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• Digestion


  The process wherein food is broken down into small molecules that the body can use to nourish the cells and to provide energy
• Phases of digestion

  1. Mechanical

  2. Chemical
• Mechanical digestion


  1. Food is broken down into small pieces by chewing or mastication

  2. Food is lubricated and softened by digestive juices
• Chemical digestion

  Food is acted upon by enzymes that change them into their simplest equivalents which the body cells can utilize
• Alimentary tract


  The organs of digestion including the mouth, pharynx, esophagus, stomach, small and large intestines, rectum and anus
• Accessory organs


  Salivary glands, liver, gallbladder, and pancreas
• Mouth


  • Contains teeth to break down food
  • Contains tongue to mix food with saliva and aid swallowing
  • Contains ducts of salivary glands that secrete saliva to lubricate and chemically digest carbohydrates
  • Contains palate to form the roof of the mouth
• Mechanical and chemical digestion in the mouth

  1. Food is lubricated and chewed until it forms a ball-shaped mass called bolus

  2. Swallowing pushes the bolus into the pharynx
• Pharynx


  Common passageway for digestion and respiration<|>Swallowing reflex relaxes sphincter muscle and raises epiglottis to cover trachea so food passes into esophagus
• Esophagus


  Muscular tube that transports the bolus from the pharynx to the stomach via peristalsis
• Stomach


  • Stores swallowed food
  • Mixes food with digestive juices
  • Conveys contents slowly into small intestine
  • Contains rugae with gastric glands that secrete mucus, hydrochloric acid, enzymes, and the hormone gastrin
• Stomach digestion

  1. Churning mixes food with gastric juice to form chyme

  2. Sphincter muscles close to prevent backflow of chyme into esophagus
• Small intestine


  • Organ of complete digestion and absorption
  • Divided into duodenum, jejunum, and ileum
  • Secretes enzymes that break down food into simple components
• Large intestine

  • Temporarily stores fecal materials
  • Absorbs vitamins produced by bacteria
  • Reabsorbs water from undigested residue
  • Divided into cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anus
• Liver and gallbladder

  • Liver produces bile to emulsify fats and neutralize stomach acid
  • Gallbladder stores and concentrates bile
• Pancreas

  • Exocrine part secretes digestive enzymes into duodenum
  • Endocrine part secretes hormones important for sugar metabolism
• Enzymes


  Organic catalysts that initiate or speed up chemical reactions
• Enzyme specificity

  Enzymes have complementary geometric shapes to their substrates, forming a "lock and key" fit
• Factors affecting enzymes

  Temperature (optimal 30-40°C)<|>pH (optimal for each enzyme)
• Types of digestive enzymes

  • Proteases and peptidases (break down proteins)
  • Carbohydrases (break down carbohydrates)
  • Lipases (break down fats)
  • Nucleases (break down nucleic acids)
• Carbohydrate digestion

  1. Begins with salivary amylase in mouth

  2. Continues with pancreatic amylase in small intestine

  3. Mechanical digestion in stomach
• Enzymes classified based on the substrate they work on

  • Proteases and peptidases act on proteins breaking them into amino acid units
  • Carbohydrases act on carbohydrates (starch and sugar) breaking them into simple sugars (example: Glucose)
  • Lipases break fats or lipids into fatty acids and glycerol
  • Nucleases break down nucleic acids into nucleotides
• Problems involving the digestive system

  • Pica
  • Heartburn and acid reflux (GERD)
  • Flatulence
  • Indigestion/dyspepsia
  • Colitis
  • Constipation
• The different food groups

  • Carbohydrates
  • Protein
  • Fats
  • Nucleic acids