There is much to say about how confusing, or difficult to understand, certain terms in the lexicon of scientists and physicians can actually be. For many of these terms however, knowing a few key prefixes and selected words can make understanding them a great deal more straightforward.
Metric Units
For measures of weight or volume, the metric system and its particular prefixes define fractions or multiples of a specific unit of measure. Many of these terms are already familiar to most people. The most common ones in use include:
- Kilo: one thousand times something
- Deci: one tenth of something
- Centi: one hundredth of something
- Milli: one thousandth of something
Thus a kilogram is 1,000 grams while a milligram is one one thousandth of a gram. A liter of a solution contains 1000 milliliters, while 10 milliliters is 1 centiliter. A meter contains 100 centimeters and also contains 1000 millimeters. In some cases, more than one term can refer to the same thing, the best example of which is that 1 milliliter (abbreviated 1 ml) is the same measure as 1 cubic centimeter (or 1 cc). So 1 ml = 1 cc.
All of the above terms, being in the metric system, are mathematical alterations based on powers of ten. In the scientific realm, it is commonplace to find the array of fractional units (values less than 1) carried to an extreme degree in jumps of one thousand. Using weight measurements as an example:
1 milligram is one one thousandth of a gram (milli = 0.001 or 10 to the negative 3 power)
1 microgram is one one thousandth of a milligram (micro = 0.000001 or 10 to the negative 6 power)
1 nanogram is one one thousandth of a microgram (nano = 0.000000001 or 10 to the negative 9 power)
1 picogram is one one thousandth of a nanogram (pico = 0.000000000001 or 10^-12)
1 femtogram is one one thousandth of a picogram (femto = 0.000000000000001 or 10^-15)
And 1 attogram is one one thousandth of a femtogram (atto = 10^-18)
Terms that Describe Relative Position or Placement
It would be relatively simple if localizing particular body structures was as easy as saying something was either front or back, above and below, etc. But in the medical and scientific world there are specific terms that are used to describe where a particular item is in relation to either the body as a whole or to other items around the structure in question.
The most commonly used terms typically are considered as pairs: There is anterior versus posterior, superior versus inferior, distal versus proximal, and lateral versus medial.
For anterior and posterior they relate to whether a structure of interest is towards the front or towards the back of something. For example, in the knee joint the anterior cruciate ligament is closer to the front of the knee while the posterior cruciate ligament is closer to the back of the knee. Relative position can also be stated with these terms such as the heart is anterior (in front) of the spinal column.
In the case of superior and inferior, they are most directly used to describe whether something is above or below something else respectively. For example, the atria of the heart are superior to the ventricles.
For distal versus proximal, the measure is of a relative distance from a particular point or structure. So using the fingers as an example, the fingertip is distal to the main structure of the hand while the bottom of the finger, which is much closer, is proximal.
In the instance of lateral versus medial, these terms describe structures as to how their orientation relates to the middle (the midline or center) of the body or its sides. Using the knee as an example again, the medial collateral ligament is nearer to the center of the body, on the inside portion of the knee, while the lateral collateral ligament is on the outside portion of the knee joint away from the center of the body.
All of the above terms are used in many different settings, but they always provide an insight as to a specific orientation or positioning.
Read a complete listing of anatomical positioning terms at Medterms or look up specific terms in the online Stedman’s Medical Dictionary.
Kenneth Rosen - I am a medical research doctor with more than 20 years of experience studying how the nervous system and skeletal muscle develop and ...
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