Questions on Substance

I'd like to get more details on how the various Substance types are meant
to be used.

1) What is BodySubstance for?  Can someone provide an example of a
BodySubstance?  And how it differs from BiologicalSubstance or
AnatomicalEntity?

2) What is BiologicalSubstance for?  I'm wondering if this shouldn't be
under ChemicalSubstance.  For example, is estrogen, taken for estrogen
therapy, a BiologicalSubstance or Chemical Substance?  Or both depending on
context?  What's the current logic behind the differentiation of
BiologicalSubstance and ChemicalSubstance?

It would really help to have examples for each of these types.


Thanks,
-Mark