The internal anal sphincter can not close the anal canal completely.
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.
Lestar
B
B
Department of Abdominal Surgery, University Clinics Gasthuisberg, Catholic University of Leuven, Belgium.
Penninckx
F
F
Rigauts
H
H
Kerremans
R
R
D001003:Anal Canal / Q000033:anatomy & histology / Q000502:physiology*; D005260:Female; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D011312:Pressure