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Transcript of PsychExchange.co.uk Shared Resource
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Biological Explanations of Eating Behaviour
The role of neural mechanisms involved in controlling eating and
satiation
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Key Terms
• Ventromeidal hypothalamus (VMH)
• Functions as a satiety centre
• Lateral Hypothalamus• Functions as a feeding
centre
• Hypothalamus• Part of the forebrain that
controls the pituitary gland and the ANS. Contains centres for eating behaviour. Controls many homeostatic processes such as thirst and hunger
• Homeostasis• Is how the body maintains
a constant internal environment
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Hormones
• Insulin and glucagons are released from the pancreas and play a vital role in eating behaviour
• Insulin controls blood glucose levels• Also converts glucose to glycogen to be
stored in the liver• Along with fatty tissue makes up the main
energy reserve
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Hormones
• Hunger increases as glucose levels decrease and this decline in blood sugar stimulates the lateral hypothalamus
• This results in hunger• Eating causes rise in blood sugar• This activates the VMH • This leads to feelings of satiation• Further feeding is inhibited
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What happens when you lesion the VMH?
Hetherington and Ranson (1942) created lesions to the VMH in rats and found these animals overate and became dramatically obese.
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Anand and Brobeck (1951) created lesions to the lateral hypothalamus. This resulted in aphagia
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Problems with the role of the hypothalamus
• Gold (1973) found that lesions only to the VMH did not result in hyperphagia but only when the lesions affected other areas of the brain as well
• Not replicated and VMH findings are
• Damage to the LH causes problems in other aspects of behaviour such as thirst and sex
• Eating behaviour affected by other areas of the brain
• Suggesting the hypothalamus is not the eating centre
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The Role of Leptin
Read about this study in handout
But the relationship is not a simple one – few obese people have genetic leptin deficiency and in some cases have higher levels
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Signals for Starting a Meal
• In humans there is a set schedule for meals – a learned response.
• Taste and smell
• An empty stomach – ghrelin a hormone secreted as the stomach becomes empty
• In animals injections of ghrelin increase food intake and body weight
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http://www.elyzea.co.uk/gastric/patient.html#ancre3
See AQA book page 155 for evidence of the influence of ghrelin and use this study for bringing in methodology
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Adipocytes
• Cells where fat is stored
• The number is fixed from childhood
• The only thing that can vary is how full they are
• This is how the body maintains the body weight
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http://www.eufic.org/page/en/page/LS/fftid/Fat-cell-number-stays-constant-in-adults/
Adipocytes in childhood
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Commentary
• Complex area with interlinked biology including hormones, neurotransmitters, hypothalamus and proteins
• Strong applications of research • Reductionist – which is both necessary and
problematic• Non human animals in research• Cognitive factors must be considered• Problems with identifying biological causes include
a fatalist attitude towards obesity