Jaymie TicknorIntro Nutrition Science 2460 Sect. 0024 June 2014Chapter #3 : The Human Body: Are We Really What We Eat? 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 appetiteThe 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 cellsa. Detect changes in pressure according to whether the organ is empty or distended with foodb. Relay these data to the hypothalamus2. Chemicals (hormones): a chemical messenger secreted into the bloodstream by one of the many glands of the bodya. Acts as a regulator of physiologic processes at a site remote from the gland that secretes itb. Glucose and insulin are responsible for maintaining blood glucose levelsi. Glucose is the body’s most readily available fuel supplyc. Satiated: feeling full3. Amount and type of food we eata. Foods containing protein have the highest satiety (full) valueb. Bulky meals tend to stretch the stomach and small intestinei. Sends signals back to the hypothalamus telling us that we are fullAre 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 metabolismCells 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 membraneCells 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■ Further processed and packaged for transport■ Responsible for the breakdown of lipids and for storage of mineral calcium○ Mitochondria: called the cell’s powerhouses■ Produce the energy molecule ATP from basic food components● Stored form of energyCells 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 functionWhat Happens to the Food We Eat?● Digestion: the process by which foods are broken down into their component molecules, either mechanically or chemically● Absorption: the physiologic process by which molecules of food are taken from the gastrointestinal tract into the circulation● Elimination: the process by which undigested portions of food and waste products are removed from the body● 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 gallbladderDigestion 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 mouthand 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 bodyprocesses but are not apparently changed during those processesThe 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 trachea● Esophagus: a muscular tube of the GI tract connecting the back of the mouth to the stomach○ Upper Esophageal Sphincter: sphincter muscle at the top of the esophagus○ Contracts two sets of muscles:1. Inner sheets of circular musclea. Squeeze the food2. Outer sheets of longitudinal musclea. Push food along the length of the tube● Peristalsis: waves of squeezing and pushing contractions that move food in one directionthrough 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 stomachThe Stomach Mixes, Digests, and Stores Food● Stomach: a J-shaped organ where food is partially digested, churned, and stored until it isreleased into the small intestine○ Volume is about 6 fl. oz (¾ 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