Download The Digestive System

The Digestive System
Functions of the Digestive System
1. Breaks down food into molecules the
body can use.
2. Absorbs nutrient molecules into the
blood and carries them throughout the
body.
3. Eliminates wastes from the body.
Digestion
• The process where food molecules are
broken down into nutrients that are then
carried by the blood to the body’s cells
where they are used to produce energy.
Forms of Digestion
• Mechanical
– Foods are physically broken down into
smaller pieces
• Food is broken down by moving it.
• Chemical
– Chemicals produced by the body break foods
down into their smaller building blocks.
• For example, proteins are broken down into amino
acids; large sugars are broken down to glucose
Absorption
• The process by which nutrient molecules
pass through the wall of the digestive
system into the blood.
Elimination
• Materials that are not absorbed are
eliminated (removed) from the body as
wastes.
The Mouth
• Both mechanical and
chemical digestion
begin in the mouth.
• Mechanical Digestion
– Teeth cut, tear, grind,
and crush food into
smaller pieces.
– Saliva moistens the
pieces of food into a
slippery mass.
The Mouth
• Chemical Digestion
– Salivary glands in the
mouth produce saliva, a
mixture of water and
enzymes.
• Enzymes in saliva digests
starch, changing it into
simpler sugars.
– Enzymes are proteins
that speed up chemical
reactions in the body.
» The shape of an
enzyme allows it
to bind only to
certain types of
substances.
The Esophagus
• When you swallow, food
travels from your mouth
into your esophagus.
• The esophagus connects
the mouth to the
stomach.
– Lined with mucus, which
makes food easier to
swallow and move along.
– Food only stays in the
esophagus for 10 seconds.
Peristalsis
• After food enters the esophagus,
contractions of smooth muscle push food
toward the stomach.
– Involuntary muscle contractions.
• Squeezes food through the digestive system
– Also occurs in the stomach and farther down
the digestive system.
• Keeps food moving in one direction
The Stomach
• Most mechanical
digestion and some
chemical digestion
take place in the
stomach.
• The stomach is a Jshaped muscular
pouch.
– Also used to store
food temporarily.
The Stomach
• Mechanical Digestion
– Three layers of smooth muscles produce a churning motion.
– Mixes food with fluids like clothes move in a washing machine
• Chemical Digestion
– As the food churns in the stomach it mixes with chemicals which
breaks food molecules into its building blocks.
• Pepsin is an enzyme that changes proteins into short chains of
amino acids.
• Hydrochloric acid helps the pepsin to work; it also kills bacteria that
enter your stomach
– The acid does not burn a hole in your stomach because your stomach
is lined with mucus.
Ulcers
• When the lining of the
stomach is damaged,
the stomach acid can
burn holes in the
stomach.
– When this happens,
an ulcer forms.
Chyme
• The mixture of partially digested food and
digestive juices that is formed in the
stomach.
Small Intestine
• Chyme leaves the
stomach and enters into
the small intestine.
• Most chemical
digestion takes place
here.
• Makes up 2/3 of the
digestive tract.
– About 6 meters long, but
is only 2-3 centimeters
wide.
Small Intestine
• By the time chyme
reaches the small
intestine, starches and
proteins have been
partially digested. Fats
have not been digested at
all.
– Chyme mixes with
chemicals produced by the
accessory organs which
will do most of the rest of
the chemical digestion of
the food molecules.
• Almost all absorptions of
nutrients takes place in
the small intestine.
The Liver
• Breaks down medicines
and helps eliminate
nitrogen from the body
• The role of the liver is
to produce bile.
– Bile breaks up fat
molecules
• It is not an enzyme; it acts
more like a soap.
• Mixes with the fats in the
food to form small fat
droplets.
– Fat droplets are
chemically broken down
by enzymes from the
pancreas.
Cirrhosis
• Cirrhosis of the liver
can be caused by the
over-consumption of
alcohol over long
periods of time.
Gall Bladder
• Bile flows from the
liver into the gall
bladder.
– The job of the gall
bladder is to store
bile.
• After eating, bile passes
through a tube from the
gall bladder into the
small intestine.
Gall Stones
• Whenever the bile
hardens inside the gall
bladder, gall stones are
formed.
• If the stones clog the bile
duct into the small
intestine, it becomes very
painful.
– The gall bladder can be
safely removed to prevent
further complications.
• Bile will flow directly from
the liver into the small
intestine.
– No bile will be stored.
Pancreas
• The pancreas
produces enzymes
that flow into the
small intestine and
help break down
starches, proteins,
and fats.
– The pancreas also
produces insulin, a
hormone that controls
the level of sugar
(glucose) in the blood.
Absorption
• After chemical digestion takes
place, the small nutrient
molecules are ready to be sent
to the body’s cells by the
blood.
– The small intestine is lined
with finger-like projections that
absorb the nutrient molecules.
• These structures are called
villi.
– The villi contain capillaries
that allow the nutrients to
pass through them.
» Villi greatly increase
the surface area
available for
absorption.
Large Intestine
• By the time material
reaches the end of the
small intestine, most of
the nutrients have been
absorbed.
• The remaining material
moves into the large
intestine.
– About 1.5 meters long.
• Contains bacteria that
feed on the material
passing through it.
– Helpful bacteria because
they produce vitamins.
Large Intestine
• Also called the colon.
• The material entering the
large intestine contains
water and undigested
food, such as fiber.
– As the material moves
through the large
intestine, water is
absorbed into the
bloodstream.
• The remaining material
is readied for elimination
from the body.
Rectum
• The large intestine ends in a short tube
called the rectum, which compresses
waste materials into a solid form.
• Waste material is eliminated from the body
through the anus, a muscular opening at
the end of the rectum.