Digestive System
Digestion
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Three main functions:
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Ingest food
Break it down into nutrients the body can use
Eliminate waste
2 Types of Digestion:
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Mechanical: physically breaking food down into
smaller pieces
Chemical: chemically altering food, breaking
things down into their chemical components:
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Starches  simple carbohydrates
Proteins  amino acids
Digestion
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All throughout the
digestive tract,
mechanical digestion
occurs.
Chemical digestion of
specific types of
molecules occurs in
different organs.
Mouth/Esophagus
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In the mouth, mechanical
breakdown occurs with the help of
the tongue and teeth.
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Saliva in the mouth contains an
enzymes called amylase, which
starts to break starches down into
simple sugars.
As food is broken down, it is
shaped into small semi-circular
chunks called a “bolus” which is
swallowed down into the
esophagus.
Esophagus
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The esophagus is a tube that
connects the mouth to the
stomach.
It is lined with smooth muscle
(you can’t control this type of
muscle).
The muscle rhythmically
contracts, pulling the food
towards the stomach. This
process is known as peristalsis.
Before food enters the stomach,
it encounters a ring of smooth
muscle known as the cardiac
sphincter.
Choking
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Area before the esophagus
called the pharynx splits!
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Esophagus  stomach
Trachea  lungs
To prevent food from
entering the lungs and
people choking, flap of
tissue called epiglottis
covers the trachea when
we swallow.
Stomach
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The environment of the
stomach is very acidic, pH of
about 2, due to gastric glands
secreting stomach acid.
•In the stomach 3 layers of smooth
muscle control its contraction 
mechanical breakdown of food.
•Also enzymes pepsin is released here
which breaks down proteins.
(chemical breakdown)
Small Intestine
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The pyloric sphincter separates the
stomach from the small intestine.
The small intestine is 7m long and
2.5cm wide.
Smooth muscle continues peristalsis
and mechanical digestion of food.
Chemical digestion relies on 3 accessory
organs: liver, pancreas and gallbladder.
Small Intestine
The pancreas has 2
functions in digestion:
 secretes enzymes
that break down
sugars, proteins and
fats.
 Raises the pH to
above 7, allowing
intestinal enzymes to
work properly.
 The liver produces bile,
which breaks
fats as
down
The gallbladder
serves
a
chemically
bile storage
unit..
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The juices of the pancreas and
liver enter the small intestine
via the common bile duct.
Small Intestine
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As food is chemically digested
the particles are absorbed by
the walls of the small intestine
into the bloodstream.
Finger-like projections called
villi line the walls of the small
intestine, to increase the
surface area, maximizing
nutrient absorption.
Villi
Villi
Large Intestine
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Large intestine is 6.5cm in
diameteer and about 1.5m
long.
Includes the colon, rectum,
and appendix.
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As food enters the colon it is
called chyme.
The function of the large
intestine is to absorb water from
the chyme.
The leftover, undigested material
is known as feces.
This material is expelled
through anus.
Time for Digestion
Structure
Function
Time of food in
structure
Mouth
Mechanical/chewing
Some chemical
digestion
5-30 seconds
Esophagus
Transport (swallowing) 10 seconds
Stomach
Mechanical and
Chemical digestion
2-24 hours
Small Intestine
Mechanical and
chemical digestion
3-4 hours
Large Intestine
Water absorption
18 – 48 hours
Malfunctions
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Stomach problems:
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Ulcers in the stomach are often caused
by a bacteria infection. Ulcers are holes in
the stomach’s lining.
Acid reflux occurs when some acid gets
regurgitated into the esophagus.
Large intestine problems:
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Diarrhea is a result of not enough water
absorbed from undigested material in the
large intestine.
Constipation occurs when too much
water is removed.
Your Turn
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Create a fairytale story about
the digestive system.
Your main character must be
a type of food that can be
successful digested. Make it
interesting, choose something
that has fats, protein, and
carbs in it!
Tell the story of this items
adventures through digestion.