Organization of the Human Body

To answer the question of how nutrients relate to overall function, let’s begin at the beginning. Our bodies are made up of seven layers of structure and function. Each of these levels interacts and supports the next level of structure. This is a key concept, that the level below supports the structure and function above. It is similar to the way that a footing supports the foundation of a house, and the foundation supports the framing, and so on. However, unlike a house, your body’s ‘footing’ requires constant reinforcement or nourishment through the diet.

The lowest level of organization in the human body is the chemical level. This level includes individual atoms, compounds (simple combinations of atoms like water), and substances essential for maintaining life. The foods that we eat must be broken down to these levels before they can be utilized. The body then uses these chemicals to build molecules. Molecules are larger and more complex structures such as proteins, enzymes, fats, and sugars. The body uses some of these to make even larger molecules like DNA. 

These smaller structures are organized into the living units that we call cells. Cells are the smallest functioning unit in the living organism. There are more than 200 different types of cells in your body. Among the many kinds of cells in your body you’ll find muscle cells, nerve cells, and blood cells, just to name three.

The next higher level of organization is the tissue level. Tissues are a mixture of cell types and are grouped together to perform a more specific function. Examples of tissues in your body are muscle tissue, connective tissue, and nerve tissue.

Tissues are joined together to form the next level of organization: the organ level. Organs are structures that are composed of two or more different tissues. They have more specialized and specific functions, and usually have identifiable shapes. Examples of organs are the heart, liver, lungs, and the brain.

The system level is the next level of organization in the body. A system is composed of several organs that share a common function. An example of a system is the digestive system, which functions to break foods down to the molecular and chemical level and then absorb it. This system is composed of the mouth, saliva producing glands, called salivary glands, pharynx (throat), esophagus, stomach, small intestine, large intestine, rectum, liver, gallbladder, and pancreas.

The highest level is the whole organism. All the systems and parts of the body, functioning with one another, constitute the complete organism –one living individual.[1]

When you are fully grown, your body will have about 50-60 trillion cells. That’s about 600 times more cells than there are stars in the Milky-way galaxy. Now think for just a minute, every single cell has about one quadrillion molecules, that’s about 10,000 times the number of stars in the Milky-way. Now realize that every single cell needs to be nourished every single day. That’s an incredible amount of chemical nutrients that your body will need just to maintain itself. If you are still growing, you may need even more.

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[1] Tortora G. J., Anagnostakos N.P. Principles of Anatomy and Physiology. 6^th Edition. Harper & Row, New York. 1990.

Alberts B., Bray D., Lewis J., Raff M., Roberts K., Watson J.D. Molecular Biology of the Cell. 3^rd Edition. Garland Publishing, Inc. New York. 1994.

Campbell N.A. Biology. 2^nd Edition. Benjamin/ Cummings Publishing company, Inc. Redwood City, California. 1990.

A Healthy Diet and Essential Nutrients

We have come to learn that a healthy diet satisfies three physiological needs.

·         Fuel for cellular respiration (energy)

·         Organic raw materials for the body to make its own molecules

·         Essential nutrients – elements and compounds that cannot be made by the body from any raw material and must be supplied in the diet.

Nutrients are divided into two basic categories; macronutrients and micronutrients.

Macronutrients typically provide calories or energy but are also needed for other body functions.[1] “Macro” refers to large, and applies to this group of nutrients because they are needed in relatively large quantities. There are three groups of macronutrients:

·         Carbohydrates

·         Proteins (includes amino acids)

·         Fats (includes essential fatty acids)

Micronutrients on the other hand are needed in much smaller amounts.[2] These nutrients are characteristically coenzymes or cofactors[3] required for enzymatic activity. These can be divided into two groups:

·         Vitamins which are organic (carbon based compounds) and,

·         Minerals (metal ions) which are derived from inorganic elements.

So what are essential nutrients?

—  More than 40 essential nutrients, including:

◦       16 Minerals

◦       14 Vitamins

◦       9 Amino acids (there are between 8 and 10, depending on the source)

◦       2 Essential fatty acids

◦       Conditionally essential nutrients

[1] Macronutrients: the Importance of Carbohydrate, Protein, and Fat. Retrieved 09 Feb. 2011. http://www.mckinley.illinois.edu/handouts/macronutrients.htm

[2] Micronutrients. Retrieved 09 Feb. 2011. http://www.who.int/nutrition/topics/micronutrients/en/

[3] Coenzymes and cofactors. Retrieved 09 Feb. 2011. http://academic.brooklyn.cuny.edu/biology/bio4fv/page/coenzy_.htm

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My first experience with the concept of nutritional deficiency came indirectly during a biochemistry class while at University. We were studying enzyme kinetics which is the study of the rates of chemical reactions that are catalyzed by enzymes.

In simple terms my professor was explaining that an enzyme reaches peak efficiency (or Vmax) when there is enough substrate, or raw material, for it to act on.

Referenced from http://en.wikipedia.org/wiki/File:Michaelis-Menten_saturation_curve_of_an_enzyme_reaction.svg

We then examined a human enzyme that required a cofactor, in this case magnesium, in order to function. Even when completely saturated with substrate this enzyme would not function without its cofactor. In fact the reaction would reach its peak efficiency only when a minimum concentration of magnesium was added to the reaction.

Our professor then made a comment that would forever change my life. He said you might want to go out and get magnesium, but you get all you need in your food. It didn’t happen in that moment, but over the next couple of days the nagging question surfaced in my consciousness. What if you don’t get all you need in your food?