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THE INTERNAL ENVIRONMENT OF THE BODY 



Part III 



Afferent 



orferiole 



To collecting 

 tubule 



Efferent 

 arteriole 



Region of 



convoluted 



tubules 



Blood from 



efferent 



arterioles 



Henle's 

 loop 



Fig. 14.6. Diagram of the general exchange of substances in the formation of 

 urine. During filtration all the components of the blood plasma pass into the 

 renal capsule except proteins. This includes water; urea; glucose; and various salts. 

 During reabsorption urea is concentrated in the kidney tubule and water and 

 glucose are reabsorbed in the blood. Salts may or may not be reabsorbed. 



It is estimated that about 45 gallons of blood are filtered per 24 hours in the 

 human kidneys. Of course this includes the same blood passing through the 

 glomeruli many times. The first filtrate is a very different fluid from urine. It 

 is probably like the watery urine of man's aquatic ancestors in which water 

 came through the skin and flooded into the body and was then filtered out of 

 the blood, creating the same kind of watery urine as that of present-day frogs. 



Here, stimulated by a hormone released from the pars nervosa of the pitui- 

 tary gland, about 99 per cent of all the sugar and the water is reabsorbed into 

 the blood as it passes through these capillaries at comparatively low pressure 



