Gastrointestinal Tract

Gastrointestinal Tract Components

  • Overview of the main components of the gastrointestinal tract.
    • Salivary Glands
    • Parotid
    • Sublingual
    • Submandibular
    • Oral Cavity
    • Tongue
    • Pharynx
    • Esophagus
    • Stomach
    • Liver
    • Gallbladder
    • Common Bile Duct
    • Pancreas
    • Pancreatic Duct
    • Duodenum
    • Jejunum (small intestine)
    • Ileum (small intestine)
    • Colon
    • Transverse
    • Ascending
    • Descending
    • Cecum
    • Appendix
    • Rectum
    • Anus

Accessory Organs

  • Overview of the accessory organs of the gastrointestinal tract.
    • Oral cavity
    • Salivary glands
      • Parotid
      • Sublingual
      • Submandibular
    • Tongue
    • Liver
    • Gallbladder
    • Common bile duct
    • Pancreas
    • Pancreatic duct

Digestive Tract Layers

  • The digestive tract generally consists of four layers:
    • Mucosa
    • Epithelium
    • Lamina propria
    • Muscularis mucosae
    • Submucosa
    • Gland in submucosa
    • Submucosal plexus (Meissner's plexus)
    • Vein & artery
    • Muscularis externa
    • Circular muscle
    • Longitudinal muscle
    • Myenteric plexus (Auerbach's plexus)
    • Serosa
    • Mesentery
    • Duct of gland outside tract

Features of Digestive Tract Layers

  • Mucosa
    • 3 sublayers: epithelial tissue, lamina propria, muscularis mucosae
  • Submucosa
    • Contains nerves, circulatory and lymphatics
  • Muscularis Externa
    • Mostly muscle tissue
    • Contains myenteric plexus (nerves)
    • MOTILITY
  • Serosa
    • Contiguous with mesenteries
    • Contains blood vessels, nerves, lymphatics
    • CONNECTIONS
    • SECRETIONS
    • Also regulates secretion

Regional Specializations

  • Regional specializations within the GI tract.
    • Esophagus
    • Esophageal submucosal gland
    • Stomach
    • Pits
    • Rugae
    • Gastric gland
    • Duodenum
    • Brunner's gland
    • Liver and pancreatic secretions
    • Jejunum
    • Villi
    • Ileum
    • Peyer's patch
    • Colon
    • Submucosal plexus (Meissner's plexus)
    • Myenteric plexus (Auerbach's plexus)

Motility

  • Motility is a major digestive process.
    • Peristalsis
    • Coordinated muscle contraction and relaxation
    • Wavelike movements
    • Bolus moves forward
    • Segmentation
    • Simultaneous muscle contractions
    • Back and forth movements
    • Bolus gets mixed with digestive secretions

Gastric Pits

  • Gastric pits are openings for secretions into the stomach
    • Surface epithelium
    • Parietal cell
    • Chief cell
    • G cell (gastrin)
    • D cell (somatostatin)
    • Enterochromaffin cell
    • Oblique layer
    • Circular layer
    • Longitudinal layer
    • Mucosa
    • Lamina propria
    • Muscularis mucosae
    • Submucosa
    • Muscularis externa
    • Serosa

Regulation of Stomach Secretion

  • Regulation of stomach secretion by the CNS.
    • Cephalic Phase
    • Sight and thought of food
    • Taste and smell of food
    • Cerebral cortex
    • Loss of appetite, depression
    • Hypothalamus and medulla
    • Vagus nerve (parasympathetic neurons)
    • Sympathetic neurons
    • Stomach acid secretion
    • Gastric Phase
    • Stomach distension
    • Vagovagal reflex
    • Medulla
    • Peptides, caffeine, rising pH in stomach
    • Local reflexes
    • Gastrin
    • Histamine
    • Vagus nerve (parasympathetic neurons)
    • Sympathetic neurons
    • Stomach G cell
    • Stomach neuroendocrine cell
    • Emotional upset
    • Excessive stomach acid
    • Intestinal Phase
    • Peptides and amino acids in duodenum
    • Intestinal Phase
    • Medulla
    • Vagus nerve (parasympathetic neurons) → Gastrin
    • Enterogastric reflex
    • Distension, fats, high osmolarity, and irritants in duodenum
    • Secretin, GIP, CCK & VIP
    • Stomach acid secretion
    • Stomach G cell
    • Stomach neuroendocrine cell