SECRETIONS 



107 



from the pelvis to the circumference (h); into these the smallest 

 veins of the medulla also empty (/). e 



3 . Conditions of renal secretion. 



(a) The quantity of urine secreted 

 depends upon the blood pressure in 

 the renal artery; it decreases when, 

 e.g. by bleeding, the blood pressure 

 decreases; it increases when, e.g. by 

 ligaturing of other blood vessels, the 

 pressure in the renal arteries is in- 

 creased. 



Partial closure of the renal vein (venous 

 istatis) decreases renal secretion, whicn 

 appears to be due to the compression of 

 the urinary tubules by the strongly dilated 

 capillaries and smaller veins. 



(b] The renal secretion ceases for 

 a long time when the supply of blood 

 to the kidneys has been cut off by 

 compression of the renal artery for 

 but a few minutes. 



(c) There are certain substances 

 which, taken into the body, increase 

 renal secretion, e.g. water, urea, so- 

 dium chloride, sodium nitrate, caffein, 

 grape-sugar. The action of these 

 diuretics still takes place when the 

 renal secretion has been entirely 

 stopped by a too low blood pressure. 

 On the other hand, there are sub- 

 stances, e.g. atropin, which inhibit 

 renal secretion. 



(d} Concerning the effect of the 

 nervous system upon renal secretion 

 leaving out of consideration the in- 

 direct influence of the vaso-motor nerves nothing is yet 

 known. 



Notwithstanding the fact that renal secretion depends 



NEYS. 



