The Digestive System

• Digestion is the break down of large, insoluble food molecules into small, soluble food molecules so food can be absorbed into the blood stream
• Types of digestion:

  • Mechanical digestion: is the physical breakdown of food into smaller pieces by either teeth or muscles. This increases surface area of food
  • Chemical digestion: is the breakdown of insoluble food molecules(e.g. starch) into a soluble form by the use of enzymes
• Organs included: mouth, esophagus, stomach, gallbladder, small intestine, large intestine, rectum and anus.
• Associated organs: Liver & Pancreas
• Ingestion: the introduction of food in the mouth
• Salivary glands produce saliva
• It also contains an enzyme called salivary amylase that break down into maltose/ glucose
• Saliva softens/ moisturises food for swallowing
• Mastication: is the chewing/grinding of food in the mouth
• The movement of food along the alimentary canal is facilitated by wave-like contraction of the muscles in the gut in a process known as peristalsis
• Gastric juices are secreted by the stomach walls and mixed with food.
• This gastric juice contains:

  • HCL: which kills germs, dissolves food siding in digestion and lowers the pH of the stomach for optimum functioning of pepsin enzyme.
  • Mucus: prevents corrosion of the stomach lining by HCL acid and if this happens, ulcers develop
  • Pepsin: enzyme that breaks down proteins to amino acids
• Enzyme: are biological catalysts and made from amino acids
• Liver produce bile juice in gallbladder
• Emulsification: the process by which large, fat droplets, are broken down are taken into small fat droplets to increase the surface area for chemical breakdown of lipids by lipase
• Lipase: breaks down lipids into fatty acids and glycerol

  Pancreatic amylase: breaks down starch into maltose

  Maltose: breaks down maltose to glucose

  Trypsin: breaks down proteins into amino acids
• Absorption: is the process by which products of digestion (amino acids, fatty acids, glycerol and glucose) are taken into the bloodstream across the intestinal walls
• Assimilation: is the process by which the body utilizes the nutrients that have been absorbed. Examples include:

  1. Glucose: used as a source of energy
  2. Fatty acids and glycerol: insulation layer under the skin
  3. Amino acids: hormones, antibodies, enzymes, haemoglobin etc.
• Egestion: is the process by which the undigested and indigestible food is removed from the body
• Factors affecting enzyme action:

  • pH
  • Temperature