ABSTRACT
The rectum has a continuous layer of longitudinal muscle outside the inner circular muscle, unlike the sigmoid colon where the longitudinal muscle is in three bands, the taeniae. The ano-rectal junction forms a right angle, held in this position by the puborectalis muscle. At the anus, the gut joins the skin. The anus is lined by squamous epithelium, while the rectum is lined by columnar epithelium. The location where the epithelium changes is known as the mucocutaneous junction, and is visible as a wavy white line in the lower third of the anal canal (sometimes called Hilton’s white line). Embarrassment often inhibits patients from describing their ‘ano-rectal’ symptoms in precise detail, although as ever the history is often crucial in making the correct diagnosis. Blood ‘mixed in’ with the faeces should theoretically have come from above the sigmoid colon to give sufficient time for mixing, while blood ‘on’ the faeces has usually come from the rectum or anal canal.
