252 THE INTERNAL ENVIRONMENT OF THE BODY Part III 



Diuhetcs Mellitus. This is a condition in which sugar appears in the urine, 

 and is commonly called sugar diabetes. It is due to a defect in the glands 

 (called the isles of Langerhans) within the pancreas which secrete insulin. 

 Because of this the body is unable to use or to store carbohydrates and the 

 blood becomes loaded with sugar. So much sugar is filtered out of the glomeru- 

 lus that the kidney tubules are unable to reabsorb and return it to the blood, 

 consequently it passes out with the urine. 



Diabetes Insipidus. A less common form of diabetes in which too much 

 water is lost but no sugar is diabetes insipidus. The kidney tubules are unable 

 to reabsorb the water filtered out of the blood in the glomerulus. Experiments 

 upon animals have shown that the water-absorptive function of the kidney 

 tubules is dependent upon pitressine, a hormone secreted by the pars nervosa 

 of the pituitary gland (Chap. 15). The disease may be controlled by in- 

 jections of pituitary extract just as was first done experimentally in treat- 

 ing the similar disease in rats and dogs. 



Factors Influencing Urine Volume. The volume of blood is reduced if no 

 water or other fluid is taken, or blood may be lost by hemorrhage. In any such 

 case, the blood pressure is lowered in the kidneys; there is less filtration, and 

 less urine. Conversely, the more fluid that is taken, the greater the pressure in 

 the vessels, and the more urine produced. 



Diuresis, or increased production volume of urine, is caused by a variety of 

 conditions and substances, such as nervous stimuli affecting the circulation, 

 temperature affecting the circulation, and certain stimulants. A swim in cold 

 water drives blood into deep vessels, increases the blood pressure in the kid- 

 ney, and consequently the filtration of urine. Tea and coffee act as diuretics, 

 especially if a person is not accustomed to them. 



Other Organs that Eliminate Metabolic Wastes 



Gills and Lungs. The respiratory organs remove most of the carbon dioxide 

 brought to them by the blood. Molecules of it diffuse into the water through 

 the thin membrane of the gills, and into the air within the lungs through their 

 equally thin membranes. Water is carried from the lungs with the expired air; 

 in man it usually amounts to about a cupful in 24 hours. Molecules of other 

 substances are carried out with the breath; those of whiskey, gin, onions, and 

 garlic are among the most vivid of the broadcasts. 



Sweat Glands. These glands remove water, salts, traces of nitrogenous sub- 

 stances, and very little carbon dioxide. The amounts especially of water vary 

 greatly with metabolic activity. It is common expedence that the sweating 

 incident to high temperature and exercise stimulates drinking of quarts of 

 water. 



Liver. The liver may be said to deal with the raw waste products of metabo- 

 lism since it manufactures the urea from the nitrogenous waste released by all 



