Respiratory System

• Digestion


  The breaking down of carbohydrate, protein and fat molecules into products small enough to be absorbed into the blood and cells
• Six basic activities of the digestive system


  • Ingestion of food and water
  • Mechanical digestion of food
  • Chemical digestion of food
  • Movement of food along the alimentary canal
  • Absorption of digested food and water into the blood and lymph
  • Elimination of material that is not absorbed
• Mechanical digestion


  • Physical breakdown of food particles to increase surface area for more effective chemical digestion
• Chemical digestion


  • Large, complex molecules broken down into smaller, simpler molecules which can be absorbed into the bloodstream using enzymes
• Products of chemical digestion


  • Monosaccharides (e.g. glucose)
  • Peptides
  • Amino acids
  • Fatty acids and glycerol
  • Nucleotides
• Alimentary canal


  A continuous tube from the mouth to the anus that works with accessory organs like the pancreas, liver and gall bladder to digest and absorb nutrients
• Mechanical digestion in the mouth


  1. Action of jaws and teeth

  2. Chewing (mastication)
• Chemical digestion in the mouth


  Food mixed with saliva containing salivary amylase enzyme
• Bolus


  The rounded lump of chewed food
• Teeth


  • Incisors (biting/cutting)
  • Canines (tearing)
  • Premolars and molars (crushing and grinding)
• Peristalsis in the oesophagus


  Circular muscle contractions behind the bolus narrowing the tube, pushing the food along
• Stomach


  • J-shaped, enlarged section of the alimentary canal
  • Mechanical digestion achieved by waves of muscular contraction along stomach wall
  • Oblique layer of muscle enables 'churning' of food with gastric juices to form chyme
  • Pyloric sphincter prevents contents moving until pushed by peristalsis
• Gastric juices

  Secreted by gastric glands in the stomach lining, contains hydrochloric acid, mucus, and the enzyme pepsinogen
• Conversion of pepsinogen to pepsin

  Hydrochloric acid in gastric juice activates pepsinogen into the enzyme pepsin which breaks down proteins
• Regions of the small intestine


  • Duodenum
  • Jejunum
  • Ileum
• Pancreatic juice


  Secreted by the pancreas, helps neutralise stomach contents and contains enzymes like amylase, trypsin, pancreatic lipases, Ribonuclease and deoxyribonuclease.
• Bile


  Produced by the liver, stored in the gall bladder, and secreted into the small intestine to emulsify fats into tiny droplets
• Intestinal juice


  Secreted by glands in the small intestine lining, contains enzymes that complete digestion of carbohydrates, proteins and lipids. Peptidase (peptides to amion acids), Sucrase, lactase, maltase (disaccharides to monosaccharides) and lipases (lipids to fatty acids and glycerol)
• Small intestine absorption


  • Large surface area achieved by long length, folded lining, villi, and microvilli
  • Nutrients absorbed through blood capillaries and lacteal lymph vessels
• VilliStructure


  Finger-like projections (approx 1mm long) on the small intestine lining that increase surface area for absorption (covered by a single layer of cells).
• Elimination


  The removal of undigested material (faeces) from the body, not the removal of metabolic wastes (excretion)
• Components of faeces


  • Water
  • Undigested food (cellulose)
  • Bacteria
  • Bile pigments
  • Remains of cells from the alimentary canal lining
• The large intestine absorbs water and vitamins, stores faeces, and facilitates defecation
• The mouth breaks food into small particles by chewing (mastication) and saliva containing salivary amylase begins starch digestion
• The oesophagus transports food from the mouth to the stomach
• The stomach's mechanical digestion churns food with gastric juice, and its chemical digestion uses pepsin to break down proteins
• The small intestine's mechanical digestion uses muscular contractions and bile salts to churn food, while its chemical digestion uses pancreatic and intestinal enzymes to further digest carbohydrates, proteins, and lipids
• Simple sugars, amino acids, water and water-soluble vitamins are absorbed into blood capillaries.
• Fatty acids and glycerol recombine in cells of villi to form fats, along with fat-soluble vitamins, and enter the lacteal. 
• Most of the remaining water is absorbed during this time making contents more solid.

  Bacteria in large intestine break down remaining organic compounds – some also produce vitamins which are absorbed through walls into blood.

  Mineral nutrients absorbed.
• Main Functions of the Large Intestine

  Most of the remaining water is absorbed during this time making contents more solid.

  Bacteria in large intestine break down remaining organic compounds – some also produce vitamins which are absorbed through walls into blood.

  Mineral nutrients absorbed.