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Digestion: How
Food Becomes
Nutrition
Concept 6
PowerPoint® Lecture Slide Presentation
Created by Susan Tripp, MS, RD, LDN
UMass Memorial Medical Center
Copyright © 2011 Pearson Education, Inc.
Pop Quiz
True or False?
ANSWER
1. The GI tract is essentially a long tube.
2. You absorb only 75 percent of the nutrients in your
food. ANSWER
3. Heartburn occurs when stomach acid leaks into the
chest cavity and contacts heart muscle. ANSWER
4. We absorb most of the nutrients in foods via our
stomach. ANSWER
5. Stool is mostly made up of food remnants and
bacteria. ANSWER
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What Is Digestion and Why Is It
Important?
 Digestion
Occurs in the GI Tract
 Digestion Allows You to Absorb Nutrients from
Foods
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What Is Digestion and Why Is It
Important?
 To use food for energy, it must be broken
down into molecules small enough to be
absorbed.
 Digestion: the breakdown of foods into
absorbable components in the
gastrointestinal (GI) tract using mechanical
and chemical means
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Digestion Occurs in the GI Tract
 The GI tract is a 23-foot-long tube consisting of:





Mouth
Esophagus
Stomach
Small and large intestines
Other organs
 The main roles of the GI tract are to:
 Break food down into its smallest components
 Absorb the nutrients
 Prevent microorganisms or other harmful compounds in
foods from entering the tissues of the body
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Digestion Occurs in the GI Tract
 Digestion is mechanical and chemical.
 Mechanical—breaking down food through
chewing and grinding
 Peristalsis: rhythmic muscular contractions that move
food through the GI tract and mix it with enzymes
 Chemical—breaking down food with enzymes or
digestive juices
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Digestion Allows You to Absorb
Nutrients from Foods
 Absorption is the process by which digested
nutrients move into the tissues to be
transported and used by the body’s cells.
 The body has two transport systems for
absorption:
 The circulatory system
 The lymphatic system
 You digest and absorb 92 to 97 percent of the
nutrients from your food.
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Animation: Overview Digestion
Absorption
Animation: Overview Digestion
Absorption
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How Does Digestion Happen?

You Begin Breaking Down Food in Your Mouth
 The Esophagus Propels Food into the Stomach
 The Stomach Stores, Mixes, and Prepares Food for
Digestion
 Most Digestion and Absorption Occurs in the Small
Intestine
 The Large Intestine Absorbs Water and Some
Nutrients
 The Liver, Gallbladder, and Pancreas Are Accessory
Organs
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How Does Digestion Happen?
 Begins before we eat
 Hunger and thirst
 Physical needs for food and water that drive how much
and how often we eat
 Appetite
 A powerful drive to eat, but less reliable
 Influenced by environmental and psychological cues
 May cause eating without being hungry or needing
nourishment
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Digestion and the Organs of the GI Tract
Figure 6.1
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You Begin Breaking Down Food in Your
Mouth
 Saliva, a watery substance produced by glands in
the mouth, helps moisten and soften food.
 By chewing, your teeth grind the food into smaller
pieces and mix it with saliva.
 Your tongue also helps mix food and saliva and
pushes the food mass (bolus) to the back of the
mouth into the pharynx.
 The epiglottis closes off the trachea during
swallowing to prevent food from lodging in the
windpipe.
 Food is directed down the esophagus.
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The Epiglottis Prevents Food from
Entering the Larynx When You Swallow
Figure 6.2
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The Esophagus Propels Food into the
Stomach
 Once swallowed, the food bolus is pushed down the
esophagus by peristalsis.
 The lower esophageal sphincter (LES)—the circular
muscle at the bottom of the esophagus—relaxes and
allows food into the stomach.
 The LES closes to prevent backflow of hydrochloric
acid (HCl) from the stomach.
 Reflux of stomach acid causes heartburn, an irritation of
the lining of the esophagus.
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Peristalsis Helps Move Food Down the
Esophagus
Figure 6.3
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The Stomach Stores, Mixes, and
Prepares Food for Digestion
 The stomach churns and contracts to mix food with
powerful digestive secretions, forming chyme.
 The stomach can hold 2 to 4 liters of chyme.
 Hydrochloric acid (HCl) has important digestive
functions:




Activates the digestive enzyme pepsin
Enhances absorption of minerals
Breaks down connective tissue in meats
Destroys ingested microorganisms
 Mucus protects the stomach lining from damage.
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The Stomach Stores, Mixes, and
Prepares Food for Digestion
 Low-calorie, high-carbohydrate foods require
minimal digestion and exit the stomach faster.
 Foods high in fat, protein, and fiber exit
slower, and keep you feeling full longer.
 The pyloric sphincter—the circular muscle
between the stomach and the small
intestine—slowly releases chyme and
prevents backflow of intestinal contents.
 Allows about 1 tsp of chyme to enter small
intestine every 30 seconds
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Most Digestion and Absorption Occurs
in the Small Intestine
 Small intestine: long, narrow, coiled segment
of the GI tract
 Inner lining covered with villi and microvilli, which
increase surface area and maximize absorption
 Blood vessels and lymphatic vessels pick up absorbed
nutrients and transport them throughout the body.
 Circular folds further increase surface area and
cause chyme to spiral forward.
 Food takes 3 to 10 hours to pass through the
small intestine.
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Surface Area in the Small Intestine
Figure 6.4
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The Large Intestine Absorbs Water and
Some Nutrients
 Most nutrients in chyme are absorbed before it
enters the large intestine through the ileocecal
sphincter.
 The large intestine is wider than the small intestine
and not as tightly coiled.
 Helpful bacteria living in the large intestine play a
role in chemical digestion.
 Produce some vitamins
 Break down fiber
 Ferment some undigested dietary carbohydrates into
methane gas, carbon dioxide, and hydrogen
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The Large Intestine Absorbs Water and
Some Nutrients
 The cells of the large intestine absorb fluid, leaving a
semi-solid mass of fecal matter (stool, or feces).
 Transit time ranges from 12 to 70 hours, depending
on a person’s age, health, diet, and fiber intake.
 The rectum is the final portion of the large intestine
where stool is stored.
 Distention of the rectum stimulates the defecation
reflex and the internal sphincter of the anus is
relaxed to voluntarily eliminate stool.
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The Liver, Gallbladder, and Pancreas
Are Accessory Organs
 The liver is the largest abdominal organ in the
body.
 Helps regulate metabolism of carbohydrates, fats,
and protein
 Stores some nutrients, including certain vitamins,
minerals, and glycogen
 Essential for processing and detoxifying alcohol
 Makes bile, a greenish yellow liquid that is
important for fat digestion
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The Liver, Gallbladder, and Pancreas
Are Accessory Organs
 Bile has two main functions:
 Breaks up large fat globules to increase surface
area of the droplets and enhance absorption of fat
 Acts as an emulsifier by dispersing fat throughout
the chyme and helping enzymes make contact
with it and digest it
 Bile is collected, drained, and released into
the gallbladder, a small organ responsible for
storing bile and releasing it into the intestine in
response to fat ingestion.
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The Liver, Gallbladder, and Pancreas
Are Accessory Organs
 The pancreas produces important digestive
enzymes that are released into the small intestine.
 Enzymes made by the pancreas are responsible for
the digestion of 90 percent of ingested fat and 50
percent of ingested protein and carbohydrate.
 The pancreas also produces sodium bicarbonate to
neutralize acidic chyme and protect the tissues of
the small intestine.
 It produces two substances important in regulating
the level of sugar in your blood.
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What Other Body Systems Affect Your
Use of Nutrients?
 The
Nervous System Stimulates Your Appetite
 The Circulatory and Lymphatic Systems
Distribute Nutrients
 The Excretory System Passes Urine Out of
the Body
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The Nervous System Stimulates Your
Appetite
 Your brain communicates and interprets the
messages of hunger and thirst.
 If you ignore the signals of hunger and thirst
you may feel dizzy or weak, or develop a
headache.
 The nervous system helps us to decide what
to eat, when to eat, where to eat, and when to
stop eating.
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The Circulatory and Lymphatic
Systems Distribute Nutrients
 The blood transports oxygen, nutrients, and other
substances throughout the body and removes waste
products from the cells to be excreted.
 Blood picks up nutrients absorbed through the lining
of the small intestine and transports them to the liver,
then to the cells of the body.
 The lymphatic system is a network of vessels,
valves, lymph nodes, and ducts.
 Picks up a fluid called lymph that has seeped into tissues
and filters it before returning it to the bloodstream
 Fats and fat-soluble vitamins travel in lymph from the GI
tract to your blood
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The Circulatory and Lymphatic
Systems
Figure 6.5
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The Excretory System Passes Urine
Out of the Body
 The excretory system eliminates wastes from
the circulatory system.
 The kidneys filter the blood and excrete the
waste products into urine, which is stored in
the bladder until it is released.
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The Excretory System
Figure 6.6
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What Are Some Common Digestive
Disorders?
 Disorders
of the Mouth and Esophagus
 Disorders of the Stomach
 Gallbladder Disease
 Disorders of the Intestines
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Disorders of the Mouth and Esophagus
 Properly nourishing yourself is difficult if you
have extensive tooth decay, gingivitis, or
periodontal disease.
 Gingivitis: gum swelling, bleeding, and oral pain
 Periodontal disease: more severe inflammation
caused by infections or plaque on the teeth
 These conditions are serious but treatable
with various dental procedures, optimal food
choices, and excellent oral hygiene.
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Disorders of the Mouth and Esophagus
 Heartburn affects 25 to 35 percent of adults
occasionally and 7 percent of the population on a
daily basis.
 HCl flows from the stomach into the esophagus.
 Symptoms include a sour taste in the mouth, nausea,
bloating, belching, or a burning sensation.
 Chronic heartburn can lead to gastroesophageal reflux
disease (GERD).
 It is often caused by a weak LES.
 Certain foods or lifestyle factors can worsen the condition.
 Treatment includes dietary changes, behavior
modification, over-the-counter antacids or prescription
drugs, or surgery in very severe cases.
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Disorders of the Stomach
 Stomachache may be caused by overeating, eating
too fast, or eating foods that are spicy, acidic, or high
in fat or fiber.
 Gastroenteritis is an inflammation of the stomach or
intestines caused by a virus or bacteria.
 Rest, oral rehydration therapy, and a soft diet are the
recommended treatment.
 A peptic ulcer is an erosion of the stomach lining
caused by drugs, alcohol, or a bacterium.
 Symptoms include abdominal pain, vomiting, fatigue,
bleeding, and general weakness.
 It is treated with prescription drugs and dietary
modification.
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Peptic Ulcer
Figure 6.7
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Gallbladder Disease
 Gallstones: small, hard, crystalline structures
formed in the gallbladder or bile duct due to
abnormally thick bile
 May be asymptomatic or cause pain, fever,
nausea, vomiting, cramps, and obstruction of
the bile duct
 Treated with prescription medications, shockwave therapy, or surgical removal of the
gallbladder
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Disorders of the Intestines
 Serious intestinal problems are often
characterized by malabsorption.
 Malabsorption diseases are characterized by
abdominal pain, nausea, vomiting, bloating,
loss of appetite, diarrhea, anxiety, weight loss,
and fatigue.
 Celiac disease is a more common cause of
malabsorption.
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Celiac Disease: An Issue of Absorption
 Celiac disease: immune system response to gluten,
causing damage to the lining of the small intestine
and malabsorption
 Gluten is a protein found in wheat, rye, and barley.
 More common in people of European descent
 Affects 1 in 133 Americans
 Symptoms include abdominal bloating, cramping,
diarrhea, gas, fatty and foul-smelling stool, weight
loss, anemia, fatigue, bone or joint pain, or a skin
rash.
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Celiac Disease: An Issue of Absorption
 Complications of celiac disease include:
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Osteoporosis
Diminished growth
Possible seizures
Increased risk of cancer of the small intestine
 Gold standard for diagnosis is surgical detection of
damaged villi
 Treatment for celiac disease is a gluten-free diet.
 Many processed foods contain hidden sources of gluten.
 Even traces of gluten can set off an immune reaction.
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Disorders of the Intestines
 Constipation: difficulty in passing stool
 Often due to insufficient fiber or water intake
 Stress, inactivity, certain medications, and various
illnesses can contribute
 Diarrhea: the passage of frequent, watery,
loose stools
 Results in the loss of fluids, certain minerals, and
nutrients
 Many causes, including contaminated water,
microorganisms, stress, or excessive fiber intake
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Disorders of the Intestines
 Irritable bowel syndrome (IBS): a disorder
of bowel function caused by hypersensitivity
to stimuli in the large intestine
 Alternating patterns of diarrhea, constipation, and
abdominal pain
 Cause is unknown
 Dietary modification, stress management, and
occasional use of prescription drugs can help
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The Top Five Points to Remember
1. Digestion is the process of breaking down food into
absorbable nutrients through mechanical or
chemical processes.
2. Digestion begins in the mouth when food is chewed
and mixed with saliva. The stomach mixes foods
with enzymes and stores it. Most digestion and
absorption occurs in the small intestine. The villi in
the small intestine greatly increase the surface area
for absorption. The large intestine absorbs water
and some nutrients before waste is eliminated
through the anus. Sphincters control entry and exit
of food and chyme through the organs of the GI
tract.
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The Top Five Points to Remember
3. The liver produces bile, metabolizes and stores
certain nutrients, and detoxifies alcohol. The
gallbladder stores and releases bile. The pancreas
produces enzymes important for digestion.
4. Other body systems, including the nervous,
circulatory, lymphatic, and excretory systems, help
you use the nutrients you eat.
5. Common digestive disorders include heartburn,
peptic ulcers, celiac disease, constipation, diarrhea,
and irritable bowel syndrome.
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Answers to the Pop Quiz
1. TRUE. The GI tract runs through the
body and connects the mouth to the
anus.
BACK TO QUIZ
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Answers to the Pop Quiz
2. FALSE. Your body is very efficient and
absorbs over 90 percent of the nutrients
in your food.
BACK TO QUIZ
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Answers to the Pop Quiz
3. FALSE. Heartburn is actually caused
by a backflow of stomach acid into the
lower esophagus.
BACK TO QUIZ
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Answers to the Pop Quiz
4. FALSE. The small intestine is the
primary organ responsible for nutrient
absorption.
BACK TO QUIZ
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Answers to the Pop Quiz
5. TRUE. Stools contain leftover food
residue, nondigestible fibers, bacteria,
gases, and sloughed-off intestinal cells.
BACK TO QUIZ
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