NEURAL/ HORMONAL MECHANISMS OF EATING BEHAVIOUR

• EXAMPLE OF MODEL?

  dual centre model
• WHAT DOES THE DUAL CENTRE MODEL CONSIST OF?

  ventromedial hypothalamus, lateral hypothalamus, leptin and ghrelin
• VENTROMEDIAL HYPOTHALAMUS?

  • "eating off switch"
  • activates when glucose levels rise
  • damage = hyperphagia
• LATERAL HYPOTHALAMUS?

  • "eating on switch"
  • activates when glucose levels drop
  • damage = aphagia
• LEPTIN?

  • hormone
  • released from fatty tissue
  • lowest when hungry
  • rises as someone eats
  • increases satiety
  • suppress eating behaviours
  • linked to ventromedial hypothalamus
• GHRELIN?

  • hormone
  • released from stomach and small intestine
  • lowest after meal
  • rises as someone abstains from eating
  • increases hunger
  • stimulates eating behaviour
  • linked to lateral hypothalamus
• PROCESS OF DUAL CENTRE MODEL?

  1. Hunger so eating begins
  2. Ghrelin decreases, leptin increases
  3. Ventromedial hypothalamus activated
  4. Satiety so eating stops
  5. Ghrelin increases, leptin decreases
  6. Lateral hypothalamus activated
• EVALUATION?

  + Anand and Brobeck

  + Hetherington and Ranson

  -Gold

  -Valassi et al

  -Woods
• ANAND AND BROBECK?

  • lesioning of lateral hypothalamus
  • in rats
  • caused aphagia
• HETHERINGTON AND RANSON?

  • lesioning of ventromedial hypothalamus
  • in rats
  • lead to hyperphagia
  • rats became severely obese
• GOLD?

  • lesioning surgical procedures not precise enough to be restricted to only one area
  • other areas damaged
  • PVN (paraventricular nucleus) damaged
  • when only ventromedial hypothalamus lesioned no hyperphagia occured
  • two centres control physiological mechanisms of eating behaviours
• VALASSI ET AL?

  • oversimplified
  • CCK (cholecystokinin) important hormone
  • produced in duodenum
  • activates nerve sending impulses from gastrointestinal tract to hypothalamus to indicate satiety
  • CCK more powerful appetite suppressant
  • serotonin/ dopamine role not considered (interact to inhibit/ enhance)
• WOODS?

  • lateral hypothalamus stimulates hunger in emergency only
  • eating behaviours controlled by social or cultural factors relating to lifestyle
  • outdated view
  • biological approach ignores important factors