This document provides an overview of Chapter 2 of a nutrition textbook. It discusses the digestive system and how food is broken down and absorbed. The key points covered include the roles of hunger and appetite, how the foods we eat are used to build cells, the organs and processes involved in digestion and absorption, and some common digestive disorders like heartburn, ulcers, food allergies, and irritable bowel syndrome. The learning outcomes focus on understanding digestion, absorption, and gastrointestinal health.

1. Chapter 2 Lecture
Chapter 2:
The Human Body:
Are We Really
What We Eat?
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2. Learning Outcomes
1. Compare and contrast the feelings of hunger
and appetite, and the factors contributing to
each.
2. Identify the relationship between the foods we
eat and the structures and functions of our cells.
3. Name and state the function of each of the major
organs of the gastrointestinal tract and the four
accessory organs.
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3. Learning Outcomes
4. Explain how the food you eat is broken down
mechanically and chemically.
5. Identify the unique features of the small
intestine that contribute to its ability to absorb
nutrients.
6. Describe how the body eliminates food wastes.
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4. Learning Outcomes
7. Discuss the causes, symptoms, and treatment
of gastroesophageal reflux disease and peptic
ulcers.
8. Distinguish between food intolerance and food
allergy, and between celiac disease and non-
celiac gluten sensitivity.
9. Compare and contrast diarrhea, constipation,
and irritable bowel syndrome.
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5. Why Do We Want to Eat What We Want to
Eat?
• Appetite: psychological desire to eat specific
foods
• Some cravings, even when we're not hungry,
are due to appetite.
• Hunger: physiological drive that prompts us to
eat nonspecific foods
• Anorexia is a lack of appetite despite the
physical need for food.
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6. Why Do We Want to Eat What We Want to
Eat?
• Signals that prompt us to eat:
• Hunger is detected by the hypothalamus–
a region of the brain.
• Stomach cells sense emptiness or fullness.
• Blood glucose levels trigger the release of
certain hormones.
• The hypothalamus receives these hormone
signals to tell us if we are hungry.
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7. Why Do We Want to Eat What We Want to
Eat?
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8. Why Do We Want to Eat What We Want to
Eat?
• Nerve Cells: particularly the ones lining the
stomach and small intestine that detect changes
in internal pressure when the organ is empty or
filled with food. These nerve cells relay that
information to the brain's hypothalamus and
contributes to sensations of hunger.
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9. Why Do We Want to Eat What We Want to
Eat?
• Hormones: chemicals introduced by specialized
glands that enter the bloodstream and target
organs in other parts of the body
• Some hormones, such as insulin and glucagon,
stimulate food intake.
• Rising levels of glucose and responses from
nerve cells produce feelings of satiety.
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10. Why Do We Want to Eat What We Want to
Eat?
• Role of the amount and type of food
• Protein
• Higher satiety (feeling of fullness) value
• Bulkiness
• Amount of fiber and water within the food
• Solid food versus liquid food
• Beverages tend to be less satisfying than solids
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11. Environmental Cues Trigger Appetite
• Sensory data
• Social cues
• Cultural cues
• Learned preferences
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12. Environmental Cues Trigger Appetite
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13. Are We Really What We Eat?
• Atoms: the smallest units of matter
• Atoms bond to each other to form molecules.
• Molecules: groups of atoms bonded in specific
configurations
• Example: water is H2O
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14. Are We Really What We Eat?
• Molecules are the building blocks of cells.
• Chemical reactions that join atoms and
molecules and break compounds apart are
called metabolism.
• Cells: the smallest unit of life
• Molecules that result from the digestion of food
are used to build the cells of the body.
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15. Are We Really What We Eat?
• Cells join together to form tissues.
• Tissue: group of cells acting together to perform
a common function
• Examples: muscle tissue, nerve tissue
• Different tissues combine to form organs.
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16. Are We Really What We Eat?
• Cell membrane: outer layer enclosing each cell
of the body
• The cell membrane defines the cell's boundaries
and acts as a gatekeeper.
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17. Are We Really What We Eat?
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18. Are We Really What We Eat?
• The cell membrane is semipermeable, allowing
it to control the passage of materials into and out
of the cell.
• The cell membrane encloses:
• Cytoplasm, the liquid within the cell;
• Mitochondria and nucleus
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19. What Happens to the Food We Eat?
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20. What Happens to the Food We Eat?
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Clink on the Digestion Absorption
link separate from the power point.

21. What Happens to the Food We Eat?
• The food we eat undergoes three processes:
• Digestion
• Absorption
• Elimination
• These processes occur primarily in the
gastrointestinal (GI) tract.
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22. What Happens to the Food We Eat?
• Digestion: the process of breaking large food
molecules down into smaller molecules
• Digestion includes breaking food down:
• Mechanically
• Physically
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23. What Happens to the Food We Eat?
• Digestion begins in the mouth.
• Chewing is the mechanical digestion that
breaks food into smaller pieces.
• Some chemical digestion takes place.
• Saliva contains amylase, an enzyme produced by
the salivary glands.
• Salivary amylase begins the chemical digestion of
carbohydrates.
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24. What Happens to the Food We Eat?
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25. What Happens to the Food We Eat?
• GI tract: series of organs arranged as a long tube
• The GI tract includes:
• Organs such as the stomach and intestines
• Sphincters, which are muscles that control the
passage of material from one organ to the next
• Accessory organs, which assist digestion but
are not part of the GI tract
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26. What Happens to the Food We Eat?
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Click on the Enzymes link separate
from the power point.

27. What Happens to the Food We Eat?
• Enzyme: a protein that induces a chemical
change in another substance
• Enzymes speed up the rate of chemical reactions.
• Digestion is dependent on many different
enzymes.
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28. The Action of Digestive Enzymes
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29. Some Digestive Enzymes and Their Actions
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30. Digestion
• The epiglottis covers the opening to the trachea
during swallowing.
• Food travels from the mouth to the stomach
through the esophagus.
• Peristalsis is the muscular contractions moving
food through the GI tract.
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31. Chewing and Swallowing
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32. The Esophagus and Peristalsis
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33. Mechanical Digestion in the Stomach
• The gastroesophageal sphincter separates
the esophagus from the stomach.
• Digestion in the stomach includes:
• Extensive mechanical digestion, mixing food
with gastric juice to produce chyme
• Chemical digestion of proteins and fats
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34. Chemical Digestion in the Stomach
• Gastric juice contains:
• Hydrochloric acid (HCl): to denature proteins
and activate pepsin
• Pepsin: an enzyme to digest protein
• Gastric lipase: an enzyme to digest fat
• Mucus: to protect the stomach lining
• Chyme: semi-solid product of mechanical and
chemical digestion in the stomach
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35. The Stomach Mixes, Digests, and Stores
Food
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36. Most Digestion and Absorption Occurs in
the Small Intestine
• From the stomach, chyme is slowly released
through the pyloric sphincter to the small
intestine.
• Most digestion and absorption occur in the small
intestine.
• Absorption: the process by which molecules of
food are taken from the GI tract into the body.
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37. Most Digestion and Absorption Occurs in
the Small Intestine
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38. The Gallbladder and Pancreas Aid in
Digestion
• Accessory organs of the GI tract include:
• Liver: produces bile, which emulsifies fats
• Pancreas
• Produces many digestive enzymes
• Produces hormones involved in regulation of
metabolism
• Gallbladder: stores bile
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39. Absorption Mechanisms
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Click the Basic Absorption link for
separate from the power point.

40. A Specialized Lining Enables the Small
Intestine to Absorb Food
• The lining of the GI tract has special structures
to facilitate absorption.
• Villi are folds in the lining that are in close
contact with nutrient molecules.
• The brush border is composed of microvilli,
which greatly increases the surface area.
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41. Small Intestine Structure and Function
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42. Small Intestine Structure and Function
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43. Small Intestine Structure and Function
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44. Absorption Mechanisms
• The nutrient products of digestion are absorbed
by villi lining the small intestine.
• The nutrients are picked up by blood and lymph
and carried to all parts of the body.
• The liver plays a major role in processing,
storing, and regulating the blood levels of the
energy nutrients.
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45. Absorption Mechanisms
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46. The Large Intestine
• Undigested food components move to the large
intestine, where they mix with intestinal bacteria.
• In the large intestine:
• Intestinal bacteria complete digestion
• Material is stored 12–24 hours prior to
elimination
• Water and some nutrients are absorbed
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47. The Large Intestine
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48. Probiotics
• Probiotic bacteria
• Manufacture enzymes
• Supply key nutrients
• Produce certain vitamins
• Degrade potential carcinogens
• Oppose excessive inflammation
• Need to consume daily
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49. Prebiotics
• Prebiotic bacteria
• Nondigestible substances that stimulate
growth of probiotics
• Inulin is one example.
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50. Disorders Related to Digestion
• Belching
• Most common cause is swallowed air
• Flatulence
• Normal body function
• Partially digested carbohydrates
• Olestra, sugar alcohols, and quorn
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51. Disorders Related to Digestion
• The lining of the stomach is designed to cope
with hydrochloric acid, but other regions of the
GI tract are not.
• Heartburn is caused by hydrochloric acid in the
esophagus.
• GERD, or gastroesophageal reflux disease, is
painful, persistent heartburn.
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52. The Mechanism of Heartburn and GERD
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53. Disorders Related to Digestion
• Peptic ulcers are regions of the GI tract that
have been eroded by HCl and pepsin.
• The bacterium Helicobacter pylori contributes to
the production of both gastric and duodenal
ulcers.
• Some peptic ulcers have been traced to use of
nonsteroidal anti-inflammatory drugs such as
aspirin and ibuprofen.
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54. Disorders Related to Digestion
• Food intolerance is a group of GI symptoms
associated with eating a particular food.
• Symptoms may include gas, pain, and diarrhea.
• Lactose intolerance is an example.
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55. Disorders Related to Digestion
• Food allergies: a response of the immune
system caused by a particular food
• In some people, food allergies can be mild.
• In others, food allergies can be quite severe and
require immediate medical attention.
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56. Food Allergy Myths
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Click the next slide for the
video.

57. Disorders Related to Digestion
• Celiac disease is an immune system response
to eating gluten, a protein found in wheat, rye,
and barley.
• The immune response damages the villi in the
small intestine, leading to decreased absorption
of certain nutrients.
• Celiac disease is considered a genetic disorder.
• Treatment involves a gluten-free diet although
there is no known cure.
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58. Disorders Related to Digestion
• Non-celiac gluten sensitivity (NCGS)
• The patient presents with symptoms but does
not have the genetic marker, antibodies, or
intestinal damage associated with true celiac
disease.
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59. Disorders Related to Digestion
• Diarrhea:
• Can be caused by infection of the GI tract,
chronic disease, food intolerances, stress,
and bowel disorders
• Can lead to severe dehydration
• Is more dangerous for infants and young
children
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60. Disorders Related to Digestion
• Constipation:
• Difficulty passing stools
• Can be caused by the disruption of a person's
schedule, a change in diet, or certain
medications
• May be treated by increasing fluid and fiber
consumption
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61. Disorders Related to Digestion
• Irritable bowel syndrome (IBS) is a disorder
that interferes with normal colon function.
• Symptoms of IBS include:
• Abdominal cramps and bloating
• Either diarrhea or constipation
• IBS is more common in women than in men.
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