Section 1 Fundamentals of Nutrition Copyright 2003 Delmar

Section 1 Fundamentals of Nutrition Copyright © 2003 Delmar Learning, a Thomson Learning company

Chapter 3 Digestion, Absorption, and Metabolism Copyright © 2003 Delmar Learning, a Thomson Learning company

Objectives § § Chapter 3 Describe the processes of digestion, absorption, and metabolism Name the organs in the digestive system and describe their functions Name the enzymes or digestive juices secreted by each organ and gland in the digestive system Calculate your basal metabolic rate (BMR) Copyright © 2003 Delmar Learning, a Thomson Learning company 3

Digestion The breakdown of food in the body in preparation for absorption. Mechanical digestion: food is broken up by teeth and moved along GI tract by peristalsis. Chemical digestion: carbohydrates, proteins, and fats are broken down into nutrients tissues can absorb and use. Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 4

Digestion Chemical changes occur through hydrolysis (the addition of water and breaking down of food molecules). Enzymes act on food substances, causing them to break down into simple compounds. An enzyme can act as a catalyst, which speeds up the chemical reactions without itself being changed in the process. Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 5

Absorption The passage of nutrients into the blood or lymphatic system. Nutrients must be in their simplest form • • • Chapter 3 Carbohydrates: simple sugars Proteins: amino acids Fats: fatty acids and glycerol Copyright © 2003 Delmar Learning, a Thomson Learning company 6

Absorption Most absorption occurs in the small intestine; some occurs in the large intestine. Water is absorbed in the stomach, small intestine, and large intestine. Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 7

The Digestive System Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 8

Mouth Digestion begins here Enzyme (salivary amylase) acts on starch Starch is a complex carbohydrate Teeth break up food; food mixes with saliva “Bolus” formed Length of time food is in mouth is brief Small amounts of carbohydrates changed Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 9

Esophagus Food travels through this muscular tube Connects mouth to stomach Peristalsis and gravity act to move bolus Cardiac sphincter opens at lower end of esophagus to allow passage of bolus into stomach Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 10

Stop and Share What symptom results when the cardiac sphincter does not close properly? What is the name of the condition? What prevents this condition from occurring? Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 11

Stop and Share Indigestion or heartburn occurs as a result of stomach acid flowing back into the esophagus. This is called gastroesophageal reflux. The proper closing of the cardiac sphincter prevents the acidic content of the stomach from flowing back into the esophagus. Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 12

Stomach Temporary storage of food Mixing of food with gastric juices Regulation of a slow, controlled emptying of food into the intestine Secretion of the intrinsic factor for vitamin B 12 Destruction of most bacteria inadvertently consumed Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 13

Stomach Hydrochloric acid prepares the gastric area for enzyme action Pepsin breaks down proteins In children, rennin breaks down milk proteins Lipase acts on emulsified fats Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 14

Stop and Share You are preparing a teaching plan for the nursing staff working on a GI floor. You plan to review anatomy and physiology of the stomach. Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 15

Stop and Share Complete the following objectives to prepare for your class: • • • Chapter 3 Identify the 3 parts of the stomach Define chyme Identify the condition that results from lack of the intrinsic factor in the stomach Copyright © 2003 Delmar Learning, a Thomson Learning company 16

Stop and Share Fundus: upper portion of the stomach Body of the stomach: middle area Pylorus: end of stomach near small intestines Chyme: semiliquid mass of food and gastric juices Pernicious anemia: lack of intrinsic factor Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 17

Small Intestine Hormones released • • Secretin causes pancreas to release sodium bicarbonate to neutralize acidity of chyme Cholecystokinin triggers gallbladder to release bile Bile • • Chapter 3 Emulsifies fat after it is secreted into small intestine Produced in liver; stored in gallbladder Copyright © 2003 Delmar Learning, a Thomson Learning company 18

Small Intestine Enzymes are found in the pancreatic juice that is secreted into small intestine. • • • Chapter 3 Pancreatic proteases (trypsin, chymotrypsin, carboxypeptidases): split proteins Pancreatic amylase: converts starches (polysaccharides) to simple sugars Pancreatic lipase: reduces fats to fatty acids and glycerol Copyright © 2003 Delmar Learning, a Thomson Learning company 19

Small Intestine Produces enzymes Prepares foods for absorption Lactase, maltase, sucrase convert lactose, maltose, sucrose to simple sugars Peptidases reduce proteins to amino acids Twenty-two feet long Villi, hairlike projections, increase surface area for maximum absorption Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 20

Small Intestine Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 21

Stop and Share A patient with a duodenal ulcer asks you where the ulcer is located. How do you respond? Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 22

Stop and Share The small intestine is divided into three sections. The duodenum is the first section of the small intestine. The jejunum is the middle section and the ileum is the last section. Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 23

Large Intestine Colon walls secrete mucus to protect against acidic digestive juices in chyme. Major tasks of the large intestine: • • • Chapter 3 Absorb water Synthesize some B vitamins and vitamin K Collect food residue Copyright © 2003 Delmar Learning, a Thomson Learning company 24

Stop and Share You are providing pre-op teaching to a patient who is going to have intestinal surgery. The patient asks you to explain the structure of the large intestine. How do you respond? Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 25

Stop and Share The cecum (blind pocket), colon and rectum make up the large intestine. Contents travel through: • • • Chapter 3 Ascending colon Transverse colon Descending colon Sigmoid colon Rectum Anal canal Copyright © 2003 Delmar Learning, a Thomson Learning company 26

Large Intestine Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 27

Metabolism The use of food by the body after digestion Results in energy Occurs after digestion and absorption; nutrients are carried by the blood to the cells of the body Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 28

Metabolism Oxidation • • Nutrients combine with oxygen Carbohydrates reduce to carbon dioxide and water Protein to carbon dioxide, water, and nitrogen Also known as aerobic metabolism Energy is released as nutrients are oxidized. Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 29

Metabolism Anaerobic metabolism reduces fats without the use of oxygen. The complete oxidation of carbohydrates, proteins, and fats is commonly called the Krebs cycle. Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 30

Metabolism Anabolism is the process of using energy from oxidation to create new compounds. Catabolism is the breakdown of compounds during metabolism. Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 31

Metabolism Controlled primarily by hormones secreted by the thyroid gland: Triiodothyronine (T 3) and thyroxine (T 4). Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 32

Stop and Share What condition is associated with too much thyroid hormone? What condition is associated with too little thyroid hormone? Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 33

Stop and Share Hyperthyroidism: metabolism speeds up and the body metabolizes its food too quickly, weight is lost. Hypothyroidism: metabolism slows down and the body metabolizes its food too slowly; patient tends to become sluggish and accumulate fat. Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 34

Energy Needed for involuntary and voluntary activity Involuntary activity: maintenance of body tissue, temperature, growth Voluntary activity: walking, swimming, eating, reading, typing Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 35

Energy Three groups of nutrients provide energy • • • Carbohydrates Proteins Fats Carbohydrates should be primary source of energy. Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 36

Energy The unit used to measure the energy value of foods is the kilocalorie. kcal: amount of heat needed to raise the temperature of 1 kilogram of water 1 degree Celsius. kcal is commonly called calorie. Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 37

Energy 1 gram of carbohydrate yields 4 kcal 1 gram of protein yields 4 kcal 1 gram of fat yields 9 kcal 1 gram of alcohol yields 7 kcal Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 38

Stop and Share If you eat a dessert with 19 grams of fat in it, how many calories from fat does it have? Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 39

Stop and Share 171 calories Fat contains 9 kcal per gram Dessert has 19 grams of fat 9 kcal/gram × 19 grams of fat = 171 kcal Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 40

Basal Metabolic Rate (BMR) The rate at which energy is needed for body maintenance. The energy necessary to carry on all involuntary vital processes while the body is at rest. Also known as resting energy expenditure (REE). Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 41

Basal Metabolic Rate (BMR) Factors that affect BMR: lean body mass, body size, sex, age, heredity, physical condition, and climate. BMR is greater in men than women. BMR increases during growth and fever. BMR decreases with age and during starvation. Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 42

Calculating BMR Harris-Benedict equation • • Used by dietitians for persons over age 18 Uses height, weight, and age Female BMR 655 + (9. 6 × weight in kg) + (1. 8 × height in cm) – (4. 7 × age) Male BMR 66 + (13. 7 × weight in kg) + (5 × height in cm) – (6. 8 × age) Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 43

Calculating BMR Another method used to estimate BMR • • • Chapter 3 Convert body weight from pounds to kilograms Multiply kilograms by 24 (hours per day) Multiply the answer obtained by 0. 9 for a woman and by 1. 0 for a man Copyright © 2003 Delmar Learning, a Thomson Learning company 44

Stop and Share Calculate the BMR for a woman who weighs 110 pounds. Calculate the BMR for a man who weighs 170 pounds. Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 45

Stop and Share 110 pound woman: BMR 1, 080 kcal 110 pounds 2. 2 (pounds per kg) = 50 kg × 24 hours in a day = 1, 200 kcal × 0. 9 =1, 080 kcal Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 46

Stop and Share 170 pound man: BMR 1, 854 kcal 170 pounds 2. 2 (pounds per kg) = 77. 27 kg × 24 hours in a day = 1, 854 kcal × 1. 0 =1, 854 kcal Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 47

Conclusion Food is broken down through the processes of mechanical and chemical digestion into nutrients that can be absorbed. Enzymes act to break down nutrients. Absorption occurs mostly in the small intestines. Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 48

Conclusion During metabolism, carbohydrates and proteins are combined with oxygen in a process called oxidation. Energy released during oxidation is measured by the kcal. A person’s energy requirement can be measured in part by estimating the basal metabolic rate (BMR). Chapter 3 Copyright © 2003 Delmar Learning, a Thomson Learning company 49