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Chapter 12

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PSYC 370
Monica Valsangkar- Smyth

Chapter 12: Hunger, Eating, and Health- Why Do Many People Eat Too Much? - Set point: the value of a physiological parameter that is maintained constantly by physiological or behavioural mechanisms; for example, the body’s energy resources are often assumed to be maintained at a constant optimal level by compensatory changes in hunger - Digestion: the process by which food is broken down and absorbed through the lining of the gastrointestinal tract - Steps in digestion diagram, page 300 - Energy is delivered to the body in three forms: lipids, amino acids, and glucose - Energy is stored in the body in three forms: fats, glycogen, and proteins ; most of the bodies energy reserve is stored as fats - Two reasons why fat is the primary mode of energy storage: (1) a gram of fat can store almost twice as much energy as a gram of glycogen, (2) glycogen attracts and holds substantial quantities of water unlike fat o This water retention would cause a person to weight a lot more - Three phases of energy metabolism: o Cephalic phase: the metabolic phase during which the body prepares for food that is about to be absorbed o Absorptive phase: the metabolic phase during which the body is operating on the energy from a recently consumed meal and is storing the excess as body fat, glycogen and proteins o Fasting phase: the metabolic phase that begins when energy from the preceding meal is no longer sufficient to meet the immediate needs of the body and during which energy is extracted from fat and glycogen stores - During rapid weight gain people may completely skip the fasting phase and just go between the cephalic phase and absorptive phase o During these two phases pancreas releases a great deal of insulin (a pancreatic hormone that facilitates the entry of glucose into cells and the conversion of bloodborne fuels to forms that can be stored) into bloodstream and very little glucagon - Insulin does three things: 1. Promotes the use of glucose as the primary source of energy by the body 2. Promotes the conversion of bloodborne 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 protein in muscle - Function of insulin during cephalic phase lower levels of bloodborne fuels, primarily glucose, in anticipation of the impending influx - Function of insulin during absorptive phase minimize the increasing levels of bloodborne fuels by utilizing and storing them - Fasting phase is characterized by high blood levels of glucagon and low levels of insulin - Glucagon: a pancreatic hormone that promotes the release of free fatty acids from adipose tissue, their conversion to ketones, and the use of both as sources of energy - Insulin is needed for glucose to enter cells, therefore, low levels of insulin help save glucose for the brain, and also promote the conversion of glycogen and protein to glucose o Gluconeogenesis: the process by which protein is converted to glucose - High levels of fasting-phase glucagon promote the release of free fatty acids (main source of energy during fasting phase) from adipose tissue - High glucose levels stimulate the conversion of free fatty acids to ketones; used by muscles as a source of energy during fasting phase - Summary of three stages on page 302 - Set-point assumption: the assumption that hunger is typically triggered by the decline of the body’s energy reserves below their set point - All set-point systems have a three components a set point mechanism, a detector mechanism, and an effector mechanism (acts to eliminate the deviations) - Negative feedback systems: systems in which feedback from changes in one direction elicit compensatory effects in the opposite direction - They act to maintain homeostasis (the stability of an organisms constant internal environment) - Glucostatic theory: the theory that eating is controlled by deviations from a hypothetical blood glucose set point - Lipostatic theory: the theory that eating is controlled by deviations from a hypothetical body-fat set point - These two theories were viewed as complementary - Positive-incentive theory: the idea that behaviours (i.e., eating and drinking) are motivated by their anticipated pleasurable effects - Positive-incentive value: the anticipated pleasure associated with a particular action, such as taking a drug - Most humans have a special fondness for sweet, fatty and salty tastes - Bitter tastes typically have an aversion often associated with toxins - Hunger is caused by expectation of food but not by an energy deficit - Satiety: the motivational state that terminates a meal when there is food remaining o Play a role in determining how much we eat - Nutritive density: calories per unit volume of food o Satiety signals depend on nutritive density - Sham eating: the experimental protocol in which an animal chews and swallows food, which immediately exists the body through a tube implanted in its esophagus - Appetizer effect: the increase in hunger that is produced by the consumption of small amounts of palatable food - Amount of consumption is influenced by the size of what we eat - Cafeteria diet: a diet offered to experimental animals that is composed of a wide variety of palatable foods - Sensory-specific satiety: the fact that the consumption of particular food produces increased satiety for foods of the same taste than for other foods - It appears that signals from taste receptors produce an immediate decline in the positive- incentive value of similar tastes and that signals associated with the postingetive consequences of eating produce a general decrease in the positive-incentive value of all foods - Suggestion that sensory-specific satiety has two kinds of effects: o Relatively brief effects that influence the selection of foods within a single meal o Relatively enduring effects that influence the selection of foods from meal to meal - Sensory-specific satiety has two adaptive consequences o It encourages the consumption of a varied diet o Encourages animals to eat a lot - The drop in glucose before a meal does not have to do with the body needing more glucose but more so with the body preparing for the influx of glucose - Ventromedial hypothalamus (VMH): the area of the hypothalamus that was once thought to contain the satiety center - Lateral hypothalamus (LH): the area of the hypothalamus once thought to be the feeding center o Both turned out to be wrong - Hyperphagia: excessive eating; caused by large bilateral electrolytic lesions to the ventromedial hypothalamus o VMH Syndrome (as known at the time) has two different phases: dynamic phase and static phase
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