THE
DIGESTIVE
SYSTEM
C15L2
The food you eat goes
through four steps:
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Ingestion: intake of nutrients; the act
of eating, or putting food in your mouth
Digestion: breakdown of food into small
particles and molecules that your body
can absorb and use
Absorption: uptake of nutrient
molecules
Defecation: elimination of undigested
residues
Two types of digestion


mechanical digestion
chemical digestion
mechanical
digestion
food is physically
broken down
the process of
breaking food into
smaller pieces and
mixing it with the
digestive juices
chemical digestion
the breaking
down of food into
smaller
molecules
Chemical Digestion
• Enzymes are proteins that help
break down larger molecules into
smaller molecules.
• Enzymes also speed up, or catalyze,
the rate of chemical reactions.
• The digestive system produces
enzymes that are specialized to help
break down each type of food
molecule.
Some Digestive Enzymes
• Amylase: breaks down starch in
the mouth
• Lipase: breaks down fats when it
enters the stomach
• Pepsin: digests proteins in the
stomach
• Renin: digests milk in the stomach
GROUPING OF ORGANS OF
THE DIGESTION SYSTEM
alimentary
canal
(digestive
tract)
 accessory
organs

alimentary
canal
the digestive tract:
mouth, pharynx,
esophagus,
stomach, small
intestine, large
intestine, and anus
accessory
organs
organs that
secrete
substances that
are carried
through ducts
(tubes) to the
alimentary canal
accessory
organs




liver
pancreas
gallbladder
salivary glands
MOUTH
mixed with saliva from the
salivary glands (3 pairs of salivary
glands) the saliva moistens and
lubricates the food for easy
swallowing
MOUTH
salivary glands secrete a digestive
enzyme--amylase
amylase
A digestive
enzyme that
begins the
breakdown of
starch to sugar
and neutralizes
acidic foods
mastication
The
chewing
of food
4 different types of teeth
are involved in mastication
 incisors (8): flat, narrow,
bladelike surfaces for cutting
and biting food
 canines [cuspids] (4): tear food
 premolar (8): crush food
 molars (12): grinding food
4 different types of teeth
are involved in mastication
ESOPHAGUS
a muscular tube that connects the
mouth to the stomach
ESOPHAGUS
the word esophagus
means "I will carry
down."--its only
function
it only requires 3-6
seconds for food to
move from the
mouth to the
stomach
peristalsis
muscular contractions that
move food along the
alimentary canal
cardiac sphincter
Lower Esophageal Sphincter
muscular valve
that controls
food going into
the stomach;
keeps food in
the stomach
STOMACH
The stomach is a
large, hollow
organ that
temporarily
stores food and
aids in chemical
digestion.
STOMACH
the thick,
muscular walls
of the stomach
churn the food
and mix it with
the acidic gastric
juices which
contains the
enzyme pepsin
for protein
digestion
STOMACH
The acid would
also digest the
walls of the
stomach if the
walls were not
protected by the
slimy mucous
from the mucous
membrane lining
the stomach
STOMACH
the duration of
churning may be
4 hours for coarse
foods like celery
and spinach;
foods like oatmeal
and pudding move
through the
stomach quickly
STOMACH
Food mixes with gastric juice in the stomach
to form a thin, watery liquid called chyme.
chyme: food in a semi-liquid state
STOMACH
Although the stomach lining does
not absorb many food molecules,
it does absorb alcohol, water, and
certain drugs.
STOMACH
pyloric
sphincter:
muscles that
control the pyloric
valve; controls
food moving into
the small
intestine
SMALL INTESTINE
about 7 m (23 feet) long;
about 2.5 cm (1 inch) in diameter
SMALL INTESTINE
Most of the chemical digestion and
absorption of food occurs here.
SMALL INTESTINE
Chemical digestion of
proteins,
carbohydrates and fats
takes place in the first
part of the small
intestine, called the
duodenum.
duodenum: first section of the
small intestine; about 10 inches
SMALL INTESTINE
As partially digested food from
the stomach passes into the
duodenum, the acidity of the
SMALL
INTESTINE
food stimulates the intestinal
lining to secrete hormones
SMALL
INTESTINE
these
hormones
stimulate the
pancreas,
gallbladder,
and intestinal
lining to
secrete
SMALL
INTESTINE
enzymes and other materials
into the duodenum for
digestion.
Small Intestine
The remainder of the small intestine
absorbs nutrients from food.
The folds of the small intestine are covered
with fingerlike projections called villi.
VILLUS
villi: (singular,
villus)
microscopic,
fingerlike
structures that
line the wall of
the small
intestine
VILLI
LARGE INTESTINE (COLON)
about 1.5 M
(5-6 feet)
long;
5 cm (2 1/2
inches) in
diameter
Large Intestine (colon)
• Food not absorbed in
the small intestine move
by peristalsis into the
large intestine, also
called the colon.
• Materials that pass
through the large
intestine are the waste
products of digestion.
LARGE INTESTINE (COLON)
little or no digestion occurs
LARGE INTESTINE (COLON)
functions:
1)removal of
waste
materials
(called
feces)
2) absorb
water and
minerals
LARGE INTESTINE (COLON)
also serves as
an ideal site for
growth of
bacteria and
yeasts
LARGE INTESTINE (COLON)
there are
many
beneficial
bacteria and
yeasts
reproducing in
the colon
LARGE INTESTINE (COLON)
Bacteria and
yeasts
produce
vitamins
(B1, B2,
B12, and K)
and some
amino acids.
accessory
organs

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liver
pancreas
gallbladder
salivary glands
LIVER
called "master
chemist of the
body"
LIVER
Liver receives
blood by way of
the portal vein
LIVER
makes bile, a
greenish fluid
that breaks up
lipids into
droplets so they
can be
digested.
GALLBLADDER
bile is stored
in the
gallbladder
PANCREAS
pancreas
a soft, pinkishwhite gland
about 6-9
inches long;
1 inch wide
PANCREAS
pancreas
about 97% of the
pancreas cells
produce digestive
juices that contain
enzymes for
digesting
carbohydrates,
fats, and proteins
PANCREAS
most of the
remaining
pancreas cells
produce hormones
(insulin)
involved in
regulating the
amount of sugar
in the blood
The Digestive System and
Homeostasis
Nutrients absorbed
by the body through
the digestive system
are necessary for
other body systems
to maintain
homeostasis.