BHSC 205
Systems Anatomy & Physiology
The Digestive System
Basic Health Sciences (BHSC) Program
Academic Year 2024–2025
, 1. Overview
The digestive system processes food to provide nutrients for cellular metabolism. It
performs four main processes: ingestion, digestion, absorption, and defecation.
2. Anatomy of the GI Tract
2.1 Layers of the GI Wall (from lumen outward)
1. Mucosa: epithelial lining, lamina propria, muscularis mucosae
2. Submucosa: connective tissue; contains blood and lymph vessels, submucosal
plexus
3. Muscularis externa: inner circular and outer longitudinal smooth muscle;
myenteric plexus
4. Serosa (or adventitia): outer protective layer
2.2 The Oral Cavity
• Teeth: mastication (mechanical digestion)
• Tongue: taste; manipulates food; initiates swallowing
• Salivary glands: parotid, submandibular, sublingual
• Saliva: amylase begins starch digestion; lysozyme antibacterial; lubricates food
bolus
2.3 The Esophagus
• Muscular tube connecting pharynx to stomach
• Upper third: skeletal muscle; lower third: smooth muscle
• Peristalsis propels food bolus downward
• Lower esophageal sphincter (LES): prevents gastric reflux
2.4 The Stomach
• Regions: cardia, fundus, body, pylorus
• Rugae: folds allowing distension (~1 L capacity)
• Gastric glands contain: chief cells (pepsinogen), parietal cells (HCl + intrinsic
factor), G cells (gastrin), mucous cells
Systems Anatomy & Physiology
The Digestive System
Basic Health Sciences (BHSC) Program
Academic Year 2024–2025
, 1. Overview
The digestive system processes food to provide nutrients for cellular metabolism. It
performs four main processes: ingestion, digestion, absorption, and defecation.
2. Anatomy of the GI Tract
2.1 Layers of the GI Wall (from lumen outward)
1. Mucosa: epithelial lining, lamina propria, muscularis mucosae
2. Submucosa: connective tissue; contains blood and lymph vessels, submucosal
plexus
3. Muscularis externa: inner circular and outer longitudinal smooth muscle;
myenteric plexus
4. Serosa (or adventitia): outer protective layer
2.2 The Oral Cavity
• Teeth: mastication (mechanical digestion)
• Tongue: taste; manipulates food; initiates swallowing
• Salivary glands: parotid, submandibular, sublingual
• Saliva: amylase begins starch digestion; lysozyme antibacterial; lubricates food
bolus
2.3 The Esophagus
• Muscular tube connecting pharynx to stomach
• Upper third: skeletal muscle; lower third: smooth muscle
• Peristalsis propels food bolus downward
• Lower esophageal sphincter (LES): prevents gastric reflux
2.4 The Stomach
• Regions: cardia, fundus, body, pylorus
• Rugae: folds allowing distension (~1 L capacity)
• Gastric glands contain: chief cells (pepsinogen), parietal cells (HCl + intrinsic
factor), G cells (gastrin), mucous cells
