Lesson 6

The Digestive System

The digestive system breaks down food into nutrients that cells can absorb. The alimentary canal (GI tract) runs 25+ feet from mouth to anus. Accessory organs (liver, gallbladder, pancreas) produce enzymes and bile. Gastroenterology is a rich field involving everything from peptic ulcers to colorectal cancer to inflammatory bowel disease.

60 min3 sections5 objectives

Learning Objectives

1Trace the path of food through the alimentary canal
2Identify combining forms for each GI organ
3Describe accessory digestive organs and their functions
4Recognize common GI diseases and their terminology
5Interpret GI diagnostic procedures

1The GI Tract

Mouth (oral cavity): Mechanical digestion (mastication), salivary amylase begins starch breakdown

Pharynx → Esophagus (peristalsis carries bolus to stomach)

Stomach: Gastric acid (HCl) and pepsin begin protein digestion; creates chyme

Regions: Fundus, body, antrum, pylorus

Pyloric sphincter controls passage to small intestine

Small Intestine (~20 feet): Main site of digestion and absorption

Duodenum: First 12 inches; bile and pancreatic enzymes enter here

Jejunum: Most absorption

Ileum: Absorbs B12, bile salts; ileocecal valve enters large intestine

Large Intestine (~5 feet): Water/electrolyte absorption, feces formation

Cecum → Ascending → Transverse → Descending → Sigmoid colon → Rectum → Anus

2Accessory Organs

Liver: Largest internal organ (1.5 kg).

Produces bile (emulsifies fats)

Detoxifies blood

Synthesizes plasma proteins, clotting factors

Stores glycogen (glucose buffer)

Gallbladder: Stores and concentrates bile; contracts when fat enters duodenum

Pancreas: Dual function:

Exocrine: Pancreatic enzymes (lipase, amylase, proteases) into duodenum

Endocrine: Insulin (lowers glucose), glucagon (raises glucose), somatostatin

3GI Diseases

GERD (Gastroesophageal Reflux Disease): Stomach acid refluxes into esophagus → heartburn, Barrett's esophagus risk

Peptic Ulcer Disease (PUD): Ulcers in stomach (gastric) or duodenum; *H. pylori* bacteria is major cause

Inflammatory Bowel Disease (IBD):

Crohn's disease: Entire GI tract, transmural; skip lesions

Ulcerative colitis (UC): Colon only, mucosal; continuous

Appendicitis: Inflammation of appendix → McBurney's point tenderness; emergency appendectomy

Colorectal Cancer: 3rd most common cancer; screened with colonoscopy starting at age 45

Liver conditions: Cirrhosis, hepatitis A/B/C, liver failure

Clinical Connections

►H. pylori infects ~50% of the world's population and causes 80% of peptic ulcers
►Colonoscopy with polyp removal (polypectomy) can prevent colorectal cancer development
►NASH (Non-alcoholic steatohepatitis) is the fastest-growing cause of liver disease in developed countries

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L5: The Respiratory System

L7: The Urinary System