PART VI 



THE EXCRETION OF URINE 



CHAPTER I. VIII 



THE EXCRETION OF URINE 



By R. <;. Pear< i. B.A., M.D. 



It will be advisable to introduce the aubjecl by a brief review of the 

 essentia] structural features of the kidney, in so far us they apply to 

 the excretory function of the organ. 



STRUCTURE OF THE KIDNEY 



The ki.lncy is mainly derived from the surface of the celom, and is 

 mesodermal structure. In this respecl it differs from ordinary ting 



glands, which are endodermal in origin. Jusl as it is more or 

 unique in its developmenl as a gland, it is also unique in its method 

 of functioning. The physiological theories of the mechanism of urinary 

 secretion are closely related to the highly characteristic structure of 

 kidney. For this reason a brief Burvey "t' the structure of the different 

 parts of the ariniferous tubules ami the epithelial cells with which ti 

 are lined, is advisable. 



The ariniferous tubule, which is the secreting unit of the kidn< 

 takes its origin in the capsule of Bowman, which may l>e likened '■ 

 hollow sphere of very delicate epithelium, one side of which is 

 invaginated by a very much convoluted capillary mass, the glomerulus. 



The capsule opens up l'.\ a narrow twisted neek into a luhule. which is 



rather tortuous in the cortex the proximal convoluted tubule), hut soon 

 takes a sharp descending course iii the medulla towards the pelvis of the 

 kidney, and doubles back (loop of Henle) in a straight again ' 



the cortex, where it again makes a twisted course the distal convoluted 



tubule), ami terminates in a collecting tubule, which, uniting with other 



tubules, collects the urine and Conducts it to the pelvis of the kidney. 

 The capsule is lined with very thin epithelial eel the 



capillaries coniprisiii'_ r the glomerulus. The proximal and distal tubll 



