4. If you were attempting to tell whether an animal produces its primary urine by ultrafiltration or secretion, what measurements would you make on the primary urine? If your measurements indicated that ultrafiltration might be occurring, what other types of measurements would you make to determine whether physical and physicochemical conditions favorable to ultrafiltration exist? Explain. 9. Drugs that increase urine flow (diuretic drugs) are often employed in the treatment of hypertension (high blood pressure) or other disease states. Three physiological categories of such drugs are ones that (i) function as loop diuretics, (ii) inhibit the action of aldosterone, and (iii) block Na+ channels in the collecting ducts. Explain why each of these categories would be expected to increase Na+ excretion and urine flow. (Hint: Rereading the section on hormones at the end of Chapter 28 might prove helpful.)