What are polymorphs?

'Polymorph' is the short name for polymorphonuclear granulocytes. The term 'granulocyte' was coined during the light microscope days, when it the various white blood cells had to be identified. The first step in this process was usually to identify whether or not the white cell in question had 'granules' or not.

Thus, this one:


had granules,



but this one:



didn't.



As for the 'polymorphonuclear' part of the word,the granulocytes seemed also to have lobulated nuclei (see above), whereas the 'agranulocytes' (no granules) tended not to. Thus, the agranulocytes are sometimes referred to as mononuclear leukocytes.

Once you had decided between a granulocyte and an agranulocyte, you could then go on to identify the specific cell type:

• Granulocytes (a.k.a. polymorphs) incorporates neutrophils, basophils and eosinphils
• Agranulocytes (a.k.a. mononuclear leukocytes) incorporates lymphocytes, macrophages and monocytes.

Oh, and what are the granules? They're mostly membrane-bound collections of the nasty chemicals that the white blood cells use to kill or destroy their targets. For what it's worth, agranulocytes actually do have 'granules' too - they're just harder to see.

Addendum

Polymorphs can also, more informally, be taken to mean "neutrophils". Presumably this is because the vast majority of polymorphs are in fact neutrophils, but this only adds to the confusion of the term. My advice: stick to better, more definitive terms, depending on what you mean - such as phagocytes, neutrophils or lymphocytes.