Anorectal closing mechanisms.

The thrust of this contribution is contained in an analysis of the refined sealing devices which supplement the co-operative interactions between the anorectum and its surroundings. They include an active smooth-muscle complex which, with elastic tissue, is closely related to vascular anal cushions. These, when distended, plug the anal lumen and complete continence. Additional objectives are: (i) to draw attention to new concepts on the nature of haemorrhoids; (ii) to add illustrations to support the idea of tripartite sealing plugs in the form of anal "cushions"; (iii) to note discrepancies in the literature on the exact siting of the pectinate/dentate line in the anal canal which have a bearing on the theory of the anal cushion; (iv) to give reasons why the musculus submucosae ani should not be termed Treitz's muscle; (v) to review some morphological, pressure, motility and electromyographic sutdies of the neuromusculature of the anorectal region in normal subjects and in patients with haemorrhoids; and (vi) to add explanations and suggestions to fit the concept of the anal cushion into a broader framework of use to the surgeon.