Digestion and Nutrition

4 Stages of Food Processing

1. Ingestion

   1. Swallowing

   2. Saliva: lubrication + enzyme

2. Digestion

   1. Mechanical: 

      • Chewing optional; teeth, radula, mandibles

      • Churning & mixing: stomach, gizzard, crop, rumen

   2. Chemical: Digestive enzymes

      1. Proteins: pepsin, trypsin, peptidases

      2. Carbohydrates: amylase, disaccharidases

      3. Fats: lipase, bile salts

   3. How the body protects itself from its own digestive juices

      1. Digestive compartments

         • Paramecium digestion

         • Gastrovascular cavity

         • Alimentary canals

      2. Mucus

      3. Enzymes secreted as precursors

3. Absorption

   1. Fat-soluble nutrients pass through membrane

   2. Transporters carry sugars, amino acids

   3. Water absorption by osmosis

4. Elimination

   1. Reflexes

The human digestive system

1. Mouth
   1. Mastication
   2. Saliva
   3. Amylase
2. Salivary glands (3)
3. Esophagus
   1. Swallowing
   2. Epiglottis
   3. Sphincters
4. Stomach
   1. Churning
   2. HCl Acid production
   3. Digestive enzymes: Pepsin
5. Small intestine
   1. Folds, villi and microvilli: surface area!
   2. Mixing & peristalsis
   3. Absorption of nutrients
   4. Digestive enzymes: disaccharidases
6. Pancreas
   1. Bicarbonate
   2. Digestive enzymes: trypsin, peptidases, amylase, lipase
7. Gallbladder
   1. Bile
8. Liver
   1. Produces bile
   2. Processes nutrients after absorption
9. Large intestine
   1. Absorption of water
10. Rectum & anus

Nutrition

1. Feeding patterns
   • Omnivores
   • Herbivores
   • Carnivores
2. Essential nutrients
   • 8 Essential AAs
   • 13 essential vitamins
   • 21 essential minerals
   • 2 essential fatty acids
3. Homeostasis and nutrient balance
   • Insulin and glucagon
   • Leptin: 
     • Regulation of appetite
     • Role in obesity

Applications

1. Malnutrition & obesity
2. Caprophagy
3. Stomach ulcers
4. The role of bacteria in digestion
5. Ruminants