Neural Hormonal Mech

• The hypothalamus - neural and hormonal mechanisms

  • The hypothalamus is the main area in the brain involved in the regulation of appetite
  • Maintains homeostasis - balancing hormones to maintain a steady internal environment.
  • Part of the homeostatic mechanism is detecting whether the body has enough glucose and correcting the situation if doesn't
• Dual Centre Model

  • Two significant eating control centres in the hypothalamus
  • Lateral hypothalamus
  • Ventromedial hypothalamus
  • These work together to control food consumption and weight
• Lateral Hypothalamus - associated with ..., acts as ... and contains ...

  • Is associated with hunger
  • Acts as the "on switch" for eating behaviour
  • Contains cells which detect levels of glucose by the liver communicating when there are low levels of glucose
• Lateral Hypothalamus - What happens when there are low levels of glucose

  • Where there's low levels of blood glucose, it is communicated to the LH which leads to the LH stimulating the release of Neuro peptide Y
  • NPY acts as an appetite stimulant
• Lateral Hypothalamus - What does NPY lead to

  • Feelings of hunger which causes us to search for and to eat food which leads to glucose levels rising
• Ventromedial Hypothalamus - cells communicate..., VMH triggers..., damage leads to...

  • Liver cells communicate a rise in glucose levels to the VMH (aka satiety centre)
  • VMH triggers feelings of satiation which stops further eating
  • Damage to the VMH leads to the inability to stop eating
• Leptin - produced by..., released to..., proportional to..., short term....

  • Leptin is produced by fat cells and released into the bloodstream
  • The amount of leptin released is directly proportional to fat content in the body
  • Short term fluctuations in leptin provides the VMH information about calorie intake
• Leptin - As we eat..., acts as..., leads to...,

  • As we eat, the amount of fat in our body increases so leptin release also increases
  • Leptin acts as an appetite suppressant as it leads to triggering satiety
• Leptin - How does leptin act as an appetite suppressant

  • It binds to receptors in the VMH
  • This counteracts the effects of NPY (appetite stimulant)
  • Leads to a reduction in hunger which leads to feelings of satiety
• Ghrelin - what, where, acts as, undereating...

  • Ghrelin is a hormone that is secreted by the stomach
  • Acts as an appetite stimulant
  • If a person is undereating, their ghrelin levels increase
• Ghrelin - detected by, signals..., triggers...

  • Ghrelin is detected by the arcuate nucleus which signals the LH to release NPY
  • This triggers hunger
• Ghrelin - hormonal marker of..., the amount of ghrelin ... before a meal and ... after

  • Ghrelin is a hormonal marker of how long since we have last eaten because the amount produced is closely related to how empty your stomach is (emptier the stomach, the higher the levels)
  • The amount of ghrelin in the bloodstream doubles just before a meal and decreases very quickly after
• Evaluation points for Neural and Hormonal

  • S - Dual Center Model - supporting evidence
  • W - R into neural/hormonal - animal extrapolation
  • S - hormonal - support for the role of leptin
  • S - hormonal - support for the role of ghrelin
• S - Dual Center Model - supporting evidence. Anand and Brobeck found that damaging the lateral hypothalamus in rats led to a loss of interest in food, decreased eating and weight loss. Hetherington and Ranson showed damage to the ventromedial hypothalamus led to the animals over eating until they were grossly obese. S bc...
• (S of Dual Center Model - supporting evidence)... S bc this validates the supposed roles of each part of the DCM. The rats losing weight due to damage to the LH proves they didn't eat which was caused by a lack of feeling of hunger. This proves that the LH is responsible for hunger. This also proves the role of the VMH regards satiety as when this function isn't executed, the rats overate a lot and gained weight. Increases the validity of DCM
• W of R into neural/hormonal mechanisms beh - issues with animal extrapolation. The R is mainly done on rats as humans rarely survive damage to the hypothalamus. This is an issue as although there are broad similarities between the human brain and the brain of other mammals, you cannot assume findings always apply as the human brain and endocrine system and the way humans regulate feeding behaviour is more complex...
• (W - animal extrapolation)... There are differences in how neural/hormonal activity affects eating behaviour. Human feeding mechanisms are more complex as humans are affected by influences like conscious choices and health concerns. Such mediating factors aren't an influence on rats, therefore we can't use results from rats to understand human eating behaviour. This decreases the validity of our understanding of neural/hormonal mechanisms of eating behaviour
• S - hormonal - support for the role of leptin. R has shown that some mice receive two copies of the gene for obesity (ob/ob mice). ob/ob mice have a tendency to overeat, especially foods high in sugar or fat. Zhang et al have discovered that ob/ob mice have defective genes which makes them deficient in the hormone leptin. Also injecting ob/ob mice with leptin causes them to lose weight dramatically. S bc...
• (S - hormonal - support for the role of leptin)... S bc this proves the role of leptin regarding it being an appetite suppressant as when there is a deficiency of leptin, the mice overeat as they don't feel satiety. When injected with leptin, they lose weight as eating in a regulated way returns due to feelings of satiety. Increases the validity of our understanding of the role of leptin
• S - hormonal - support for role of ghrelin. Wren et al provided support for the role of ghrelin in appetite control in a randomised double blind study of nine healthy volunteers. The participants received intravenous ghrelin or a saline infusion and one week later, the same participants received the other condition. Appetite was measured in terms of the amount of food taken and consumed at a buffet under each condition. The results showed...
• (S - hormonal - role of ghrelin) ... The results showed a significant increase in food consumption in the ghrelin condition compared to the saline condition with a mean difference of 28% between both conditions. S bc since high levels of ghrelin led to an increase in eating, this demonstrated that ghrelin is in fact an appetite stimulant which drives eating behaviour an increase in food intake. As this is in line with our understanding, it increases in validity