Lecture on Digestion and Energy in Food

Introduction to Digestion

• Definition: Digestion is the chemical and mechanical breakdown of food into small soluble molecules that can be absorbed into the blood and assimilated into cells.
• Process: Converts large insoluble molecules into smaller soluble molecules for transport and usage in the body.

Organs of the Digestive System

• Primary Organs (food travels through):
  • Mouth
  • Esophagus
  • Stomach
  • Duodenum (small intestine)
  • Ileum
  • Colon
  • Rectum
  • Anus
• Accessory Organs (aid in digestion):
  • Saliva glands
  • Liver
  • Gallbladder
  • Pancreas
  • Appendix

Digestive Process for a Cheese Sandwich

1. Mouth

   • Mechanical Digestion: Chewing increases surface area.
   • Chemical Digestion: Saliva contains amylase to break down starch into maltose.
   • Forms a bolus for swallowing.

2. Esophagus

   • No digestion; muscular tube that transports food to the stomach.

3. Stomach

   • Mechanical Digestion: Churning of food.
   • Chemical Digestion: Hydrochloric acid kills bacteria; pepsin (protease enzyme) breaks down proteins into amino acids.

4. Duodenum

   • Pancreatic Juice: Contains amylase, trypsin (protease), and lipase.
   • Bile: Neutralizes stomach acid; emulsifies lipids.

5. Ileum

   • Absorption of small soluble molecules into the blood.
   • High surface area due to villi and microvilli.
   • Blood vessels and lacteals absorb nutrients.

6. Large Intestine (Colon)

   • Absorbs remaining water.
   • Remaining material (dietary fiber) becomes feces.

Enzyme Summary

• Know the enzymes, their classes, locations, substrates, and products.

Practical: Investigating Energy Content in Food

• Energy Measurement: Dependent on carbohydrates, fats, and proteins.
  • Measured in kilojoules.
  • Use a calorimeter to determine energy content.
• Lab Method:
  • Weigh food sample.
  • Use 20 cm³ of water in a boiling tube.
  • Burn food to heat water and measure temperature change.
  • Use formula:
    • ( \text{Energy (J)} = \text{temperature change} \times 20 \times 4.2 / \text{mass of food (g)} )

Conclusion

• Digestive system breaks down food for body use.
• Experiments can help measure food energy content.