The digestive System
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WHAT HAPPENS TO THE FOOD AFTER IT IS EATEN?
No matter what you eat, your food goes through 4 steps:
• Ingestion is the act of eating, or putting food in your
mouth.(mechanical)
• Digestion is the mechanical and chemical breakdown of
food into small particles and molecules that your body can
absorb and use.
• Absorption occurs when the cells of the digestive system
take in small molecules of digested food.
• Elimination is the removal of undigested food and other
wastes from your body.
All 4 steps happen in the organs and tissues of
the digestive system
Before your body can absorb nutrients from food, the food
must be broken into small molecules by digestion.
There are TWO types of digestion:
Mechanical digestion
• In mechanical digestion, food is physically
broken into smaller pieces.
Chemical digestion
• In chemical digestion, chemical
reactions break down pieces of food
into small molecules.
• It cannot occur without substances
called: Enzymes
Chemical digestion
•Enzymes are proteins that
-help break down larger food molecules into smaller molecules.
-speed up, or catalyze, the rate of chemical reactions.
Chemical digestion
step 1: an enzyme attaches
to a food particle
step 2: the enzyme speeds up a
chemical reaction that breaks down
the food particle
step 3: the enzyme releases
the broken down food
particles.
Notice that the food molecule breaks apart, but the enzyme does not change. Therefore, the enzyme can immediately be used to break down another food
molecule.
Properties of enzymes
There are many kinds of enzymes.
Each one is specialized to help break down a specific
molecule at a specific location.
• The enzyme AMYLASE helps break down carbohydrates.
• The enzymes PEPSIN and PAPAIN help break down proteins.
• Fats are broken down with the help of the enzyme LIPASE.
Temperature affects the activity of enzymes
Answer the following questions
•List the different Functions of The Digestive System.
•Differentiate between chemical and physical
digestion.
•Why our body should break down the foods we eat?
•Define enzymes and list some examples.
•List the three properties of an enzyme.
Organs of
the digestive
system
Your Digestive system has TWO parts:
- the digestive tract
and
- different organs connected
by tube-like structures.
The digestive tract extends from
the mouth to the anus
These Organs include the tongue,
salivary glands, liver, gallbladder, and
pancreas.
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• Mechanical digestion of food begins in your mouth.
- Your teeth and tongue mechanically digest food as you chew.
• But even before chewing begins, your salivary glands produce saliva at the thought of
food.
• Saliva contains
- an enzyme that helps break down
carbohydrates.
They produce more than 1 L of saliva every day.
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It is a muscular tube
that connects the
mouth to the
stomach.
Food moves
through the
esophagus and
the rest of the
digestive tract by
waves of muscle
contractions
called peristalsis.
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• The stomach contains an acidic fluid called gastric juice.
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- Gastric juice makes the stomach acidic. Acid helps break down some of the structures
that hold plant and animal cells together.
- Gastric juice also contains pepsin, which is an enzyme that helps break down the
proteins in foods into amino acids.
Mechanical &
Chemical digestion
Food and gastric juices mix as
muscles in the stomach
contract through peristalsis.
As food mixes
with gastric juice in the
stomach, it forms a thin,
watery liquid called CHYME
(PH<7)
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I Most chemical digestion and
nutrient absorption take place in the
small intestine.
• Chemical digestion by
receiving pancreatic juice,
takes place in the first part of
the small intestine, called the
duodenum.
• The remainder of the small
intestine absorbs nutrients
from food.
The wall of the intestine is folded like the stomach.
The folds of the intestine are covered with fingerlike projections called
villi.
Each villus contains small blood vessels.
Nutrients in the small intestine diffuse into the blood through these
blood vessels.
The pancreas and liver produce substances that enter
the small intestine and help with chemical digestion.
Liver
The liver produces bile.
Bile makes it easier to digest fats.
The gallbladder stores bile until
it is needed in the small intestine.
Pancreas
The pancreas produces:
- the enzyme amylase that
helps break down
carbohydrates.
- a substance that neutralizes
stomach acid.
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• Also called Colon.
• More water is absorbed there.
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Any food that is not absorbed in
the small intestine moves by
peristalsis into the large
intestine.
Materials that pass through the
large intestine are the waste
products of digestion
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As these waste products travels
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through the large intestine, even
more water is absorbed.so The waste
products become more solid.
• The rectum, the last section of the
large intestine, where undigested
food is eliminated & rejected outside.
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