Medical Prefixes to Indicate Size

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  • 0:01 Prefixes
  • 0:41 Micro as a Prefix
  • 2:16 Macro as a Prefix
  • 3:52 Mega as a Prefix
  • 4:46 Lesson Summary
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Lesson Transcript
Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

We will get familiar with medical prefixes that are used to indicate size in this lesson. This lesson will also contain examples of how these prefixes are used.


There are three basic word parts to a medical term. They are the prefix, word root, and suffix. The prefix is the word part that is found at the beginning of the term that gives more information to make the term more specific. Prefixes may give information such as time, location, color, amount, and size. There are other prefixes that don't fit into any of those categories, but they still function to narrow the meaning of the term to make it more specific. There are a good number of prefixes to learn, so let's break this up and learn them by category. This lesson will focus on the size prefixes.

Micro as a Prefix

The prefixes that let you know about the size belong to a rather small subset of prefixes. We can begin with a prefix that you've probably used at some point in time or another in your life. 'Micro-' is a prefix that means 'tiny' or 'small.' Terms that may include this prefix are 'microscope,' 'microorganism,' 'microcyte,' 'microcardia,' and 'microcephalus.'

'Microscope' is a term that may take you back to your early years in school when you had to do those sometimes interesting and sometimes boring science experiments! 'Microscope' is the term used to describe an instrument used for viewing small objects, since 'scope' means 'instrument used for viewing.' When you were doing one of those experiments, you may have even been looking at a microorganism. 'Organism' is a word that we use to describe living things. Therefore, a 'microorganism' is a 'small or tiny living thing.' This term is actually reserved for organisms that are too tiny to be seen with the naked eye.

Other objects that you may have viewed under the microscope are microcytes. '-Cytes' is a suffix that means 'cells,' so 'microcytes' are 'tiny cells.' Can you figure out what the medical terms 'microcardia' and 'microcephalus' mean? If you determined that 'microcardia' means 'small heart' and that 'microcephalus' means 'small head,' then you are correct. The word roots, 'card' and 'cephal' mean 'heart' and 'head,' respectively.

Macro as a Prefix

Another prefix indicating size is the one that is the opposite of micro-. It's macro-. 'Macro' means 'large.' Terms that may include this prefix are 'macromolecules,' 'macroscopic,' 'macrophage,' and 'macromyocardia.' The term 'macromolecules' means 'large molecules.' This can refer to molecules inside or outside of the body that are large. This can include things such as proteins, carbohydrates, fats, and our DNA. 'Macroscopic' is used as a term to describe anything that is 'large enough that it can be seen with the naked eye.' You are an example of something that is macroscopic.

'Macrophage' is composed of the word parts 'macro-' and '-phage.' The suffix '-phage' means something that eats or engulfs, so 'macrophage' means 'something large that eats or engulfs.' This term is reserved for describing the immune cells in our bodies that eat or engulf foreign objects in the body. These cells are considered large because they are the largest of our immune blood cells.

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