EXCRETION. 



427 



pyramids branches of the arteries form an anastomosing plexus. 

 From this plexus vessels are given off, some of which follow the straight 

 tubules toward the apex of the pyramids, vasa recta, while others 

 enter the cortex and pass to its surface (Fig. 193). In the course of 

 the latter small branches are given off, each of which soon divides and 

 subdivides to form a ball of capillary vessels known as the glomer- 

 ulus. These capillaries, however, do not anastomose, but soon re- 

 unite 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 re- 

 sistance 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 glomer- 

 ulus to the tubule is im- 

 portant from a physiologic 

 point of view. As stated 

 above, the glomerulus is 

 received into and sur- 

 rounded 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 consist- 

 ing of an extremely thin 

 basement membrane, 

 covered by flattened epi- 

 thelial cells, and an inner 

 one consisting apparently FlG I94 ._ SC HEM E OF THE RENAL OR MAL- 

 only of flattened epithelium PIGHIAN CORPUSCLE, i. Interlobular ar- 



Which is reflected over and ter ^ 2 - Afferent vessel. 3. Efferent vessel. 



4. Outer wall. 5. Inner wall. 6. Glom- 



closely invests the glomer- e mlus. 7. Neck of tubule. (Stdhr.) 



ular blood - vessels (Fig. 



194). The blood is thus separated from the interior of the capsule 

 by^the epithelial wall of the capillary and the epithelium, of the re- 

 flected wall of the capsule. During the periods of secretory 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 invests the convoluted tubules. Froonlexus 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 pyra- 

 mid's. 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. 



