516 VERTEBRATE LIFE AND ORGANIZATION 



ujxsets in carbohydrate metabolism secondarily produce many other 

 changes in tlie metabolism ol proteins, tats and other substances. 



The surgical removal of the pancreas, or its hypofunction in dia- 

 betes mellitus, produces impaired glucose utilization, which results in 

 high concentration of glucose in the blood (hyperglycemia) and the 

 excretion of large amounts of glucose in the mine (glycosuria) because 

 the concentration of sugar in the blood exceeds the renal threshold 

 (p. 564). Extra water is required to excrete this sugar, the urine volume 

 increases, and the patient tends to become dehydrated and thirsty. Be- 

 cause the tissues are unable to get enough glucose from the blood, they 

 break down protein and convert the carbon chains of the amino acids 

 into glucose. Much of this is excreted and there is a steady loss of 

 weight. The fat deposits are also mobilized and broken down, and the 

 concentration of fat in the blood may increase to the point where 

 the blood has a milky appearance. The fatty acids are not metabolized 

 completely but tend to accumulate as partially oxidized ketone bodies 

 such as acetoacetic acid. These acidic substances accumulate in the 

 blood and are excreted in the urine, causing an acidosis (loss of base) 

 which finally results in coma and death. The injection of insulin al- 

 leviates all of these symptoms; with the utilization of glucose made 

 normal by insulin all of the other metabolic conditions return to 

 normal. 



The effect of an injection of insulin lasts for only a short time, a 

 day at most, for the insulin is gradually destroyed in the tissues. A 

 person with diabetes must receive daily injections of insulin to main- 

 tain good health. Long-lasting insulins, such as protamine zinc insulin 

 and globin insulin, have been discovered which reduce the number of 

 injections to one a day for most diabetics. 



The administration of a large dose of insulin to a normal or a 

 diabetic person causes a marked decrease in the blood sugar level. The 

 nerve cells, which require a certain amount of glucose for normal 

 function, become hyperirritable and then fail to respond as the glucose 

 level decreases. The patient becomes bewildered, incoherent, and coma- 

 tose and may die unless some glucose is administered. There are rare 

 cases of pancreatic tumors which by hypersecretion of insulin cause 

 recurring attacks of convulsions and unconsciousness by reducing the 

 blood glucose level. 



The secretion of insulin is controlled by the level of glucose in 

 the blood. When the blood glucose level rises, e.g., after a meal, the 

 secretion of insulin is stimulated and it acts to restore the glucose level 

 to normal. When the glucose concentration has been lowered, the 

 stimulus for insulin secretion is removed, and it decreases or stops. 

 The long-continued injection of insulin into a nondiabetic animal or 

 person will render it diabetic. 



252. The Adrenal Glands 



The small, paired adrenal glands of mammals are located at the 

 anterior end of each kidney. The two human glands weigh less than 



