What kind of cellular machinery would be required? Where would this cellular machinery exist? Would we have a vitamin-C creating gland? How susceptible would th

What kind of cellular machinery would be required? Where would this cellular machinery exist? Would we have a vitamin-C creating gland? How susceptible would this gland be to outright failure a la diabetes? The body could do a lot of things, but without a working alternative model simply saying the existing model is faulty suggests a deep understanding we clearly lack.