ANIMAL METABOLISM 



327 



a powerful inhibitor of hexokinase, whereas insulin counteracts this in- 

 hibition. The effect of the diabetogenic hormone therefore is to raise 

 the blood sugar level by preventing the phosphorylation essential for 

 the utilization of blood glucose. Insulin has the opposite effect. The 

 disease, diabetes, may be caused either by too much diabetogenic hor- 

 mone or too little insulin. 



The normal blood sugar level in man varies between 0.07 and 0.10 per 

 cent (70 to 100 mg. per 100 ml. of blood) during fasting, but rises to 

 0.12-0.15 per cent after a meal. Some of the controlling influences which 

 operate to maintain this level have been listed above and are presented 

 diagrammatically in Fig. 13-2. Another factor which sets an upper 

 limit to the blood sugar concentration is excretion in the urine. Normally 



Controlling Factors Blood sugar Descriptive 



Increase Decrease percentage terms 



a 

 c 



a 



o 

 o 



o 



o 



a; 

 O 



o3 





0.18 



0.15 



r ^ ^ 



Renal 

 threshold 



J 

 \ 



Normal 



0.07 



0.02 



Physiological 

 effect 



Excretion 

 in urine 



Hyperglycemia 



Normal 

 well-being 



range 



J 



^ 



Insulin 

 " shock 



Listlessness, 

 Hypoglycemia fatigue 



Coma, 

 death 



0.00 •- ^ ^ 



Fig. 13-2. Blood sugar level and its control. 



only traces are excreted (an average of only 142 mg. in the urine of a 

 normal man during 24 hours), but whenever the blood sugar level rises 

 to a certain point, called the renal threshold, urinary excretion occurs. 

 Thus in cases of diabetes the urine usually contains 3-5 per cent of 

 glucose (about 50-100 g. excreted per day). The renal threshold varies 

 with the individual, but ordinarily it is about 0.15-0.18 per cent: Levels 

 of blood sugar much below 0.07 per cent lead to unconsciousness and 



