Yes, EPIPHYSIS is a Scrabble word!

Letter values in Scrabble US: E 1, P 3, I 1, P 3, H 4, Y 4, S 1, I 1, S 1.

Is it a valid word?

EPIPHYSIS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the end of a long bone; initially separated from the main bone by a layer of cartilage that eventually ossifies so the parts become fused
a small endocrine gland in the brain; situated beneath the back part of the corpus callosum; secretes melatonin

Also: pineal gland, pineal body, epiphysis cerebri.