Chapter 3 Digestion, Absorption, and Metabolism

Digestion and Absorption Biochemically, “you are what you eat” is true! Food and fluid taken into the body is broken down into smaller components so it can be used by the body. Copyright 2010, John Wiley & Sons, Inc. 2

Copyright 2010, John Wiley & Sons, Inc. The digestive tract begins at the _________ and ends at the _______.    a. esophagus; small intestine  b. mouth; pancreas  c. esophageal sphincter; stomach  d. mouth; anus Copyright 2010, John Wiley & Sons, Inc.

Overview of the Digestive System Most of you is dedicated to breaking down food to nourish yourselves Copyright 2010, John Wiley & Sons, Inc. 4

Digestion and Absorption The brain is involved in digestion and absorption. Copyright 2010, John Wiley & Sons, Inc. 5

Digestion and Absorption Pharynx and Epiglottis First place for food breakdown Copyright 2010, John Wiley & Sons, Inc. 6

Digestion and Absorption The mouth is the entry point for food into the digestive tract. Saliva contains salivary amylase, which helps to break down carbohydrates and lysozymes, which help to inhibit bacterial growth in the mouth. Chewing mechanically breaks food down, increasing the surface area in contact with digestive enzymes. Copyright 2010, John Wiley & Sons, Inc. 7

Copyright 2010, John Wiley & Sons, Inc. Chewing is an important digestive function because it improves the functionality of    a. enzymes.  b. hormones.  c. mucus.  d. peristalsis. Copyright 2010, John Wiley & Sons, Inc.

Digestion and Absorption Esophagus peristalsis Copyright 2010, John Wiley & Sons, Inc. 9

Overview of the Digestive System Digestion: process of breaking food into components small enough to be absorbed by the body Absorption: process of taking substances into the interior of the body Gastrointestinal tract: hollow tube consisting of the mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus Transit time: amount of time it takes food to pass the length of the GI tract Feces: body waste, including unabsorbed food residue, bacteria and dead cells Copyright 2010, John Wiley & Sons, Inc. 10

Digestion and Absorption Stomach Viscous Mucosal layer protects the stomach Copyright 2010, John Wiley & Sons, Inc. 11

Copyright 2010, John Wiley & Sons, Inc. Digestive Secretions Digestion inside the GI tract is assisted by digestive secretions. Mucus: viscous material produced by goblet cells; mucus moistens, lubricates and protects the GI tract Enzymes: protein molecules that speed up chemical reactions; enzymes are not changed during reactions Copyright 2010, John Wiley & Sons, Inc. 12

Copyright 2010, John Wiley & Sons, Inc. Digestive Enzymes Copyright 2010, John Wiley & Sons, Inc. 13

Copyright 2010, John Wiley & Sons, Inc. Digestive Hormones Copyright 2010, John Wiley & Sons, Inc. 14

Copyright 2010, John Wiley & Sons, Inc. Food moves through the digestive tract by wavelike contractions called   a) quickening. b) the Heimlich maneuver. c) peristalsis. d) segmentation. Copyright 2010, John Wiley & Sons, Inc.

Digestion and Absorption Copyright 2010, John Wiley & Sons, Inc. 16

Digestion and Absorption The gallbladder, liver and pancreas are involved in digestion and absorption. Copyright 2010, John Wiley & Sons, Inc. 17

Copyright 2010, John Wiley & Sons, Inc. Which of the following accessory organs releases its secretions into the GI tract?   Gallbladder Pancreas Salivary glands All answer choices are correct Copyright 2010, John Wiley & Sons, Inc.

Structure of the Gut Wall Copyright 2010, John Wiley & Sons, Inc. 19

GI Tract’s Role in Immune Function The GI tract plays an important role in protecting the body from infection. The GI tract limits the absorption of toxins and disease-causing organisms. Some cells of the immune system are present in the GI tract: Phagocytes Lymphocytes Antibodies Copyright 2010, John Wiley & Sons, Inc. 20

Digestion and Absorption The large intestine does not participate in digestion. The large intestine can absorb water and some vitamins and minerals. The large intestine contains the colon and the rectum. Water, nutrients and fecal material may spend up to 24 hours in the large intestine. Copyright 2010, John Wiley & Sons, Inc. 21

Copyright 2010, John Wiley & Sons, Inc. The primary site of nutrient absorption is the   a) liver. b) large intestine. c) stomach. d) small intestine. Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Absorption Copyright 2010, John Wiley & Sons, Inc. 23

Digestion and Absorption of a Meal Copyright 2010, John Wiley & Sons, Inc. 24

Transport of Nutrients Around the Body: The Cardiovascular System Copyright 2010, John Wiley & Sons, Inc. 25

Transport of Nutrients Around the Body: The Hepatic Portal Circulation Copyright 2010, John Wiley & Sons, Inc. 26

Metabolism of Nutrients Metabolic pathways are a series of reactions needed to transform food into a final product that can be used by the body. Catabolic pathways release energy trapped in chemical bonds. Energy from catabolic reactions is converted into ATP. ATP is the energy currency of the cell. Copyright 2010, John Wiley & Sons, Inc. 27

Copyright 2010, John Wiley & Sons, Inc. ATP Copyright 2010, John Wiley & Sons, Inc. 28

Metabolizing Nutrients: Cellular Respiration Copyright 2010, John Wiley & Sons, Inc. 29

Elimination of Metabolic Wastes: Body Organ System Copyright 2010, John Wiley & Sons, Inc. 30

Elimination of Metabolic Wastes: The Kidneys Copyright 2010, John Wiley & Sons, Inc. 31

Copyright 2010, John Wiley & Sons, Inc. The two major functions associated with the digestive system include digestion and   metabolism. absorption. circulation of nutrients in the blood. excretion of metabolic waste products. Copyright 2010, John Wiley & Sons, Inc.