The theoretically democratic senate of the Sh'areen Calipahte can always be overruled by the Caliph and is often seem as a sham more than a democratic institution. That said, it does carry some informal power. At any given time, the Senate has 71 members, with the 10 most important guilds having one representative each, plus two individuals who are chosen by those guilds. The rest of the Senators are elected representatives of the various regions of the Caliphate. Which mostly means that they're chosen by nobles, but in some regions, they are elected with some form of a democratic intent. Senators hold their title for life unless they abdicate or is removed by the body that placed them there. Abdication is much more common as those who feel like they might be forced out typically choose to go in a more graceful manner. This means that members of the Senate tend to be older and conservative. But since they have been around for so long, they also know how to influence the Caliph and the rest of the central government, even outside official channels. In fact, this is where most of their power lies and that is why they are not replaced on a whim.