HUN1201 LECTURE NOTES CHAPTER 3 The Human Body Are We Really What We Eat Why do we want to eat Hunger physiological drive for food Nonspecific Can be satisfied by a variety of different foods Appetite psychological desire to consume specific foods Aroused by environmental cues Anorexia physiological need for food yet no appetite What tells us we are hungry Hypothalamus triggers feelings of hunger or satiation fullness Located above the pituitary gland and the brain stem in an area of the brain that regulates involuntary activities Integrates signals from nerve cells chemical messengers hormones and the types of food consumed The role of nerve cells in hunger Special cells lining the stomach and small intestine detect changes in pressure which indicate whether the organ is empty or distended with food These cells then send signals to the hypothalamus The role of hormones in hunger Hormones Chemical messengers secreted into the bloodstream by endocrine glands to help regulate body functions Pancreatic hormones insulin and glucagon maintain blood glucose levels Feeling full satiated results from signals from the stomach and a rise in blood glucose The role of food type on hunger Foods have differing effects on our feelings of hunger Proteins have the highest satiety value will feel satiated for longer High fat diets have a higher satiety value than high carbohydrate diets Bulky meals high in fiber and water distend the stomach and promote a sense of satiety Solid foods are more filling than semisolid foods or liquids What happens to the food we eat Food undergoes three processes Digestion large food molecules are broken down to smaller molecules mechanically and chemically Absorption Elimination process of taking these products through the intestinal wall undigested portions of food and waste products are removed from the body The Gastrointestinal Tract A series of organs arranged in a long tube that work together to process foods Sphincters muscles that control the passage of food material from one GIT organ to the next Cephalic phase of Digestion Hunger and appetite work together to prepare the GI tract for digestion First thought of food nervous system stimulates the release of digestive juices Digestion begins in the mouth Chewing moistens the food and mechanically breaks it into smaller pieces Exposes more surface area to digestive juices Saliva contains digestive juices secreted by the salivary gland in the mouth Taste receptors detect distinct tastes Enzymes are complex chemicals that induce chemical changes in other Bitter sweet salty sour and umami Olfactory receptors detect aromas of foods Components of Saliva substances to speed up bodily processes Salivary amylase begins starch digestion Bicarbonates neutralize acids Mucus moistens the food and oral cavity Antibodies and lysozymes fight oral bacteria Chewing and Swallowing The mass of food chewed and moistened in the mouth is called bolus The epiglottis covers the opening to the trachea windpipe during swallowing Food travels from the mouth to the stomach through the esophagus Peristalsis is the muscular contractions that move food through the GI tract Digestion in the stomach Gastrin Gastric Glands a hormone secreted by stomach lining cells that stimulates the gastric glands to produce gastric juice Parietal Cells secrete HCl and intrinsic factor Chief Cells secrete pepsinogen and gastric lipase Gastric juice contains Hydrochloric acid HCl denatures proteins and activates pepsin Pepsin enzyme to digest protein Gastric lipase enzyme to digest fat Intrinsic factor protein to absorb vitamin B12 Mechanical Digestion occurs as the stomach mixes and churns the food and gastric juices Chyme liquid product of mechanical and chemical digestion in the stomach Mucus layer protects the stomach lining from the acid in gastric juices Bicarbonate neutralizes the acid Digestion in the small intestine Small intestine is composed of three sections Duodeum jejunum and ileum Ileocecal valve sphincter connects the small intestine to the large intestine Most digestion and absorption take place in the small intestine Digestion in the Large Intestine The large intestine is also referred to as the colon Bacteria assist with final digestion Its main function is to store undigested food material and absorb water short chain fatty acids and electrolytes Enzymes speed up digestion Enzymes guide digestion through hydrolysis a chemical reaction that breaks down substances by addition of water Enzymes are specific to carbohydrate protein and fat digestion Hormones assist in Digestion Released into the bloodstream and act on specific target cells that contain the receptor protein for that given hormone Hormones bind to the receptor on the cell membrane and activate a second messenger system within the cell to achieve the targeted response Key hormones involved in digestion Gastrin Secretin Cholecystokinin CCK Gastric inhibitory peptide GIP Hormones with potential digestive roles Somatostatin Ghrelin Accessory Organs Produce store and secrete enzymes and other chemicals that are involved in digestion Gallbladder Pancreas Liver Accessory Organ Gallbladder Gallbladder stores bile a greenish fluid produced by the liver Bile emulsifies the lipids CCK signals the gallbladder to release bile Lipids are dispersed into smaller globules and become more accessible to digestive enzymes Accessory Organ Pancreas Manufactures holds and secretes digestive enzymes Stores enzymes in the inactive form Pancreatic amylase digests carbohydrates Pancreatic lipase digests fats Protease digests proteins Insulin and glucagon hormones are produced to regulate blood glucose Bicarbonate is secreted to neutralize chime Accessory organ Liver The liver is one of the most important organs in the body Synthesizes chemicals for metabolism Bile for emulsification of fats Receives the products of digestion via the portal vein Releases glucose from glycogen stores Manufactures blood proteins Absorption Filters the blood removing wastes and toxins Stores vitamins Process of taking molecules across a cell membrane and into cells of the body A small amount of absorption occurs in the stomach and large Most absorption of nutrients occurs in the small intestine Process of taking molecules across a cell membrane and into cells of the body A small amount of absorption occurs in the stomach and large intestine intestine Most absorption of nutrients occurs in the small intestine 4 Types of
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