obtaining nutrients and digestion u1 AoS2

• Digestive System


  Physical/chemical breakdown of food, absorption of nutrients
• Digestive System


  • 4 main roles: Ingestion, Digestion, Absorption, Egestion
• Digestion


  1. Mechanical/Physical digestion

  2. Chemical digestion
• Mechanical/Physical digestion


  Large pieces of food are broken down into smaller pieces by mastication (chewing in mouth) or by muscular movement in stomach
• Chemical digestion


  Enzymes break down complex structures into their simplest forms (often using hydrolysis reactions)
• Ingestion


  1. Mastication in mouth

  2. Tongue moves food, increasing contact with teeth

  3. Salivary glands release amylase

  4. Food moves to oesophagus
• Digestion - Stomach


  1. Food moves down oesophagus by peristalsis

  2. Stomach is muscular and can stretch

  3. Circular muscles called sphincters regulate movement

  4. Mechanical digestion by stomach wall

  5. Gastric juice secreted containing mucus, HCl, lipase, pepsin, protease
• Digestion - Small Intestine


  1. Chyme moves from stomach to small intestine by peristalsis

  2. Pyloric sphincter controls amount of chyme entering

  3. Pancreatic juice containing amylase, trypsin, lipase, bicarbonate enters duodenum

  4. Bile from liver breaks down fats

  5. Trypsin and erepsin break down peptides into amino acids

  6. Carbohydrates broken down further

  7. Most water absorbed
• Absorption


  • Removes products of digestion
  • Nutrients move from gut to blood by diffusion/active transport
  • Lining of small intestine contains villi to increase surface area
• Egestion


  1. Large intestine compacts undigested food, absorbs water and salts

  2. Bacteria in colon act on undigested food, producing vitamins

  3. Peristalsis pushes waste to rectum

  4. Waste eliminated through anus