562 



VERTEBRATE LIFE AND ORGANIZATION 



Efferent 

 arberi'ole 



Afferent 

 arteriole. 



Bowman's 



capsule - 



Proximsd 

 convoluted tubule 



Intralobular 

 pZirt of 

 renal artaxy 



Distal 



convoluted 



tubule 



Collecting 

 tubule 



Intralobular pJii^t 

 of renal vein. 



Henle's loop 



Figure 28.2. A diagram of the mammalian nephron. (^From Campbell.) 



28.2) is known as Bowman's capsule. It is a hollow ball of squamous 

 epithelial cells, one end ot which has been pushed in by a knot of 

 capillaries called a glomerulus. Bowman's capsule and the glomerulus 

 constitute a renal corpuscle. The rest of the nephron is a tubule largely 

 composed of cuboidal epithelial cells, and subdivided in mammals into 

 a proximal convoluted tubule, a loop of Henle and a distal convoluted 

 tubule. A collecting tubule receives the drainage of several nephrons 

 and leads to the renal pelvis, an expansion within the kidney of the 

 proximal end of the ureter (Fig. 28.3). The collecting tubules and the loops 

 of Henle lie toward the center, in the medulla of the kidney; the other 

 parts of the nej)hron occur in the outer part, or cortex, of the kidney. 



Glomerular Filtration. The wall of Bowman's capsule is a semi- 

 permeable membrane, and small molecules in the glomerular capil- 

 laries should pass through it readily. By carefully inserting a micro- 

 pipette into a Bowman's capsule in a frog's kidney, and drawing off 

 and analyzing a sample of the contents (the glomerular filtrate), Dr. A. 

 N. Richards of the University of Pennsylvania demonstrated that this 

 is indeed the case. Only the blood cells, fats and plasma proteins are 

 held back in the capillaries. The other plasma components are found 

 in the glomerular filtrate in nearly the same proportion as in the 

 plasma. Other experiments have shown that this is true for glomerular 

 filtration in mammalian nephrons too. 



