Why does lack of sleep make you irritable?

right now i am annoyed. mostly by things i cant control. or have no say in.  needless to say im upset. i cant really articulate it......because if i did...it would just cause more annoyance......but its there.....oh yes its there........seems like i spend more time frustrated here of late...trying to keep my cool...trying to change...trying to be compromising....and feeling like i am getting nowhere...or nothing in return. like...i can be all those things...but.....sometimes you just feel like its all for nothing. and once again....it is frustrating.