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Renal Clearance

What factors influence the concentration of urine? Urine contains water, nitrogenous wastes, and salts. The concentration of urine can vary considerably within our species and much more widely when we compare different species of animals. The variation in concentration depends on the structure of the kidney and on the environment the organism is experiencing. If protein or salt intake is high or if water intake is low then the urine produced will be more concentrated. If water intake is high then the urine produced will have a low concentration. Chemicals such as caffeine and alcohol can reduce the ability of the nephron to diffuse water back into the blood. These chemicals result in high volumes of urine with low salt and urea concentrations.

Animals that have diets with restricted amounts of water and/or a high salt intake often have adaptations to produce highly concentrated waste material. Desert mammals often have very long loops of Henle to maximize water reabsorbance. Birds and reptiles excrete waste in the form of uric acid in a solid or semisolid form that contains very little water. In birds and reptiles the water is reabsorbed outside of the kidney.

View the animation below, then complete the quiz to test your knowledge of the concept.

1Which of the following does not enter into the calculation for renal clearance?
A)glomerular filtration rate of the waste.
B)the volume of the blood filtered.
C)the amount of waste added by tubular secretion and reclaimed by tubular reabsorption.
D)the rate of urine production.
E)the amount of waste in the urine.

2The units for renal clearance are...

3Which of the following is true about inulin?
A)some inulin filtered by the glomerulus is reabsorbed by the peritubular capillaries.
B)all inulin is either filtered by the glomerulus or secreted by the peritubular capillaries.
C)inulin is removed from the peritubular capillaries by tubular secretion.
D)all inulin filtered by the glomerulus remains in the renal tubule and appears in the urine.
E)most inulin filtered by the glomerulus is reabsorbed by the peritubular capillaries.

4Renal clearance is the volume of blood plasma from which a particular waste is completely removed in one minute.

5Inulin is freely filtered by the juxtaglomerular device.

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