MULTICELLULAR ANIMALS 



189 



blood and into the duct that drains the glomerulus. In the region 

 of the CONVOLUTED TUBULE Certain important salts and water are 

 resorbed back into the blood. The remainder of the contents are 

 carried along, and the duct joins with other ducts. These pass 

 through the medullary portion of the kidney and empty into a re- 

 ceptacle, termed the renal pelvis. From the renal pelvis a tube, the 

 URETER, leads downward to enter the base of the urinary bladder. 



ARTERY AND VEIN 



RENAL PAPILLA 



BOWMAN''^ CAPSULE 



COLLECTING 

 DUCT 



GLOMERULUS 



CONVOLUTED 

 TUBULE 



Fig. 132. — The essential excretory organs in the cortex of the human kidney, the 

 glomerulus, convoluted tubule, and collecting duct. Diagrammatic. 



Thus many hundreds of glomeruli and convoluted tubules are con- 

 stantly rectifying the blood, the resulting excretion accumulating in 

 the bladder, to be expelled through a short tube known as the 

 URETHRA. The more than a quart of urine that is excreted each 

 twenty-four hours is the sum of the excretory activity of all of 

 these small units. 



As the contents of the blood stream vary in health and disease, 

 so the constituents of the urine vary. It is thus possible to diagnose 

 disease by a chemical analysis of the urine, for characteristic changes 

 in the urinary constituents are symptoms of certain diseases. The 

 adjustment between blood constituents and the amount and nature 



