"Shakespeare turns so frequently to physiological terminology because the job of the doctor, like that of the playwright and poet, is to intuit inner reality via external demeanor." The fields of medicine and art merge in expression to create a common language of the self.
Shakespeare's frequent use of medical terms stems from his understanding that physicians, like playwrights and poets, must decipher inner realities through outward expressions.  The convergence of medicine and art creates a common language for understanding the self.