Digestive System Overview

Introduction

• Cells need oxygen and nutrients to function.
• Nutrients are obtained from food which must be broken down for energy production.

Digestive System Components

• Alimentary Canal (GI Tract): Continuous tube from mouth to anus where food is broken down and absorbed.
• Accessory Digestive Organs: Include teeth, tongue, gallbladder, salivary glands, liver, and pancreas.
• Six Digestive Actions:
  1. Ingestion: Eating and putting food into the mouth.
  2. Propulsion: Swallowing and peristalsis move food through GI tract.
  3. Mechanical Breakdown: Chewing, stomach acids, and juices.
  4. Digestion: Enzymes chemically break down food into molecular components.
  5. Absorption: Nutrients pass through intestinal lining into blood/lymph.
  6. Defecation: Expulsion of indigestible substances.

GI Tract Structure

• Mucosa: Secretes enzymes/hormones, absorbs digested food.
• Submucosa: Contains connective and lymphatic tissue, blood and nerve fibers.
• Muscularis Externa: Performs segmentation and peristalsis.
• Serosa: Connective tissue and epithelial cells.
• Intrinsic Nerve Plexuses: Control digestive activity.

Mouth and Oral Cavity

• Walls: Stratified squamous epithelium and antimicrobial peptides.
• Tongue: Skeletal muscle fibers, secured by the lingual frenulum.
• Salivary Glands: Produce saliva to clean and begin digestion.
• Teeth: Aid in mastication (chewing).

Upper Digestive Tract

• Esophagus: Muscular tube to stomach, changes from squamous to columnar epithelium.
• Stomach: Converts food to chyme, acidic environment with pepsin for protein digestion.

Small Intestine

• Sections: Duodenum, jejunum, ileum.
• Duodenum: Receives bile from liver and pancreatic juice.
• Absorption: Circular folds, villi, microvilli increase surface area.

Accessory Organs

• Liver: Produces bile for fat digestion, organized into lobules.
• Gallbladder: Stores bile, releases it to duodenum.
• Pancreas: Produces pancreatic juice for digestion.

Large Intestine

• Functions: Absorbs water, forms feces.
• Structure: Tenia coli, haustra, epiploic appendages.
• Subdivisions: Cecum, appendix, colon, rectum, anal canal.

Conclusion

• Overview of food digestion from ingestion to excretion.
• Future details on biochemical pathways and specific enzyme actions to be explored.