Neural and Hormonal Mechanisms

• Hypothalamus - NEURAL

  Hypothalamus - part of brain responsible for control of hormones, linking nervous system (neural) to endocrine system (hormonal)

  Hypothalamus - regulates homeostasis (state of steady internal environment)
• Dual centre model - NEURAL

  Lateral hypothalamus (LH) - hunger centre which initiates eating

  Ventromedial hypothalamus (VMH) - satiety centre feeling of fullness

  • Low glucose level ---> liver sends signal to LH = sensation of hunger = makes ind want to eat
  • After eating, glucose rises as its released ---> activates VMH = produces sensation of satiety = makes ind stop eating

  LH and VMH work together in dual centre model to balance hunger and eating
• Rat studies - NEURAL

  ---> used to show differing roles in VMH & LH in control of hunger

  • LH damage - causes them to stop eating, stimulation of LH stimulates eating behaviour
  • VMH damage - results in overeating, stimulation causes them to stop eating
• What are the two hormonal mechanisms?

  • Ghrelin
  • Leptin
• Ghrelin- HORMONE


  ---> secreted by stomach, acts as a hormonal marker of how long its been since we last ate

  • Emptier the stomach = more ghrelin releases which is then detected by receptors in hypothalamus
  • which sends signals to LH to secrete neuropeptide Y

  Ghrelin - appetite stimulant causing short term increase to amount of food eaten - Malik et al
• Leptin - HORMONE

  ---> suppresses appetite - tells body when satiety is reached.

  • Produced from fat cells into blood to signal to hypothalamus that calorie storage is high
  • Hypothalamus receives message = appetite decreases

  Leptin also binds to receptors in hypothalamus to counteract effects of neuropeptide Y.
• Study to support Ghrelin

  Shiiya et al - found Ghrelin levels were lower in obese & higher in anorexia than normal weight pps.

  Supports Ghrelin as appetite stimulant
• Strength of neural and hormonal mechanisms

  Strong empirical evidence

  Research supports parts of hypothalamus (LH & VMH) e.g. rat studies

  + Cummings - ghrelin levels rise before meals & decrease after it

  Shiiya - found Ghrelin levels were lower in obese & higher in anorexia than normal weight pps.

  Increases credibility
• Limitation of neural and hormonal mechanisms

  Biologically reductionist

  Focuses on biological mechanisms ignoring social and environmental factors

  • e.g. cultural influences cannot be explained by neural & hormonal mechanisms alone
• Limitation of neural and hormonal mechanisms(contradict strength for body of evidence)


  Animal research

  Most studies come from animals especially rats

  Biology between rats and humans are different

  Findings are hard to generalise
• Limitation of neural and hormonal mechanisms

  Biologically reductionist

  Focuses on biological mechanisms ignoring social and environmental factors

  • e.g. cultural influences cannot be explained by neural & hormonal mechanisms alone
• Limitation of neural and hormonal mechanisms




  Methodology issues

  • Most evidence come from small samples of male pps.
  • Limits validity of generalising findings to wider population

  + rely on correlational data meaning its difficult to establish cause and effect relationship
• Strength of neural and hormonal mechanisms




  Practical application

  • Treatments for obesity
  • Leptin therapy ---> explored to help regulate appetite for those with Leptin deficiencies

  Increases validity