Digestive System and Energy

Purpose of Eating

• Obtain energy for survival
• Obtain raw materials for building tissues

Matter and Energy in Food

• Food and the human body are made of matter (atoms)
• Both have energy stored in atomic bonds

Digestion Overview

• Human digestion converts biological matter in food into usable forms
• Six main steps in digestion

The Role of Nachos

• Nachos contain carbohydrates, fats, and proteins
• Calories measure stored energy in food

Digestive System Functions

Step 1: Ingestion

• Bulk flow of nutrients into tissues
• Mechanical (chewing) and chemical (enzymes) breakdown begins

Step 2: Propulsion

• Swallowing (voluntary)
• Peristalsis (involuntary muscle contractions)

Step 3: Mechanical Breakdown

• Pulverizes food to increase surface area

Step 4: Chemical Digestion

• Enzymes from liver, pancreas, gallbladder
• Break down food into monomers (amino acids, fatty acids, sugars)

Step 5: Absorption

• Nutrients absorbed into blood
• Active and passive transport

Step 6: Defecation

• Indigestible substances expelled as waste

Organs of the Digestive System

• Hollow organs forming the alimentary canal
  • Mouth, pharynx, esophagus, stomach, small and large intestines
• Lined with epithelial cells
  • Mouth, esophagus, anus: stratified squamous epithelial tissue
  • Stomach, intestines: simple columnar epithelial cells
  • Secrete mucus to protect from digestive enzymes

Layers of the GI Tract

• Mucosal layer: epithelium + connective tissue, supplies blood
• Submucosal layer: loose areolar connective tissue, provides elasticity
• Muscularis externa layer: muscles for moving food through tract

Accessory Digestive Organs

• Teeth, tongue, gallbladder, salivary glands, liver, pancreas
• Secrete enzymes to aid digestion

Importance of Enzymes

• Speed up chemical reactions
• Break down macromolecules into monomers

Macromolecules and Monomers

• Four kinds of biological molecules: lipids, carbohydrates, proteins, nucleic acids
• Monomers: fatty acids, sugars, amino acids, nucleotides

Nutrition and Energy

• Carbohydrates: 4 calories/gram
• Fats: 9 calories/gram

Process Summary

• Ingestion, propulsion, mechanical breakdown, chemical digestion, absorption, defecation
• Cooperation among multiple organs

Upcoming Topics

• Detailed examination of the digestive system processes

Credits

• Crash Course team acknowledgments