132 ANATOiMV OF THE RABBIT 



from those forming the main mass of the gland and have no con- 

 nection with its duct (Fig. 5, p. 17). These islets produce insulin, 

 a regulator'of oxidation of starches, sugars, and fats. 



The duodenal epithelium produces a hormone, named secretin, 

 which stimulates the secretion of the digestive juice of the pancreas 

 and also increases the discharge of bile from the liver. 



The Suprarenal Gland 



Each of the pair of suprareral bodies is double, being composed, 

 in mammals, of an inner medulla and an outer cortex which differ in 

 origin, in structure, and in function. The medulla is an aggre- 



Fic 79. riiGtoniicrograph of transverse section of suprarenal 

 body of rabbit, showing cortex and medulla. X 16. 



gation of cells which have a common origin with those of the 

 sympathetic nerve ganglia, and the adrenalin or epinephrine which 

 it secretes has an effect somewhat similar to that of stimulating 

 these nerve cells, raising the blood pressure by vasoconstriction, 

 causing release of glucose into the blood stream, and enabling the 

 animal to meet emergency conditions. The discharge of adrenalin 

 has emotional associations and its occurrence during a state of 

 fear is regarded as an adaptive reaction preparing the animal for 

 fight or flight. Actually, however, its effect in such circumstances 

 appears to be rather enervating or even paralyzing. 



The cortex is considerably more voluminous and is derived 



