Chapter 3 The Human Body Are We Really What We Eat Why Do We Want to Eat Hunger physiological drive for food Appetite psychological desire to consume specific foods o Aroused by environmental cues Anorexia physiological need for food yet no appetite 02 05 2014 What tells us we are hungry Hypothalamus triggers feelings of hunger or satiation fullness o Located above the pituitary gland and the brain stem in an area of the brain that regulates involuntary activities o Integrates signals from nerve cells chemical messengers hormones and the types of food consumed The role of nerve cells and hunger Special cells lining the stomach and small intestine o Detect changes in pressure which indicate whether the organ is empty or distended with food o 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 o Pancreatic hormones insulin glucagon maintain blood glucose levels o 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 o Proteins will make you feel full for a longer period of time o High fat foods have a higher satiety value than high carb diets o Bulky meals high in fiber and water distend the stomach and promote a sense of satiety o Solid foods are more filling than semisolid foods or liquids Why do we want to eat Foods stimulate our senses o Sight o Smell o Taste o Texture mouth feels o Hearing Social and cultural cues Learned experiences The Role of environmental cues in appetite Special and cultural Cues o Special occasions o Certain locations and activities o Being with others o Time of day o Environmental sights and sounds associated with eating o Emotions prompted by external events such as interpersonal conflicts personal failures or successes financial and other stressors Learned factors o Family o Community o Religion o Culture o New learning from exposure to new cultures new friends nutrition education and so on What happens to the food we eat Food undergoes three processes o 1 Digestion Large food molecules are broken down to smaller molecules mechanically and chemically Process of taking these products through the intestinal o 2 Absorption wall o 3 Elimination Undigested portions of food and waste products are removed from the body The Gastrointestinal GI Tract A series of organs arranged in a long tube that work together to Sphincters muscles that control the passage of food material from process foods one GIT organ to the next Cephalic Phase of Digestion Hunger and appetite work together to prepare the GI tract for First thought of food nervous system stimulates the release of Digestion Begins in the Mouth Chewing moistens the food and mechanically breaks it into smaller o Exposes more surface area to digestive juices Saliva contains digestive juices secreted by the salivary gland in digestion digestive juices pieces the mouth Taste receptors detect distinct tastes o bitter sweet salty sour and umami Olfactory receptors detect aromas of foods Components of Saliva Enzymes are complex chemicals that induce chemical changes in other substances to speed up bodily processes o 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 bolus The epiglottis covers the opening to the trachea windpipe during Food travels from the mouth to the stomach through the Peristalsis is the muscular contractions that move food through swallowing esophagus the GI tract The pH Scale pH potential of hydrogen Measures the potential of a substance to release or take up hydrogen ions in solution Put another way pH is a measure of a compound s acidity or Pure water is neutral human blood is close to neutral Tissues lining the stomach are generally protected from the effects alkalinity of acidity Digestion in the Stomach Gastrin o a hormone secreted by stomach lining cells that stimulates the gastric glands to produce gastric juice Gastric Glands o Parietal Cells secrete HCI and intrinsic factor o Chief Cells secrete pepsinogen and gastric lipase Gastric Juice contains o Hydrochloric acid HCI denatures protein and activates pepsin o Pepsin enzyme to digest protein o Gastric lipase enzyme to digest fat o 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 Mucus layer protects the stomach lining from the acid in gastric stomach juices Bicarbonate neutralizes the acid Digestion in the Small Intestine Small intestine is composed of three sections o Dueodeum Jejunum and Ileum Illeocecal 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 the 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 carbs proteins 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 CCK GIP Hormones with potential digestive roles Produce store and secrete enzymes and other chemicals that are o Somatostatin o Ghrelin Accessory Organs involved in digestion o Gallbladder o Pancreas o Liver Accessory organs Gallbladder Gallbladder stores bile a greenish fluid produced by the liver CCK signals the gallbladder to release bile Bile emulsifies the lipids o Lipids are dispersed into smaller globules and become accessible to digestive enzymes Accessory organs Pancreas Manufactures holds and secretes digestive enzymes Stores enzymes in the INACTIVE form o Pancreatic amylase digests carbs o Pancreatic lipase digests fats o Protease digests
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