248 



THI INIIRNAL ENVIRONMENT OF TUP. BODY 



Adrenal 



Part HI 



Posterior 

 vena cava 



Cut ends 

 of arteries 



Fig. 14.4. Human urinary system, ventral view. The kidneys are seen con- 

 nected with the great highways of the blood by the urinary arteries (white) and 

 the urinary veins (dark); the ureters open obliquely on the dorsal side of the 

 bladder. Half of the right kidney has been removed showing the pelvis, a cavity 

 through which the urine is delivered to the ureter; the cortex contains the renal 

 (or Malpighian) corpuscles, the functional units of the kidney; from them 

 bundles of collecting tubes extend toward the pelvis and deliver urine through 

 pores in each calyx. The adrenal glands adhere to the kidneys but have no direct 

 connections with them. 



All through their history the behavior of the kidneys has been modified by the 

 necessity of keeping water in or out of the body in order to create an adequate 

 internal environment. They have been highly important in the evolution of 

 fresh- and salt-water, and land vertebrates. 



Branches of the renal artery enter each kidney and there unite finally into 

 an arcuate artery that gives rise to the afferent arteries, one entering each 

 glomerulus. These divide into the capillaries of the glomerulus lying in the 

 renal capsule (Fig. 14.5). These capillaries join to form an efferent artery of 

 smaller diameter than the afferent one. After leaving the glomerulus the affer- 

 ent artery breaks into arterioles and capillaries that lace the walls of the 



