EXCRETIOK. 4g5 



two or three hours after the meal; and it reaches its maximum about 

 the fourth hour. From this period the excretion steadily decreases 

 until bed-time. During sleep it sinks still lower, and reaches its mini- 

 mumbeing not more than one-third of the quantity excreted during 

 the hours of digestion. The increased amount of urine passed after 

 drinking large quantities of fluid depends upon the temporary increase 

 of blood-pressure thus caused. 



The following table* will help to explain the dependence of the 

 nitration function upon the blood-pressure and the nervous system: 



TABLE OF THE RELATION OF THE SECRETION OF URINE TO ARTERIAL PRESSURE. 



A. Secretion of urine may be increased 



a. By increasing the general blood-pressure; by 



1. Increase of the force or frequency of heart- beat. 



2. Constriction of the small arteries of areas other than that of the 



kidney. 



b. By increasing the local blood-pressure, by relaxation of the renal 



artery, without compensating relaxation elsewhere ; by 



1. Division of the renal nerves (causing polyuria). 



2. Division of the renal nerves and stimulation of the cord, below 



the medulla (causing greater polyuria) . 



3. Division of the splanchnic nerves ; but the polyuria produced is 



less than in 1 or 2, as these nerves are distributed to a wider 

 area, and the dilatation of the renal artery is accompanied by 

 dilatation of other vessels, and therefore with a somewhat di- 

 minished general blood supply. 



4. Puncture of the floor of fourth ventricle or mechanical irritation 



of the superior cervical ganglion of the sympathetic, possibly 

 from the production of dilatation of the renal arteries. 



B. Secretion of urine may be diminished 



a. By diminishing the general blood-pressure; by 



1. Diminution of the force or frequency of the heart-beats. 



2. Dilatation of capillary areas other than that of the kidney. 



3. Division of spinal cord below the medulla, which causes dilata- 



tion of general abdominal area, and urine generally ceases 

 being secreted. 



b. By increasing the blood-pressure, by stimulation of the spinal cord 



below the medulla, the constriction of the renal artery, which follows, 

 not being compensated for by the increase of general blood-pressure. 



c. By constriction of the renal artery, by stimulating the renal or 



splanchnic nerves, or the spinal cord. 



Though the quantity of urine secreted corresponds closely with the 

 local blood-pressure, it must be stated that it is more directly dependent 

 on the quantity of blood flowing through the kidney in a given unit of 

 time. Under normal conditions increased blood-pressure and increased 

 blood-flow go hand in hand. But the local pressure may be enormously 



* Modified from Foster. 



