Well, the meridiens are the different flows of energy through the body in TCM. There is not really a physical route of blood or anything like that, which is why many don't see the proof in connection between the points. In other words, western medicine can't prove it in a lab.
I wouldn't have a clue how to measure it, but I know they feel around the organs a bit and read your pulse on different places in your arms and legs.
I am not educated enough in it to know for sure. I do notice that she talks about my pancreas always after measuring my right wrist.
Maybe someone who is a bit more skilled in acupuncure could chime in?