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Homeostasis & Hunger: Your Body’s Constant Drive to Stay in Balance Homeostasis • A tendency to maintain a balanced or constant internal state • The regulation of any aspect of body chemistry, such as blood glucose, around a particular level • Any change in levels, up or down, results in being motivated to bring the level back to normal. Energy Balance •Positive energy balance occurs when caloric intake exceeds calories expended for energy. The excess glucose is converted to body fat. •Negative energy balance occurs when caloric intake falls short of the calories expended for energy. Body fat stores shrink as the reserve energy in fat cells is used Basal Metabolic Rate (BMR) AKA your metabolism! • The body’s resting rate of energy expenditure • The rate at which the body uses energy for vital functions while at rest • Factors that influence BMR • Age • Gender • Size • Genetics • Food intake There is a steep decline in the rate at which your body uses energy for vital functions, such as heartbeat, breathing, and body heat. Your BMR continues to decrease by about 2 to 3 percent during each decade of adulthood. At all points in the lifespan, women’s metabolic rate is 3 to 5 percent lower than men’s Body Mass Index: A measure for human body shape based on an individual’s weight and height. (This equation doesn’t account for differences in muscle vs. fat.) We’re # 1! Factors Contributing to Being Overweight • Highly palatable food—we eat because it tastes so good • SuperSize It—food portions are larger than necessary for health • Cafeteria Diet Effect—more food and more variety leads us to eat more • Snacking—does not cause us to eat less at dinner • BMR—changes through the lifespan • Sedentary lifestyles Set Point • A person’s average weight long term • (NOT necessarily a person’s ideal weight!) • When the body falls below this weight, increased hunger and a lower basal metabolic rate (BMR) may act to restore the lost weight. Physiology of Hunger Hypothalamus – The Control Center States of the Brain Cerebral cortex Hypothalamus • The hub of many central drive systems lies in the hypothalamus Portion of limbic system Pituitary gland Brainstem Hunger Drive • Two areas of the hypothalamus, the lateral and ventromedial areas, play a central role in the hunger drive Hypothalamus Hypothalamus Ventromedial Area • Decreases Hunger • Lesions (tissue damage) alter digestive and metabolic processes • Food is converted into fat rather than energy molecules, causing animal to eat much more than normal and gain weight • Lesions = Fat rats!! Hypothalamus Hypothalamus Lateral Area • Increases Hunger • Lesions reduce hunger drive as well as general arousal • Lesions = Skinny rats! Hypothalamus Hypothalamus The Appetite Hormones • Insulin: Hormone secreted by pancreas; controls blood glucose. • Leptin: Protein secreted by “bloated” fat cells; when abundant, sends a message to “stop eating” to brain that increases metabolism and decreases hunger. • Orexin: Hunger - triggering hormone secreted by hypothalamus. As glucose levels drop, orexin levels increase and person feels hungry • Ghrelin: Hormone secreted by empty stomach; sends "I'm hungry" signals to the brain. • Corticotropin-Releasing Hormone (CRH): hormone in hypothamalus that sends "I'm not hungry" signals to the brain. Eating Disorders Eating Disorders • Anorexia nervosa —characterized by excessive weight loss, irrational fear of gaining weight and distorted body image • Bulimia nervosa —characterized by binges of extreme overeating followed by selfinduced purging such as vomiting, laxatives • Binge-eating —disorder characterized by recurring episodes of binge eating without purging. • **Body Dysmorphic Disorder Men’s & Women’s Body Images According to surveys on body image, people in our society are much more dissatisfied with their bodies now than they were a generation ago. Women are still more dissatisfied than men, but today’s men are more dissatisfied with their bodies than the men of a generation past. Anorexia Nervosa Key Features 1. Refusal to maintain a normal body weight 2. Intensely afraid of being overweight. 3. Suffer from delusions of being overweight. 4. Denies there is a problem. • Usually in adolescent females • May put themselves on selfstarvation regimens • May become dangerously underweight Bulimia Nervosa • An eating disorder characterized by episodes of overeating (usually high calorie foods) • Overeating is followed by vomiting, using laxatives, fasting, or excessive exercise • Usually stay within their normal weight. • Usually recognize they have an eating disorder. Pica • • • • Strange but True! Hippocrates the first to describe the disorder People display a compulsive craving for inedible substances such as clay, dirt, laundry starch, chalk, buttons, paper, dried paint, burnt matches, ashes, sand, oyster shells or broken crockery. Seen most often in pregnant women or nursing women but also with people with severe mental disorders. Could be a behavioral response to stress.