[<< wikibooks] Adventist Youth Honors Answer Book/Health and Science/Digestion
== 1. Have the Nutrition Honor. ==
Instructions and tips for earning the Nutrition honor can be found in the Household Arts chapter.

== 2. Keep a record of what and how much food you eat for two weeks. Compare your diet to that of the food pyramid. ==
If you have access to the Internet, you can visit the USDA's MyPyramidTracker.gov web site, the official home of the Food Pyramid.  Once you register, you can enter all the foods you eat in a day, and it will analyze your nutrient intake (among other things) based on this information.  MyPyramidTracker can retain the information you enter for up to a year, so tracking it for two weeks will be easy.
If your Pathfinders do not have access to the Internet, have them record their diets on paper.  You can then use the website to extract the necessary data by entering each food individually, or you can find a cookbook that has nutrient values of various foods in an appendix.  Another option would be to meet in a place that has public Internet access, such as a library or Internet cafe.  Then your Pathfinders can enter the data they have collected for a week and analyze it there.
The values in the table below are for children who are physically active for 60 minutes or more per day.  Use the USDA website for adults and less active children.

== 3. What is digestion? What is another name for the human digestive system? ==
Digestion is the conversion of food into substances that can be absorbed by the body.  Another name for the human digestive system is the gastrointestinal tract, or just the GI tract for short.

== 4. Where does saliva come from? What are the three functions of saliva? ==
Saliva, often informally known as spit, is the moist, clear, and usually somewhat frothy substance produced in the mouth.  Saliva is produced in and secreted from the salivary glands.

Saliva moistens food so it can be swallowed easily.
Saliva contains an enzyme that breaks some starches down into maltose and dextrin.
Saliva protects teeth from decay by plaque.  Saliva is used to neutralize acids made from sugars in the mouth, therefore helping to prevent demineralization. Remineralization is when saliva helps repair the damaged crystals of the tooth enamel.

== 5. Be able to identify the following parts of the tooth.  What role do the teeth play in digestion? ==

The primary function of teeth is to tear and chew food, reducing it into smaller pieces.  This is the first step in the digestive process.

=== Enamel ===
Enamel is the outside covering of the exposed portion of a tooth.  It is the hardest substance that is part of the human body.

=== Dentin ===
The Dentin (also called Dentine) is the substance between the enamel (substance in the crown) or cementum (substance in the root) of a tooth and the pulp chamber.

=== Pulp ===
The dental pulp is the part in the center of a tooth made up of living soft tissue.

=== Gum ===
The gums consist of the tissue surrounding the roots of the teeth and covering the jawbone.

=== Cementum ===
Cementum is a specialized bony substance covering the root of a tooth.

=== Periodontal membrane ===
The periodontal membrane is the tissue between the tooth and the tooth socket.  It holds the tooth in place.

== 6. Be able to label a diagram or model of all the organs that help with digestion, starting from where the food goes into the mouth to where it is expelled from the anus. ==

Food enters the body through the mouth where it is manipulated by the tongue and chewed with the teeth.  Salivary glands secrete saliva which is used to soften and lubricate the food.  The tongue then pushes the food down the esophagus and it enters the stomach.  The main job of the stomach is to break down large fat molecules into smaller ones, so that they can be absorbed into the intestines more easily.  Food remains in the stomach for a few hours before it is passed into the upper part of the small initestine - the duodenum.  The small intestine is the site where most of the nutrients from ingested food are absorbed.  There are microscopic finger-like projections called villi covering the small intestinal walls which increase surface area for absorption.
The large intestine comes after the small intestine in the digestive tract. It is mainly responsible for storing waste, reclaiming water, maintaining the water balance, and absorbing some vitamins, such as vitamin K.
By the time the chyme has reached this tube, almost all nutrients and 90% of the water have been absorbed by the body. The rectum comes after the large intestine and acts as a temporary storage facility for feces.  Feces are expelled from the body through the anus during the act of defecation, which is the primary function of the anus.
Related Organs
The liver secretes bile into the small intestine, employing the gallbladder as a reservoir. The pancreas secretes a fluid containing several enzymes into the small intestine. Both these secretory organs aid in digestion.

== 7. Know the difference between food bolus and chyme. ==
Bolus is any fairly large quantity of matter, usually food, making its way through the digestive tract.
Chyme is the liquid substance found in the stomach before entering the duodenum. It is made of partially digested food, water, hydrochloric acid, and various digestive enzymes.

== 8. Where does bile come from? Where is it stored? What does it do in the duodenum? ==
Bile (or gall) is a bitter, greenish-yellow fluid secreted by the liver. It is stored in the gallbladder between meals and upon eating is discharged into the duodenum where it aids the process of digestion.

== 9. What are villi? What makes them absorb the nutrients so quickly? At what point are all the nutrients removed from the food/chyme? Compare the amount of water absorbed by plain paper compared to a similar sized paper towel using an 1/8 cup (17.2 ml) of water. ==
Villi are tiny, finger-like structures that protrude from the wall of the intestine. In all humans, the villi increase intestinal absorptive surface area 9000-fold, providing exceptionally efficient absorption of nutrients. This increases the surface area of the intestine to an area about the same size as a tennis court. There are also enzymes on the surface of the villi for digestion.
Plain paper is smooth, but a paper towel is bumpy.  The bumps in the paper towel are similar to the villi, as they increase the surface area of the paper towel, and thus increase its absorption capacity.  You should see most of the water run off the surface of the plain paper, while most of it is absorbed by the paper towel.

== 10. What happens if too much water is present in the large intestine? What happens if not enough water is present? ==
Too much water in the colon results in diarrhea.  This occurs when insufficient fluid is absorbed by the colon. As part of the digestion process, or due to fluid intake, food is mixed with large amounts of water. Thus, digested food is essentially liquid prior to reaching the colon. The colon absorbs water, leaving the remaining material as a semisolid stool. If the colon is damaged or inflamed, however, absorption is inhibited, and watery stools result.
Too little water in the large intestine results in constipation.  Constipation or Irregularity, is a condition of the digestive system where a person experiences hard feces that are difficult to eliminate; it may be extremely painful.

== 11. How does fiber in your diet aid in digestion? How long should food remain in the digestive tract? What happens if food stays in the digestive system too long? ==
Increased fiber consumption appears to lower the risk of developing type II diabetes and heart disease. It may also help prevent high cholesterol and help fight obesity. High-fiber foods help move waste through the digestive tract faster and easier, so possibly harmful substances do not have as much contact with the gastrointestinal tract and reduce straining.
Food stays in the stomach between 30 minutes and two hours.  It takes another two to six hours for it to pass through the small intestine, and between six and 72 hours in the large intestine.
Since the large intestine absorbs water from the food, any food that stays there for too long has too much water removed from it resulting in constipation.
But that is not the worst of it.  Without proper digestion, food stays in the stomach for prolonged periods, fermenting and producing increasing amounts of gas and building up toxins.
If some type of antacid is taken at this point, the stomach contents will become alkaline, which will then cause this undigested food to drop into the small intestine where it continues to ferment and produce even more gas.
At this stage, nothing has happened to improve digestion because the antacid has now effectively been made worse by halting any further digestion and merely relocating the symptom by exchanging stomach gas for intestinal gas.
If the emptying time of the stomach is delayed for too long, bile is regurgitated backward into the stomach. Bile is caustic and very irritating to the stomach lining.
So in short, what happens if food stays in the digestive system too long is: #1 Toxicity. Extras: fermentation, constipation, Gastroesophageal Reflux Disease (GERD), and heartburn.

== 12. Demonstrate the digestion of starch into simple sugar using the iodine test. ==
Starch is converted into sugar by saliva, and when iodine comes into contact with starch, it turns from brown to a dark purple or black.  These two facts can be used in a simple experiment.
First, have a Pathfinder volunteer to generate some saliva, and collect it in a test tube.  You will need about 1.5 inches of saliva in the test tube.  To aid in salivation, the Pathfinder may find it advantageous to chew on some clean rubber bands.  Do not use gum, as this will put sugar into the saliva and ruin the experiment.  You will need a second test tube with an equal amount of water (1.5 inches).
Second, take a single saltine cracker and wrap it in wax paper.  Then pulverize it into a fine powder.  Add half the "powdered" cracker to a test tube of saliva, and add the rest to the test tube of water.  Allow them to sit for 30 minutes.
Finally, add a drop of iodine to each test tube.  The iodine in the cracker/water test tube should turn purple, showing the presence of starch.  The iodine in the cracker/saliva test tube should not change color (it should remain brown) showing that the starch has been converted to something else (sugar in this case).
To ensure success, do not allow the Pathfinder to mix the saliva and cracker in his mouth.  You need a LOT of saliva and only a little cracker so that all of the starch is converted to sugar before the iodine is added.

== 13. What are the six basic nutrients that are essential for life and where does the bulk of their digestion/absorption take place? ==
Carbohydrates are compounds made of sugars.  Digestion of carbohydrates begins in the mouth, continues in the stomach, and is completed in the small intestine.
Proteins are made of amino acids.  Most protein digestion takes place in the duodenum with the overall contribution from the stomach being small.
Fats consist of a glycerin molecule with three fatty acids attached.  Fats are completely digested in the small intestine.
Vitamins are organic compounds essential to the body.  Vitamins are absorbed by the small intestine.
Minerals are trace elements such as iron, copper, and salts essential to metabolism.  Minerals are absorbed in the small intestine.
Water is an essential nutrient and is directly involved in all the chemical reactions of life.  It is primarily absorbed in the large intestine.

== 14. Know the difference between monosaccharide, disaccharide, and polysaccharide. What is the most important carbohydrate? ==
Monosaccharides are the simplest form of carbohydrates. They consist of one sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste.
Disaccharides are sugars (carbohydrates) composed of two monosaccharides.
Polysaccharides are relatively complex carbohydrates.  They are made up of many monosaccharides joined together. They are therefore very large, often branched, molecules.The most important carbohydrate is the one that they are all made from: monosaccharide.

== 15. What are amino acids? How many are needed to make all the proteins in the body? What is meant by essential amino acids? How many of them are essential? Where can you get all the essential amino acids? ==
Amino acids are the molecules from which proteins are built.  There are twenty standard amino acids used by cells in protein biosynthesis.
Essential amino acids are the nine amino acids required for protein synthesis that cannot be synthesized by humans and must be obtained in the diet: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Only some foods contain all the essential amino acids. These include milk and dairy products, eggs, fish, meat and poultry. If you don't eat animal products, the only way you can get all the essential amino acids is by combining plant foods. For example: corn plus peas or beans, rice plus beans, lentils plus bread. [1]

== 16. What is ATP? What is it used for? What does your body make ATP from? What three sets of chemical reactions make ATP in your body? Why do we need to breathe oxygen? ==
ATP stands for adenosine triphosphate.  ATP is used for transporting energy around in your body.  All the energy your body uses is supplied by ATP.  ATP is made by three chemical reactions: glycolysis, the Krebs cycle, and oxidative phosphorylation.

Glycolysis is a pathway that takes place within the cytoplasm of a cell and does not require oxygen.  The reaction produces four ATP molecules, but consumes two of them during the process.
The Krebs Cycle is a pathway involved in the chemical conversion of carbohydrates, fats and proteins into carbon dioxide and water to generate a form of usable energy.  The Krebs cycle produces ATP and another chemical called NADH.
Oxidative phosphorylation converts the leftover NADH produced by the Krebs cycle into more ATP.While glycolysis does not require oxygen, the other two ATP-producing reactions do.  We need to breathe oxygen to supply it to these processes.

== 17. Know the difference between water and fat soluble vitamins. What are two common vitamins that are fat soluble? What are two vitamins that are water soluble? ==
Fat-soluble vitamins may be stored in the body and can cause toxicity when taken in excess.  Water-soluble vitamins are not stored in the body, with the exception of Vitamin B12, which is stored in the liver.
Fat-soluble vitamins include A, D, E, and K.
Water-soluble vitamins include the eight B's and C.

== 18. List four (4) Bible texts that refer to digestion. ==

== 19. List five (5) E.G. White references that promote proper digestion. Choose a variety of topics. ==
Counsels on Diet and Foods, page 175, paragraph 2
Selected Messages Book 2, page 415, paragraph 3
Testimony Studies on Diet and Foods, page 91, paragraph 7
Child Guidance, page 390, paragraph 3
A Call to Medical Evangelism and Health Education, page 36, paragraph 1

== Notes ==
Requirement 3 of the Nutrition - Advanced honor also requires that a food diary be kept, but only for one week.  The CPR honor requires that you track your diet (and exercise) for a month.

== References ==
The World's Healthiest Foods
Whitney, E. and Rolfes, S. (1999). Understanding Nutrition. (8th ed., pp. 86). Belmont, CA: Wadsworth Publishing Company.