ch6. digestive system and nutrition

• Digestion


  Breaking down complex compounds into small molecules
• Absorption


  Break-down products or nutrients are absorbed into the blood and carried to cells in the body
• Elimination


  Undigested material is removed from body as waste
• Layers of digestive tract


  • Mucosa
  • Submucosa
  • Muscularis
  • Serosa
• Mucosa


  Secretes digestive enzymes
• Submucosa


  Contains blood vessels and lymph nodules
• Muscularis


  Muscle layers - circular and longitudinal
• Serosa


  Moist, slippery connective tissue
• Main sites of digestion


  • Mouth
  • Stomach
  • Duodenum (small intestine)
• Mouth


  Chemical (salivary amylase) and Mechanical (action of tongue and teeth)
• Stomach


  Chemical (pepsin, hydrochloric acid) and Mechanical (churning)
• Duodenum (small intestine)


  Chemical (bile, pancreatic enzymes, bicarbonate)
• Main sites of absorption


  • Stomach
  • Small intestine
  • Large intestine (colon)
• Stomach


  Alcohol and other liquids
• Small intestine


  Most nutrients from digested food
• Large intestine (colon)


  Water, salts and nutrients
• Small intestine (jejunum and ileum) contains Peyer's patches - part of immune system - scan contents of gut to detect foreign antigens
• Nutrients absorbed through villi, which contain blood capillaries and lacteals
• Glucose and amino acids

  Carried directly into blood capillaries
• Fats


  Carried into lacteals before entering blood
• Hormones involved in digestive system


  • Gastrin
  • Gastric inhibitory peptide (GIP)
  • Secretin
  • Cholecystokinin (CCK)
  • Leptin
  • PYY (Peptide tyrosine tyrosine)
  • Ghrelin
  • Insulin
  • Glucagon
• Gastrin


  Released by stomach after a meal
• Gastric inhibitory peptide (GIP)


  Released by wall of duodenum, inhibits secretions produced by gastric glands in stomach
• Secretin


  Stimulates actions of pancreas, liver and gall bladder
• Cholecystokinin (CCK)


  Stimulates actions of pancreas, liver and gall bladder
• Leptin


  Made by fat cells, helps to suppress appetite, acts via receptors in hypothalamus
• PYY (Peptide tyrosine tyrosine)


  Secreted by small intestine after a meal, suppresses appetite, counteracts action of ghrelin
• Ghrelin


  Secreted by wall of stomach, triggers feelings of hunger, appetite stimulant
• Insulin


  Secreted by pancreas following rise in blood sugar after a meal, drives uptake of sugar
• Glucagon


  Secreted by pancreas, drives release of glucose
• Accessory organs


  • Pancreas
  • Liver
  • Gallbladder
• Pancreas


  Secretes insulin and glucagon (endocrine function), secretes pancreatic juices (exocrine function)
• Components of pancreatic juices


  • Sodium bicarbonate
  • Pancreatic amylase
  • Trypsin
  • Lipase
• Liver


  Secretes bile, detoxifies and removes poisons, removes and stores iron, keeps vitamins in balance, makes proteins, regulates cholesterol and glucose levels
• Gallbladder


  Stores and concentrates bile, stimulated to contract via action of cholecystokinin (CCK)
• Main jobs of gut microbiome


  • Fermentation of indigestible food components
  • Synthesis of some essential vitamins
  • Removes toxins
  • Out-competes pathogens
  • Strengthens intestinal barrier
  • Stimulates/regulates immune system
• Digestive disorders


  • Ulcers
  • Constipation
  • Diarrhoea
  • Polyps and colon cancer
• Ulcers


  Found in esophagus, stomach, and small intestine, mainly due to Helicobacter pylori bacteria
• Major nutrient classes


  • Carbohydrates
  • Fats
  • Proteins
  • Vitamins
  • Minerals
  • Water
• Underconsumption


  Results in malnutrition