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Digestion of Nutrients

  1. Mar 15, 2007 #1
    I'm looking for information about how different nutrients are digested, absorbed, and metabolized during each stage of digestion. So basically how food is digested, absorbed, metabolized and how it differs from nutrient to nutrient. This would mean the different pathway which the sugar (carbohydrate) in a muffin would take from the egg whites (protein) in the muffin. Links would be useful as well

  2. jcsd
  3. Mar 16, 2007 #2

    jim mcnamara

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    This is an enormous topic. Just the digested part is way too much.
    Are you writing a paper for school? What exactly are your goals here?
  4. Mar 16, 2007 #3


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    As jim pointed out, your question spans the content of pretty much an entire textbook chapter on digestion...maybe two or three chapters even! So, my first suggestion would be to start with a good, college-level biology textbook. The one written by Campbell is always a good one, and should be available in most decent libraries if you do not already have a textbook to refer to.

    If you then need further details or clarification, or more in-depth mechanistic information than what is available in the textbook, we can then break down the question into smaller parts based on the level of depth you need, or by specific nutrients or parts of the digestive system.
  5. Mar 16, 2007 #4
    Fats are the one's giving me the most problem. Here's what I've written so far about them:

    Fat-Fats and lipids are non-polar molecules therefore they do not dissolve in water. The lack of digestion between fats and water make it harder for enzymes to break down fat. Bile, a fluid from the liver, assists fat digesting enzymes by reducing surface tension making it easier for fat digesting enzymes. Fats help satisfy hunger for a longer period of time because they take longer to digest in comparison to other nutrients. Fats will also help absorb vitamins.

    Is their anything I can add about fats and their relation to metabolism?
  6. Mar 17, 2007 #5
    Absorption and Transport of Nutrients
    Digested molecules of food, as well as water and minerals from the diet, are absorbed from the cavity of the upper small intestine. Most absorbed materials cross the mucosa into the blood and are carried off in the bloodstream to other parts of the body for storage or further chemical change.

    Carbohydrates. It is recommended that about 55 to 60 percent of total daily calories be from carbohydrates. Some of our most common foods contain mostly carbohydrates. Examples are bread, potatoes, legumes, rice, spaghetti, fruits, and vegetables. Many of these foods contain both starch and fiber.

    The digestible carbohydrates 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 (maltase) 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.

    Table sugar is another carbohydrate that must be digested to be useful. An enzyme in the lining of the small intestine digests table sugar into glucose and fructose, each of which can be absorbed from the intestinal cavity into the blood. Milk contains yet another type of sugar, lactose, which is changed into absorb-able molecules by an enzyme called lactase, also found in the intestinal lining.

    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. Further digestion of the protein is completed in the small intestine. Here, several enzymes from the pancreatic juice and the lining of the intestine carry out the breakdown of huge protein molecules into small molecules called amino acids. These small molecules can be absorbed from the hollow of 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.

    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 intestinal cavity. The bile acids produced by the liver act as natural detergents to dissolve fat in water and allow the enzymes to break the large fat molecules into smaller molecules, some of which are fatty acids and cholesterol. The bile acids combine with the fatty acids and cholesterol and help these molecules to move into the cells of the mucosa. In these cells the small molecules are formed back into large molecules, 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 our food that is absorbed from the small intestine is the class of chemicals we call vitamins. The two different 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, and K).

    Water and salt. Most of the material absorbed from the cavity of the small intestine is water in which salt is dissolved. The salt and water come from the food and liquid we swallow and the juices secreted by the many digestive glands.

    If you need further assistance don't hesitate ask. Remember Google is your closest friend who is available 24/7.

    What level is your project for? Are you in college or high school? :uhh:
    Last edited: Mar 17, 2007
  7. Mar 20, 2007 #6
    High School

    Thanks for the help. Here's what I have so far but I'll see what I can add in from that, maybe someone can read it if they need a review regarding this stuff or something.:

    Digestion of all foods begins with the release of saliva (a digestive juice/enzyme) in the mouth. Foods in the solid form are broken down through chewing movement while liquids such as smoothies do not need to be chewed. Solid foods are carried through the esophagus by wave like muscle contractions called peristalsis. Once food enters the stomach, it is churned and mixed with gastric juices. The enzymes found in these gastric juices help in the chemical breakdown of food. After the stomach has changed the form of food into chyme, it releases chime into the small intestine which is a long winding tube. Digestive juices in the small intestine also help break down and absorb food. Tiny finger-like fragments in the small intestine known as villi absorb nutrients from chyme into the bloodstream. The remaining food which has not been absorbed is passed into the large intestine followed by the colon where it is stored as a waste product. Nutrients which are carried to the liver are either stored or taken to individual cells via blood vessels.

    Carbohydrates- Simple sugars which are already in the form of glucose are absorbed into the blood stream very quickly. An example of this would be the honey used in both muffin and smoothie. Ingredients which contain complex carbohydrates or starches however must be broken down into simpler sugars. Starches are converted into maltose and then converted to glucose. Glucose is taken to the liver where it is stored or used to provide energy. When glucose reaches the cell, it is combined with oxygen to produce energy in the form of heat and ATP power for the cell. The energy created from this process is used for automatic processes (breathing, digesting food, repairing cells) and physical activities (using energy for work). The minimum amount of energy required to maintain life is known as Basal Metabolism. The metabolism of glucose and oxygen will produce carbon dioxide and water as waste products.

    Protein-Foods which are rich in protein such as the egg whites and flour used in muffin recipes must be digested by enzymes before they perform their respective functions such as repairing body tissue. The actual digestion of proteins begins in the stomach. Stomach enzymes such as pepsin begin the digestion of protein. These large protein molecules are converted into amino acids. These smaller amino acid molecules are absorbed through the villi in the small intestine into the blood stream and carried throughout the body. Proteins are then used to build cell membranes. The enzymes which break food and assist in metabolic processes are also created from protein. If there is a lack of carbohydrates and fat storages in the body, proteins will be used to supply energy.

    Fat-Fats and lipids are non-polar molecules therefore they do not dissolve in water. The lack of digestion between fats and water make it harder for enzymes to break down fat. Bile, a fluid from the liver, assists fat digesting enzymes by reducing surface tension making it easier for fat digesting enzymes. Fats help satisfy hunger for a longer period of time because they take longer to digest in comparison to other nutrients. Fats will also help absorb vitamins.

    Vitamins and Minerals-Vitamins and minerals are small molecules found in a form which the body can use. Vitamins and minerals can therefore be absorbed into the body’s bloodstream without the need for digestion. For the most part, they are needed in small amounts to support the various chemical reactions which cells need to constantly undergo. Vitamins and minerals are often dissolved in water or other liquids such as the grape juice used in this recipe.
  8. Mar 21, 2007 #7
    If you are writing a paper, I believe you are missing your intro and the thesis.

    When is this assignment due?
    Elaborate a little more on the requirements for this particular assignment because you can't just run around talking about everything in a non-ordinary fashion. It needs to have a flow...

    What you have now looks good but needs some editing. I can not make any further comment because again, I do not know about the requirements for this assignment...
  9. Mar 22, 2007 #8
  10. Mar 22, 2007 #9


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    Not to mention that here at PF we require the link which you copied the information from. Also, DO NOT copy the entire article! The material may be copyrighted and fair use only allows you to post a small portion of the article. Post a paragraph or two and then post the link.
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