Biology - Digestion

• Ingestion


  Intake of food into the mouth
• Digestion


  Breaking down of large, complex molecules into smaller, simpler molecules
• Absorption


  Movement of digested nutrients into the blood
• Assimilation


  Nutrients becoming part of the cell to be used
• Egestion


  Removal of solid waste through anus
• Types of Digestion


  • Physical
  • Chemical
• Physical Digestion


  • To increase surface area for enzymes to react faster
• Chemical Digestion


  • To break down complex molecules using enzymes for absorption
• Enzymes


  Biological catalysts made of protein that speed up chemical reactions
• Characteristics of Enzymes


  • Can be reused again
  • Only produced in small quantity
  • Specific to its own substrate
  • Shape of enzyme must be complimentary to the shape of substrate "lock and key mechanism"
  • pH specific (stomach : 2) (mouth/duodenum : 7)
  • Temperature specific (36.5 celsius)
• Mouth


  1. Physical Digestion: Chewing

  2. Chemical Digestion: [enzyme amylase]
• Function of Mouth


  To break down food from large pieces to small pieces
• Types of Teeth


  • Incisor
  • Canine
  • Pre-Molar
  • Molar
• Incisors


  • Chisel-like
  • Cut and bite food
  • 4 top, 4 below [8]
• Canine


  • Pointed
  • Hook and tear
  • 2 upper jaw, 2 lower jaw [4]
• Pre-Molar


  • 2-3 cusps
  • 1-2 roots
  • Crush, grind food
  • 4 on top, 4 below [8]
• Molar


  • 4-5 cusps
  • 3-4 roots
  • Crush, grind food
  • 6 top, 6 bottom [12]
• Tongue


  • Helps shape bolus
  • Mixes food with saliva
• Saliva


  Made of amylase, water, mucin
• Epiglottis


  Flap that closes windpipe to prevent food from entering airway (trachea)
• Esophagus


  Peristalsis: wave-like contraction of the walls of esophagus & to push food into the stomach
• Stomach


  1. Physical Digestion: Churning

  2. Chemical Digestion: Enzyme (protease [pepsin & renin])
• Stomach


  • Made of: Smooth muscle & Gastric glands (produces gastric juice)
• Gastric Juice


  Hydrochloric acid, Mucus, Enzyme (protease)
• Hydrochloric Acid


  Kills bacteria in contaminated food, Provides acidic environment for enzymes proteases to work (pH 2)
• Mucus


  Produced by goblet cell, Prevents stomach from digesting itself
• Enzyme (Protease)


  Pepsin & Renin (Protein —> Polypeptides) [Coagulation]
• Liver


  Makes bile
• Function of Bile


  • Emulsifies fats into tiny fat droplets
  • Neutralises acidic property of chyme (2-7 pH)
• Stomach


  Chyme enters duodenum
• Gallbladder


  Stores bile
• Bile Duct


  Transports bile into duodenum
• Duodenum


  First part of the small intestine
• Pancreatic Duct


  Transports pancreatic juice into duodenum
• Pancreas


  Produces pancreatic juice
• Pancreatic Juice


  • Carbohydrase (pancreatic amylase breaks down starch into maltose)
  • Protease (trypsin breaks down protein into amino acids)
  • Lipase (breaks down fats/lipids into fatty acids and glycerol)
• Small Intestine


  Duodenum, Jejunum, Ileum
• Characteristics of Small Intestine

  • Very long (7m and folded to increase surface area for effective absorption of nutrients)
  • Has many finger-like projections called villi & microvilli (to increase surface area for absorption of nutrient)
• Function of Small Intestine

  To complete digestion to absorb digested, soluble nutrients
• Small Intestine Secretions


  Contain maltase, lactase, sucrase to digest maltose, lactose, sucrose into simple sugars