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/anatomy/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/digestive_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#What%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

• 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)• 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

• 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: 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.

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.

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”

• 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• 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)

• 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-basics-organic-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?

• 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/index.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=CM2RouOSjZMCFQlTHgodXBZHag.

– 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!*