Lecture 3 Material
Lecture 3 Material HS 331
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This 5 page Class Notes was uploaded by Sydney Brummett on Saturday September 24, 2016. The Class Notes belongs to HS 331 at Wichita State University taught by Dr. Lisa Wray in Fall 2016. Since its upload, it has received 13 views. For similar materials see Principles of Diet and Nutrition in Health Sciences at Wichita State University.
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Date Created: 09/24/16
Chapter 3 Lecture Why do we eat? o Energy for body processes o Heat for body temperature regulation o Building blocks for growth, maintenance and repair of body tissues What do we want to eat? o Food is intimately connected to our sense of taste, but also stimulates our senses of: Sight Smell Touch Hearing Why do we want to eat? o Hunger: physiological sensation to eat Regulated by internal cues o Appetite: psychological desire to eat Strong desire to eat, even when not hungry o Satiety: the felling of being full o Anorexia: physiologic need for food yet have no appetite Factors Affecting Hunger and Satiety o The hypothalamus region of the brain is the feeding center Nerve cells in stomach and small intestine sense food and send message to hypothalamus Hormones relay messages to the hypothalamus Amount and type of food consumed influence satiety Why do we want to eat? o The signals that prompt us to eat include: Nerve receptors in the stomach send signals to the hypothalamus to indicate if the stomach is full or empty Blood glucose levels trigger the release of hormones called insulin and glucagon o Hormones: chemicals produced in specialized glands that travel in the bloodstream to target organs in other parts of the body Some hormones stimulate hunger Some hormones produce a feeling of satiety o Food have differing effects on our feelings of hunger and satiety Proteins have the highest satiety value Carbs have a lower satiety value Bulky foods provide a sense of satiety Solid foods are more filling than semisolid foods or liquids Organization of the body o Carbohydrates, proteins, fats and vitamins are usually very large molecules o The goals of digestion: Break these large molecules down to smaller molecules Absorb the smaller molecules into the cells of the body o Atoms: the smallest units of matter Atoms bond to each other to form molecules o Molecules: groups of atoms bonded in specific configurations Examples: Water is H20 Carbon dioxide is CO2 o Molecules are the building blocks of life o Cells: the smallest unit of life o Molecules that result from the digestion of food are used to build the cells of the body o Cell membrane: outer layer enclosing each cell of the body Composed of two layers of phospholipids Long lipid “tails” face each other toward the interior of the membrane Phosphate “heads” line the interior and exterior surfaces of the membrane o The cell membrane is selectively permeable, allowing it to control the passage of materials into and out of the cell o The cell membrane encloses the: Cytoplasm – the liquid within the cell Organelles – tiny structures that perform many different cellular functions Example: Nucleus Mitochondria o Cells join together to form tissues o Tissue: group of cells acting together to perform a common function Examples Muscle tissue Nervous tissue o Different tissues combine to form organs o Organ: a sophisticated organization of tissues that performs a specific function Examples: Stomach Heart Brain o Organ systems: groups of organs working together for a particular function Example: Gastrointestinal system What happens to the food we eat? o Gastrointestinal (GI) tract: series of organs arranged as a long tube through which the food passes o The GI tract includes: Organs such as the stomach and intestines Sphincters: muscles that control the passage of material from one organ to the next Digestion o Digestion: the process of breaking large food molecules down to smaller molecules o It includes: Mechanical digestion: the physical breakdown of food Chemical digestion: enzymatic reactions that break down large food molecules Digestion: The Mouth o Digestion begins in the mouth Chewing is the mechanical digestion that breaks food into smaller pieces Some chemical digestion takes place in the mouth Salivary amylase: an enzyme produced by the salivary glands that begins the chemical digestion of carbs The epiglottis covers the opening to the trachea during swallowing Food travels from the mouth to the stomach through the esophagus Peristalsis is the muscular contractions moving food through the GI tract Digestion: Stomach o The gastroesophageal sphincter separates the esophagus from the stomach Prevents the flow of food from the stomach back into the esophagus o Digestion in the stomach includes: Extensive mechanical digestion to mix food with gastric juice Chemical digestion of proteins and fats o Gastric juice contains: Hydrochloric acid (HCl): to denature proteins andactivate pepsin Pepsin: an enzyme to digest protein Gastric lipase: an enzyme to digest fat Mucus: to protect the stomach lining o Chime: semisolid product of mechanical and chemical digestion in the stomach Digestion: Small Intestine o From the stomach, chime is slowly released through the pyloric sphincter to the small intestine o Chemical digestion continues in the small intestine using pancreatic enzymes and bile Digestion: Accessory Organs o Surrounding the GI tracts are several accessory organs: Salivary glands Liver: produces bile which emulsifies fats Pancreas Produces many digestive enzymes Produces bicarbonate to neutralize chime Gall bladder: store bile Absorption o Absorption: the process of taking molecules across a cell membrane and into the cells of the body o A small amount of absorption occurs in the stomach o Most absorption of nutrients occurs in the three sections of the small intestine Duodenum Jejunum Ileum o The lining of the GI tracts has special structures to facilitate absorption Villi: folds in the lining that are in close contact with nutrients molecules Brush border: compose of microvilli that greatly increase the surface area o Watersoluble nutrients (carbs, protein, minerals and some vitamins) enter the portal vein The portal vein transports these nutrients to the liver o Fatsoluble nutrients (lipids and some vitamins) enter the lymphatic vessels Lymphatic vessels transport these nutrients directly to the bloodstream Elimination o Undigested food components move through a sphincter called the illeocecal valve to the large intestine o In the large intestine: Very little digestion takes place Material is stored 1224 hours prior to elimination Water and some nutrients are absorbed Disorders related to digestion o The lining of the stomach is designed to cope with hydrochloric acid but other regions of the GI tract are not o Heartburn is caused by hydrochloric acid in the esophagus o Gastroesophageal reflux disease (GERD) is painful, persistent heartburn o Peptic ulcers are regions of the GI tract that have been eroded by HCL and pepsin o The bacterium Helicobacter pylori contributes to the production of both gastric and duodenal ulcers o Diarrhea Can be caused by Food intolerances Infection of the GI tract Stress Bowel disorders Can lead to sever dehydration Is more dangerous for children and the elderly o Constipation No stool passed for two or more days o Irritable Bowel Syndrome (IBS) is a disorder that interferes with normal colon function Symptoms of IBS include: Abdominal cramps and bloating Either diarrhea or constipation IBS is more common in women than in men In Depth: disorder related to foods o Food intolerance: a particular food causes numerous unpleasant symptoms, including: Gas Pain Diarrhea The immune system is not involved o Food Allergy: hypersensitivity reaction of the immune system to a component in a food o Celiac disease: Complete intolerance for gluten, a protein found in wheat, rye, and barley Can damage the small intestine, leading to poor absorption of nutrients Requires a diet lacking wheat, rye and barley There may be a genetic component to the disease
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