There is a protein in our body called Intrinsic factor.
So, if there is a sentence - "The" intrinsic factor is a glycoprotein. By putting "the" before intrinsic, the sense of the sentence is like a particular factor which is intrinsic. So, by putting "the" before intrinsic, the specificity is on "intrinsic" or the whole, "intrinsic factor"?
Link from where I have studied.