1. Innate, inherent, inseparable from the thing itself, essential. (wiktionary.org)
2. (of a body part, relating to anatomy) Comprising, being part of a whole. (wiktionary.org)
3. Situated entirely within or pertaining exclusively to a part. (biology-online.org)
Word origin: From Middle French intrinsèque “inner” (13c.), from Medieval Latin intrinsecus “interior, internal,” from Latin intrinsecus (adv.) “inwardly, on the inside,” from intra “within” + secus “alongside,” originally “following” (related to sequi “to follow;” see sequel).