The acidity of your precious bodily fluids is a carefully guarded parameter.
To allow this parameter to deviate out of a very narrow range would massively impair your capacity to continue living. Basic molecular services would break down. Cellular anarchy would ensue. In order for the ICU physician to wrest a form of order from this chaos, a reasonable grasp of basic acid-base chemistry is expected. An excellent medically themed foundation for acid-base chemistry is laid by Kerry Brandis in a highly acclaimed series of online articles, to which I will constantly refer. It is not my intention to supercede this resource, as it remains canonical for all critical care trainees.
So, let us have some basic definitions.
A molecular entity or chemical species capable of donating a hydron (proton) (see Brønsted acid) or capable of forming a covalent bond with an electron pair (see Lewis acid).
A chemical species or molecular entity having an available pair of electrons capable of forming a covalent bond with a hydron (proton) (see Brønsted base) or with the vacant orbital of some other species (see Lewis base).
These models compliment each other. The Brønsted-Lowry model is well suited to the discussions of acid-base chemistry which involve aqueous solutions and protic acids, whereas the Lewis model is more general and can be called upon to offer explanations of more exotic scenarios.
A molecular entity capable of donating a hydron (proton) to a base, (i.e. a 'hydron donor') or the corresponding chemical species.
A molecular entity capable of accepting a hydron (proton) from an acid (i.e. a 'hydron acceptor') or the corresponding chemical species.
A molecular entity (and the corresponding chemical species ) that is an electron-pair acceptor and therefore able to react with a Lewis base to form a Lewis adduct, by sharing the electron pair furnished by the Lewis base.
A molecular entity (and the corresponding chemical species) able to provide a pair of electrons and
thus capable of coordination to a Lewis acid, thereby producing a Lewis adduct.
The strength of an acid or a base is by convention defined as pH, which is related to the activity rather than the concentration of hydrogen ions.
This is a notional definition. It is validated by an experimental method which operates according to a well-defined measurement equation in which all of the variables can be determined in terms of SI units.