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THE DIGESTIVE SYSTEM
Chapter 7
Section 2
Pages
189-195
4 STAGES OF FOOD
PROCESSING
1.INGESTION
2.DIGESTION
3.ABSORPTION
4.ELIMINATION
INGESTION
When food enters your
mouth
Breakdown (digestion)
begins
DIGESTION
Process that breaks down food
into small molecules so that they
can be absorbed & moved into
the blood
2 kinds of digestion:
1. Mechanical
2. Chemical
MECHANICAL DIGESTION
Takes place when food is
chewed, mixed, &
churned
CHEMICAL DIGESTION
Chemical reactions occur that
break down large molecules of
food into smaller ones
Possible only because of
enzymes
ENZYME
A protein that speeds up
chemical reactions
Some reduce amount of
energy needed for a chemical
reaction to begin
DIGESTION’S ENZYMES
1. Amylase:
a) Made in glands near mouth
b) Helps speed up breakdown of complex carbs
2. Pepsin:
a) in stomach
b) Breaks down complex proteins
3. Pancreas:
a) Releases enzymes into small intestines
b) Some break down starches
c) Some—fats
d) Some--proteins
DIGESTIVE SYSTEM
HAS 2 PARTS
DIGESTIVE TRACT
 Mouth
 Esophagus
 Stomach
 Small intestine
 Large intestine
 Rectum
 Anus
ACCESSORY ORGANS
 Tongue
 Teeth
 Salivary glands
 Liver
 Gall bladder
 Pancreas
MOUTH’S DIGESTIVE JOBS
MECHANICAL DIGESTION—chew
food
CHEMICAL DIGESTION– food
mixes w/saliva
SALIVA: mostly water + mucus +
an enzyme that breaks down
starch into sugar
ESOPHAGUS
Muscular tube about 25 cm (almost 10
inches) long
Food takes 4 to 6 seconds to move
through esophagus into stomach
NO DIGESTION TAKES PLACE IN
ESOPHAGUS
Mucous glands keep food moist
Smooth muscles keep food moving down
by squeezing it
PERISTALSIS
Waves of muscle contractions
that move food through entire
digestive tract
Involuntary muscles
STOMACH
Muscular bag w/folds on inside
Food moves through stomach in 2 to 4 hours
& is changed to chyme (thin, watery liquid
made from stomach breaking down food);
moves from stomach to small intestine
Mechanical digestion: food is mixed in
stomach in peristalsis
Chemical digestion: food mixed w/enzymes &
digestive solutions to break it down
Acidic solution destroys bacteria in food
SMALL INTESTINE
 Small in diameter
 4 to 7 meters (about 13 feet to 23 feet) long
 1 st part is called DUODENUM
a. Most digestion takes place here
b. Bile from liver is added to food to break up fat particles
c. Stomach acid is neutralized by digestive solution from
pancreas
d. Pancreas make insulin, which lets glucose pass from
bloodstream into cells
e. Absorption takes place in folds & villi (fingerlike projections
on folds in small intestines)
f. Nutrients move from villi into blood & to cells
g. Undigested & unabsorbed food moves into large intestine
LARGE INTESTINE (AKA COLON)
Main job is to absorb water from
undigested mass in chyme
Chyme can stay here for up to 3
days
Rest of undigested food becomes
more solid & passes through
rectum & out of body through
anus
BACTERIA’S JOB IN DIGESTION
Bacteria is not always harmful
Feeds on undigested material in
large intestine
Makes vitamins you need
Breakdown of intestinal
materials by bacteria produces
gas
WHAT HAPPENS WHEN DIGESTION ENDS?
From the blood, food
molecules are transported
across cell membrane to be
used by cells
Unused molecules leave your
body as wastes