digestion

• Nutrition


  The process of providing or obtaining food necessary for growth and health
• Autotrophs


  Organisms which build up their own organic food, such as glucose, from inorganic substances, such as water and carbon dioxide
• Autotrophs


  • Plants which build up their food during photosynthesis
• Heterotrophs


  Organisms which eat organic food made available by other organisms, such as plants or other animals
• Digestion


  A process whereby food is broken down into small particles, small enough to be carried by the blood around the body

  
• The digested food is then used by the cells for growth, energy and for other chemical reactions which keep us alive
• Digestion


  1. Ingestion

  2. Chewing

  3. Mixing with saliva

  4. Swallowing

  5. Absorption

  6. Assimilation

  7. Defecation

  
• Alimentary canal


  • A tube running through the body
  • Has two layers of muscles in its walls: longitudinal and circular
• Peristalsis


  A wave of contraction passing along the alimentary canal pushing food in front of it
• Epithelium


  • The first layer of cells
  • Makes new cells to replace old ones
  • Goblet cells secrete mucus
  • Other cells produce digestive enzymes
• Ingestion


  Taking food into the mouth
• Saliva


  • Moistens food
  • Contains mucus
  • Contains salivary amylase
  • Contains water
• Swallowing


  Food passes through the oesophagus to the stomach

  
• Stomach


  • Stores food
  • Digests proteins
• Chyme


  The mixture of food, mucus and enzymes in the stomach
• Stomach lining


  • Contains goblet cells that secrete mucus
  • Contains cells that secrete protease enzymes
  • Contains cells that secrete hydrochloric acid
• Digestion in the stomach

  1. Pepsin breaks down proteins to polypeptides

  2. Chyme is released into the small intestine after 1-2 hours
• Small intestine


  • 5m long and very narrow
  • Made up of duodenum and ileum
• Digestion in the duodenum

  1. Receives fluids from liver, pancreas, and intestinal glands

  2. Bile emulsifies fats

  3. Pancreatic juice contains amylase, trypsin, and lipase
• Intestinal glands


  • Secrete enzymes like maltase, sucrase, lactase, peptidase, and lipase
• Villi


  Small hair-like projections on the inner walls of the small intestine
• Ileum


  • Where absorption of digested food occurs

  
• All digestive juices contain water and mucus
• The structure of the small intestine is adapted for absorption
• Summary of digestion process

  • Mouth: Saliva with amylase
  • Stomach: Gastric juice with pepsin and hydrochloric acid
  • Duodenum: Pancreatic juice with amylase, trypsin, lipase, and sodium hydrogen carbonate
  • Ileum: Enzymes like maltase, sucrase, lactase, peptidase, and lipase
• In humans, the caecum and appendix are small structures without digestive functions
• Large intestine


  Has wider tubes than the small intestine, made up of the colon and rectum
• Bile


  Does not contain enzymes, contains salts which emulsify fats, and pigments which will be eventually excreted
• Small Intestine (Ileum)


  • No juice secreted, Enzymes remain close to cells lining each villus
• Enzymes in the small intestine

  • Maltase
  • Sucrase
  • Lactase
  • Peptidase
  • Lipase
• Maltase


  Breaks down maltose into glucose
• Sucrase


  Breaks down sucrose into glucose and fructose
• Lactase


  Breaks down lactose into glucose and galactose
• Peptidase


  Breaks down polypeptides into amino acids
• Lipase


  Breaks down fats into fatty acids and glycerol
• In humans, the caecum and appendix are small structures without any digestive functions
• In grass-eating animals (herbivores) like the cow and the rabbit, the caecum and appendix are much larger and contain bacteria which digest cellulose
• Large Intestine


  Has wider tubes than the small intestine
• Colon


  Absorption of more water and salts takes place
• Rectum


  Contains food which cannot be digested such as cellulose or fibre, which is now known as faeces and stored until they are ready to be egested from the anus