Anatomy and Physiology: What We Do with Our Food

What We Do with Our Food

As I said earlier, the monomers that are ultimately produced through all these processes are absorbed by the small intestine's villi into the bloodstream and the lymphatic capillaries. Once they get to the cells of the body, these molecules have multiple functions. Some of them are used by the body for immediate energy, such as glucose, while some are stored as energy in the form of polymers. Many are used to build other polymers.

The Big Picture

We get so much energy from carbohydrates, it makes you wonder how carnivores get their energy, especially if their prey has little or no fat. The answer is that the amino acids can be broken down for energy use. The only problem is that amino acids, unlike carbohydrates, contain nitrogen. The result of their breakdown is the buildup of nitrogenous (containing nitrogen) wastes. These wastes are toxic, so they are released from the cells into the interstitial fluid, drained by the lymphatic system into the blood, and then filtered from the blood by the kidneys, where the wastes are released from the body as urine.

The following table of molecule use demonstrates the idea of the absorptive state and postabsorptive state. Whenever we are in the process of absorbing nutrients into the bloodstream, we have a constant supply of easy energy. For about 12 hours out of every day we are in the postabsorptive state, however, and we must rely entirely on the body's reserves. Blood glucose levels are critical here. Since we don't need all the glucose we eat as soon as we eat it, by reducing blood glucose in the absorptive state, we have freed the glucose up to be converted into other molecules that will remain in reserve until the postabsorptive state.

Molecule Use
Type of Organic MoleculeUses in the Body
CarbohydratesQuick energy, energy storage
LipidsEnergy storage, production of lipoproteins
ProteinsQuick energy, production of proteins (hormones, structure, and so on)
Nucleic acidsQuick energy (RNA), protein synthesis, replication

All this talk of polymers illustrates the idea that much of what you do with your food is tantamount to recycling! You break down the polymers of others, and then use the resulting monomers to build your own polymers. Much of your protein, fat, and even DNA, are merely reshuffled monomers of others. When you eat meat, the muscles of animals, you take those protein polymers and break them down into amino acids that you then use when, for example, you build up your own muscles. In a nutshell, you are what you eat!

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Excerpted from The Complete Idiot's Guide to Anatomy and Physiology © 2004 by Michael J. Vieira Lazaroff. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.

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