Hunger

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What is the first theory of hunger?
Hunger is a consequence of an energy deficit, each indivudal has an optimal level of energy resources and the body seeks to return to this set point --> homeostasis
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Why is evolutionary theory unlikely?
Need to cope with inconssitent resources in the environment, not a system that just responds to energy deficits
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Why isnt it supported by evidence?
REductions in blood glucose needed to start a meal are substantial
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What does not stop a meal?
Drinking a high calorie drink
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What is their ignorance of?
Environmental fators, such as effect of learning, preference and social factors
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What is the first stage of positive incentive theory?
Anticipation: expected pleasure: positive incentive value
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What is the second stage of this theory?
Craving
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What is this?
Eating is intiatiated by craving, enables to take advantage of good food
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What is the final stage of the positive incentive theory?
Multiple factors
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Such as?
flavour of food, knowledge about food, time since last meal and amount of food in gut, blood glucose levels
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How is food aversion learnt?
Food A- glucose, food B- nothing, rats prefer A, flavour A - LiCl and flavour B - nothing, rats avoid A
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How does a rat learn to eat vitamins and minerals?
Almond and salt: no injection - want the banana rather than almond, Banana and sugar + formalin want the almond
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What did Harris et al find?
Thyamine (vitamin B1) depleted rats, learned to chose a complete diet + avoid thyamine deplete diet, effect weakened when there was a choice between 10 different diets
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What did collier suggest?
Most mammals eat small meals thoughout the day
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What initiates a meal?
Pre meal hunger
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For example?
Not eating a meal stresses the body: influc of fuel away from homeostasis, signals for a meal evokes a cephalic phase insulin released into the blood: decreased blood glucose, hunger isnt a cry for energy --> body preparing for homeostasis disruption
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How are rats conditioned with hunger?
Buzzer +light -> food, rats ate more food when the CS was subsequently presented
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What areas of the brain are associated with eating?
The hypothalamus and ventral medial - a satiety centre
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What did Hetherington and Ranson find with a lesion to the ventral medial centre?
Lesion= hyperphagia (overeating to obesity)
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What is the dynamic phase of VMH syndrome?
Excessive eating, weight gain
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What is the static phase of VMH syndrome?
Body weight maintained, overweight returned to following deprivation will not work for food and sensitive to impalatable foods
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What is the lateral?
Feed centre
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What did Anana and Brosbeck find?
The a lesion to the lateral hyperthalamus = feeding centre leads to aphagia
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What is Aphagia?
Inability or refusal to swallow
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What is Adipsia?
REduced thirst
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How is recovery possible?
Tube feeding, milk soaked cookies, dry food pellets
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Why did the theory crumble?
VMH lesions in fact damaged the Nucleus of the hypothalamus
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What happens to the hypothalamus?
regulates metabolism not eating
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Therefore what do VMH lesions lead to?
Increase blood insulin, increase of lipogenesis (production of fats) and reduces lipolysis (break down of fats)
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What is the third reason why?
LH lesions produce a variety of motor disturbances and lack of repulsiveness
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What did Cannon find?
contractions caused by an empty stomach correlated with hunger, patients with stomachs still get hungry and stomach is sufficient for hunger
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What did Koopman find?
Transplanted an extra stomach and intestine into the rats, joined major arties and veins
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What happened to food injected into the stomach?
Decreased eating
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What did the transplated stomach not have?
Nerves
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The satiety signal must have reached the brain through the blood flow but why?
Cant be through nutrients as they are not absorbed by the stomach
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What are peptides?
Short chain of amino acids, injested food stimulates receptors in the gastoriointestinal tract to release these into the bloodstream
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What did Gibbs, young and smith find
Injected peptide Choleystokinin into the gut of hungry rats, rats ate less food
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However what could CCK do?
Induce illness
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which supports?
Flavour aversion
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what is leptin and what does it do
Spontaneous genetic mutation in a mouse coloony, ate ore converted calories to fat more efficiently, mice lacked leptin and negative feed back signals to decrease appetite and enable fat metabolism
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What did Seely and woods suggest?
Leptin receptors found in mouse brain, injections of leptin in obese mice leads to decrease eating and weight
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Other cards in this set

Card 2

Front

Why is evolutionary theory unlikely?

Back

Need to cope with inconssitent resources in the environment, not a system that just responds to energy deficits

Card 3

Front

Why isnt it supported by evidence?

Back

Preview of the front of card 3

Card 4

Front

What does not stop a meal?

Back

Preview of the front of card 4

Card 5

Front

What is their ignorance of?

Back

Preview of the front of card 5
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