Yes, you have the right idea there. In many cases, 'which' is indeed the equivalent of lequel/laquelle/lesquels/lesquelles. For example, through which = par lequel in which = dans lequel on which = sur lequel But this isn't always the case. For example, 'from which' may sometimes be translated as 'duquel', while 'to which' may be translated as 'auquel', and 'of which' may in some cases be the equivalent of the French word 'dont'. This is because French grammar is much more complex than English grammar in this area. In other situations, 'which' is a relative pronoun corresponding to either 'qui' or 'que' in French. The sentences on mammary glands which you were looking at a few days ago are examples of constructions of this type. The best advice I can give is not to try and find an exact French equivalent to English grammatical words. Our grammatical systems are not quite the same, and trying to translate word-for-word is impossible. You can translate a concrete lexical word like 'vein' or 'artery' directly from one language to another and get an exact equivalent, but you can't always translate a grammatical word like 'which' in the same way in all situations.

Hello Nasser, My French is basic but your choice of words sounds correct. Which is a referencing word So in your first sentence "The tubes, such as veins and arteries, through which the blood circulate" 'Which' refers to 'The tubes' In the second sentence "The distance over which a joint can be extended or flexed" 'which' refers to 'The distance' I hope this helps