By: Jennifer Fazzolari, Eric Hoffmann, and Lisa Lee

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The Digestive System

• By Jennifer Fazzolari, Eric Hoffmann, and Lisa
  Lee
• A.P. Biology Period C

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BACKGROUND INFORMATION ON THE DIGESTIVE SYSTEM
PART I
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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/anatomy/
  digestive

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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

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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
  /digestive_system.html

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Parts and Functions (cont)

• 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.

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Parts and Functions (cont)

• 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.

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Parts and Functions (cont)

• 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.

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Parts and Functions (cont)

• 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/g
  claypo/digestive_system.htmlWhat20is20Digestion
  

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Parts and Functions (cont)

• 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.

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Why is digestion important?

• When you eat foodssuch as bread, meat, and
  vegetablesthey 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.

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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.

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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.

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MOVEMENT (CONT)

• 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.

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MOVEMENT (CONT)

• 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.

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Production of Digestive Juices

• The digestive glands that act first are in the
  mouththe 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.

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Digestive Juices (cont)

• 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 juicebile. 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.

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Absorption and Transport of Nutrients

• 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 carbohydratesstarch and sugarare
  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.

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Absorption and Transport (cont)

• 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.

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Absorption and Transport (cont)

• 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 water-soluble 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.

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How digestive process is controlled

• 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.

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How digestive process is controlled (cont)

• 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.

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How digestive process is controlled (cont)

• 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.

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TASKS
PART II
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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

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1. Eat Healthy Day

• 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.

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THE TASK

• 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 bodys 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.htm
  l
• http//www.thefutureisorganic.net/tenreasons.html

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The Task (cont)

• 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-basi
  cs-organic-food.php
• http//yucky.discovery.com/flash/body/pg000126.htm
  l

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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.

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How is Organic grown differently?
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What are the benefits of Organic on the digestive
system?

• 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.

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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.).

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3. Calorie Counter
http//www.ohsu.edu/healthyaging/caregiving/images
/food_pyramid.gif
34
Task (cont)

• 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/?gclidCM2RouOSjZMCFQlTHg
  odXBZHag.
• 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!