1266 



THE UKO-GENITAL SYSTEM. 



Pars convoluta 



Pars radiata 



th e p kidne e y 0f 

 convolute 



lum renis 

 (glomerulus) 

 Arciform 

 arteries 



Arteriolse 

 rectse 



Collecting 

 tube 



Loop 01 

 Henle 

 Efferent 

 glomerular 

 vessel 

 Afferent 

 glomerular 

 vessel 

 Glomerulus 



with will appear as isolated streaks directed from the base of the pyramid towards 

 the surface of the kidney, and separated from one another by narrow strips, or 

 intervals, of the convoluted part. On the other hand, in sections made at right 

 angles to the axis of a pyramid, or cutting this axis obliquely, the convoluted 



portion of the cortex presents the 

 appearance of a continuous net, 

 the meshes of which are occupied 

 by the radiate parts, and these 

 latter now exhibit a circular or 

 oval outline. In a similar manner 

 interiobuiar sections through the bases of the 

 Corpuscu- pyramids differ much in the -appear- 

 ances they afford according to the 

 plane in which they are cut. 



Kidney Tubules. The glandular 

 substance of the kidney is composed 

 of a vast number of minute tubules, 

 called tubuli renales or uriniferous 

 tubules, all of which have an exceed- 

 ingly complicated course. The wall 

 of each tubule consists throughout of 

 a basement membrane and of an 

 epithelial lining, but the lumen of 

 the tubule and the character of the 

 epithelium vary much in its different 

 parts. Every tubule begins in a thin- 

 walled spherical dilatation, known as 

 capsula glomeruli (O.T. Bowman's 

 capsule), in which a complicated loop 

 of capillary blood-vessels is contained. 

 The tuft of capillaries is covered by a 

 In the middle part ; of the figure the course of one .of the kidney reflection o f the delicate wall of the 

 tubules is indicated, and in the lateral parts the disposition , . . 



of the larger arteries. A, Cortex; B, Basal portion; capsule, and IS, as it were, mvagmate. 

 and C, Papillary portion of pyramid. into the capsule (Fig. 986). 



The diagram at the right-hand side of the lower part of the capsules with their enclosed capillaries 

 figure illustrates the connexions of the structures com- are called the corpuscu l a ren is or kid- 

 posing a renal corpuscle. ney corpusclegj and are all placed 



in the convoluted portion of the kidney cortex, where they may be recognised as minute 

 red points just visible to the unaided eye and best marked when the renal vessels are con- 

 gested. The part of the tubule leading from the capsule first convoluted tubule is very 

 tortuous, and lies within the convoluted part of the cortex. Passing from the convoluted 

 part, the tubule enters a radiate part, in which its course becomes less complicated, and 

 here it receives the name of spiral tubule. From the radiate part the tubule enters the 

 basal portion of the pyramid, and, diminishing in diameter, it pursues a straight course 

 towards the apex of the pyramid, forming the so-called descending limb of Henle's loop. 

 Within the apical portion of the pyramid the tubule suddenly bends upon itself, forming 

 the loop of Henle, and reversing its direction, it passes back again through the base of the 

 pyramid into the radiate part of the cortex as the ascending limb of Henle's loop. This 

 ascending limb exhibits a slight spiral twisting. Leaving the radiate part, the tubule 

 once more enters the convoluted part of the cortex, where its outline becomes so uneven 

 that the name irregular tubule is applied to it. While still within the convoluted part, 

 its contour having acquired a more uniform appearance, the tubule receives the name of 

 second convoluted tubule ; this latter finally ends in a short junctional tubule, which passes 

 back into a radiate part of the cortex and joins a collecting tube. Each collecting tube 

 receives numerous kidney tubules, and pursues a straight course through the radiate part 

 of the cortex and the pyramid. Finally, several collecting tubes, uniting together, form 

 an excretory tube, which opens on the summit of a renal papilla into a calyx of the ureter 

 by one of the foramina papillaria already described. In microscopic sections the various 

 portions of the kidney tubule may be distinguished by the position which they occupy and 

 by the character of the lining epithelium. 



Connective Tissue of the Kidney. The tubules and the blood-vessels forming tl 

 substance of the kidney are all united together by a very small amount of connective 



Capsule 



FIG. 986. DIAGRAMMATIC REPRESENTATION OF THE 

 STRUCTURES FORMING A KIDNEY LOBE. 



