i6o 



PHYSIOLOGY FOR BEGINNERS 



is the removal from the blood of substances which are to be 

 discharged from the body. There are three chief excretory 

 organs, the lungs, the kidneys, and the skin. Of the three 

 chief waste products, the carbonic acid is removed from the 

 blood by the lungs, the urea and other nitrogenous waste 

 substances by the kidneys, and water, with other substances, 

 by the skin and by the lungs and kidneys as well. The lungs, 

 besides removing carbonic acid from the blood, supply oxygen 

 to the blood, while the kidneys and the skin supply nothing. 



v,cr 



The Urinary Organs 



The kidneys situated in the abdomen, one on each side 

 of the lumbar region of the verte- 

 bral column are dark-red organs 

 4 inches long and 2j, inches across, 

 and are flattened so that they are 

 not much more than an inch in 

 thickness. The inner edge of each 

 kidney, that is, the edge next to the 

 vertebral column, is concave, while 

 the outer edge is convex. The 

 concavity at the middle of the inner 

 edge is called the hilus, and there 

 the arteries enter the kidney and 

 the veins leave it. The arteries 

 are derived from a single vessel 

 one for each kidney which 

 springs from the aorta. The 

 veins unite into a single vein from 

 each kidney, and this empties its 

 blood into the inferior vena cava. 

 From the hilus of each kidney 

 there proceeds another vessel, the 

 ureter. The ureters are narrow 

 whitish-looking tubes, about 15 

 inches long. They pass to the 

 bladder. The bladder, situated in 

 the pelvic cavity, or the lowest part 



FIG. 72. The urinary organs. 

 A", kidneys ; Ur, ureters ; Bl, bladder ; 

 i, openings of ureters, and 2, 

 opening of urethra in the bladder ; 

 A a, aorta; /'.(."./., inferior vena 

 cava. 



