Nutrition Science and Everyday Application - beta v 0.1

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THE DIGESTIVE SYSTEM 145 macronutrients into their chemical building blocks (for example, starch into glucose). Enzymes are chemicals that help speed up or facilitate chemical reactions in the body. They bring together two compounds to react, without undergoing any changes themselves. For example, the main chemical reaction in digestion is hydrolysis.Hydrolysis is the splitting of one molecule into two with the addition of water. For example, the sugar sucrose (a double sugar) needs to be broken down to its building blocks, glucose and fructose (both single sugars), before it can be absorbed. This breakdown happens through hydrolysis, and the enzyme, sucrase, brings together the sucrose molecule and the water molecule to react. This process is illustrated in the following animation. Video: Enzyme Action and the Hydrolysis of Sucrose by McGraw-Hill Animations, YouTube (June 3, 2017). 1:46 minutes. A YouTube element has been excluded from this version of the text. You can view it online here: https://openoregon.pressbooks.pub/ nutritionscience/?p=1147
146 ALICE CALLAHAN, PHD, HEATHER LEONARD, MED, RDN, AND TAMBERLY POWELL, MS, RDN Nutrients are of little to no value to the body unless they enter the bloodstream. This occurs through the process of absorption, which takes place primarily within the small intestine. There, most nutrients are absorbed from the lumen (or inside space) of the GI tract into the bloodstream. Lipids are absorbed into lymph but eventually enter the bloodstream as well. In excretion, the final step of digestion, undigested materials are removed from the body as feces. The feces is stored in the rectum until it leaves the body through the anus. FUNCTIONS OF THE DIGESTIVE ORGANS Now that you have an overview of the digestive organs and the digestive process, let’s discuss in more detail what types of mechanical and chemical digestion take place in each of the organs of the GI tract. Let’s imagine eating a peanut butter and jelly sandwich that contains carbohydrates, proteins, fats, vitamins, and minerals. How does each organ participate in breaking this sandwich down into units that can be absorbed and utilized by cells throughout the body? Mouth Ingestion of the peanut butter and jelly sandwich happens in the mouth or oral cavity. This is where mechanical and chemical digestion also begin. Teeth physically crush and grind the sandwich into smaller particles and mix the food particles with saliva. Salivary amylase (a digestive enzyme) is secreted by salivary glands (salivary glands produce saliva which is a mixture of water, enzymes, and other chemicals) and begins the chemical breakdown of carbohydrates in the bread, while lingual lipase (another digestive enzyme) starts the chemical breakdown of triglycerides (the main form of fat in food) in the peanut butter. Esophagus The esophagus is a muscular tube that transports food from the mouth to the stomach. No chemical digestion occurs while the bolus is mechanically propelled through this tube by peristalsis. Stomach The stomach is an expansion of the GI tract that links the esophagus to the first part of the small intestine (the duodenum). The empty stomach is only about the size of your fist but can stretch to hold as much as 4 liters of food and fluid—more than 75 times its empty volume—and then return to its resting size when empty. An important function of the stomach is to serve as a temporary holding chamber. You can ingest a meal far more quickly than it can be digested and absorbed by the small intestine. Thus, the stomach holds food and secretes only small amounts into the small intestine at a time. (The length of time food spends in the stomach varies by the macronutrient composition of the meal. A high-fat or high-protein meal takes longer to break down than one rich in carbohydrates. It usually takes a few hours after a meal to empty the stomach contents completely into the small intestine.) When the peanut butter and jelly sandwich enters the stomach, a highly muscular organ,
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Nutrition: Science and Everyday App
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Nutrition: Science and Everyday App
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UNIT 3 - MOLECULES OF LIFE: PHOTOSY
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UNIT 9 - VITAMINS AND MINERALS PART
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2 ALICE CALLAHAN, PHD, HEATHER LEON
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About the Authors ALICE CALLAHAN, P
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Updates Made to OER Date Unit Page
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Introduction to Designing a Healthy
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Classification of Nutrients Food is
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Introduction to Nutrition Science a
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The Scientific Method Similar to th
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Types of Research Studies and How T
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Glucose Regulation and Utilization
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Sugar: Food Sources, Health Implica
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UNIT 5- LIPIDS 246
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The Functions of Fats Fats serve us
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Lipid Types and Structures Lipids a
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Digestion and Absorption of Lipids
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UNIT 6- PROTEIN 304
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Protein Digestion and Absorption Wh
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Protein Food Choices and Sustainabi
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Introduction to Energy Balance On D
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Energy Balance: Energy In, Energy O
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Indicators of Health: BMI, Body Com
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Best Practices For Weight Managemen
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UNIT 8 - VITAMINS AND MINERALS PART
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Dietary Supplements By now you know
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Vitamins and Minerals Involved In F
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Vitamins Important for Vision Visio
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Introduction to Vitamins and Minera
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Introduction to Bone Health The hum
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Vitamin D: Important to Bone Health
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UNIT 11 — NUTRITION THROUGHOUT TH
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Nutrition in Early Infancy Infancy
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Raising Healthy Eaters “Raising a
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