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• Major parts of the digestive system

  • Oral cavity (mouth) with salivary glands
  • Pharynx (throat)
  • Esophagus
  • Stomach
  • Small intestine (duodenum, ileum, jejunum) with liver, gallbladder and pancreas as accessory organs
  • Large intestine including cecum, colon, rectum and anal canal
  • Anus
• Digestive tract


  • Also called alimentary tract – continuous tube
  • Accessory organs - Primarily glands, secrete fluids into tract
• Histological layers of the digestive tract

  • Mucosa: innermost layer, secrets mucus
  • Submucosa: connective tissue layer, contains blood vessels, nerves etc.
  • Muscularis: 2/3 muscle layers, movement & secretion
  • Serosa / Adventitia: outermost layer, connective tissue, stability
• Accessory organs of the digestive system

  • Liver
  • Gallbladder
  • Pancreas
• Contribution of the liver, gallbladder and pancreas to digestion

  • Liver - makes bile, filters blood, stores glucose and lipids, detoxifies
  • Gallbladder - stores and concentrates bile
  • Pancreas - produces digestive enzymes, produces insulin and glucagon
• Digestion


  Breakdown of food molecules for absorption into circulation
• Absorption


  Nutrients from the small intestine, water from the large intestine. Molecules are moved out of digestive tract and into circulation for distribution throughout body (via liver)
• Macronutrients


  • Carbohydrates
  • Proteins
  • Lipids
• Vitamins and minerals are needed by the body
• Enzymes


  Protein catalysts that increase the rate at which a chemical reaction proceeds, without the enzyme being permanently changed. Highly specific - active site can only bind to specific reactant.
• Enzymes


  • Lipase - breaks down lipids
  • Protease - breaks down proteins
• Many different enzymes are needed in the body for different chemical reactions
• Nutrients are chemicals taken in to the body to produce energy and provide building blocks to build other molecules
• Enzymes


  Protein catalysts that increase the rate at which a chemical reaction proceeds, without the enzyme being permanently changed
• Enzyme Action


  1. The enzyme brings the two reacting molecules together

  2. After the reaction, the unaltered enzyme can be used again
• Enzymes


  • Highly specific – active site on an enzyme can only bind to specific reactant
  • Many different enzymes needed in the body for different chemical reactions
  • Often named by adding 'ASE' as a suffix to their reactant
• Enzymes


  • Lipase – enzyme that breaks down lipids
  • Protease – breaks down proteins
• Nutrients


  • Carbohydrates
  • Proteins
  • Lipids
  • Vitamins
  • Minerals
  • Water
• Nutrients


  • Chemicals taken in to body to produce energy
  • Provide building blocks to build other molecules
• Major organic nutrients


  • Carbohydrates
  • Proteins
  • Lipids
• • Need large amounts of carbs, proteins, lipids & water
  • Only need small amounts of vitamins & minerals
• Essential nutrients


  Chemicals that must be taken in to the body, because we can't make them ourselves
• Essential nutrients


  • Some amino acids/fatty acids/carbs, water, most vitamins & minerals
• Chemicals that we use to produce energy to make ATP for our cells to function so we can make antibodies, homeostasis etc
• Six major classes of nutrients

  • Carbohydrates
  • Lipids
  • Proteins
  • Vitamins
  • Minerals
  • Water
• Carbohydrates


  Mono / di / polysaccharides - plants, vegetables
• Lipids


  Triglycerides - oils, dairy, animal fat, eggs
• Proteins


  Chains of amino acids - meat, fish, poultry
• Vitamins


  Organic molecules (vit A,B,E) – animal and plants products
• Minerals


  Inorganic nutrients (calcium, iron) – animal and plant products
• Recommended amounts: Carbohydrates 45-65%, Lipids 20-35% or less, Proteins 10-35% of total daily kilocalories
• Carbohydrates > Lipids > Proteins
• The more processed a macromolecule is, the less nutrients it contains
• Monosaccharides


  Glucose, fructose, galactose
• Disaccharides


  Sucrose, lactose, maltose
• Polysaccharides


  • Long chains - 3000+ monosaccharides
  • Glycogen (animal)
  • Starch & cellulose (plant)
• Carbohydrate absorption


  1. Polysaccharide chain digested by saliva & pancreatic amylase

  2. Disaccharide chain digested by sucrase in intestine

  3. Monosaccharide absorbed into blood via villi/microvilli
• Humans can store glycogen but can't break down cellulose
• Carbohydrate uses


  • Produce ATP (energy)
  • Excess stored as glycogen or fat
• Sugars also become part of DNA, RNA, ATP, glycoproteins, glycolipids