Suppose I want to say "reproductive organs of the human body".
Of course, since we don't have a word meaning "organ" as in "organ of the human body",
Something for the {chabal tetlh}?
I choose the next best thing I can find which is {'ay'}. So I ask..
{porgh 'ay'}?
{ngaghmeH 'ay'mey} or {ngaghmeH 'ay'Du'}?
Leaving aside the question of whether {ngaghmeH 'ay'} says what you want, for {'ay'} referring to body parts, I'd use {'ay'Du'}.
We don't have any canon examples with {'ay'}, but we know from some other words that the plural suffix on a noun can change depending on what it's referring to. For example, {DIr} takes the suffix {-Du'} when still on a body, but {-mey} otherwise:
The plural {latlhpu'} has appeared several times in canon when referring to people:
{Heghpu'bogh latlhpu' ghuHmoH bey.} (SkyBox 31)
{yIntaH qIrq 'e' vIneH. DaSwIj bIngDaq latlhpu' vItap.} (Star Trek Constellations p.232)
{latlhpu' law' pIlmoHpu' lutvam} (paq'batlh p.131)
And lastly, there is a non-canon precedent: the plural {'ay'Du'} for body parts has also been used in the Tribble Song:
--
De'vID