GI Overview Model Lecture Notes

Introduction to the GI Tract

• GI tract: Stands for gastrointestinal tract.
  • Series of connected hollow organs through which food travels.
  • Digestion and absorption occur at different stages.

Oral Cavity

• Mechanical Digestion: Involves the teeth, tongue, and hard palate.
• Chemical Digestion: Involves salivary enzymes.
  • Salivary amylase: Breaks down carbohydrates.
  • Salivary lipases: Break down lipids.

Pharynx and Esophagus

• Pharynx: Food travels from the mouth to the esophagus.
• Epiglottis: Prevents food from entering the trachea.
• Esophagus: A muscular tube that propels food to the stomach using peristalsis.
• Lower Esophageal Sphincter (LES): Controls entry of food into the stomach.

Stomach

• Parts of the Stomach: Cardia, fundus, body, and pylorus.
• Chemical Digestion: Gastric juices like hydrochloric acid and pepsin help break down proteins.
• Mechanical Digestion: Three layers of muscle (circular, longitudinal, and oblique) churn stomach contents.
• Formation of Chyme: Mixed bolus and gastric juices.

Small Intestine

• Duodenum: First part; receives chyme from the stomach.
• Pancreas and Gallbladder: Secrete substances to aid digestion.
  • Pancreatic Enzymes: Further break down chyme.
  • Sodium Bicarbonate: Neutralizes acidic chyme.
  • Bile: Emulsifies fats.
• Segments of Small Intestine: Duodenum, jejunum, and ileum.
  • Mnemonics: DJ Ill (Duodenum, Jejunum, Ileum).
• Majority of Absorption: Occurs in the small intestine.

Large Intestine

• Pathway of Chyme: Ilium -> Ileocecal Valve -> Cecum -> Ascending Colon -> Transverse Colon -> Descending Colon -> Sigmoid Colon -> Rectum -> Anus.
• Absorption: Reabsorbing water and solidifying stool.
• Parts of the Large Intestine: Cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum.
• Feces Storage: Rectum, pushed out through the anus.
• Anal Sphincters:
  • Internal Anal Sphincters: Involuntary control.
  • External Anal Sphincters: Voluntary control.

Accessory Organs

• Appendix: Holds bacteria important to gut flora; complications can lead to appendicitis and peritonitis.
• Liver: Detoxifies blood and produces bile.
• Gallbladder: Stores bile.
• Pancreas: Secretes pancreatic enzymes and sodium bicarbonate.
• Spleen: Breaks down old red blood cells.

Key Points Recap

• Oral Cavity: Mechanical and chemical digestion.
• Esophagus and Stomach: Peristalsis, sphincters, and formation of chyme.
• Small and Large Intestines: Digestion, absorption, and passage of chyme.
• Accessory Organs: Roles of the liver, pancreas, gallbladder, and appendix.