CHAPTEK XIV 

 DIURETICS 



Synonyms. Hydragogues, litholytics, lithothryptics 



Diuretics are agents that increase the flow of urine. Diuresis 

 is a copious flow of urine. They may produce this action : 1. By 

 increasing the general arterial pressure; 2. By dilating the vessels 

 of the kidney; 3. By increasing the water content of the blood (salt 

 action) ; 4. Directly stimulating the renal epithelium; 5. Me- 

 chanically. 



(1) General circulatory stimulants. The representative diuret- 

 ics of this class are: 



Digitalis Convallaria 



Strophanthus Apocynum 



Squill 



A portion of the diuretic action of squill is due to its action on 

 the renal epithelium. 



(2) Dilators of the renal vessels. Local dilatation of the vessels 

 of the kidneys, if not accompanied by a reduction of blood pressure, 

 increases the secretion of urine (vasodilators). 



(3) Salines. Salts that are readily absorbed from the diges- 

 tive tract cause diuresis in the following manner : When diffusible 

 substances find their way into the blood, whether directly by injection 

 or absorption from the digestive tract, the flow of urine is increased. 

 Bodies such as sodium chloride, potassium nitrate, potassium acetate, 

 urea, and sugar produce this effect in a typical manner. The pri- 

 mary action of salts, no matter in what concentration or how in- 

 troduced, is to increase the liquid part of the blood. Isotonic and 

 hypotonic solutions pass directly into the blood but hypertonic first 

 draw liquid from the tissues and assume an isotonic condition, so 

 that the effect becomes the same as if an isotonic solution had been 

 directly injected into the blood. This causes an increased amount 

 of fluid in the blood and a condition of hydremic plethora results. 



In hydremic plethora the blood becomes less viscid and arterial 

 pressure slightly raised. These factors, together with the swollen 

 volume of blood, tend to produce a rapid blood flow and as a conse- 

 quence to form transudation of the excess of fluid through the 

 capillaries. The kidney capillaries are the ones by which the body 



rids itself of excessive fluid. Therefore if they are functioning 



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