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Section 10.1 Your Digestive System
Your Digestive System
Objectives
Describe the three main functions of the
digestive system.
Identify the organs of the digestive system and
their functions.
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Section 10.1 Your Digestive System
Myth Food is digested in the stomach.
Fact Although protein digestion does begin in the
stomach, most digestion occurs in the small intestine.
List three questions you have about how the
digestive system functions. Look for the answers in the
chapter.
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Section 10.1 Your Digestive System
Functions of the Digestive System
Your digestive system has three main functions
• digestion
• absorption
• elimination
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Section 10.1 Your Digestive System
Digestion
• The process by which the digestive system breaks
down food into molecules that the body can use is
called digestion.
• During mechanical digestion, foods are physically
broken apart into smaller pieces.
• During chemical digestion, chemicals produced
by your body break large molecules into smaller
ones that your body can use.
• Most of the chemicals involved in digestion are
enzymes, substances that speed up reactions.
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Section 10.1 Your Digestive System
Absorption and Elimination
• Absorption is the process by which nutrients pass
through the lining of your digestive system into your
blood.
• Materials that are not absorbed are eliminated from
the body as wastes.
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Section 10.1 Your Digestive System
For: More on the digestive system
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Section 10.1 Your Digestive System
Structures of the Digestive System
The organs of the digestive system include the
• mouth
• pharynx
• esophagus
• stomach
• small intestine
• large intestine
• liver
• gallbladder
• pancreas
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Section 10.1 Your Digestive System
Mouth
• Your teeth tear, crush, and grind your food.
• Your tongue pushes the food around.
• An enzyme in saliva begins to break down starches
in your food.
• Saliva moistens the bites of food.
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Section 10.1 Your Digestive System
Pharynx
• The pharynx is the junction between the digestive
tract and the respiratory system.
• A flap of tissue called the epiglottis seals off the
trachea, or windpipe, preventing food and liquid from
entering your lungs.
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Section 10.1 Your Digestive System
Esophagus
• After passing through the pharynx, the food enters
the esophagus, a muscular tube that connects the
pharynx to the stomach
• Waves of muscle contractions, called peristalsis,
push food through the rest of the digestive system.
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Section 10.1 Your Digestive System
Pharynx
Epiglottis
Liver
Mouth
Salivary gland
Esophagus
Stomach
Pancreas
Small intestine
Gallbladder
Large intestine
Rectum
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Section 10.1 Your Digestive System
Enzymes in Action
In this activity, you will observe the effect on enzymes
on foods.
Materials
crackers • meat tenderizer • milk • orange juice
2 clear glasses • 2 stirrers
Try This
Chew a cracker for 5 seconds. Do not swallow it. Note
how the cracker tastes.
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Section 10.1 Your Digestive System
Enzymes in Action
Continue chewing the cracker for 5 minutes. Note how
the taste of the cracker changes before swallowing it.
Place 2 tablespoons of milk into one glass. Place 2
tablespoons of orange juice into another glass.
Add 1 tablespoon of meat tenderizer to each glass. Stir
well with separate stirrers.
After 30 minutes, look closely at the contents of the two
glasses. Record your observations.
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Section 10.1 Your Digestive System
Enzymes in Action
Think and Discuss
How did the taste of the cracker change during the five
minutes it was in your mouth?
Why do you think the taste of the cracker changed the
longer it was in your mouth?
After 30 minutes, how did the appearance of the milk
solution compare to that of the orange juice solution?
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Section 10.1 Your Digestive System
Enzymes in Action
Think and Discuss
Meat tenderizer contains an enzyme called papain.
Based on your observations, what nutrient does papain
act on?
Why do you think meat tenderizer makes cooked
meat tender?
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Section 10.1 Your Digestive System
Stomach
• From the esophagus, food passes through a valve
and into the stomach, a muscular pouch located in
the abdomen.
• Mechanical digestion occurs as three layers of
muscle produce a churning motion.
• Chemical digestion occurs as cells lining the
stomach release gastric juice.
• Peristalsis moves the food, which is now a thick
liquid called chyme (kym), into the small intestine.
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Section 10.1 Your Digestive System
Small Intestine
• The small intestine is where most chemical digestion and
absorption of nutrients takes place.
• Liver The role of the liver is to produce bile. Bile is a
substance that physically breaks up large fat droplets that
clump together.
• Gallbladder Bile flows from the liver into the gallbladder, the
organ that stores bile.
• Pancreas The pancreas secretes enzymes into the small
intestine that complete the breakdown of carbohydrates,
proteins, and fats.
• The lining of the small intestine is covered with millions of tiny
fingerlike projections called villi (singular, villus).
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Section 10.1 Your Digestive System
The Large Intestine
• The large intestine is about 5 feet long and 3 inches
wide.
• As the material moves through the large intestine,
most of the remaining water is absorbed into the
blood.
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Section 10.1 Your Digestive System
Vocabulary
digestion
enzyme
absorption
The process by which the digestive system
breaks down food into molecules that the body
can use.
A chemical that speeds up reactions in the body.
The process by which nutrients pass through
the lining of the digestive system.
pharynx
The upper portion of the throat; the junction
between the digestive and respiratory systems.
epiglottis
A flap of tissue that seals off the trachea when
food or liquid is swallowed.
peristalsis
Waves of muscle contractions that push food
through the digestive system.
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Section 10.1 Your Digestive System
Vocabulary
chyme
A thick mixture of food and gastric juices formed
in the stomach.
bile
A substance produced by the liver that aids in
digestion by breaking up large fat droplets.
gallbladder
The organ that stores bile and releases it into
the small intestine.
villi
Tiny fingerlike projections lining the small
intestine, through which nutrients are absorbed
into the blood.
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Section 10.1 Your Digestive System
QuickTake Quiz
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Section 10.1 Your Digestive System
End of Section 10.1
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