- Digestion
- Parts of the Digestive System
- Problems
III. Glycolysis and the Krebs cycle
IV. Nutrition
- Classes of nutrients
- Minerals
- Vitamins
VI. Conclusion
Introduction
We have all heard the phrase "you are what you eat," and I guess to some extent this statement is true. Obviously what we eat goes through the digestive system and the useful components, vitamins, minerals, proteins, fats and Carbohydrates are broken down and used by the body. Everything else is sent out of the body as waste. So how does the digestive system work? How are nutrients taken from our food and used? What foods are good for us and what should we stay away from?
Digestive System
Digestion
Many of us eat for pleasure, I know I do, but we also need to eat in order to survive. The food that we take in is composed primarily of carbohydrates, fats, and proteins, which are the macromolecules necessary for life. The purpose of digestion is to break down the food that we eat into single unit molecules like sugars, and amino acids. Ingestion is what we take in, in other words what we eat. Digestion is both mechanical and chemical. Mechanical digestion is the process of making food small enough to be acted upon by the digestive enzymes. Most of this process happens in the mouth and stomach. Digestive enzymes are a large part of chemical digestion, these enzymes hydrolyze food into molecular units. The partly digested food with a semi fluid consistency that is passed from the stomach to the small intestine is known as chime. The contents of the GI tract moves from one organ to the next and those components that could not be digested are eliminated. Unit molecules are absorbed into the cells lining the tract and nutrients enter the bloodstream.
Parts of the Digestive System
A graphic of Glycolysis and the Krebs cycle taken fro Professor Frolich's presentation.
Glycolysis and the Krebs cycle are the main way the cells make ATP. As we learned in the last unit, ATP provides energy and this process occurs in the mitochondria of the cell. Glucose is the reactant for this process. Glucose is diffused through the cell membrane. Insulin, produced by the pancreas, stimulates cells to pick up glucose to be used in cellular metabolism. Sometimes glucose is stored as glycogen in the liver or muscle.
I will tell you, I watched the videos on the web links on this subject and it is a bit over my head!
Table taken from Professor Frolich's power point illustrating what happens to food after it is digested and how it is used by the body.
Nutrition
Classes of Nutrients
A nutrient is a component of food and is used to perform a physiological function of the body. The purpose of nutrients is to give us energy, promote growth and development, and regulate cellular metabolism. Carbohydrates, proteins, and lipids, "the molecules of life' are where we get most of our nutrients. Basically people need a balanced diet with a variety of different foods for good health
I get frustrated with foo guides because they are always changing and vary depending on culture. I appreciated the web link showing the pyramids for different cultures.. The one above is from the textbook, Human Biology page 164, Sylvia S. Mader
Carbohydrates: The preferred energy source of the body is carbohydrates. Plants are a good source of Carbohydrates. Carbohydrates can be simple or complex. Products made from refined grains like white bread and cakes should be minimized in the diet because processing causes these products to lose much of their nutritional value.
I am mostly including this picture because I like the way it looks, it is appetizing to me. The foods above are rich in fiber and carbohydrates, Human Biology, page 158. Sylvia S. Mader.
Proteins: Proteins become amino acids which cells use to synthesize cellular proteins. There are 20 different amino acids and 8 of them are essential and must be a part of the diet. Food taken from animals like eggs, milk, and meat contain all the amino acids needed. Protein can also be found in legumes, seeds, and nuts however alone each is an incomplete protein source. If one essential amino acid is missing, it will prevent the use of the other 19 amino acids.
Lipids: Cholesterol, fats, and oils are all lipids. Those lipids that are solid at room temperature are called saturated fats, for example butter. Oils have unsaturated fatty acids. Remember lipids are used in forming plasma membranes.
Minerals
Certain minerals are required in the diet. There are major minerals and trace minerals. Major minerals are structural components of tissues. and trace minerals are parts of larger molecules. Iron is an example of a mineral that our bodies need, so is calcium. Lack of these minerals can lead to deficiencies like anemia. or osteoporosis. Below is a mineral table from the textbook.
Mineral chart showing different minerals, the sources, and conditions caused by too much or too little. Human Biology, page 161. Sylvia S. Mader
Vitamins
Unlike minerals, vitamins are organic compounds that are used by the body for metabolic purposes. The body is unable to adequately produce these compounds on its own. There are fat soluble vitamins that are stored in the liver, and water soluble vitamins. Deficiencies due to lack of certain vitamins can lead to illnesses like scurvy or rickets.
The above to tables give a listing of vitamins, fat soluble and water soluble. Sources and conditions associated with different vitamins are also listed. Human Biology page 163, Sylvia S. Mader
What is healthy food anyway?
Briefly I wanted to acknowledge Professor Frolich's short portion in the presentation regarding the nutritionism approach. I am not going to talk a lot about this as I covered much of it in the ethical issues essay. What I will say that it had never occurred to me that we need to look at food as food and not nutrients. As I mentioned in my essay, I do not have any health problems or weight issues so I did not always to look at labels. However I did worry that my children might not get all the nutrients they needed and would buy food items with packages proclaiming "vitamin fortified" or "extra C" for that very reason. In some ways I now see that I did them a disservice as my son especially is adverse to eating most fresh fruits and vegetables. I wonder if this is caused by his comfort level being conditioned toward the packaged foods. Remember in Supersize Me where the filmographer talked about an addictive component to McDonald's food? I wonder if that is true of packaged food as well.
I will also say that I have never thought of food as a spiritual experience. I do have have cravings, mostly for fresh vegetables which I thoroughly enjoy. I do know that I am not satisfied with just eating quick meals all the time and I feel happiest when I have cooked something from scratch using whole foods. An example of this is the traditional Thanksgiving meal. About two years ago my daughter and I were watching a morning news program about cooking yams and making your own cranberry sauce. Well we decided to try it ourselves and guess what, our yams and cranberries tasted way better than what comes out of the can, and we felt like we accomplished something.
I found this cute kid's website and thought I would include these cartoons from it. The website deals with making good food choices and it even talks about buying food locally and staying away from processed foods. http://tiki.oneworld.net/food/home.html
Conclusion
There are so many differing opinions out there about food and nutrition that trying to eat healthy can be a confusing experience. The best advice I have heard is just simply to eat a variety of foods from all food groups. Unfortunately Americans often think of food as almost a form of entertainment rather than looking at it as a basic human need. We want our food to be attractive and we are easily influenced by advertising. We are also in a hurry all the time. They say it takes three years to break a habit and I know I have a fast/processed food habit. I have just begun to work on making changes...two years, nine months to go.
Works Cited
Human Biology, Sylvia S. mader
Nutrition presentation, Professor Frolich
tiki.oneworld.net/food/home.html
www.firodiyaheartfoundation.org/Health%20Tips...
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