The Digestive System
General Structure & Function
Series of connected hollow organs and
accessory organs
 Food molecules are digested and absorbed
to be used by cells as for energy

Main Organs
• Mouth
• Esophagus
• Stomach
• Small Intestine
• Large Intestine
Accessory Organs
• Liver
• Gall Bladder
• Pancreas
How is food digested?
Digestion involves:
 Mechanical
– Chewing/grinding/mixing of food into smaller
pieces
– Movement through the digestive tract
(Peristalsis)

Chemical
– breakdown of the large molecules of food into
smaller molecules by enzymes
What is absorption?
Transfer of nutrients from the digestive
system into the lymphatic and circulatory
systems (diffusion) for eventual use by
cells.
 Most absorption takes place in small
intestine

– Except for water, sodium and end products of
bacterial digestion which are absorbed in the
large intestine
What are Enzymes?

Chemicals that break down specific large
food molecules into smaller, usable
molecules
Main Organs
Mouth
 Opening in which animals take in food. In
humans the mouth includes teeth, tongue,
salivary glands, and saliva.
– Mechanical Digestion: Teeth bite off and chew
food into a soft pulp and moisten with saliva so
that is easy to swallow.
– Chemical Digestion: Enzymes in the saliva begin
digestion of carbohydrates..
Main Organs
Esophagus
 A muscular tube that leads to the
stomach.
 Moves food by waves of smooth muscle
contractions called peristalsis.
Main Organs
Stomach
 J-shaped organ
– Mechanical Digestion: Thick muscular walls
contract to mash the food into a watery soup
called chyme.
– Chemical Digestion: Stomach lining produces
strong digestive juices which cause chemical
reactions, breaking down food into simpler parts
and dissolving its nutrients.
 Pepsin: Helps digest proteins into amino acids
Main Organs
Small Intestine
 Narrow, but very long - about 20 feet.
– Mechanical Digestion/Absorption: Diffusion of
nutrients out through the linings in the villi
into capillaries.
– Chemical Digestion: Enzymes continue the
chemical reactions on the food.
Main Organs
Large Intestine
 Large tube-like structure (1.5 meters)
responsible for the final stages of digestion.
 Where the remains are formed into brown,
semi-solid feces, ready to be removed from
the body
– Mechanical Digestion/Absorption: Diffusion of
useful substances that were not absorbed in the
small intestine (water and minerals).
– Chemical Digestion: Bacteria in the large
intestine process any remaining nutrients
releasing minerals.
Main Organs
More Large Intestine
 Rectum
– The end of the large intestine and the next
part of the tract, the rectum, store the feces.

Anus
– Feces are finally squeezed through a ring of
muscle, the anus, and out of the body.
Accessory Organs
Liver
 The largest gland of the body. The liver is
reddish-brown and primarily rests on the top
right of the abdomen.
– Mechanical Digestion: Produces bile to be secreted
into the small intestine to break up fat particles.
– Chemical Digestion: Blood from the intestines
enters to the liver, carrying nutrients, vitamins and
minerals, and other products from digestion. The
liver stores some nutrients, changes them from
one form to another, and releases them into the
blood according to the activities and needs of the
body.
Accessory Organs
Gall Bladder
 A small baglike sac under the liver which
stores bile made in the liver.
– Mechanical Digestion: Secretes bile through a
tube connected to the small intestine which
breaks up fat particles into smaller and
smaller pieces.
Accessory Organs
Pancreas
 The pancreas is a triangular shaped organ
that lies between the stomach and the
first part of the small intestine.
– Chemical Digestion: Like the stomach, the
pancreas makes digestive juices called
enzymes which help to digest food further as
it enters the small intestines.
Describe water
Most 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.
 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.

Helpful Websites

Animation Site
http:/www.kitses.com/animation/swfs/digestion.swf

Review Site
http:/www.anatomyarcade.com/games/jigsaws/DigestiveJigsaw/digestiveJigsaw.html

Digestive Overview
http://kidshealth.org/kid/body/digest_noSW.html