Dr. Ryan Chapter 3

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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 © 2013 John Wiley & Sons, Inc. All rights reserved.

Digestion and Absorption


Organ Systems of the Body


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


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Overview of the Digestive System


Structure of the Gut Wall


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


Digestive Enzymes


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Digestive Hormones


Mouth

  Cephalic phase   Sense of smell and sight

  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.


Pharynx and Epiglottis


Pharynx and Epiglottis


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Esophagus


Stomach


Stomach


Small Intestine


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Segmentation


Brain


Gallbladder, Liver and Pancreas

  Gallbladder stores bile which is produced by the liver.

  Pancreas secretes digestive enzymes and bicarbonate ions into the small intestine during digestion.


Digestion Nutrient Breakdown


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Nutrient Absorption


Large Intestine

  The large intestine can absorb water and some vitamins and minerals.

  Intestinal microflora are produced here.   The large intestine contains the colon and the

rectum.   Water, nutrients and fecal material may

spend up to 24 hours in the large intestine.


Probiotics


Prebiotics


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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


Common Digestive Problems


Common Digestive Problems


Antacids: Getting the Drug Facts


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Alternate Feeding Methods   If an individual cannot take adequate food or

fluid by mouth:   Enteral or tube feeding   TPN: total parenteral nutrition


Transport of Nutrients Around the Body: The Cardiovascular System


Transport of Nutrients Around the Body: The Hepatic Portal Circulation


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.


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Adenosine Triphosphate (ATP)


Metabolizing Nutrients: Cellular Respiration


Elimination of Metabolic Wastes: Body Organ System


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Dr. Ryan Chapter 3