Elimination Of Urine

Urine from the collecting ducts flows through the renal pelvis and into a narrow tube called a ureter (yoo-REET-uhr). A ureter leads from each kidney to the urinary bladder, a muscular sac that stores urine. Muscular contractions of the bladder force urine out of the body through a tube called the urethra (yoo-REE-thruh). Locate the ureters, urinary bladder, and urethra in Figure 48-18.

At least 500 mL (17 oz) of urine must be eliminated every day because this amount of fluid is needed to remove potentially toxic materials from the body and to maintain homeostasis. A normal adult eliminates from 1.5 L (1.6 qt) to 2.3 L (2.4 qt) of urine a day, depending on the amount of water taken in and the amount of water lost through respiration and perspiration.

figure 48-18

Analyzing Kidney Filtration

Materials disposable gloves, lab apron, safety goggles, 20 mL of test solution, 3 test tubes, filter, beaker, 15 drops each of biuret and Benedict's solution, 2 drops IKI solution, 3 pipets, wax marker pen

Procedure

1. Put on your gloves, lab apron, and safety goggles.

2. Put 15 drops of the test solution into each of the test tubes. Label the test tubes "Protein," "Starch," and "Glucose."

3. Add 15 drops of biuret solution to the test tube labeled "Protein." Record your observations.

4. Add 15 drops of Benedict's solution to the test tube labeled "Glucose." Record your observations.

5. Add two drops of IKI solution to the test tube labeled "Starch." Record your observations.

6. Discard the tested solutions, and rinse your test tubes as your teacher directs.

7. Pour the remaining test solution through a filter into a beaker. Using the test solution from the beaker, repeat steps 3-5.

Analysis Which compounds passed through the filter paper? If some did not, explain why. How does the filtration of this activity resemble the activity of the kidney?

figure 48-18

Urine travels from each kidney through a ureter to the urinary bladder, where it is stored until it is eliminated from the body through the urethra.

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