The kidneys secrete an enzyme called renin that aids in the regulation of blood pressure.
A patient with advanced kidney disease is likely to be suffering from azotemia, which is an unusually high blood urea nitrogen (BUN) level.
A disease that results in an increase in the breakdown of muscle tissue would result in an increase in the presence of ammonia in the blood, which the liver would convert to urea and would then be excreted in the urine.