The Digestive System
Digestion is the process of breaking down
food into molecules the body can use
How is food digested?
Digestion involves:
Breaking down of food into smaller pieces
 The mixing of food
 Movement through the digestive tract
 Chemical breakdown of the large
molecules of food into smaller molecules.

Two Types of Digestion

Mechanical – physically changing the size
of food
– Ex: grinding action of teeth
– Ex: churning action of stomach

Chemical – a change in the chemical
nature of the nutrients
– Ex: amylase (in saliva) working on starch
Gastrointestinal Tract

a series of hollow organs
that food passes through

Also known as the
alimentary canal
– Alimentary: of or relating
to nourishment or nutrition
Identify the organs of the digestive
system
Identify the organs of the digestive
system
Mouth (oral cavity)
Teeth
-mechanical digestion

Chemical Digestion:
– Amylase Enzymes in saliva
chemically digest
carbohydrates.
Mouth (oral cavity)
Tongue:
o Keeps food in place
o Push bolus to back of
mouth
o Bolus: a soft mass of
chewed food
More to the Mouth

Uvula
– Dangling “thing” in back
of throat
– Catches bacteria and dirt
particles
– Can be destroyed by
bulimics
Pharynx
Open area at back of the
mouth
 Passageway for both food
& air
 Epiglottis – thin flap that
prevents food from
entering the trachea

http://www.cortexity.com:8080/nicksblog/images/pharynx.jpg
Esophagus
Tube about 25cm long
 connects the pharynx to
the stomach.
 2 layers of muscle.

http://www.massgeneral.org/cancer/crr/types/thoracic/illustrations/images/esophagus_front.jpg
Esophogus

peristalsis
– Wavelike, involuntary
muscle contractions
that pushes food
through the digestive
tract

http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter26
/animation__organs_of_digestion.html
http://www.easttroy.k12.wi.us/hs/dept/science/bottum/Adv%20Biolog
y/digestive/danatomy/images/peristalsis.gif
Stomach
Both mechanical and
chemical digestion
 Mechanical Digestion

– 3 layers of muscle that twist
and turn the stomach
– Results in churning action =
mechanical
– Makes your stomach “growl”
Stomach

Chemical digestion:
– Stomach lining produces
HCl (hydrochloric acid)
to breakdown and
dissolve nutrients
– Enzyme – Pepsin begins
to digest proteins
– Bolus becomes Chyme
http://www.health.com/health/static/hw/media/medical/hw/hwk
b17_010.jpg
Small Intestine
7 meters long (22feet)
 Site of nutrient
diffusion into blood
from mesentary

http://www.nlm.nih.gov/medlineplus/ency/images/ency/full
size/19221.jpg
Small Intestine

Mesentary:
– Contains blood vessels
that Absorb the nutrients
Large Intestine

Water and Minerals
(NaCl) are absorbed
back into the blood

The remains are
formed into brown,
semi-solid feces
Large Intestine

Diarriaha
– Water was not
reabsorbed

Constipation
– Too much water was
reabsorbed
Rectum and Anus

Rectum = store the feces.

Anus: ring of muscle that squeezes the
feces out of the body.
Accessory Organs
Aid (help with) in digestion but food never
travels through
 Liver, Pancreas, Gall bladder

Liver

The liver is like a processing factory with
more than 200 different jobs.
– Produces bile
 Bile: breaks down fats in the small intestine.
– Stores some nutrients
 brought from the blood after the small intestine
– Produces cholesterol
– Detoxifies
Pancreas
Produce insulin and
enzymes
 Enzymatic juices travel
through the common
bile duct into the small
intestine

http://www.fairview.org/healthlibrary/content/pancreas.gif
Gall Bladder

A small baglike sac
under the liver.

It stores bile.

Empties the bile into
the small intestine via
the common bile duct
Common Bile Duct

Collects from liver,
gallbladder, pancreas
and empties into the
small intestine
To quiz yourself over the
parts of the digestive
system, click here:
http://www.tvdsb.on.ca/westmin/
science/sbi3a1/digest/digdiag.htm
Describe water

Most of the nutrients in your body can't be
used unless they are carried in a solution.
This means that they have to be dissolved
in water.

In cells, chemical reactions take place in
solutions.
Describe water

Most of the material absorbed from the
cavity of the small intestine is water in
which salt is dissolved.

The salt and water come from the food
and liquid we swallow and the juices
secreted by the many digestive glands.
For more information about
the digestive system, click
here:
http://kidshealth.org/kid/body/dig
est_noSW.html