Kidney regulation of pH and osmolarity






This lab will allow you to test various hypotheses about how kidneys maintain homeostasis through urine production.  You and your peers will be consuming liquids with different properties and in different volumes.  You will then measure indicators of the kidneys’ responses to these fluids.




Prior to beginning the experiment, each person should collect their urine in a clean container.  You will make the same measurements on it as you will for later samples.


Consume ONE of the following substances. Each person only eats or drinks one thing.  




Your Predictions about hormone levels and urine composition

1000 mL

Tap water



TUMS antacids


500 mL

Cranberry juice (acidic)


500 mL







DO NOT CONSUME ANYTHING THAT MAY CAUSE YOU HEALTH PROBLEMS.  IF YOU ARE UNSURE, ASK THE INSTRUCTOR.  Do not force yourself to drink or eat too rapidly, but go as quickly as you comfortably can.  After you finish, note the time.  Your subsequent samples will be taken every 30 minutes after this. If you are unable to urinate at any particular time, wait until the next 30 minute interval.  If you are drinking large volumes, you may have to void into a larger container. Reuse the sample containers.



For the people who took TUMS and drank cranberry juice, you may also see an effect on respiration. What do you expect to happen? Decide how you will measure respiration and test your hypothesis.


Since several people took in a volume of water, it may affect their blood volume and baroreceptor reflex. What do you expect this to do to resting heart rate? Decide how you will measure heart rate and test this hypothesis.


For each urine sample, measure and record the following data:


1.      Time of collection

2.      Volume (ml)

3.      Color (clear, pale yellow, medium yellow, or dark yellow)

4.      pH (Use the pH meters or papers provided)

5.      Specific gravity (a measurement of solute concentration)


Specific gravity is measured using the dipsticks or a urinometer.  To use a urinometer, fill the tube about 2/3 full, then gently place the float in the cylinder.  If it doesn’t float at all, add more urine and try again.  Don’t overfill the tube or the urine will overflow when you add the float.  Read the specific gravity at the urine meniscus.  Note that the numbers increase DOWN the scale because liquids with more dissolved solutes will cause the float to “ride higher”.


Urine Specific Gravity Calculation


If you don’t have enough urine to fill a urinometer, you must record the initial volume of urine and then dilute it with distilled water until you have enough to make the urinometer float.


The Specific Gravity of the initial urine sample can be calculated as follows:


SGi =  [(SGf)(Vi + Va)]Va




SGi = the specific gravity of the initial urine


SGf = the specific gravity of the diluted sample


Vi = the volume of the initial urine


Va = the volume of distilled water added to the urine



The urinometers are not very sensitive, so DO NOT DILUTE THE URINE any more than the absolute minimum necessary or the value you get will be too small for you to read.



Clean items as soon as you use them. Keep the food and beverages out of the urine area and vice versa.  Clean any surface on which you have set a urine container.  Be very careful not to drop the urinomometer floats when you’re cleaning them!


You may wish to use this table for recording your data.  You will need to exchange data with others to answer your hypothesis.






30 mins.

60 mins.

90 mins.

120 mins.

150 mins.






















Specific gravity














Heart rate








1. Which of these treatments caused an increased ADH secretion? How do you know?





2. Which of these treatments caused decreased aldosterone secretion? What’s your reasoning?





3. Were your hypotheses about respiration supported? Explain.






4. Were your hypotheses about heart rate supported? Explain.