Trim the stems and pull the outside leaves off the artichokes. Cut the artichokes in half and scoop out the choke with the tip of a small spoon. Halve lengthwise. Add the lemon juice to a bowl of cold water and add the artichokes to prevent discoloration.
In a large deep skillet combine the oil, onion, garlic, carrot and celery. Cover and cook over low heat, stirring occasionally until the vegetables are tender, but not browned, about 8 minutes.
Drain the artichokes; add to the skillet along with the broth. Add the oregano, salt and pepper. Cover and cook over very low heat until the artichokes are tender, about 25 minutes.
Meanwhile cook the pasta in plenty of boiling salted water until al dente or firm to the bite, according to package directions. Drain. Add to the skillet with artichokes. Heat, stirring to coat and adding small amounts of additional chicken broth, if needed, to keep th pasta moistened. Serve cheese on the side.