Chapter 9:
Digestive System and Nutrition
Quiz Next
1. Which of the following best describes the overall function of the
digestive system in the human body?
a. Maintain homeostasis within the body
b. Break down food and absorb nutrition into the blood stream
c. Pump stomach contents into the blood stream
d. Break down food and absorb nutrition to perform
photosynthesis in the body
2. Name one organ of the digestive system:
Chapter 9:
Digestive System and Nutrition
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Overview of digestion
The mouth, pharynx, and esophagus
The stomach and small intestine
The accessory organs and regulation of secretions
The large intestine and defecation
Nutrition and weight control
Overview of Digestion
The organs of the digestive system
are located within a tube called
the gastrointestinal (GI) tract.
Digestive system: break down
food into molecules that can be
absorbed by the digestive system
and carried by the blood to our
cells
Overview of Digestion
Once broken down by the
digestive system, these molecules
can cross plasma membranes
using facilitated and active
transport
Food also contains water, salts,
vitamins, and minerals that help
the body function normally.
Processes of Digestion
• Ingestion
• Digestion
• Movement
• Absorption
• Elimination
Processes of Digestion
• Ingestion: food is taken
in through the mouth
• Digestion
• Movement
• Absorption
• Elimination
Processes of Digestion
• Ingestion
• Digestion: The breakdown on larger
pieces of food into smaller pieces 
smaller pieces can be acted on by
digestive enzymes
• Mechanical digestion: Chewing in the
mouth and wavelike contractions of
smooth muscle in the stomach
• Chemical digestion: Digestive enzymes
break down food molecules. Occurs in
the mouth, stomach, and small intestine.
• Movement
• Absorption
• Elimination
Processes of Digestion
• Ingestion
• Digestion: The breakdown on
larger pieces of food into
smaller pieces  smaller pieces
can be acted on by digestive
enzymes
• Mechanical digestion: Chewing
in the mouth and wavelike
contractions of smooth muscle
in the stomach
• Chemical digestion: Digestive
enzymes break down food
molecules. Occurs in the mouth,
stomach, and small intestine.
• Movement
• Absorption
• Elimination
Processes of Digestion
• Ingestion
• Digestion: The breakdown on
larger pieces of food into smaller
pieces  smaller pieces can be
acted on by digestive enzymes
• Mechanical digestion: Chewing in
the mouth and wavelike
contractions of smooth muscle in
the stomach
• Chemical digestion: Digestive
enzymes break down food
molecules. Occurs in the mouth,
stomach, and small intestine.
• Movement
• Absorption
• Elimination
Processes of Digestion
• Ingestion
• Digestion: The breakdown on
larger pieces of food into smaller
pieces  smaller pieces can be
acted on by digestive enzymes
• Mechanical digestion: Chewing in
the mouth and wavelike
contractions of smooth muscle in
the stomach
• Chemical digestion: Digestive
enzymes break down food
molecules. Occurs in the mouth,
stomach, and small intestine.
• Movement
• Absorption
• Elimination
Processes of Digestion
• Ingestion
• Digestion
• Movement of GI contents along
the digestive tract: by
contractions of the smooth
muscle
• Absorption
• Elimination
Processes of Digestion
• Ingestion
• Digestion
• Movement
• Absorption occurs as molecules
broken down by chemical
digestion (nutrients) cross the
wall of the GI tract and enter the
cells lining the tract  enter the
blood for delivery of cells
• Elimination
Processes of Digestion
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Ingestion
Digestion
Movement
Absorption
Elimination: removes molecules
that cannot be digested and need
to be discharged from the body.
Defecation: Removal of
indigestible wastes through
the anus
Processes of Digestion
• Ingestion
• Digestion
• Movement
• Absorption
• Elimination
Wall of the Digestive Tract
Think of the GI tract
as a garden hose
that has a beginning
(mouth) and an end
(anus).
Lumen: central,
open, hollow area
in an organ
Wall of the Digestive Tract
Think of the GI tract
as a garden hose
that has a beginning
(mouth) and an end
(anus).
Mucosa: inner
mucous membrane
of lumen
The Mouth, Pharynx, and Esophagus
The mouth,
pharynx, and
esophagus are in
the upper portion
of the GI tract.
The Mouth
The mouth (oral
cavity) receives
food and begins
the process of
mechanical and
chemical
digestion.
The Mouth : Teeth
Mechanical
digestion occurs
when our teeth
chew food into
pieces
convenient for
swallowing.
The Mouth : The Tongue
The tongue
assists the teeth
in mechanical
digestion: move
food around the
mouth and
prepares it for
swallowing
The Pharynx and Esophagus
The Pharynx and Esophagus
• Both the mouth and the
nasal passages lead to
the pharynx (throat).
• The pharynx opens into
both the food passage
(esophagus) and the air
passage (trachea, or
windpipe)
The Pharynx and Esophagus: Swallowing
• Food enters the
esophagus: muscular
tube that moves food
into the stomach
• Other possible passages
are blocked by the soft
palate and epiglottis
The Pharynx and Esophagus: Swallowing
The Pharynx and Esophagus: Peristalsis
The Pharynx and Esophagus
• Esophagus: moves the
food from the mouth to
the stomach.
Pharynx  Esophagus  Esophageal sphincter  Stomach
Pharynx  Esophagus  Esophageal sphincter  Stomach
The Pharynx and Esophagus
• Sphincters: muscles that
encircle tubes and act as
valves.
• Heartburn occurs when
the lower esophageal
sphincter is opened and
food moves from the
stomach back to the
esophagus.
Biology Today: Heartburn (GERD)
The Stomach
• The stomach is an organ that
stores food, initiates the digestion
of protein, and controls the
movement of food into the small
intestine.
• Nutrients are not absorbed by
the stomach.
• The stomach does absorb
alcohol- it can pass through
membranes easily
The Stomach
• The stomach is an organ
that stores food,
initiates the digestion of
protein, and controls
the movement of food
into the small intestine.
• Nutrients are not
absorbed by the
stomach.
• The stomach does
absorb alcohol- it can
pass through
membranes easily
The Stomach
• Why does your
stomach growl?
Peristalsis in your
empty stomach!
Explain the process of:
the digestion of food from the
mouth to the stomach.
Where does mechanical
digestion take place in the body?
Where does chemical digestion
take place in the body?
Chapter 9:
Digestive System and Nutrition
•
•
•
•
•
•
Overview of digestion
The mouth, pharynx, and esophagus
The stomach and small intestine
The accessory organs and regulation of secretions
The large intestine and defecation
Nutrition and weight control