Jaymie Ticknor Intro Nutrition Science 2460 Sect 002 4 June 2014 The Human Body Are We Really What We Eat Chapter 3 Why Do We Want to Eat What We Want to Eat Hunger a physiologic sensation that prompts us to eat The drive is nonspecific Appetite a psychological desire to consume specific foods Aroused when environmental cues stimulate senses Anorexia an absence of appetite The Hypothalamus Prompts Hunger in Response to Various Signals Hypothalamus a region of the forebrain above the pituitary gland where visceral sensations and involuntary activity such as hunger and thirst are regulated Triggers feelings of either hunger or satisfaction fullness by integrating signals from three sources 1 Nerve cells a Detect changes in pressure according to whether the organ is empty or distended with food b Relay these data to the hypothalamus 2 Chemicals hormones a chemical messenger secreted into the bloodstream by one of the many glands of the body a Acts as a regulator of physiologic processes at a site remote from the gland that secretes it b Glucose and insulin are responsible for maintaining blood glucose levels i Glucose is the body s most readily available fuel supply c Satiated feeling full 3 Amount and type of food we eat a Foods containing protein have the highest satiety full value b Bulky meals tend to stretch the stomach and small intestine i Sends signals back to the hypothalamus telling us that we are full Are We Really What We Eat Molecules Join to Form Cells Cells the smallest unit of matter that exhibits the properties of living things such as growth reproduction and metabolism Cells Are Encased in a Functional Membrane Cell Membrane the boundary of an animal cell that separates its internal cytoplasm and organelles from the external environment Composed of two layers of molecules called phospholipids Consist of a long lipid tail that repels water Bound to a round phosphate head that interacts with water Cholesterol helps keep the membrane flexible Studded with various proteins Assist in the gatekeeper function Allowing the transport of nutrients and other substances across the cell membrane Cells Contain Organelles Which Support Life Cytoplasm the interior of an animal cell not including its nucleus Organelle a tiny organ within a cell that performs a discrete function necessary to the cell Nucleus genetic information in the form of DNA is located Ribosomes use the instructions from DNA to assemble proteins Endoplasmic Reticulum ER proteins assembled on the ribosomes enter this network of channels calcium Further processed and packaged for transport Responsible for the breakdown of lipids and for storage of mineral Mitochondria called the cell s powerhouses Produce the energy molecule ATP from basic food components Stored form of energy Cells Join to Form Tissues Organs and Systems Tissues a grouping of like cells that performs a function Organs a body structure composed of two or more tissues and performing a specific function System a group of organs that work together to perform a unique function What Happens to the Food We Eat Digestion the process by which foods are broken down into their component molecules Absorption the physiologic process by which molecules of food are taken from the either mechanically or chemically gastrointestinal tract into the circulation removed from the body Elimination the process by which undigested portions of food and waste products are Gastrointestinal GI Tract a long muscular tube consisting of several organs Mouth esophagus stomach small intestine and large intestine Digestion absorption and elimination occur here Food within this tube is digested into molecule small enough to be absorbed by cells lining the GI tract and thereby passed into the bloodstream Sphincters a tight ring of muscle separating some of the organs of the GI tract and opening in response to nerve signals indicating that food is ready to pass into the next section Surrounding the GI tract are the salivary glands liver pancreas and gallbladder Digestion Begins in the Mouth Cephalic Phase the earliest phase of digestion in which the brain thinks about and prepares the digestive organs for the consumption of food Saliva a mixture of water mucus enzymes and other chemicals that moistens the mouth and food binds food particles together and begins the digestion of carbohydrates and process of chemical breakdown One component called amylase starts the process of carbohydrate digestion Contains antibodies that Protect the body from foreign bacteria entering the mouth Keep the oral cavity free from infection Salivary Glands a group of glands found under and behind the tongue and beneath the jaw that release saliva continually as well as in response to the thought sight smell or presence of food Enzymes small chemicals usually proteins that act on other chemicals to speed up body processes but are not apparently changed during those processes The Esophagus Propels Food into the Stomach Bolus a mass of food that has been chewed and moistened in the mouth Epiglottis tiny flap of tissue acts as a trapdoor covering the entrance to the Esophagus a muscular tube of the GI tract connecting the back of the mouth to the trachea stomach Upper Esophageal Sphincter sphincter muscle at the top of the esophagus Contracts two sets of muscles 1 Inner sheets of circular muscle a Squeeze the food 2 Outer sheets of longitudinal muscle a Push food along the length of the tube Peristalsis waves of squeezing and pushing contractions that move food in one direction through the length of the GI tract Gastroesophageal sphincter located at the end of the esophagus is this sphincter muscle Normally tightly closed When food reaches the end of the esophagus this sphincter relaxes to allow the food to pass into the stomach The Stomach Mixes Digests and Stores Food Stomach a J shaped organ where food is partially digested churned and stored until it is released into the small intestine Volume is about 6 fl oz cup when empty When full it can expand to hold about 32 fl oz or about 4 cups Gastric Juice acidic liquid secreted within the stomach Contains hydrochloric acid pepsin and other compounds Hydrochloric acid HCl keeps the stomach interior very acidic Denature the action of the unfolding of proteins in the stomach Proteins must be denatured before they can be digested Converts pepsinogen inactive substance into the active enzyme pepsin Begins to digest proteins into smaller components Activates many