CHAPTER XLV. 



THE KIDNEY AND SKIN AS EXCRETORY ORGANS. 



Structure of the Kidney. The kidney is a compound tubular 

 gland. The uriniferous tubules composing it may be roughly 

 separated into a secreting part comprising the capsule, convoluted 

 tubes, and loop of Henle, and a collecting part, the so-called straight 

 or collecting tube, the epithelium of which is assumed not to 

 have any secretory function. Within the secreting part the epithe- 

 lium differs greatly in character in different regions ; its peculiarities 

 may be referred to briefly here so far as they seem to have a physio- 



D E F 



Fig. 298. Portions of the various divisions of the uriniferous tubules drawn from 

 sections of human kidney: A, Malpighian body; x, squamous epithelium lining the cap- 

 sule and reflected over the glomerulus; y, z, afferent and efferent vessels of the tuft; e. 

 iiuclei of capillaries; n, constricted neck marking passage of capsule into convoluted tu- 

 bule; B, proximal convoluted tubule; C, irregular tubule; D and F, spiral tubules; E t 

 ascending limb of Henle's loop; G, straight collecting tubule. (Piersol.) 



logical bearing, although for a complete description reference must 

 be made to works on histology. 



The arrangement of the glandular epithelium in the capsule with 

 reference to the blood-vessels of the glomerulus is worthy of special 

 attention. It will be remembered that each Malpighian corpuscle con- 

 sists of two principal parts, a tuft of blood-vessels, the glomerulus, and 

 an enveloping expansion of the uriniferous tubule, the capsule. The 

 glomerulus is an interesting structure (see Fig. 298, A). It consists 

 of a small afferent artery which after entering the glomerulus, breaks 

 up into a number of capillaries. These capillaries, although twisted 

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