Comments: PAT *š́a-ṗǝ (-ṗǝ the same as in *na-ṗǝ 'hand'). PAT *š́a 'foot' is frequent in compounds (*š́a-xʷa 'shin', *š́a-mǝqA 'knee', *š́a-cʷǝ 'toe' etc.). Cf. also the preverb *š́a-/*š́ǝ- 'from the foot, on the foot'. The root is employed also in PAT *š́a-ta (Abkh. á-š́ata, Abaz. š́ata) 'root' ('foot part').
PAK *ʎa-q:ʷá; meaning of the element -q:ʷa is not quite clear (possible interpretations see in Шагиров 1, 246). The root is used also separately in Kab. ʎa 'foot' and in a lot of compounds (*ʎa-pádǝ 'stocking', *ʎa-gʷá(n)ža 'knee', *ʎa-sǝ́ 'barefooted' etc.).
In Ub. -ṗa = PAT *-ṗǝ. Cf. also ʎa in compounds (ʎa-ṗc̣ǝ 'barefooted', ʎa-q̇á (á-ʎaq̇a) 'trace, footprint' etc.). See Trubetzkoy 1922, 188-189, Шагиров 1, 246. Note that despite Lomtatidze (1966, 157-158, 161) the PAK *-q:ʷa has nothing to do with PAT *-ṗǝ and Ub. -ṗa.