Lecture Discovering nutrition - Chapter 3: The human body: From food to fuel

Chapter 3
The Human
Body: From
Food to Fuel


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Taste and Smell:
The Beginnings of Our Food
Sight, smell, thought, taste, and sound
Experience
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Trigger a set of responses that prepare the
digestive tract to receive food



The Gastrointestinal Tract
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Variety of functions, including:
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Ingestion of food

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Transport of ingested food

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Secretion of digestive enzymes, acid,
mucus, and bile

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Absorption of end products of digestion

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Movement of undigested material

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Elimination of digestive waste products



The Gastrointestinal Tract
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Several layers to the GI tract, including
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Mucosa

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Circular muscle

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Longitudinal muscle

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Sphincters




Overview of Digestion
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Physical movement
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Peristalsis
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•

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Wavelike, muscular contractions
Transport food and nutrients along
the GI tract

Segmentation

•

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Series of muscular contractions in
the small intestines
Divides and mixes the chyme


Overview of Digestion
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Chemical breakdown
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Enzymes
•

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Proteins that catalyze chemical reactions

Other secretions
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Acid

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Base

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Bile

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Mucus


Overview of Absorption
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The road to nutrition absorption
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Passive diffusion

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Facilitated diffusion

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Active transport



Assisting Organs
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Salivary glands
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Moisten food

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Supply enzymes


Assisting Organs
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Liver
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Produces bile

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“Chemical factory”

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“Dynamic warehouse”


Assisting Organs
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Gallbladder
–

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Stores and secretes bile

Pancreas
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Secretes bicarbonate

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Secretes digestive enzymes


Putting it All Together:
Digestion and Absorption

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Mouth
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Enzymes
•

•

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Salivary amylase
acts on starch
Lingual lipase
acts on fat

Saliva
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Moistens food for
swallowing


Putting it All Together:
Digestion and Absorption

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Esophagus
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Transports food to
stomach

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Esophageal
sphincter

Putting it All Together:
Digestion and Absorption

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Stomach
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Hydrochloric acid prepares protein for
digestion and activates enzymes

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Pepsin begins protein digestion

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Gastric lipase has some fat digestion

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Gastrin (hormone) stimulates gastric
secretion and movement

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Intrinsic factor is needed for absorption of
vitamin B12

Putting it All Together:
Digestion and Absorption

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Small intestine
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Sections of small intestine
•

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Duodenum, jejunum, and ileum

Nutrient digestion
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Bicarbonate neutralizes stomach acid

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Pancreatic and intestinal enzymes
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Carbohydrates

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Fat

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Protein


Putting it All Together:
Digestion and Absorption
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Small intestine
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Absorption
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Folds, villi, and microvilli expand absorptive
surface

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Most nutrients absorbed here

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Fat-soluble nutrients go into lymph

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Other nutrients go into blood



Putting it All Together:
Digestion and Absorption

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Large intestine
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Sections
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Cecum, colon, rectum, anal canal

Digestion
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Peristaltic movement is slow, taking 18–24 hours
for material to travel
Some digestion of fiber by bacteria

Putting it All Together:
Digestion and Absorption
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Large Intestine
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Absorption
•
•

•

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Water
Sodium,
potassium, and
chloride
Vitamin K
(produced by
bacteria)

Elimination