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Chapter 12 - Hunger, Eating and Health

Chapter 12 - Hunger, Eating and Health - HU GER EATI G and...

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HUglyph1197GER, EATIglyph1197G and HEALTH (Chap. 12) Biology of ingestive behavior How is eating regulated? Hunger and satiety. Eating disorders are prevalent, indicating that the mechanisms that regulate eating behavior are complex and not well understood. By one estimate, over half of the adul U.S. population meets the current criteria of clinical obesity. Digestion and energy flow. Digestion is the gastrointestinal process of breaking down food and drink and absorbing them into the body. Digestive system and steps in Digestion (FIG. 12.1). 1. Chewing mixes food with saliva , and initiates digestion (action of enzymes in saliva). 2. Swallowing passes food through esophagus. 3. Stomach acts as a reservoir. HCl (hydrochloric acid) breaks up food into small particles and Pepsin (digestive enzyme), secreted by stomach, breaks down protein into aminoacids (aa). 4. Stomach empties content into duodenum, where most of the absorption takes place. Here, digestive enzymes from liver (gall bladder) and pancreas act on proteins and sugars . The products can be absorbed into the blood stream and transported to the liver. 5. Bile, produced by the liver and stored in the gall bladder, emulsifies fat (droplets), which then passes into the limphatic system. 6. The large intestine absorbs most of the remaining water and electrolytes, and what is left exits the system through the anus. As a consequence of digestion, energy is delivered to the body in three main forms : 1) Lipids (fats) 2) Aminoacids (aa), the breakdown products of proteins 3) glucose, the breakdown product of carbohydrates (starches and sugars) Energy is stored as: (Fig. 12.2) -fats in adipose tissue (85%) Why so much? fats store twice as much energy as glycogen, and holds less water. A person would weigh 600 lb if energy were stored as glycogen
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(which is readily converted to glucose)! -proteins in muscle (14.5%) -glycogen in muscle and liver (.5%) Phases of energy metabolism : (Fig. 12.3) Cephalic : Preparatory phase, from seeing and smelling food to the beginning of absoption into the bloodstream. Absorptive : Food absorbed meets immediate energy needs. Fasting : Energy in stores is used, leading to weight loss. The flow of energy during these three phases is regulated by two hormones produced by the pancreas: insulin and glucagon . During the cephalic and absorptive phases, insulin is high, and glucagon is low. High levels of insulin promote: -the use of glucose by body cells. -the conversion of glucose into fats and glycogen, and aa into proteins. -the storage of fats, glycogen and proteins During the fasting phase, glucagon is high and insulin is low. Because insulin is low, glucose cannot be easily utilized by the body. But most brain cells do not need insulin to use glucose. Thus, glucose is reserved for the brain. Low levels of insulin also promote gluconeogenesis : convertion of proteins to glucose.
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Chapter 12 - Hunger, Eating and Health - HU GER EATI G and...

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