Transcript The Digestive Process Begins chap 15 2

The Digestive Process Begins
Chapter 15
Section 2
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Key Concepts
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What functions are carried out in the
digestive system?
What roles do the mouth, esophagus and
stomach play in digestion?
Key Terms
Digestion
Absorption
Saliva
Enzyme
Epiglottis
Esophagus
Mucus
Peristalsis
Stomach
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Functions of the Digestive System
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Breaks down food into molecules the body
can use
Then the molecules are absorbed into the
blood and carried throughout the body
Waste are eliminated from the body
Digestion
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There are two types of digestions. Both types
begin in the mouth. Fluid released when your
mouth waters is saliva
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Chemical
Mechanical
Mechanical digestion
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Foods are physically broken down into
smaller pieces
This occurs when you bite into something
such as sandwich and chew it into small
pieces. Your teeth carry out the first stage of
mechanical digestion.
As the teeth do their work saliva moistens the
pieces of food into one slippery mass
Chemical digestion
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Chemicals produced by the body break foods
into their smaller chemical building blocks
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Ex-starch in bread is broken down into individual
sugar molecules. If you take a bite of a cracker
and suck on it, the cracker begins to taste sweet.
This is because a chemical in the saliva has
broken down the starch molecules in the cracker
into sugar molecules
(2)
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The chemical in saliva that digests starch is
an enzyme
They are proteins that speed up chemical
reactions in the body
Each enzyme your body produces has a
specific chemical shape
Its shape enables it to take part in only one
kind of chemical reaction
Absorption and Elimination
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After your food is digested the molecules are
ready to be transported throughout your body
In the process of absorption nutrient
molecules pass through the wall of your
digestive system into your blood
Materials that are not absorbed are
eliminated from the body as waste
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Ex. fiber
The Mouth
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Have you ever walked past a restaurant or
bakery and noticed your mouth watering?
Smelling or even just thinking about food
when you are hungry is enough to start your
mouth watering. When your mouth waters
your body is preparing for the delicious meal
it expects
Esophagus
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A muscular tube that connects the mouth to
the stomach.
When you swallow a flap of tissue called the
epiglottis seals off your windpipe preventing
the food from entering.
The esophagus is lined with mucus, a thick
slippery substance produced by the body.
Mucus makes food easier to swallow and
move along
(2)
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Food remains in the esophagus for only about 10
seconds
After food enters the esophagus contractions of
SMOOTH muscles push the food toward the
stomach
The involuntary waves of muscle contraction are
called peristalsis
Peristalsis also occurs in the stomach and farther
down the digestive system these muscular waves
keep food moving in one direction
The Stomach
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When food leaves the esophagus it enters
the stomach
The stomach is a J-shaped, muscular pouch
located in the abdomen
Most mechanical and some chemical
digestion occur in the stomach
Mechanical Digestion in the Stomach
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Mechanical digestion occurs in the same way
that clothes and soapy water are mixed in a
washing machine. The layers of smooth
muscle contract to produce a churning
motion
Chemical Digestion in the Stomach
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Chemical digestion occurs as the churning
food makes contact with digestive juice, a
fluid produced by cells in the lining of the
stomach
Digestive juice contains the enzyme pepsin
Pepsin chemically digests the proteins in
your food breaking them down into short
chains of amino acids
(2)
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Digestive juices also contain hydrochloric acid
Without this strong acid your stomach could not
function properly
Pepsin works best in an acid environment
Acid kills many bacteria that you swallow with your
food
This acid doesn’t burn a hole in your stomach lining
due to the coating of thick mucus which protects the
stomach lining
(3)
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Food remains in the stomach until all of the solid
material has been broken down into liquid form
The stomach completes mechanical digestion after a
few hours
By that time mot of the proteins have been
chemically digested into shorter chains of amino
acids
The food now a thick liquid is released into the next
part of the digestive system
This is where final chemical digestion and absorption
will take place
1. What are the functions of the
digestive system?
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To absorb the food molecules into the blood
To eliminate wastes from the body
2. What happens to the pizza during
chemical digestion
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It is broken down into molecules that the
body can use
3. What nutrients in the cheese and
crust would be absorbed?
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Cheese-protein, fat and calcium
Crust-carbohydrates and B vitamins
4. Swallow and try to breath at the
same time.
Why weren’t you able to breathe?
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The epiglottis sealed off the windpipe
5. How do the muscles of the
esophagus help food to move through
the digestive system?
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Muscles in the esophagus push food toward
the stomach
6. What key chemicals do the mouth
and stomach contain?
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Mouth: saliva which contains an enzyme that
breaks down starch
Stomach: pepsin and hydrochloric acid
7. What could happen if your stomach
didn’t produce enough mucus?
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The stomach lining would become irritated
and might develop sores from the acid
produced by the stomach