CHAPTER XVII 1 

 THE URINARY SYSTEM 



The Kidney 



The kidney is a compound tubular gland. It is enclosed by a 

 firm connective-tissue capsule, the inner layer of which contains 

 smooth muscle cells. In many of the lower animals and in the human 



foetus, septa extend from the cap- 

 sule into the gland, dividing it 

 into a number of lobes or renculi. 

 In some animals, e.g., the guinea- 

 pig and rabbit, the entire kidney 

 consists of a single /o5e (Fig. 221). 

 In the adult human kidney the 

 division into lobes is not complete, 

 the peripheral parts of the differ- 

 ent lobes blending. Rarely the 

 foetal division into lobes persists 

 in adult life, such a kidney being 

 known as a "lobulated kidney." 



On the mesially directed side of 

 the kidney is a depression known 

 as the hilum (Fig. 221). This 

 serves as the point of entrance for 

 the renal artery and of exit for the 



Fig. 221. —Longitudinal Section renal vein SiUd Ureter . 

 Through Kidney of Guinea-pig, includ- ^ cprtinn t Hi'vi'm'nn af fhp 



ing hilum and beginning of ureter. X5. ^^ section, a QU ISlon 01 tne 



(Technic I, p. 338.) a, Pelvis; 6, papilla; organ into two zones is apparent 



c, wall of pelvis; d, ureter; e, ducts of , . , 



BeUini;/, cortical pyramids; g, medullary tO the naked eye (rigS. 221 and 



rays; h, cortex; /, medulla; j, renal cor- 322). The OUter ZOne Or COrtCX 



puscles. ^ 



has a granular appearance, while 

 the inner zone or medulla shows radial striations. This difference 

 in appearance between cortex and medulla is mainly due, as will be 

 seen subsequently, to the fact that in the cortex the kidney tubules 

 are convoluted, while in the medulla they run in parallel radial lines 

 alternating with straight blood-vessels. The medullary portion of 



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