15. Hunger and Satiety - Lecture notes 15 PDF

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Summary

Hunger and SatietyAmount of food consumed vs energy spent = determines body fatOverweight and obesity trends At least 60% of adults in the UK are overweight, 20% considered obese (BMI > 30) Over 30,000 deaths a year are caused by obesity in England alone Disruption of biological control syste...

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Hunger and Satiety Amount of food consumed vs energy spent = determines body fat

Overweight and obesity trends -

At least 60% of adults in the UK are overweight, 20% considered obese (BMI > 30)

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Over 30,000 deaths a year are caused by obesity in England alone

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Disruption of biological control systems is thought to be a major factor

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Social and cultural factors play a major role in development of eating disorders

Socioeconomic factors -

Increase in portion size

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Increase in sedentary activities

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recreational internet use close to equalling

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television viewing (internet usage, less active) also less active in jobs

Changing ideals of female beauty

Other life threatening eating disorders -

Anorexia nervosa – a syndrome in which individuals severely deprive themselves of food

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Bulimia – marked by periodic gorging and purging by vomiting or laxatives

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Binge eating – gorging with more food than is necessary to satisfy hunger

Food for energy – body uses energy in 3 primary ways 1. Basal Metabolism (BMR) -

55% of energy usage is to maintain body heat -

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(varies as a function of body size)

Bigger organisms have bigger BMRs -

(eg : elephants>humans; humans > mouse)

2. Digestion of Food -

33% of energy is used to process food and break it down into molecules to be used by the body

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(taking in energy, requires energy)

3. Active Behavioural processes -

12/13% of energy usage is for behaviours other than rest (varies greatly depending on activity level) -

Doing shit (running, picking things up etc (varies at diff times in the day ))

4. Remaining energy -

is typically stored as energy reserves

Sources of Energy Carbohydrates (saccharides) - Sugars -

~4kcal per gram,

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Non essential source of energy (if u take these out (low-carb diet), ur body uses fat stores)

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provide a principal source of energy.

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Carbs get converted to glucose

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Storable form of carbohydrates are called Glycogens

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You get from others too (lipids, amino acids etc but carbs give u energy)

stores in liver and muscles, short term storage (non-essential)

Amino acids (proteins) -

~4kcal per gram

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comes from proteins,

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basic building blocks for all cells.

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20 amino acids,

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9 cannot be produced by body = essential amino acids; -

can be converted to glucose (but u can get glucose from others)

Lipids (fats) -

~9kcal per gram,

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long term energy storage

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fats can be converted to free fatty acids as alternate energy source

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(essential) as building blocks (cell membranes are made of lipids)

Vitamins and minerals -

needed to assist in bodily functions (digestion, cell building, cell homeostasis etc.),

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essential

Glucose = primary fuel for the body -

Insulin -

Increases from pancreas when digestive system has food -

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Decreases when digested system is empty -

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glucose

Gucagon

takes excess glucose when you have too much and converts into a complex sugar (glycogen) so it can be used if you later don’t consume enough, -

Then it will be reconverted from glycogen to glucose by a hormone called ‘glucagon’

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Fats are converted into fatty acids aka ‘glycerol’ -> glucose -> energy -

(this is why carbs are not a necessity, they can be converted from other things to produce energy)

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Adipose tissue = fat

Amino acids = minor source -

to create protein synthesis

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Adipose tissue -> Glycerol -> glucose -> energy

Homeostasis and drive reduction maintaining a stable internal state Motivational drive emerges from need to avoid deviations from the narrow set-point 1. Set point – physiological parameter (thermostat) 2. Error detector – compares actual versus set-point state 3. Error correction mechanism – negative feedback mechanism

Feeding to maintain homeostasis Glucostat theory’ (Mayer, 1954) He saw absolute blood glucose as likely signal for hunger ●

Glucose is the main source of energy

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Lack of glucose would represent nutrient deficit (drive)

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(Campfield and smith, 2003) correlated glucose levels in blood with when you eat/hunger ○

Glucose levels dipped

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Then glucose levels rise

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(cause no food) (glycogen -> glucose (cause the animal is hungry and uses its stored complex sugars)

You get meal initiation (hunger) while it slowly rises after having dipped.

Types of set points To regulate food intake ●

Glucostatic Set-Point Theory ○

Eating is controlled by deviations from a hypothetical blood glucose set-point ■

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(glucostat receptors)

Lipostatic Theory ○

Eating is controlled by a hypothetical body-fat set-point ■

(long term homeostatic maintenance)

The dual-centre hypothesis – feeding dedicated brain areas? Which areas inhibit/motivate feeding? ●

Ventromedial hypothalamus (VMH) lesions increase feeding (hyperphagia) and weight – Satiety Center

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Damage/lesions to lateral hypothalamus (LH) causes large decrease feeding (aphasia) and reduced body size – Hunger Center ○

Recent work shows that the LH contains glucose receptors (along with the liver) ->> cause it makes u eat.

Experiment Light is being shone in the lateral hypothalamus (LH)’s light sensitive channels are. -

Light on = immediately starts eating -

Blue = long wavelength = start eating alot and fast

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Green = short = slow eating

Problems with dual centre hypothesis : James olds and Elliot Valenstein -

Press level, put light into LH, LH is activated. LH is the hunger center right?

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Rat presses level many times

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Brain sites where stimulation causes eating (induces state of hunger) are the same sites where self-stimulation is rewarding

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If LH is a hunger centre, then why is it pressing the lever so many times?

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LH stimulation sometimes produces feeding, but just as often as other behaviours (drinking, aggressions etc)

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Effects of LH stimulation depends on the situation -

So LH is a motivational centre… not just for food

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Instead… maybe there are hormones dedicated to hunger/satiety...