DIGESTION 435 



IliK Lualcs sonicwliaL wilh the Iccding schedule and is a[)j)areiiLly sub- 

 ject to some sort oi partial control. Bile (lows Ironi the liver along 

 a duct and through another valve-like sphincter which controls 

 passage into the intestine. Passage of acidic chyme through the 

 pyloric sphincter into the duodenum causes the sphincter of the bile 

 duct to open. When the bile sphincter is closed, the continuing flow 

 of bile is stored in the adjoining gall bladder, which is provided with 

 muscle fibers and imposes a gentle pressure somewhat in the manner 

 of the stomach. This pressure expels bile from the gall bladder on 

 opening of the sphincter. 



The gall bladder is primarily a storage organ, but it does modify 

 in two ways the bile as originally secreted by the liver. First, the 

 bladder reduces the water content and thus relatively increases the 

 concentrations of other materials. Second, the gall bladder secretes 

 additional supplies of some of the bile components. Although the 

 storage, concentrating, and secretory functions are important, they 

 are not essential since surgical removal of the gall bladder still allows 

 the animal to digest comparatively normal diets. Such operations 

 are, of course, fairly common in hinnan beings, occasioned mainly by 

 the formation of "stones" in the gall bladder. These stones originate 

 by precipitation of cholesterol from the concentrated bile stored in 

 the bladder. Although such precipitation is commonplace, other 

 components normally prevent aggregation to an extent causing block- 

 age of the duct. 



The composition of bile is summarized in Table i7-i. Two columns 



TABLE 17—1. Composition of Human Bile 



Percentage Composition 



are given to permit comparison of bile directly from the liver with 

 that from the gall bladder. With a change in water content leading 

 to an increase in the total solids from 3 per cent to 14 per cent, an 

 increase by a factor of about 4.5 should occur for the individual 



