The internal anal sphincter can not close the anal canal completely

Int J Colorectal Dis. 1992 Sep;7(3):159-61. doi: 10.1007/BF00360358.


We determined the maximum closing capability of the internal anal sphincter muscle ring in vitro and in vivo. The internal sphincter, 4 to 6 mm thick, cannot close the anal canal hermetically, not even during maximal contraction. The blood-filled anal cushions have to fill up an intrasphincteric gap of at least 7 to 8 mm in diameter.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anal Canal / anatomy & histology
  • Anal Canal / physiology*
  • Female
  • Humans
  • Magnetic Resonance Spectroscopy
  • Male
  • Middle Aged
  • Muscle Contraction
  • Pressure