Digestion and Nutrition, Third Edition

Robert Sullivan, Mary Kinkel

Description

Digestion is the process of taking food and nutrients into the body and making them available for use in all of the body’s processes. The digestive system breaks down food and extracts the important nutrients, eliminating the excess substances that cannot be used. These nutrients provide energy for the body to grow, function, and make repairs to itself. Digestion and Nutrition, Third Edition describes the path that food takes through the system, the organs involved, and how the body uses different types of nutrients, while highlighting the importance of healthy eating and the problems and diseases that can affect the digestive tract. Packed with full-color photographs and illustrations, this absorbing book provides students with sufficient background information through references, websites, and a bibliography.

Sujets

• Life Sciences
• Medical
• Sciences et techniques
• Digestión
• Biology
• Medicine
• Anatomy
• Health
• Human
• Digestion
• Science
• Nutrition

Informations

• Publié par: Infobase Publishing
• Date de parution: 01 novembre 2021
• Nombre de lectures: 0
• EAN13: 9781646937196
• Langue: English

Extrait

Digestion and Nutrition, Third Edition
Copyright © 2021 by Infobase
All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For more information, contact:
Chelsea House An imprint of Infobase 132 West 31st Street New York NY 10001
ISBN 978-1-64693-719-6
You can find Chelsea House on the World Wide Web at http://www.infobase.com
Contents Chapters Introduction to Digestion and Nutrition Nutrition and Major Nutrients Minor Nutrients and Metabolism Digestion, Absorption, and Elimination Chewing and Swallowing The Stomach and Small Intestine The Large Intestine and Elimination Common Health Problems Guidelines for Healthy Eating Support Materials Glossary Bibliography Further Resources About the Authors Index
Chapters
Introduction to Digestion and Nutrition
On the way home from her morning classes, Amy stops for lunch at a fast-food restaurant. She orders a hamburger, French fries, and a chocolate milkshake. She knows the burger and French fries have lots of fat and salt that she does not need. She also knows the milkshake is risky for her. She has a form of lactose intolerance that sometimes results in abdominal cramping and diarrhea after consuming dairy products. However, Amy is in a hurry and knows that the food will be served quickly. Besides, she has been thinking about that chocolate shake all morning.
After Amy eats her lunch, her digestive system will process the burger, French fries, and chocolate milkshake into nutrients her body can use. This process takes the food we can see, smell, and taste and breaks it down, first physically into smaller and smaller pieces, and then chemically into nutrients. These nutrients are relatively simple (small) chemicals that can pass through the cells in the digestive tract wall and into the blood. The blood will transport the nutrients to the cells of the body, where they will be used.
Digestion is the physical and chemical breakdown of food into nutrients, the simpler, smaller elements that can be used by the body's cells. The process begins in the mouth when a bite of food is chewed. Chewing breaks the food into smaller pieces and mixes it with saliva. The food mass is then swallowed. Although the food has been physically reduced to a smaller size, it is not yet small enough to enter the blood. Digestion must continue in the stomach and intestines. There, the food will be chemically reduced to nutrients. These nutrients are small enough to pass through the walls of the digestive tract in a process called absorption. The absorbed nutrients then enter the blood and are transported to the cells of the body. There, they are further processed to provide energy or are simply used as raw materials for assembling cell or tissue components.
In the following chapters, you will follow Amy's lunch on its journey through her body. You will read about what is really in her food; how it is digested, or broken down; and how it is absorbed into the cells. The burger and French fries she eats contain a lot of fat and salt, and the milkshake will most likely make her feel sick. You will learn how this is related to her lactose intolerance. You will also read about why we need nutrients and how these nutrients are obtained. Why do we need a variety of carbohydrates, proteins, lipids, vitamins, and minerals? How does the digestive tract work with the pancreas, liver, and gallbladder to extract nutrients from a meal?
To answer these questions, each region of the digestive tract will be explained in terms of its structure and function, also called its anatomy and physiology. We will discuss common health problems related to digestion and nutrition and we will consider some basic guidelines for healthy eating.
Nutrition and Major Nutrients
Why Do Humans Have to Eat?
Humans and other animals need to eat because they need resources that their bodies cannot otherwise provide. These resources are the nutrients derived from food. Nutrients are the raw materials that are used to replace worn-out cells and repair damaged tissues. Nutrients are also used to fuel every bodily function including growth, movement, and thinking.
The body’s activities are carried out by chemical reactions that require energy. Chemical reactions involve making or breaking chemical bonds. The energy derived from food is used to continuously make and break chemical bonds, even while you are sleeping. The digestive system has evolved to break down food into the nutrients that supply this energy.
What is a chemical bond? There are three types of chemical bonds to consider here: ionic bonds, hydrogen bonds, and covalent bonds. An ionic bond forms between charged atoms where positive and negative charges attract each other. For example, sodium (Na + ) is attracted to chloride (Cl - ) to form sodium chloride (NaCl), also known as table salt. These bonds are somewhat strong, but not so strong that energy is needed to alter them. Similarly, a hydrogen bond is a weak chemical bond that is easily formed and broken. Hydrogen bonds hold atoms together during chemical reactions or help form the structure of complex molecules, such as proteins, so that they can function properly. Hydrogen bonds also exist between water molecules and anything mixed (dissolved) in water. These bonds allow the water molecules to support the compounds that are dissolved in the solution, but are weak enough to allow the compounds to diffuse through the water. Hydrogen bonds are so weak that the chemicals held with them can separate just by drifting off into the surrounding water. Unlike the relatively weak ionic bonds and hydrogen bonds, a covalent bond is strong and requires energy to make or break it. A covalent bond is formed when atoms share electrons. The electrons are found in the space around the nuclei of the atoms. When two atoms share electrons, a strong bond is formed and the atoms stick together tightly.
Covalent bonds not only require energy to form or break, they also store energy. This is the chemical energy that can be released to be used by cells. Until it is needed, the chemical energy is stored in the bonds of adenosine triphosphate (ATP), a nucleotide (see figure below). The three phosphates in ATP are attached to the adenosine in series, in negatively charged phosphate groups. Since negative charges repel each other, it takes high energy to attach the phosphate groups to each other, to make the covalent bonds. The energy used to make the bonds is stored in the bonds. When energy is needed to fuel a chemical reaction, the energy stored in ATP can be released by breaking a covalent bond. To do this, the third phosphate group is removed from ATP by breaking its bond with the second phosphate group. Breaking the bond releases the stored energy and makes it available to fuel a chemical reaction.

ATP is an energy-storage compound that contains three phosphate groups. Cells obtain the energy they need to carry on their life functions from the breakdown of ATP. When the bond between the last two phosphate groups is broken, the energy released can be used by the cell for anything from replication and division to making proteins and extracting nutrients from food.
When ATP loses the third phosphate group, it becomes adenosine diphosphate (ADP), with only two phosphate groups. ADP functions like a rechargeable battery. A third phosphate group can be attached (using energy) so that it once again becomes ATP, ready to supply energy for another chemical reaction.
How much energy is in Amy’s lunch? The potential energy in food is measured as calories. Amy’s lunch has 1,190 calories. Adults typically require a daily intake of at least 2,000 calories. The number of calories depends on age, activity level, and sex. For example, a young adult female who is moderately active may require 2,000-2,200 calories per day, while a young adult male who is moderately active may require 2,600-2,800 calories per day. 1  Amy’s lunch has at least half the daily calories that she needs to fuel her body’s activities.
Types of Nutrients
There are major and minor nutrients. Major nutrients–carbohydrates, proteins, and lipids–serve as energy sources or as building blocks for larger biochemical compounds. Minor nutrients, which include all vitamins and minerals, assist the chemical reactions that occur with major nutrients. A balanced diet includes all of the necessary major and minor nutrients. If the diet is not balanced, some energy sources or building blocks will be missing, and the body will not function properly.
Carbohydrates
Amy’s fast-food lunch is rich in carbohydrates. The hamburger bun, French fries, and milkshake are carbohydrates because they include sugars and starches. What makes a molecule a carbohydrate? All carbohydrates contain at least six carbon atoms, as well as hydrogen and oxygen atoms. They come in many forms and are categorized by size, from smallest to largest, as monosaccharides, disaccharides, and polysaccharides.
Monosaccharides
Monosaccharides are simple sugars. (“Mono” means “one” and “saccharide” means “sugar”). The simple sugars include glucose, fructose, and galactose. Usually, the ratio of carbon to hydrogen to oxygen is 1:2:1. This means that there is one carbon to two hydrogens to one oxygen. Most of the sugars used in the body are six-carbon sugars, so their formula is written as C 6 H 12 O 6 . The body's sugar biochemistry is based on breaking down the covalent bonds that hold the glucose’s six carbons together, using a series of chemical reactions. Fructose and galactose feed into the pathway of these chemical reactions. As monosaccharides are the smallest carbohydrate, they can be absorbed by cells. By contrast, disaccharides and polysaccharides are larger and must be broken down into monosaccha