476 



TEXT-BOOK OF PHYSIOLOGY. 



The Histology of the Kidney. The kidney is composed of a connective- 

 tissue framework supporting secreting tubules, blood-vessels, lymphatics, 

 and nerves, all of which are directly connected with the removal of the urinary 

 constituents from the blood. The kidney is structurally a compound tubular 

 gland. If the apex of each pyramid be examined with a lens, it will present 

 a number of small orifices which may be regarded as the beginnings of the 

 uriniferous tubules. From this point the tubules pass outward in a straight 



y, but somewhat diverging 



I/ 1 ' manner toward the cortex, 



giving off at acute angles a 

 number of branches (Fig. 

 217). From the apex to the 

 base of the pyramids they 

 are known as the tubules of 

 Bellini. In the cortical por- 

 tion of the kidney the tubule 

 becomes enlarged and twist- 

 ed, and, after pursuing an 

 extremely convoluted course, 

 turns backward into the 

 medullary portion for some 

 distance, forming the ascend- 

 ing limb of Henle's loop; it 

 then turns upon itself, form- 

 ing the descending limb of 

 the loop, reenters the cortex, 

 again expands and becomes 

 convoluted, and finally ter- 

 minates in an ovoid enlarge- 

 ment known as Muller's or 

 Bowman's capsule, in which 

 is contained a small tuft of 

 blood-vessels the glomeru- 

 fas. Each tubule consists of 

 a basement membrane lined 



thrO ughout its entire extent 

 . , . , . ; p 



Labyrinth, or cortex proper. 2. Medulla, by epithelial Cells. I lie epl- 



thelium as Well as the tubule 

 . -L j 



FIG. 216. LONGITUDINAL SECTION THROUGH THE 

 KIDNEY, THE PELVIS OF THE KIDNEY, AND A NUMBER 

 OF RENAL CALYCES A. Branch of the renal artery. 

 U. Ureter. C. Renal calyx, i. Cortex, r. Medullary 

 rays. i". Labyrinth, or c 



2'. Papillary portion of medulla, or medulla proper, 

 2". Border layer of the medulla. 3, 3. Transverse sec- 

 tion through the axes of the tubules of the border layer. 

 4. Fat of the renal sinus. 5, 5. Arterial branches, different parts of its course. 

 *. Transversely coursing medulla rays. (Tyson, after j n fa Q ca p su l e the epithelium 



is flattened, lining not only 



the inner surface of the capsule but reflected over the blood-vessels as well. 

 This is known as the glomerular epithelium. In the convoluted portions of 

 the tubules the epithelium is cuboid, granular, and somewhat striated; in 

 Henle's loop it is more or less flattened. 



The Blood-vessels of the Kidney. The renal artery enters the kidney 

 at the hilum behind the ureter; it soon divides into several large branches 

 which penetrate the substance of the kidney between the pyramids and pass 



