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