digestive

• Digestive System


  • Oral Cavity
  • Lip
  • Gingiva (gum)
  • Teeth
  • Hard palate
  • Soft palate
  • Retromolar trigone
  • Tongue
  • Uvula
  • Tonsil
  • Buccal mucosa
  • Floor of mouth
• Lips


  • Central core of striated or skeletal muscle
  • Embedded in elastic fibroconnective tissue
  • Skeletal muscle: Orbicularis Oris
  • Externally covered by skin, hair follicles, sebaceous glands, sweat glands
• Vestibule


  Space between the lips and cheeks and outer aspect of the gums and teeth
• Gingiva


  • Thick Stratified Squamous Epithelium
  • Dense Connective Tissue
  • Fixed to the bone
  • Covers hard palate
  • Greater thickness
  • Firmer attachment
  • Greater degree of keratinization
  • More resistant to attrition when chewing
• Mucus Membrane


  • Non-Keratinized: Floor of the Mouth, Lower surface of the tongue, Inside the lips, Cheeks
  • Keratinized: Hard Palate, Gingiva, Dorsal surface of the tongue, Tonsils, Soft Palate
• Layers of the Mucous Membrane

  • Stratum basale
  • Stratum spinosum
  • Stratum granulosum
  • Stratum corneum
• Tongue


  • Stratified Squamous Epithelium
  • Consists of interlacing bundles of striated muscle
  • Oriented vertically, horizontally, longitudinally, and intersecting at right angles
  • Undersurface: Non keratinized
  • Dorsal portion: Covered by relatively thick epithelium, Firmly bound to connective tissue, Keratinized or incomplete keratinized, Covered by lingual papillae
• Taste Buds


  • 3,000 in the human tongue
  • Pale ovoid bodies, 50-80 um x 30-50 um
  • Consists of 50 to 90 fusiform cells, Wider at the base than the apex
  • Have sensory nerve fibers
• Salivary Glands


  • Minor Glands: Small aggregates of salivary gland, Short branching tubules lined with mucous cells
  • Major Glands: Parotid Gland, Submandibular Gland, Sublingual Gland
• Salivary Glands


  • Usually in pairs
  • Situated at some distance from oral epithelium
  • Acini: Mucous cells, Serous cells, Seromucous acini
• Mucous Acini


  • Lumen is larger than serous acini
  • Single layer of plump pyramidal cells
  • Cytoplasm filled with mucigen (antecedent or mucus)
• Serous Acini


  • Smaller lumen than mucous acini
  • Columnar, pyramidal form
  • Cytoplasm crowded with secretory granules
  • Produce watery secretions containing most salivary proteins
• Layers of the Small Intestine

  • Mucosa
  • Submucosa
  • Muscularis Externa
  • Serosa
• Duodenum


  • First portion and the shortest segment of the small intestine
  • 25 cm long
  • Lined with simple columnar epithelium
  • Firmly fixed to the dorsal wall of the abdomen
  • Fixed, largely retroperitoneal
• Jejunum


  • Greater bulk of absorption takes place
  • Freely moveable
  • Leaf-like
  • Suspended by the mesentery from the dorsal wall of the cavity
  • Occupies 2/5 of the length of the small intestine
• Duodenum


  • C-shaped around the head of the pancreas
  • Continuous at its distal end with the jejunum
  • Receives bile from the liver and digestive juices from the pancreas via the common bile duct and pancreatic duct
• Ileum


  • Occupies the lower 3/5 portion without distinct boundaries
  • Villi are even more leaf-like
  • Peyer's patches are located in the submucosa
• Functions of the Small Intestine

  • Absorption of nutrients
  • Neutralization of acidic chyme for stomach with alkaline buffers from pancreas and bile from liver
  • Digestion of enzmatic and biliary digestion of fats, CHO, and CHON
  • Immune surveillance (GALT: Gut-Associated Lymphoid Tissue)
  • Endocrine and Exocrine function largely restricted to digestion
• Appendix


  • Tonsil of the gut
  • Arises from the blind end of the cecum
  • Thickened by extensive accumulation of lymphoid tissue
• Cecum


  • Villi are absent
  • Allows easy movement of large amounts of dry material
  • Functions: Reabsorb water, Compact fecal material, Contains Glands of Lieberkuhn
• Cecum and Colon


  • Lacks lymphatics
  • Scattered lymphoid nodules always present
  • Mucosa has a smooth surface with epithelium constantly being renewed (extrusion zones)
  • Life span of cells: 6 days
  • Lamina propria is similar to that of the small intestine
• Rectum


  • Terminal portion of the intestinal tract
  • 12 cm in length
  • Extends from the sigmoid colon to the pelvic diaphragm
  • Rectal ampulla: slightly dilated at the lower portion
  • Mucosa similar to the colon except for longer cryptes
• Anal Canal


  • 4 cm in length
  • Internal Anal Sphincter: thickened circular layers of smooth muscle
  • External anal sphincter: distal to the anal sphinchter; circumferential annulus of striated muscles