Hunger Digestion gastrointestinal process of breaking down food and absorbing its constituents into the body Energy delivered to body in three forms Lipids stored in Fats a b Amino Acids stored in Proteins c Glucose stored in Glycogen a Glycogen is preferred readily converted to glucose Primary Fats store twice as much energy as glycogen and glycogen attracts water 1 Cephalic Phase preparatory phase starts with sight smell thought of food ends when food is absorbed in bloodstream 2 Absorptive Phase energy absorbed into bloodstream and meal meets body s immediate 3 Fasting Phase unstored energy has been used and body is withdrawing energy from 3 Phases of Energy Metabolism needs reserves Flow of 3 Phases Controlled by 1 Insulin during first 2 phases a Promotes glucose use b Conversion of blood borne fuels to forms that can be stored c d Cephalic phase function decrease levels of blood borne fuels glucose in Storage of glycogen in liver and muscle fat in adipose tissue and proteins in muscle anticipation of impending flux e Absorptive phase function lower increasing levels of b b fuels by using and storing them 2 Glucagon Fasting phase a b c Low levels of insulin glucose can t enter body cells saves glucose for brain Low levels of insulin also promote gluconeogenesis glycogen and protein to glucose Increase levels of glucagon release free fatty acids of adipose tissue primary fuel d Free fatty acids to ketones muscles as source of energy Hunger Peptides 1 Ghrelin a Produced and released by stomach b Lesser amounts produced by duodenum upper part of small intestine and pancreas Increased during fasting and highest before meals c d Results in perception of hunger time to eat e Stimulates appetite f 2 Neuropeptide Y Levels decrease after meal a Released by neurons in hypothalamus b Specifically in arcurate nucleus c Appears to increase appetite d Potent stimulator of eating behavior e Increase in fasting phase f Decrease in absorptive phase Satiety Signals how much Food in gut prompts absorptive phase Glucose in blood Volume of food Nutritive density of food Appetizer effect and satiety Social Influences and satiety Stimulates cephalic phase increase in insulin Eat more Social setting Food competition biological basis Sensory specific satiety Satiety Peptides 1 CCK Tasting a food immediately decreases the positive incentive value of similar tastes Decreases the palatability of all foods about 30 mins later Adaptive encourages a varied diet Some foods resistant to S S S o Milk greens bread rice potatoes sweets fruits a Secreted by small intestines i Response to fats in intestines b Controls rate of stomach emptying slows it down i Sphincter closing between stomach and intestine c Decreases hunger 2 Peptide YY a Secreted by cells in ileum small intestine and colon b In proportion to amount of calories i Increase in calories increase in peptide yy Inhibits gastric motility Increase water and electrolyte absorption in colon c d e Decrease in eating 3 Leptin Inhibits release of Neuropeptide Y a Secreted by adipose cells b c Decreases eating d Increases metabolic rate Seratonin and satiety Serotonin agonists consistently reduced rat food intake o Rats resisted attraction of highly palatable diet o Reduced consumption o Shift away from fatty food preferences Similar effects in humans Fenfluramine and dexfenfluramine Seratonin agonists o In appetite suppressants o Controversy stroke and heart attack Combination of fenfluramine and fenturamine Set Point Theories Motivation to eat because of energy deficit o Eat to bring our energy resources back up to optimal level 1 Glucostatic Theory a Hunger waxes and wanes because of blood glucose levels b Short term meal initiation and termination 2 Lipostatic a Related to fats b Long term regulation Positive Incentive Theory Pleasure of eating Feeling of hunger depends on all factors that affect incentive value Settling Point Model Weight tends to drift around natural settling point Various factors that affect body weight each equilibrium Settling Point better explanation for food weight regulations Body weight tends to remain relatively constant in many adult animals over time Accounts for higher weight gains during adult years Weight that is less likely to come back off later because of newly established state of homeostasis Leaky Barrel Model o Increase resources increase metabolism o Better predictor of weight stable o Plateau around 15 weeks reach equilibrium Brain Mechanisms 1 Old View a Ventromedial Hypothalamus i Satiety center ii Lesion hyperphagia overeat 1 No signal for rats to stop eating 2 Start to eat less but don t lose weight b Lateral Hypothalamus i Feeding center ii Lesion aphagia and adipsia under eat and drink 1 Stimulation results in increase of eating and drinking 2 New Research a Ventralnoradrenergic bundle i Close to left hemisphere LH 1 Lesions through the bundle norepinephrine decrease food reinforcement a Rats stopped working for food ii From lateral hypothalamus 1 Melanin concentrating hormone increase eating arousal motivation 2 Orexin stimulated increase hunger and eating 3 Decrease food increase in MCH and orexin iii Arcurate Nuclei 1 Neuropeptide Y stimulates MCH and orexin a NPY has receptors for ghrelin and leptin and Peptide YY i ii iii iv Paraventricular nuclei Increase NPY increase ghrelin Increase leptin decrease NPY Increase PYY decrease NPY 1 Receptors for NPY 2 PVN stimulation leads to activation of brain stem nuclei that controls ANS and other digestive functions