<prompt> What is true about ulcerative colitisInvolves rectum and then whole colon backwardsInvolves only colonSkip lesions seenIleum not involved  <response>: Classically, ulcerative colitis begins in the rectum, and in continuity extends upwards into the sigmoid colon, descending colon, transverse colon, and sometimes may involve the entire colon. The colonic contents may rarely backflow into the terminal ileum in continuity, causing back-wash ileitis in about 10 of cases. Grossly, the characteristic feature is the continuous involvement of the rectum and colon without any uninvolved skip areas compared to Crohns disease. TEXTBOOK OF PATHOLOGY 6TH EDITION HARSH MOHAN PAGE NO:567,568 IMAGE REF: GENERAL AND SYSTEMIC PATHOLOGY RAMDAS 2ND EDITION, PAGE 509 