Digestive

• 5 steps of digestion

  • Ingestion
  • Digestion
  • Absorption
  • Assimilation
  • Egestion
• Ingestion

  Taking food in
• Digestion

  Breaking larger molecules down into smaller molecules
• Absorption

  Taking small molecules into the blood
• Assimilation

  Using useful substances
• Egestion/excretion

  Removal of waste or undigested food
• Mouth

  • Ingestion occurs
  • Mechanical digestion = chewing to increase the surface area for amylase to work on
  • Chemical digestion = salivary glands secrete amylase to digest starch into maltose/glucose
  • Saliva is produced
• Name 2 types of digestion

  Mechanical and chemical
• Mechanical digestion

  • Chewing in the mouth
  • Churning in the stomach
  • Bile emulsifying fats
  • Involves increasing the surface area for chemical digestion
• Chemical digestion

  Secretion of enzymes to covert large molecules into smaller molecules
• Amylase

  Starch to maltose
• What do salivary glands secrete?

  Amylase
• Maltase

  Maltose to 2 alpha glucose molecules
• Sucrase

  Sucrose to alpha glucose and fructose
• Lactase

  Lactose to alpha glucose and galactose
• Pepsin/pepsidases

  Proteins to amino acids
• Lipase

  Triglycerides to fatty acid and glycerol
• What does saliva contain?

  • Amylase to digest starch
  • Mucus for lubrication
  • Lysozyme to destroy pathogens
  • Sodium hydrocarbonate to provide the optimum pH for amylase
• Bolus

  Chewed food + saliva
• Oesophagus

  • Food passes from the mouth to the stomach via a wave of muscular contractions known as peristalsis
  • Contains mucus for lubrication
  • Epiglottitis is a flap of cartilage which covers the trachea when swallowing to prevent choking
• Peristalsis 


  A wave of muscular contractions
• Epiglottitis

  A flap of cartilage which covers the trachea when swallowing to prevent choking
• Stomach

  • Digestion occurs
  • Mechanical digestion = churning
  • Chemical digestion = pepsinogen is secreted as an inactive form of pepsin to digest proteins
  • Pepsinogen is secreted by chief cells
  • Hydrochloric acid is secreted by parietal cells
  • Goblets cells secrete mucus
• What does the stomach wall contain?

  Gastric glands
• What 3 cells make up gastric glands?

  • Goblet
  • Chief
  • Parietal
• Goblet cells secrete mucus for lubrication and to prevent autodigestion in the stomach.
• Chief cells secrete pepsinogen which is an inactive form of pepsin to prevent autodigestion of the stomach and is activated by hydrochloric acid.
• Parietal cells secrete hydrochloric acid to activate pepsinogen, reduce the pH for pepsin and kills pathogens
• Protein digestion occurs in the stomach
• Name 2 enzymes which digest proteins

  Endopeptidase

  Exopeptidase
• Endopeptidase

  Hydrolyses peptide bonds within a polypeptide chain
• Exopeptidase

  Hydrolyses peptide bonds at the ends of a polypeptide chain
• Why is it best to have a mixture of exo and endopeptidases to make digestion efficient?

  Endopeptidases create more ends for exopeptidases to work on
• Where is pepsin produced?

  Stomach
• Where is trypsin produced?

  Pancreas
• Name 2 examples of endopeptidases

  Pepsin

  Trysin
• Small intestine - Duodenum

  • Final stages of digestion occurs
  • Receive secretions from the gallbladder and pancreas
  • Trypsinogen is secreted and is an inactive form of trypsin which is used to digest proteins
  • Amylase is secreted to digest starch
  • Maltose, lactase, and sucrase are secreted
  • Lipase is secreted to digest triglycerides
• What creates bile?

  Liver
• What stores bile?

  Gallbladder
• How is bile secreted into the duodenum?

  Via the bile duct