Biological Explanations of Eating Behaviour

The role of neural mechanisms involved in controlling eating and

satiation

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

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

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

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.

Anand and Brobeck (1951) created lesions to the lateral hypothalamus. This resulted in aphagia

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

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

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

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

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

http://www.eufic.org/page/en/page/LS/fftid/Fat-cell-number-stays-constant-in-adults/

Adipocytes in childhood

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