After feeding a dog, forceful contractions of the gall bladder occur that are sufficient in strength to expel part of the contents of the viscus against a considerable pressure resistance.
The pressure within the gall bladder of a healthy, unanesthetized dog fasted 24 to 48 hours is usually about equal to a column of bile 100 mm. high. After a few swallows of food there is a rapid increase in the pressure to more than 200 mm. with a gradual fall in it again, and repeated similar rises and falls occur thereafter. The gall bladder contractions responsible for these alterations are accompanied by a lessening in the resistance to the passage of bile to the intestine, a resistance which is maintained by the muscles at the lower end of the common duct. There would appear to be a reciprocal response on the part of the two structures to the one stimulus.
The maximum pressure developing within the temporarily obstructed biliary tract in an animal with the gall bladder excluded about equals that of a column of bile slightly more than 300 mm. in height. The taking of food acts as a stimulus on the rate of bile secretion, but does not alter the maximum secretion pressure. When the gall bladder is connected with the duct system, obstruction does not lead until after some hours to the development of a pressure of more than 100 to 150 mm. within the biliary tract,—that is to say the pressure does not rise above the normal. Its failure to rise further is referable to the activity of the gall bladder to store and concentrate the bile as secreted.
The physiological and clinical significance of these findings is discussed.