THE UROGENITAL SYSTEM 



305 



functional units of the kidney. In the cortex, the renal tul)ules are 

 convoluted and connected with knots of blood capillaries, the glomeruli. 

 The pyramids, on the other hand, consist chiefly of straight collecting 

 tubules, which open into the renal pelvis by numerous apertures lying 

 at the ends of the papillae. 



Each renal tubule begins in a spherical capsule surrounding a glomeru- 

 lus, the combined structure being known as a renal corpuscle, (Fig. 271) 

 The swollen termination of a tubule is a Bowman's capsule (Fig. 64). The 

 portion of the tubule adjacent to the corpuscle is convoluted and thickened 



PROXIMAL CONVOLUTED TUBULE. 

 DISTAL CONVOLUTED TUBULE.^ 



ARCUATE ARTERY- 

 ARCUATE VEIN 



COLLECTING TUBULE PAPILLARY DUCT' 



EXCRETORY TUBULE 



CALYX-Y- B. I 



Fig. 271. — A diagram of the finer structure of a kidney. A is a section of the entire 

 kidney showing the contrast between cortical and medullary fegions. The relations 

 of the chief arteries and veins are indicated. B is a reconstruction of a single tubule, 

 showing its relations to the blood and the pelvis of the kidney. (Reproduced in modi- 

 fied form from "The Human Body " by Dr. Logan Clendening, (Copyright 1927, 1930 by 

 Alfred A. Knopf, Inc.) by permission of and special arrangement with Alfred A. Knopf, 

 Inc., authorized publishers.) 



and is known as the proximal convoluted part of the tubule. Passing into 

 one of the pyramids, the tubule becomes slender and straight and is 

 known as the descending limb of Henle's loop. Bending sharply, it 

 forms the ascending limb of Henle's loop, and returns to the cortex, where 

 it becomes convoluted again, the distal convoluted portion, and unites 

 with a collecting tubule. As an element in a cortical ray, each collecting 

 tubule passes from the cortex into a pyramid. Usually a group of col- 

 lecting tubules unite and open by a common aperture into the pelvis 

 of the ureter. There is evidence that the secretion of urine takes place 

 chiefly in the renal corpuscles and in the convoluted portions of the 

 tubules, while the limbs of Henle's loop are chiefly absorptive in function. 

 The high degree of concentration of the constituents of urine leads physi- 



