Endocrine Mechanisms 



761 



tubules. Parathyroidectomy is rapidly lethal; there is a rapid decline in blood 

 calcium and finally death in tetanus. 



The posterior lobe influences the rate of water loss through the kidneys.** 

 Destruction of this portion of the pituitary results in an increased urine flow 

 and an increase in the consumption of water by the organism (diabetes in- 

 sipidus). A hormone, the antidiuretic principle, is essential for the normal 

 extensive water resorption by the kidney tubules. 



The kidney, on reduction of its blood supply by any means, liberates a 

 globulin protein, renin, into the blood.^^**- ^^ Renin is a proteolytic enzyme 

 which acts on a serum globulin, hypertensinogen, converting it into a frac- 

 tion, hypertensin. Hypertensin, a powerful agent in elevating blood pressure 



prevents No* and Z\' 



Fig. 287. Diagram summarizing influences of hormones on maintenance of the normal 

 water and salt balance of the mammalian organism. 



within the animal, appears to be a protein derivative of polypeptide charac- 

 ter which is normally destroyed slowly in the blood stream by an enzyme, 

 hypertensinase. The production of renin by the kidney would therefore ap- 

 pear to be an adaptive reaction to assure the organism of sufficiently high 

 blood pressure to permit adequate kidney function. 



Most of the more irnportant influences of hormones on water and salt bal- 

 ance are diagrammatically portrayed in Figure 287. 



