Nutrition 4

• Digestion & Nutrition


  Controlling energy balance
• Homeostatic mechanisms contribute to energy balance
• Energy stores


  • ATP generation from oxidation of carbohydrates, proteins and fats in cellular respiration
  • Glycogen, a polymer of glucose, stored in liver and muscle
  • Fat stored in adipose cells
• Obesity


  Overnourishment (consuming too many calories) causes obesity, the excessive accumulation of fat
• Ob + db genes

  Mutations in these genes lead to obesity in mice
• Obesity causes health problems: Type 2 diabetes, Cardiovascular disease, Colon cancer, Breast cancer
• Body fat


  • Leptin release from adipose cells
  • Appetite
• FTO gene


  • Encodes a deoxygenase enzyme, demethylates RNA
  • Mutations in this gene are associated with increased food intake and higher rates of obesity
• Obesity has an evolutionary basis - storing fat would have helped ancestors survive lean times
• Mammalian hibernation


  1. Prolonged bouts of torpor

  2. Reduced metabolic rate

  3. Dramatic reduction in size/weight of digestive organs

  4. Preservation of intestinal gene expression
• Ground squirrel hibernation


  • Consume no food for 5-6 months
  • Rely on fat stores for energy
  • Dramatic reduction in pancreatic enzyme activity
• Burmese python digestion


  1. Rapid increase in organ size after feeding

  2. Massive increase in transport proteins and metabolic rate

  3. Rapid lengthening of intestinal microvilli

  4. Increased enzyme activity and nutrient uptake
• Burmese pythons are an invasive species in the Florida Everglades, competing with alligators as a dominant predator
• Severe mammal declines in the Everglades coincide with the proliferation of Burmese pythons
• Ghrelin


  Secreted by stomach wall

  Triggers hunger at meal times
• Insulin


  Produced by pancreas after rise in blood sugar

  Also suppresses appetite
• Leptin


  Produced by adipose tissue and suppresses appetite

  Decrease in body fat causes levels to fall, hence appetite increase
• PYY

  Secreted by small intestine after meals

  Appetite suppressant that counters effect of ghrelin
• ob gene


  Required to produce satiety factor

  Encodes for hormone, leptin

  Mutation i ob gene lead to mouse eating voraciously=obese
• db gene


  required to respond to satiety factor

  Encodes for leptin recptor