Unit 4

• Mechanical digestion


  The physical break up of food into smaller pieces, which increases the surface area for enzymes to work
• Chemical digestion


  The chemical breakdown of the complex molecules in food to simple substances
• Enzymes


  Act as catalysts for chemical reactions in digestion
• Hydrolysis reactions


  1. A water molecule is inserted, breaking a bond

  2. Bonds broken are glycosidic bonds in carbohydrates, peptide bonds in proteins, ester bonds in lipids
• Condensation reactions


  The reverse of hydrolysis, with components joining and water being eliminated
• Assimilation


  The processes by which an organism incorporates absorbed nutrients into the body
• Digestive fluids


  • Hydrochloric acid
  • Bile
  • Mucus
• Hydrochloric acid


  Produced in the stomach, kills bacteria and provides a suitable pH for pepsin enzyme
• Bile


  Produced in the liver, stored in the gall bladder, acts in the small intestine to emulsify fats
• Mucus


  Lubricates the gut wall to allow food to pass down smoothly, protects the gut wall
• Carbohydrases act in the mouth and small intestine to break down carbohydrates into simple sugars
• Proteases act in the stomach and small intestine to break down proteins into amino acids
• Lipases act in the small intestine to break down lipids into fatty acids and glycerol
• Emulsification


  The breakdown of large fat molecules into small ones, providing an increased surface area for lipase enzymes to act on the fats
• Small intestine


  • Divided into duodenum and ileum
  • Digestion is completed in the duodenum and absorption occurs in the ileum
• Villi


  • Projections on the small intestine wall that increase the surface area for absorption
  • Epithelial cells are only one cell thick with microvilli to further increase surface area
  • Good blood supply to absorb glucose and amino acids
  • Lacteals absorb glycerol and fatty acids
• Absorption of glucose and amino acids


  Co-transport mechanism where sodium ions and either glucose or amino acids are carried through the cell membrane together
• Gastrin


  Hormone produced in the stomach that stimulates growth of the stomach lining, movement of the stomach, and secretion of hydrochloric acid
• Increased gastrin levels can be linked to some stomach cancers
• Macro- and micronutrients are needed by the body
• Gastrin


  Hormone that stimulates growth of the lining of the stomach, movement of the stomach and secretion of hydrochloric acid into the stomach
• Gastrin secretion


  Stimulated by the presence of protein in the stomach, stretching of the stomach wall or a raised pH in the stomach
• Gastrin levels are sometimes monitored in patients
• An increased gastrin level is thought to cause some stomach cancers, and some tumours in the stomach produce gastrin
• Gastrin monitoring can be used to assess risk and for cancer diagnosis
• Nutrients required by the body

  • Macronutrients
  • Micronutrients
• Macronutrients


  Nutrients required in larger quantities
• Micronutrients


  Nutrients only needed in minute quantities, and an excess of these may even be harmful
• Bones are initially made from cartilage, which is softer and more flexible than bone. The cartilage is then hardened by calcium to form the bone.
• Rickets tends to be a disease of children rather than adults.
• Musculoskeletal system


  • Provides support for the body
  • Allows movement through joints and muscles
• Axial skeleton


  The skeleton's central axis, consisting of the skull, vertebral column and rib cage
• Appendicular skeleton


  The limbs, together with the bones of the shoulders and the pelvis
• Bone development (ossification)


  1. Intramembranous ossification - bone forms directly from connective tissue

  2. Endochondral ossification - bone forms from pre-existing cartilage
• Osteoblasts


  Specialised cells that lay down new bone
• Osteoclasts


  Cells that break down (resorb) bone tissue to release calcium
• Bone is a living and dynamic tissue that can respond to increased stress by adding more bone, or remove it if the stress is lessened
• Synovial joints


  • Allow movement between bones
  • Cartilage is softer than bone to prevent grating
  • Synovial fluid lubricates the joint
• Types of synovial joints

  • Gliding
  • Hinge
  • Ball and socket
  • Pivot
• Myofibrils


  Made up of two types of myofilament: thin filaments made of the protein actin and thick filaments made of the protein myosin