The Digestive System
What It Is and How it Works!
Where does it hurt?
• Have you ever had a
stomach ache?
• How about heartburn?
• Was it your heart that was
burning?
• Have you ever heard your
stomach growl?
• Why would it do that?
And for some gross things…..
• Why do we throw
up?
• What causes
diarrhea?
• And what about
gas?
It all starts with your Digestive
System!
• The digestive system is
basically a long tube through
your body starting at your
mouth and ending at your
anus.
• The function of the digestive
system is to break down the
food you eat into small
molecules that are absorbed,
or taken into, the cells of your
body.
Start
Finish
Different types of Digestion
Think About This:
• What do you think happens to
food in your mouth?
• What do you think happens to
food in your stomach?
• How are the actions that occur in
the mouth similar to the actions
that happen in the stomach?
• How are their actions different?
Stomach
Mechanical and Chemical
Digestion
• Mechanical Digestion- this is when food is
broken into smaller pieces, but its chemical
structure is not changed. Can you think of
places where this might happen?
• Answer: Teeth grinding, tongue turning,
muscles squeezing.
• Chemical Digestion- food is broken into
smaller molecules that can be absorbed by
the cells. Its chemical structure is changed.
Can be done by acids, enzymes and other
chemicals. Where could this happen?
• Answer: Saliva in the mouth, acid in the
stomach, enzymes in the small intestine.
Digestion Begins
• Digestion of food begins in the mouth.
• Even before we eat something, the brain
sends a message to the salivary glands to
start producing saliva.
• As we take a bite, the teeth tear and chop
the food we eat.
• The food is mixed with the saliva from the
salivary glands.
• The saliva moistens the food as well as
starts to digest the food because saliva has
an enzyme called amylase that starts to
break down some of the carbohydrates in
food before it even leaves the mouth!
• How much saliva do you think a human
produces in a day?
• Answer: Between 1 and 2 liters!
That’s a lot of saliva!
A Long Passage
• When you are ready, you swallow the food. A flexible flap of tissue called
the epiglottis closes the trachea or windpipe to prevent food from going into
it.
• Have you ever had food “go down the wrong way?”
• After the food is swallowed, it travels down a long muscular tube called the
esophagus.
• Waves of muscular contractions called peristalsis force the food down
through the esophagus into to stomach.
• At the end of the esophagus, a muscular ring called a sphincter relaxes to let
food enter the stomach.
Look how long the esophagus is in a horse!
An intense environment
• Once the food leaves the
esophagus, it enters the stomach.
• The stomach is a muscular organ
that produces hydrochloric acid
and enzymes to help chemically
digest food. It squeezes and mixes
the food with the acid and
enzymes. The enzymes in the
stomach work to digest protein.
• The acid in the stomach is very
strong. Why do you think it
doesn’t “burn” through the walls
of the stomach?
• Answer: The stomach has special
cells that produce a thick mucous
that protects the stomach from
being digested! *
Stomach
Inside
the
Stomach
Heartburn
• Heartburn is described as a
burning sensation in the chest.
• Many times, it is actually acid
from the stomach that moves up
into the esophagus that causes this
burning. This is also called acid
reflux.
• The esophagus does not have
mucous that keeps the stomach
acid from burning it, therefore, the
acid can cause pain and damage
there.
• Many times this is caused by
overeating or eating fatty or spicy
food.
• Occasionally people can mistake
the pain of a heart attack for
heartburn or vice versa.
Click here for information regarding heartburn, chest pain and heart attacks
When You are Sick
• Vomiting is when all of the
contents of your stomach are
forcibly emptied through the
mouth. For some reason, your
body has decided to get the
contents of your stomach OUT!
• Many things can cause vomiting.
It is common for vomiting to occur
from a viral infection, food
poisoning, milk allergy, motion
sickness, overeating, coughing,
blocked intestines and illnesses in
which the person has a high fever.
What’s that sound?
• Stomach growling occurs when the
stomach receives signals from your
brain to begin digestion but the stomach
is empty.
• Your brain might sense you're running
low on energy or even seeing or
smelling something you want to eat can
get things going.
• The motion of the stomach muscles
begins, but the organ is hollow.
• The movement of the muscles mixing
the acids of the stomach in the hollow
space of the stomach produces
vibrations we hear as growling, or
rumbling, or gurgling.
*See slide note
Review Break #1:
• What is the digestive system and what
is its main function?
• What are the two types of digestion that
occur in the digestive system?
• What happens in the mouth to start
digestion?
• What is the passage from the mouth to
the stomach called?
• What occurs when the food reaches the
stomach?
Where nutrients are absorbed
The small intestines are coiled
inside of the body. If they
weren’t, you would be almost
two-stories tall!
• The food, now a pasty mixture called
chyme, moves into the small intestine.
• The small intestine is where the majority
of the absorbing of the nutrients occur.
!!
• The small intestine is very long-an
average of 16 feet in humans!
• How long do you think the small
intestine of a cow is?
• Answer: In a cow, the small intestine can
be over 140 ft long!
• The food spends a long time in the small
intestine where digestive juices from the
pancreas and liver further break it down
into the small molecules that can be
absorbed into the bloodstream.
Pancreas, Liver and Gallbladder
• The liver has many functions. It’s main role in digestion is to produce
bile, which helps break up fats into small units that are easier to digest.
• The bile can go directly into the small intestine, or it can be stored for
later use in the gallbladder.
• The pancreas also plays a vital role in digestion. It secretes digestive
juices that contain enzymes that help break down carbohydrates, fats
and proteins.
Liver
Gallbladder
Stomach
Small Intestine
Pancreas
click here for more information on the liver and pancreas
Folds upon Folds
• The inside of the small intestine itself is also folded and is lined
with millions of microscopic, finger-like projections called villi.
• These villi increase the surface area of small intestine and allow
the nutrients to be absorbed into the bloodstream.
A magnified
view inside the
small intestine
Small Intestine
A cross-section of
the villi showing
the blood vessels
that receive the
nutrients.
Drying Out and Exiting the Body
• By the time the food that was eaten leaves the
small intestine, most of the usable nutrients
have been digested and absorbed.
• The remaining undigested material moves
into the large intestine where large amounts of
water are removed and the final undigested
wastes exit the body through the rectum and
anus.
• The large intestines also contain large amounts
of bacteria (some sources say over 700 types!)
that digest some of the remaining material and
produce certain vitamins.
• These bacteria also produce GAS as a by
product!
So that’s
where it
comes from!
Large Intestine
Appendix
Rectum
Anus
Diarrhea…..
• If you have a sickness or condition that
increases the speed at which the undigested
material goes through your large intestine,
water might not be absorbed and the result
could be diarrhea.
• Other types of diarrhea could occur when the
organs of the digestive system produce too
much fluids, when water is actually drawn into
the intestines, or when the intestines are
inflamed.
• Causes of diarrhea include bacteria, viruses,
parasites, anxiety, use of certain medications,
certain foods, and even chronic diseases like
Crohn’s disease.
Review Break #2:
• Where does the majority of digestion
and absorption of nutrients occur?
• What are the functions of the liver,
pancreas, and gallbladder?
• What are villi and what is their
purpose?
• What happens in the large intestine?
Fun Digestive Facts:
• On average, the stomach produces 2 -2.5 liters of Hydrochloric Acid
daily.
• After you eat, it takes usually between 24 and 72 hours in healthy
adults for the complete process of digestion to occur.
• In the mouth, food is either cooled or warmed to a more suitable
temperature.
• Food stays in your stomach for 2 to 3 hours.
• The average male will eat about 50 tons of food during his lifetime in
order to sustain a weight of 150 pounds.
• The liver is the largest and heaviest internal organ of the body and
weighs about 1.6 kilos.
• The Liver is the only organ of the body, which has the capacity to
regenerate itself completely even after being removed almost
completely.
• Scientists estimate that the average adult releases between 12 and 122
cubic inches of intestinal gas each day. Most of that gas is made up of
hydrogen and methane produced by the bacteria as they ferment the
fiber that was not digested in the stomach or small intestine.
Nutrition and Digestive System Health
• Fiber is an important part of your
diet that helps keep your digestive
system healthy.
• Unlike other food components
such as fats, proteins or
carbohydrates — which your body
breaks down and absorbs — fiber
isn't digested by your body.
• It passes relatively intact through
your stomach, small intestine,
large intestine and out of your
body.
• It might seem like fiber doesn't do
much, but it has several important
roles in maintaining health.
Benefits of Fiber
• Fiber helps keep the digestive system
“regular” which helps your body avoid
many digestive system complaints.
• Fiber may help prevent certain types of
cancer in the large intestine and prevent
pouches from forming in the large intestine.
These pouches can become inflamed and
lead to diverticulitis, which is a serious
digestive system disease with symptoms like
pain, cramping, nausea, and vomiting.
• Fiber can by a aid for weight loss. It is shown
to help lower cholesterol formation and
increase the feeling of being “full.”
• Fiber is found in whole grains, bran, nuts,
vegetables, peas, beans, apples, citrus fruits,
carrots, and other plant products.
Nutrition and Digestive System Health:
Too much fat is not healthy for your
digestive system!
• A condition called gall stones can be
caused by a diet too high in cholesterol.
Small hard “stones” made of cholesterol
can build up in the gallbladder and cause
pain, nausea, vomiting and other
digestive symptoms.
• Too much fat in food can also contribute
to indigestion, Irritable Bowel Syndrome,
and the development of small growths in
the large intestine called colon polyps that
can become cancerous.
Nutrition and Digestive System Health
• Other good nutritional
principles, like drinking
plenty of water, can aid
digestive health as well!
• Eating well has many
benefits to your health, both
inside and out!
Review Break #3:
• What are some of the benefits of eating
fiber?
• Why is eating too much fat unhealthy
for your digestive system?
Summarize it!
• Take time to summarize the structure
and function of the digestive system.
• With a partner, go through each organ
of the digestive system and tell its
location and function. Be sure to say
whether mechanical, chemical, or both
types of digestion occur there.
• Use the diagram in your notes or your
flow chart to help!