Why does a full bladder give the impression of being to head to increased flatulence?

The bladder and the bowel are both stimulated by sacral and pudendal nerves. A variation of stimulation to these nerves can impose increased function(incontinence) or decreased function(retention/constipatio. Therefore if the full bladder stimulates the nerves, the bowel may be stimulated also.
It is a concern of increasing pressure in a set space.