Overview of the Digestive System

Purpose of Digestion

• Humans need to consume food primarily for energy to power movement and metabolism.
• Key nutrients: carbohydrates (e.g., starch, glucose), proteins, and fats.
• Digestion breaks down large food molecules into tiny pieces for cellular absorption.
  • Involves physical breakdown and chemical breakdown by enzymes.

Digestive Process

1. Mouth

• Chewing: Physically breaks down food.
• Saliva:
  • Produced by salivary glands.
  • Contains salivary amylase enzyme to begin carbohydrate digestion.

2. Esophagus (Gullet)

• Swallowed food passes down to the stomach.

3. Stomach

• Functions:
  1. Muscular walls contract to mix food.
  2. Produces pepsin (protease enzyme) to break down proteins.
  3. Produces hydrochloric acid to kill bacteria and create an optimal environment for pepsin.

4. Small Intestine

• Absorption: Main site for nutrient absorption into the bloodstream.
• Digestion: Continues digestion using enzymes produced by the intestine and pancreas.
• Pancreas:
  • Produces most digestive enzymes released into small intestine as pancreatic juices.
• Gallbladder:
  • Stores bile produced in the liver.
  • Releases bile into small intestine to neutralize stomach acid and emulsify fats, increasing surface area for enzyme action.

5. Absorption in Small Intestine

• Villi: Finger-like projections increasing surface area for faster absorption.
  • Single layer of surface cells: Short diffusion distance.
  • Good blood supply: Maintains concentration gradient.

6. Large Intestine

• Absorbs excess water from indigestible material.
• Remaining material forms feces, stored in the rectum until removal.

Recap of Digestive Process

1. Chewing in the mouth and salivary enzyme action.
2. Passage through the esophagus.
3. Digestion in the stomach with enzymes and acid.
4. Further digestion and absorption in the small intestine aided by pancreatic juices and bile.
5. Water absorption in the large intestine and formation of feces.

Conclusion

• Digestive system is crucial for breaking down food into absorbable nutrients.
• Key organs: mouth, esophagus, stomach, small intestine, pancreas, liver, gallbladder, and large intestine.
• Next focus: Detailed examination of digestive enzymes.