fundic, pyloric), secrets gastric juices.
    • Cell Types: Parietal (HCl), Chief (pepsinogen), Enteroendocrine (hormones).
    • Muscularis Externa: Three smooth muscle layers (inner oblique, middle circular, outer longitudinal).
    • Serosa: Visceral peritoneum covering outer stomach surface.

  • Small Intestine:

    • Sections: Duodenum (initial digestion), Jejunum (nutrient absorption), Ileum (absorbs bile acids/B12).
    • Epithelium: Columnar cells with villi for absorption; rich in goblet cells.
    • Crypts of Lieberkühn: Glands with various cell types (absorptive, goblet, Paneth).
    • Muscularis Externa: Inner circular/outer longitudinal layers for peristalsis.
    • Serosa: Covers outer surface.

  • Colon:

    • Epithelium: Lined with columnar cells; contains crypts of Lieberkühn.
    • Lamina Propria: Connective tissue for nutrient absorption/support.
    • Muscularis Externa: Similar structure to small intestine, includes taeniae coli for contraction.

  • Anal Canal:

    • Epithelium: Transitions from columnar to keratinized stratified squamous.
    • Sphincters: Internal (involuntary smooth muscle) and external (voluntary skeletal muscle) for defecation control.