Download The Digestive System

By: Jennifer Fazzolari, Eric Hoffmann,
and Lisa Lee
A.P. Biology – Period C
BACKGROUND INFORMATION
ON THE DIGESTIVE SYSTEM
What does the Digestive
System consist of?
•
•
•
The digestive system includes the mouth, esophagus,
liver, stomach, large intestine and small intestine.
The mouth chews the food. The food goes down
the esophagus, then into the stomach. It is mixed
with the hydrochloric acid in your stomach. Then
it goes into your small intestines and then to your
large intestine. The rest is left up to the excretory
system.
http://www.enchantedlearning.com/subjects/anatom
y/digestive
How does the Digestive System
break down food?
• The digestive system breaks down food two ways:
 Mechanical digestion- the chewing (in the mouth)
and churning (in the stomach)
• The stomach has three mechanical tasks. First, it stores
the swallowed food and liquid. To do this, the muscle
of the upper part of the stomach relaxes to accept
large volumes of swallowed material. The second job is
to mix up the food, liquid, and digestive juice produced
by the stomach. The lower part of the stomach mixes
these materials by its muscle action. The third task of
the stomach is to empty its contents slowly into the
small intestine.
• Chemical digestion- with the help of enzymes, into
substances that cells can absorb and use. This occurs
in the mouth, stomach and small intestines.
 http://www.leeds.ac.uk/chb/lectures/anatomy8.html
Parts and Functions of the
Digestive System
•
1. Mouth
– Saliva or spit, begins to form in your mouth. When
you eat, the saliva breaks down the chemicals in the
food a bit, which helps make the food easy to swallow.
Your tongue helps out, pushing the food around
while you chew with your teeth. When you're ready to
swallow, the tongue pushes a bolus toward the back
of your throat and into the opening of your
esophagus, the second part of the digestive tract.
– To view specific locations of the organs starting from
the mouth and the functions they serve, go to
http://www.kidshealth.org/misc/movie/bodybasics/digesti
ve_system.html
Parts and Functions (con’t)
•
2. Esophagus
– The esophagus is like a stretchy pipe that's about 10 inches (25
centimeters) long. It moves food from the back of your
throat to your stomach. But also at the back of your
throat is your windpipe, which allows air to come in and out
of your body. When you swallow, a flap called the epiglottis
flops down over the opening of your windpipe to make sure
the food enters the esophagus and not the windpipe.
– Once food has entered the esophagus, it doesn't just drop
right into your stomach. Instead, muscles in the walls of the
esophagus move in a wavy way to slowly squeeze the food
through the esophagus. This takes about 2 or 3 seconds.
Parts and Functions (con’t)
•
3. Stomach
– Your stomach is attached to the end of the esophagus.
It's a stretchy sack shaped like the letter J. It has three
important jobs:
– to store the food you've eaten
– to break down the food into a liquefied mixture
– to slowly empty that mixture into the small intestine
– The stomach is like a mixer, churning and mashing
together all the food that came down the esophagus
into smaller pieces. It does this with help from the
strong muscles in the walls of the stomach and
gastric juices that also come from the stomach's
walls. In addition to breaking down food, gastric
juices also help kill bacteria that might be in the eaten
food.
Parts and Functions (con’t)
•
4. Small Intestine
– The small intestine is a long tube that's about 1½ inches to 2
inches (about 3.5 to 5 centimeters) around, and it's packed
inside you beneath your stomach. If you stretched out an
adult's small intestine, it would be about 22 feet long (6.7
meters)
– The small intestine breaks down the food mixture even more
so your body can absorb all the vitamins, minerals, proteins,
carbohydrates, and fats. The small intestine can help extract
proteins from food with a little help from the pancreas,
liver, and gallbladder.
– Those organs send different juices to the first part of the
small intestine. These juices help to digest food and allow the
body to absorb nutrients. The pancreas makes juices that help
the body digest fats and protein. A juice from the liver called
bile helps to absorb fats into the bloodstream, and the
gallbladder serves as a warehouse for bile, storing it until
the body needs it.
– Your food may spend as long as 4 hours in the small intestine
and will become a very thin, watery mixture. Once the
nutrients are in the blood, your body is closer to benefiting
from the complex carbohydrates in the food you have
consumed.
Parts and Functions (con’t)
•
4.5. Liver
– The nutrient-rich blood comes directly to the liver
for processing. The liver filters out harmful substances
or wastes, turning some of the waste into more bile.
The liver even helps figure out how many nutrients
will go to the rest of the body, and how many will
stay behind in storage. For example, the liver stores
certain vitamins and a type of sugar your body uses
for energy.
– *For answers to miscellaneous questions on the
digestive system, go to
http://hes.ucf.k12.pa.us/gclaypo/digestive_system.html#Wh
at%20is%20Digestion*
Parts and Functions (con’t)
•
5. Large Intestine
– At 3 or 4 inches around (about 7 to 10 centimeters), the large
intestine is fatter than the small intestine and it's almost the
last stop on the digestive tract. Like the small intestine, it is
packed into the body, and would measure 5 feet (about 1.5
meters) long if you spread it out.
– The large intestine has a tiny tube with a closed end coming
off it called the appendix. It's part of the digestive tract, but
it serves little to no purpose.
– Food passes through the part of the large intestine called
the colon which is where the body gets its last chance to
absorb the water and some minerals into the blood. As the
water leaves the waste product, what's left gets harder and
harder as it keeps moving along, until it becomes a solid. This
waste is also called stool or a bowel movement.
– The large intestine pushes the stool into the rectum, the
very last stop on the digestive tract. The solid waste stays
here until you are ready to excrete it out of your body. You
get rid of this solid waste by pushing it through the anus.
– *Go to http://www.innerbody.com/image/digeo3.html for a
more detailed insight on the individual activities of the
digestive organs.*
Why is digestion
important?
•
•
When you eat foods—such as bread, meat, and
vegetables—they are not in a form that the body
can use as nourishment. Food and drink must be
changed into smaller molecules of nutrients before
they can be absorbed into the blood and carried to
cells throughout the body.
Digestion is the process by which food and drink
are broken down into their smallest parts so the
body can use them to build and nourish cells and
to provide energy.
HOW IS FOOD DIGESTED?
•
Digestion involves mixing food with digestive juices,
moving it through the digestive tract, and
breaking down large molecules of food into
smaller molecules. Digestion begins in the mouth,
when you chew and swallow, and is completed in
the small intestine.
Movement of food through
the Digestive System
•
•
The large, hollow organs of the digestive tract
contain a layer of muscle that enables their walls
to move. The movement of organ walls can propel
food and liquid through the system and can also
mix the contents within each organ. Food moves
from one organ to the next through muscle
action called peristalsis. Peristalsis looks like an
ocean wave traveling through the muscle. The
muscle of the organ contracts to create a
narrowing and then propels the narrowed portion
slowly down the length of the organ. These waves
of narrowing push the food and fluid in front of
them through each hollow organ.
The first major muscle movement occurs when food
or liquid is swallowed. Although you are able to
start swallowing by choice, once the swallow
begins, it becomes involuntary and proceeds under
the control of the nerves.
MOVEMENT (CON’T)
•
•
Swallowed food is pushed into the esophagus, which
connects the throat above with the stomach
below. At the junction of the esophagus and
stomach, there is a ring-like valve, called the pyloric
valve, closing the passage between the two organs.
As food approaches the closed valve, the
surrounding muscles relax and allow the food to
pass through to the stomach.
The stomach has three mechanical tasks. First, it
stores the swallowed food and liquid. To do this,
the muscle of the upper part of the stomach relaxes
to accept large volumes of swallowed material. The
second job is to mix up the food, liquid, and
digestive juice produced by the stomach. The lower
part of the stomach mixes these materials by its
muscle action. The third task of the stomach is to
empty its contents slowly into the small intestine.
MOVEMENT (CON’T)
•
•
Several factors affect emptying of the stomach,
including the kind of food and the degree of
muscle action of the emptying stomach and the
small intestine. Carbohydrates, for example, spend
the least amount of time in the stomach, while
protein stays in the stomach longer, and fats the
longest. As the food dissolves into the juices from
the pancreas, liver, and intestine, the contents of
the intestine are mixed and pushed forward to
allow further digestion.
Finally, the digested nutrients are absorbed
through the intestinal walls and transported
throughout the body. The waste products of this
process include undigested parts of the food,
known as fiber, and older cells that have been shed
from the mucosa. These materials are pushed into
the colon, where they remain until the feces are
expelled by a bowel movement.
Production of Digestive
Juices
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•
The digestive glands that act first are in the
mouth—the salivary glands. Saliva produced by
these glands contains an enzyme that begins to
digest the starch from food into smaller molecules.
An enzyme is a substance that speeds up chemical
reactions in the body.
The next set of digestive glands is in the stomach
lining. They produce stomach acid and an enzyme
that digests protein. A thick mucus layer coats the
mucosa and helps keep the acidic digestive juice from
dissolving the tissue of the stomach itself. In most
people, the stomach mucosa is able to resist the juice,
although food and other tissues of the body
cannot.
Digestive Juices (con’t)
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•
After the stomach empties the food and juice
mixture into the small intestine, the juices of two
other digestive organs mix with the food. One of
these organs, the pancreas, produces a juice that
contains a wide array of enzymes to break down
the carbohydrate, fat, and protein in food. Other
enzymes that are active in the process come from
glands in the wall of the intestine.
The second organ, the liver, produces yet another
digestive juice—bile. Bile is stored between meals in
the gallbladder. At mealtime, it is squeezed out of
the gallbladder, through the bile ducts, and into
the intestine to mix with the fat in food. The bile
acids dissolve fat into the watery contents of the
intestine, much like detergents that dissolve grease
from a frying pan. After fat is dissolved, it is digested
by enzymes from the pancreas and the lining of the
intestine.
Absorption and Transport of
Nutrients
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Most digested molecules of food, as well as water and minerals,
are absorbed through the small intestine. The mucosa of the
small intestine contains many folds that are covered with tiny
fingerlike projections called villi. In turn, the villi are covered
with microscopic projections called microvilli. These structures
create a vast surface area through which nutrients can be
absorbed. Specialized cells allow absorbed materials to cross the
mucosa into the blood, where they are carried off in the
bloodstream to other parts of the body for storage or further
chemical change. This part of the process varies with different
types of nutrients.
Carbohydrates. The Dietary Guidelines for Americans 2005
recommend that 45 to 65 percent of total daily calories be from
carbohydrates. Foods rich in carbohydrates include bread,
potatoes, dried peas and beans, rice, pasta, fruits, and vegetables.
Many of these foods contain both starch and fiber.
The digestible carbohydrates—starch and sugar—are broken
into simpler molecules by enzymes in the saliva, in juice produced
by the pancreas, and in the lining of the small intestine. Starch is
digested in two steps. First, an enzyme in the saliva and pancreatic
juice breaks the starch into molecules called maltose. Then an
enzyme in the lining of the small intestine splits the maltose into
glucose molecules that can be absorbed into the blood. Glucose
is carried through the bloodstream to the liver, where it is
stored or used to provide energy for the work of the body.
Absorption and Transport
(con’t)
•
•
•
Sugars are digested in one step. An enzyme in the lining of the
small intestine digests sucrose, also known as table sugar, into
glucose and fructose, which are absorbed through the intestine
into the blood. Milk contains another type of sugar, lactose,
which is changed into absorbable molecules by another enzyme
in the intestinal lining.
Fiber is indigestible, and moves through the digestive tract
without being broken down by enzymes. Many foods contain
both soluble and insoluble fiber. Soluble fiber dissolves easily in
water and takes on a soft, gel-like texture in the intestines.
Insoluble fiber, on the other hand, passes essentially unchanged
through the intestines.
Protein. Foods such as meat, eggs, and beans consist of giant
molecules of protein that must be digested by enzymes before
they can be used to build and repair body tissues. An enzyme in
the juice of the stomach starts the digestion of swallowed
protein. Then in the small intestine, several enzymes from the
pancreatic juice and the lining of the intestine complete the
breakdown of huge protein molecules into small molecules
called amino acids. These small molecules can be absorbed
through the small intestine into the blood and then be carried
to all parts of the body to build the walls and other parts of
cells.
Absorption and Transport
(con’t)
•
•
•
Fats. Fat molecules are a rich source of energy for the body. The
first step in digestion of a fat such as butter is to dissolve it
into the watery content of the intestine. The bile acids produced
by the liver dissolve fat into tiny droplets and allow pancreatic
and intestinal enzymes to break the large fat molecules into
smaller ones. Some of these small molecules are fatty acids and
cholesterol. The bile acids combine with the fatty acids and
cholesterol and help these molecules move into the cells of the
mucosa. In these cells the small molecules are formed back into
large ones, most of which pass into vessels called lymphatics near
the intestine. These small vessels carry the reformed fat to the
veins of the chest, and the blood carries the fat to storage
depots in different parts of the body.
Vitamins. Another vital part of food that is absorbed through
the small intestine are vitamins. The two types of vitamins are
classified by the fluid in which they can be dissolved: watersoluble vitamins (all the B vitamins and vitamin C) and fat-soluble
vitamins (vitamins A, D, E, and K). Fat-soluble vitamins are stored in
the liver and fatty tissue of the body, whereas water-soluble
vitamins are not easily stored and excess amounts are flushed
out in the urine.
Water and salt. Most of the material absorbed through the
small intestine is water in which salt is dissolved. The salt and
water come from the food and liquid you swallow and the
juices secreted by the many digestive glands.
How digestive process is
controlled
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Hormone Regulators
– The major hormones that control the functions of the
digestive system are produced and released by cells in the
mucosa of the stomach and small intestine. These hormones
are released into the blood of the digestive tract, travel back
to the heart and through the arteries, and return to the
digestive system where they stimulate digestive juices and
cause organ movement.
– The main hormones that control digestion are gastrin,
secretin, and cholecystokinin (CCK):
• Gastrin causes the stomach to produce an acid for
dissolving and digesting some foods. Gastrin is also
necessary for normal cell growth in the lining of the
stomach, small intestine, and colon.
• Secretin causes the pancreas to send out a digestive juice
that is rich in bicarbonate. The bicarbonate helps
neutralize the acidic stomach contents as they enter the
small intestine. Secretin also stimulates the stomach to
produce pepsin, an enzyme that digests protein, and
stimulates the liver to produce bile.
• CCK causes the pancreas to produce the enzymes of
pancreatic juice, and causes the gallbladder to empty. It
also promotes normal cell growth of the pancreas.
How digestive process is
controlled (con’t)
•
•
Additional hormones in the digestive system regulate
appetite:
– Ghrelin is produced in the stomach and upper
intestine in the absence of food in the digestive system
and stimulates appetite.
– Peptide YY is produced in the digestive tract in
response to a meal in the system and inhibits appetite.
Both of these hormones work on the brain to help
regulate the intake of food for energy. Researchers are
studying other hormones that may play a part in
inhibiting appetite, including glucagon-like peptide-1 (GPL-1),
oxyntomodulin (OXM), and pancreatic polypeptide.
How digestive process is
controlled (con’t)
•
Nerve Regulators
– Two types of nerves help control the action of the digestive
system.
– Extrinsic, or outside, nerves come to the digestive organs
from the brain or the spinal cord. They release two chemicals,
acetylcholine and adrenaline. Acetylcholine causes the
muscle layer of the digestive organs to squeeze with more
force and increase the “push” of food and juice through the
digestive tract. It also causes the stomach and pancreas to
produce more digestive juice. Adrenaline has the opposite
effect. It relaxes the muscle of the stomach and intestine and
decreases the flow of blood to these organs, slowing or
stopping digestion.
– The intrinsic, or inside, nerves make up a very dense network
embedded in the walls of the esophagus, stomach, small
intestine, and colon. The intrinsic nerves are triggered to act
when the walls of the hollow organs are stretched by food.
They release many different substances that speed up or delay
the movement of food and the production of juices by the
digestive organs.
– Together, nerves, hormones, the blood, and the organs of the
digestive system conduct the complex tasks of digesting and
absorbing nutrients from the foods and liquids you consume
each day.
TASKS
Tasks
• We have come up with 3 different tasks as a way
to learn more about the digestive system in a
creative way.
 Task 1: “EAT HEALTHY DAY”
 Task 2: Interactive Activities
 Task 3: “calorie counter”
1. “Eat Healthy Day”
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•
On Saturday May 10, 2008 Whole Foods Markets are
sponsoring an “Eat Healthy Day” for people of all
ages.
This event is to promote the importance of a
healthy diet and how it can aid in digestion.
THE TASK
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Before the event, go to www.Wholefoods.com and create a
shopping list that you think is healthy for your diet. (keep in
mind that this list should entail foods from each group on the
food pyramid, and should try to abide by your own personal
daily caloric intake).
After you have done that, bring your shopping list to the event
and have it approved by one of the Whole Foods consultants.
the consultant will then educate you on which foods are
good for your diet, and how they benefit your body and the
digestive system.
for participating, you will be able to get one product on your
list for free. In addition, there will be free snacks and drinks
available all day with signs containing information to educate
you about how beneficial they are to you and your body (such
as fruits, nuts, cereal, granola, yogurt, and water). For example,
besides helping to hydrate your body, water helps to purify and
clean out your body’s system. In addition, foods that are high in
fiber, such as nuts, help ease the bowel movements in your body.
http://www.wholefoodsmarket.com/products/index.html
http://www.thefutureisorganic.net/tenreasons.html
The Task (con’t)
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•
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•
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For the youngsters who will be there- bring them
to the Veggie tales tent where they will learn
about basic nutrition and be taught about
organic food.
Also while there, we will have them write letters to
their local supermarket telling them why they
should carry more organic and healthy foods, and
why it is important for prices to be reasonable so
that everyone can afford it.
Also in the tent, there will be free food for the kids.
It will be fun organic food to show them that
healthy food is not always unappetizing.
http://www.treehugger.com/files/2007/09/green-basicsorganic-food.php
http://yucky.discovery.com/flash/body/pg000126.html
What is Organic?
•
The word “organic” refers to the way farmers grow
and process agricultural products, such as fruits,
vegetables, grains, dairy products and meat. Organic
farming practices are designed to encourage soil
and water conservation and reduce pollution.
Farmers who grow organic produce and meat don't
use conventional methods to fertilize, control
weeds or prevent livestock disease. For example,
rather than using chemical weed killers, organic
farmers conduct sophisticated crop rotations and
spread mulch or manure to keep weeds at bay.
How is Organic grown
differently?
What are the benefits of Organic
on the digestive system?
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Organic, whole foods are a benefit to digestion;
processed foods and foods full of antibiotics,
hormones and pesticides may tax the liver and make
the body work harder to extract nutrients.
Foods that are not organic usually have been
sprayed with pesticides. Pesticides kill insects, often
by paralyzing the nervous system. The reason the
government says that it is okay to eat the pesticides
left in the sprayed foods is because the poisons are
not in great enough quantity to destroy your
nervous system. The point is pesticide sprayed foods
are often toxic and diabetics cannot afford
additional stress such as toxins found in fruits
and vegetables.
Processed foods also contain chemicals that do
not help ease the digestive system.
2. Interactive Activities
•
•
Visit the website below in order to have an
interactive and ‘hands-on’ experience with the
digestive system.
http://www.harcourtschool.com/activity/digest/ind
ex.htm
On this website, you can label the different parts of
the digestive system by dragging and placing the
particular body part in its appropriate spot, click on
a particular part of the digestive system in order to
learn more about it, and drag a piece of food
(proteins, carbohydrates, dairy, etc.) to the mouth
and track its journey through the digestive system
(the digestive process varies depending on whether
the food is protein, vegetable, carbohydrate, dairy,
etc.).
3. Calorie Counter
http://www.ohsu.edu/healthyaging/caregiving/images/food_
pyramid.gif
Task (con’t)
•
For this task, you will come up with 3 meals that must be healthy
and sufficient according to the food pyramid, based on the
required servings of each food group. Make sure to stay within
your own calorie limit.
– In order to find out what your own personal calorie limit
is, visit the website
http://www.mypyramid.gov/?gclid=CM2RouOSjZMCFQlTHgodXBZ
Hag.
– On this website, you enter information such as your weight,
age, and daily exercise schedule, and you will be provided with
your estimated daily caloric intake, as well as a food pyramid
that outlines foods you should have more of and foods you
should have less of.
* Please note that even healthy foods must be eaten in
moderation!*