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Chapter 12

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University of Guelph
PSYC 2410
Boyer Winters

BEHAVIOURAL NEUROSCIENCE Week 9 Chapter 12- Hunger, Eating and Health 12.1- Digestion, Energy Storage, and Energy Utilization Digestion- is the gastrointestinal process of breaking down food and absorbing its constituents into the body E is delivered to the body in 3 forms: lipids, amino acids and glucose - E is used continuously but its consumption is intermittent therefore the body stores E (in the form of: fats, proteins and glycogen) between meals. The body stores mostly fat and little of proteins and glycogen Why is fat the bodys preferred way of storing E? - a gram of fat can store almost twice as much energy as a gram of glycogen -glycogen, unlike fat, attracts and holds substantial quantities of water 3 Phases of Energy Metabolism 1. Cephalic Phase- preparatory phase; often begins with the sight, smell of thought of food, and it ends when the food starts to be absorbed into the bloodstream 2. Absorptive Phase- the E absorbed into the bloodstream from the meal is meeting the bodys immediate E needs 3. Fasting Phase:- all of the unstored E from the previous meal has been used and the body is withdrawing E from its reserves to meet its immediate E requirements; it ends with the beginning of the cephalic phase -(rapid) weight can likely arises when a person frequently skips of the fasting phase 2 Pancreatic hormones: insulin and glucagon - control the flow of E during the 2 phases of E metabolism Cephalic & Absorptive - pancreas releases a lot of insulin into the bloodstream and a little bit of glucagon Insulin 1. Promotes the use of glucose as the primary source of E by the body 2. Promotes the conversion of blood-borne fuels to forms that can be stored: glucose to glycogen and fat, and amino acids to proteins 3. Promotes the storage of glycogen in liver and muscle, fat in adipose tissue, and proteins in muscle Fasting -characterized by high levels of glucagon blood levels and low levels of insulin -w/o high levels of insulin, glucose has difficulty entering most body cells; thus glucose stops being the bodys primary fuel source - this saves the bodys glucose for the brain, because insulin is not required for glucose to enter most brain cells. -the low levels of insulin also promote the conversion of glycogen and protein to glucose (gluconeogenesis- conversion of protein o glucose) -high levels of fasting-phase glucagon promotes the release of free fatty acids from adipose tissue and will be used as the bodys primary fuel source. Free fatty acids are also converted into ketones, which are used by the bodys muscles through the fasting phase -the brain will begin to use ketones after a prolonged period of fasting 12.2 Theories of Hunger and Eating: Set Points vs. Positive Incentives Set-point Assumption- after a meal, a persons E resources are assumed to be near their set point and to decline thereafter as the body uses E to fuel its physiological processes. When the level of the bodys E resources falls far enough below the set point, a person becomes motivated by hunger to initiate another meal. The meal continues, according to the set-point assumption, until the E level returns to its set point and the person feels satiated (no longer hungry) All set point systems have 3 components: 1. Set-point Mechanism- defines the set point (ex. Thermostat) 2. Detector Mechanism- detects deviations from the set point (ex. Thermometer) 3. Effectors Mechanism- acts to eliminate the deviations (ex. Heater) - All set points are negative feedback systems- systems in which feedback from changes in one direction elicit compensatory effects in the opposite direction; act to maintain homeostasis- a stable internal environment Glucostatic and Lipostatic Set-Point Theories of Hunger and Eating Glucostatic Theory- eating regulated by a system that is designed to maintain a blood glucose set- pointthe idea being we become hungry when our blood glucose levels drop significantly below their set point and that we become satiated when eating returns out blood glucose levels to their set point Lipostatic Theory- every person has a set-point for body fat, and deviation from this set point produce compensatory adjustments in the level of eating that return levels of body fat to their set point. A support to this theory is the fact that the body weights of adults stay relatively constant *the GT was thought to account for meal initiation and termination, whereas the LT was through to account for long-term regulation Problems with Set-Point Theories of Hunger and Eating -there is an epidemic of obesity and overweight, which should not occur if eating is regulated by a set pointPositive-Incentive Perspectives (PIP) Positive-incentive Theory- humans and other animals are not normally driven to eat by internal E deficits but are drawn to eat by the anticipated pleasure of eatingthe anticipated pleasure of a behaviour is called its positive-incentive value -acknowledges that many factors interact to determine a persons hunger at any time According to the PIP, it is the presence of good food, or the anticipation of it, that normally makes us hungry, not an E deficit. The degree of hunger you feel at any particular time depends on the interaction of all the factors that influence the positive-incentive value (ex. Flavour, the effects you have learned about the food, last time you ate until now, quantity and type of food already in your gut, etc) 12.3 Factors That Determine What, When, and How Much We Eat Factors That Determine What We Ea -certain tastes have a high +ve incentive value for virtually all members of a species (ex. Sweet, fatty, and salty for humans) -bitter tastes, for which humans have an aversion, are often associated with toxins Learning to Eat Vitamins and Minerals 2 patterns: 1. Sodium- when an animal is deficient in sodium, it develops and immediate and compelling preference for the t
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