2O4 



THE UROGENITAL SYSTEM 



verted into vesicles with eccentrically placed lumina. The vesicle elon- 

 gates, its thicker outer wall forming an S-shaped tubule which unites with 

 a collecting tubule, its thin inner wall becoming the capsule (Bowman's) 

 of a renal corpuscle. The uriniferous tubules of the adult kidney have a 

 definite and peculiar structure and arrangement (Fig. 213 A). Beginning 

 with a renal corpuscle, each tubule forms a proximal convoluted portion, a 

 \3-shaped loop (of Henle) with descending and ascending limbs, a connecting 



Arch of collecting tubule 

 A 



Arch of collecting tubule 



Distal convoluted tubule 



Stoerck's loop 



Proximal convoluted tubule 



Connecting piece 

 Glomerulus 



Bowman's capsule 



Arch of collecting tubule 

 Proximal convoluted tubule 



Distal convoluted tubule 

 Connecting piece 

 Glomerulus 



Bowman's capsule 

 Stoerck's loop 



FIG. 213. Diagrams showing the differentiation of the various parts of the uriniferous 

 tubules of the metanephros (based on the reconstructions of Huber and Stoerck): A, From an 

 adult human kidney; B, C, from human embryos. 



piece, which lies close to the renal corpuscle, and a distal convoluted portion 

 continuous with the collecting tubule. These parts are derived from the 

 S-shaped anlage, which is composed of a lower, middle and upper limb. 

 The middle limb, somewhat U-shaped, bulges into the concavity of Bow- 

 man's capsule (Fig. 213 B). By differentiation the lower portion of the 

 lower limb becomes Bowman's capsule, ingrowing arteries forming the 

 glomerulus (Fig. 213 B, C). The upper part of the same limb by enlarge- 

 ment, elongation, and coiling becomes the proximal convoluted tubule. 

 The neighboring portion of the middle limb forms the primitive loop (of 

 Stoerck) ; the base of the middle limb gives rise to the connecting piece, 

 and the rest of it, with the upper limb of the S, forms the distal convoluted 





