THE URINARY ORGANS 321 



voluted tubules and straight tubules, and is returned 

 through the renal vein to the venous system. 



The Urine. The urine is the fluid by which the 

 end-products resulting from tissue metabolism are 

 excreted or, literally speaking, are secreted by the 

 kidneys from the body. The phenomena, however, is 

 essentially the same as takes place during secretion of 

 fluids by the body cells. It must be remembered that 

 to perform work, create energy, nourish, and develop 

 the body from birth to death, food is necessary. The 

 body receives its nourishment from the food we eat, and 

 the essential constituents of the same are used by the 

 tissues to perform the various and complex processes 

 necessary to carry on and maintain the normal physio- 

 logical functions of the human body. Were this 

 intake of food not used or eliminated, there would 

 be a general interference of the normal functions of 

 cell life, but as we have demonstrated in previous 

 chapters, it is used and then undergoes changes, the 

 residue forming products which must be eliminated, 

 and the urine is the fluid by means of which this 

 occurs. 



Normal urine is a pale yellow or amber-colored 

 fluid, with an aromatic odor and acid reaction. Its 

 specific gravity is 1.020, but varies between 1.015 to 

 1.025. It is usually transparent, except when mucus, 

 phosphates, urates, render it cloudy in appearance. 



The color varies from a pale yellow to a reddish 

 brown, dependent upon the physiologic processes 

 occurring prior to elimination. Its color is due to 

 the presence of a pigment-urobilin, urochrome, uro- 

 erythrin, derived from the bile pigments absorbed 

 from the liver or alimentary canal. The acidity of 

 the urine is due to the presence of acid phosphates 

 of sodium and calcium. Urine is usually acid in the 

 morning, alkaline or neutral following digestion. 



The quantity of urine passed in twenty-four hours 

 amounts to 40 to 50 ounces (2| to 3 pints 2 ounces). 

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