510 PHYSIOLOGICAL PROCESS OF URINARY SECRETION. 



amount of filtered urinary water. Injections of water directly into the 

 vessels, or the ingestion of considerable quantities of fluid, operates in 

 this direction. If the increase in blood-pressure exceeds a certain 

 level, albumin may even pass into the urine. Conversely, loss of water 

 in consequence of profuse sweating or diarrhea, or copious venesection, 

 as well as prolonged thirst, will cause diminution in the amount of 

 urinary secretion. The circumstance that the blood-pressure does not 

 rise constantly after free drinking is evidence of the functional activity 

 of the cells of the glomeruli, as is also the fact that the amount, of urine is 

 not increased after large transfusions. 



2. Diminution in the vascular capacity will operate in a similar 

 manner: contraction of the cutaneous vessels under the influence of 

 cold, stimulation of the vasomotor center or of considerable areas of 

 the vasomotor nerves, ligation or compression of arteries of large size, 

 envelopment of the extremities in tight bandages. Naturally the op- 

 posite conditions will be followed by a reduction in the amount of urine : 

 the influence of heat upon the skin to the point of redness and dila- 

 tation of the vessels, enfeeblement of the stimulation of the vasomotor 

 center, or paralysis of considerable areas of the vasomotor nerves. 



3. Increased cardiac activity, in consequence of which the tension 

 and the rapidity of the current in the arterial distribution are increased, 

 augment the amount of urine. Conversely, enfeeblement of the heart's 

 action (paresis of the motor nerves of the heart, disease of the heart- 

 muscle, valvular lesions) diminishes the amount of urine. Artificial 

 irritation of the vagi, in consequence of which, with slowing of the heart- 

 beats, the average blood-pressure fell in animals from 130 to 100 mm. 

 of mercury, with slowing of the pulse, was followed by a reduction in 

 the amount of urine to about one-fifth. At 40 mm. of aortic pressure 

 the secretion of urine ceases. 



4. The amount of urine secreted rises or falls with increasing or 

 diminishing fulness of the renal artery. Even moderate compression 

 of the artery in animals is followed by distinct reduction. 



Pathological. In the presence of fever, there is diminished fulness of the 

 renal vessels, with consecutive reduction in the amount of urine. The observation 

 is of especial significance for the pathogenesis of certain diseases of the kidney 

 that ligature of the renal artery, even if continued for only two hours, causes 

 necrosis of the epithelium of the urinary tubules. In case of arterial anemia of 

 longer duration, necrosis of the entire renal structure takes place. Ribbert found 

 the epithelial cells of the convoluted tubules greatly altered after compression of 

 the renal artery for some time. 



Most diuretic medicaments act in one or another of the directions 

 indicated. In case of increased diuresis, the lumen of the urinary 

 tubules is increased. 



The pressure within each afferent vessel must be relatively large, because (i) 

 the duplicate capillary arrangement in the kidney offers considerable resistance, 

 and because (2) the efferent vessel has a much narrower lumen than the afferent 

 vessel. In accordance with these facts, an excretion from the blood into the 

 capsules of the urinary tubules will take place from the capillary loops of the 

 glomerulus in consequence of the filtration-pressure. Dilatation of the afferent 

 vessels, as, for instance, from the action of the nerves upon the unstriated muscular 

 fibers, will increase the filtration-pressure; while constriction will diminish the 

 secretion. If the reduction in the pressure has become so considerable that the 

 blood-current in the renal vein is distinctly slowed, the secretion of urine begins 

 to diminish. It is a remarkable fact that occlusion of the renal veins completely 

 suppresses the secretion. C. Ludwig has concluded from this that the secretion 



