digestive system

• Key nutrients in food and their basic functions

  • Carbohydrates (sugars)
  • Lipids (fats)
  • Proteins
  • Minerals (e.g. iron, calcium)
  • Vitamins (e.g. vitamin C)
  • Water
• Organic molecules

  Relatively large, carbon-based molecules (carbohydrates, lipids, proteins, nucleic acids)
• Inorganic molecules


  Relatively small, non-carbon-based molecules (water, minerals, vitamins)
• Monomer


  Basic unit of a molecule
• Polymer


  Chemically joining together many monomers
• Major chemical elements that form carbohydrates, proteins and lipids

  • Carbon
  • Hydrogen
  • Oxygen
  • Nitrogen
• Monomers for carbohydrates, proteins and lipids

  • Monosaccharides (e.g. glucose, fructose, galactose)
  • Amino acids
  • Fatty acids and glycerol
• Types of carbohydrates

  • Monosaccharides
  • Disaccharides (e.g. sucrose, lactose, maltose)
  • Polysaccharides (e.g. starch, glycogen, cellulose)
• Carbohydrates


  • Short term energy source for cellular respiration
• Proteins


  • Form cellular structures (e.g. haemoglobin, actin, myosin)
  • Control cellular activities (e.g. enzymes, hormones)
• Lipids


  • Long term energy storage
  • Form some cellular structures (e.g. cell membrane, internal membranes)
• Digestion


  The process of breaking down food into particles small enough to be absorbed into the blood and cells
• Basic activities of digestion

  • Ingestion of food
  • 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

  The physical breakdown of food into smaller pieces to increase surface area
• Chemical digestion

  Using enzymes to break large, complex substances into small, simpler chemicals
• Alimentary canal


  A continuous muscular tube that winds through the body from the mouth to the anus
• Organs of the digestive system

  • Organs of the alimentary canal
  • Accessory digestive organs (e.g. teeth, tongue, gall bladder, salivary glands, liver, pancreas)
• Structure of the alimentary canal

  • Outer layer of tough connective tissue
  • Layer of smooth muscle (circular and longitudinal)
  • Layer of connective tissue with blood vessels, lymph vessels and nerves
  • Inner layer of secretory and absorptive epithelial cells
• Structures of the digestive system that form the alimentary canal

  • Mouth
  • Oesophagus
  • Stomach
  • Small intestine
  • Large intestine
• Digestive organs associated with the alimentary canal

  • Salivary glands
  • Liver
  • Gallbladder
  • Pancreas
• Mechanical and chemical digestion in the mouth

  1. Intake of food (ingestion)

  2. Chewing of food (mastication)

  3. Mixing with saliva containing salivary amylase to begin chemical digestion of starch
• Types, numbers, and functions of teeth

  • 4 incisors (biting/cutting)
  • 2 canines (tearing)
  • 4 premolars (crushing/grinding)
  • 6 molars (crushing/grinding)
• Peristalsis in the oesophagus

  1. Contraction of circular muscle behind food to narrow tube

  2. Successive contraction of circular muscle causes constriction to move in a wave (peristalsis)

  3. Pushes food towards stomach
• Mechanical and chemical digestion in the stomach

  1. Muscular contraction to churn food and mix with gastric juice

  2. Gastric juice contains hydrochloric acid, mucus, and digestive enzymes (pepsin)

  3. Pepsin breaks down proteins into peptides
• Nutrients are not absorbed into the bloodstream through the stomach, except for some alcohol and drugs
• Small intestine


  • Approx. 6-7m long, narrow diameter
  • Highly vascular with large folds and finger-like projections (villi) to increase surface area for absorption
  • Duodenum, jejunum, and ileum sections
• Mechanical and chemical digestion in the small intestine

  1. Bile emulsifies fat droplets to increase surface area for lipase enzymes

  2. Pancreatic and intestinal enzymes complete digestion of carbohydrates, proteins, and lipids
• Digestive enzymes and their substrates/products

  • Salivary amylase (starch -> maltose)
  • Pepsin (proteins -> peptides)
  • Pancreatic lipase (lipids -> fatty acids and glycerol)
  • Pancreatic amylase (starch -> maltose)
  • Pancreatic proteases (proteins -> amino acids)
  • Intestinal enzymes (complete digestion of carbohydrates, proteins, lipids)
• Digestive enzymes produced by salivary glands, stomach, pancreas and small intestine

  • Amylase
  • Protease
  • Lipase
• Substrate

  The substance that an enzyme acts upon
• Products


  The substances formed as a result of the enzyme's action
• Mechanical digestion


  Bile salts emulsifying fat droplets
• The problem with fats (lipid) is that small droplets will clump together into larger clumps if they come in contact
• This will slow down the chemical digestion of lipid molecules by the lipases
• Bile


  A digestive juice that solves the problem of fat clumping
• Bile production and release


  1. Produced by the liver

  2. Transported to gallbladder where it is stored and concentrated

  3. When required the gall bladder contracts and releases stored bile into the common bile duct to the duodenum
• Emulsification


  The process where bile breaks down large fat droplets into smaller droplets
• Emulsification does not contain enzymes, so it is not a chemical digestive process
• Segmentation


  1. Consists of localized contractions of circular muscle in the intestinal tract

  2. Contractions of the circular muscles narrow the intestine which helps break up the chyme and mix it with the juices and bile
• Pancreas


  A thin 15cm organ that lies behind the stomach and under the liver