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TEXT-BOOK OF PHYSIOLOGY. 



ulus. These capillaries, however, do not anastomose, but soon reunite to 

 form an efferent vessel the caliber of which is less than that of the afferent 

 artery. In consequence of this, there is a greater resistance to the outflow 

 of blood than to the inflow, and therefore a higher blood-pressure in the 

 glomerulus than in capillaries generally. The relation of the glomerulus to 

 the tubule is important from a physiologic point of view. As stated above, 

 the glomerulus is received into and surrounded by the terminal expansion 

 or capsule of the tubule. This capsule, formed by an indentation of the 

 terminal portion of the tubule, consists of two walls, an outer one consisting 

 of an extremely thin basement membrane, covered by flattened epithelial 

 cells, and an inner one consisting apparently only of flattened epithelium 

 which is reflected over and closely invests the glomerular blood-vessels 

 (Fig. 218). The blood is thus separated from the interior of the capsule 

 by the epithelial wall of the capillary and the epithelium of the reflected wall 



of the capsule. During the periods 

 of secretor activity the blood-vessels 

 of the glomerulus are filled with blood 

 to such an extent that the sac cavity 

 is almost obliterated. After its exit 

 from the capsule the efferent vessel 

 of the glomerulus soon again divides 

 and subdivides to form an elaborate 

 capillary plexus which surrounds and 

 closely in vests the convoluted tubules. 

 From this plexus as well as from the 

 plexus which surrounds the straight 

 tubules veins arise which pass toward 

 and empty into veins at the base 

 of the pyramids. The renal vein 

 formed by the union of these latter 

 veins emerges from the kidney at the 

 hilum and finally empties into the 

 vena cava inferior. 



The nerves of the kidney are de- 

 rived directly from small ganglia near 



the semi-lunar ganglion. From this origin they pass through the renal plexus 

 and follow the course of the blood-vessels to their termination. Experi- 

 ment has shown that these nerves are both vaso-constrictors and vaso- 

 dilatators. 



The Renal Duct. The excretory duct of the kidney, the ureter, is a 

 musculo-membranous tube about 5 mm. in diameter when distended, 30 cm. 

 in length, and extends from the hilum to the base of the bladder into which 

 it empties. The upper extremity is expanded and within the renal sinus 

 becomes irregularly branched, giving rise to a number of short tubes, called 

 calyces, each of which embraces the apex of a Malpighian pyramid. The 

 interior of the expanded portion of the ureter is known as the pelvis. The 

 wall of the ureter consists of a mucous membrane, a muscle coat, and an 

 external fibrous investment. 



FIG. 218. SCHEME OF THE RENAL OR MAL- 

 PIGHIAN- CORPUSCLE, i. Interlobular artery. 

 2. Afferent vessel. 3. Efferent vessel. 4. Outer 

 wall. 5. Inner wall. 6. Glomerulus. 7. Neck 

 of tubule. (Stohr.) 



