KIDNEY REGULATION OF OSMOLARITY
Urinalysis.doc 30 November 2008
One of the kidney’s main functions is to regulate the osmolarity of body fluids at around
300mOsm per liter. In these experiments, the kidneys will be presented with an excess water
and/or salt load and the response will be monitored by measuring the volume and concentration
of the urine produced.
Overview of Lab:
1. Empty bladder 2 hrs before lab, and note the time.
2. When lab period begins, collect bladder contents, label as “control”, and
3. Drink test solution within 5 minutes.
4. Analyze “control” urine sample for volume and salt conten.
5. Collect urine at 30 minute intervals to measure volume and salt content.
6. Determine the percentage of the water and/or salt intake has been excreted during our
lab.
1. Drink plenty of water on the day of the experiment. Avoid eating or drinking caffeine or
theophylline (all soft drinks, tea, chocolate). EMPTY YOUR BLADDER ONE OR TWO
HOURS BEFORE THE LABORATORY BEGINS and RECORD THE EXACT TIME.
Do not save this urine sample. It is not necessary to measure the volume of this sample.
2. Upon entering the laboratory, each student will take a urine collection bottle to the restroom
and void into the bottle, emptying the bladder completely. Record the exact time. This sample
will be designated as “control” urine. Take the specimen back to the lab and label. You will
analyze this control sample after you have consumed the experimental solution.
3. After collecting and labeling the “control” specimen, each student will return to the laboratory
and immediately drink one of the following solutions as quickly as possible. You and your lab
partners should agree on who will drink which solution.
800 ml of distilled water
800 ml of water plus 7 grams of NaCl
80 ml of water plus 7 grams of NaCl.
These solutions are safe for humans with normal healthy kidneys. Do not drink one of the
solutions containing salt if you have blood pressure problems or if you are on medications that
might be affected by water or salt loading. You may elect not to participate in these
experiments. Once you have consumed the test solution, you may not drink anything until the
last urine sample is collected at about 150 minutes after drinking the test beverage.
4. Every 30 minutes after drinking the solution, each student will empty the entire bladder into a
clean collection bottle. If unable to void, retain the urine in the bladder until the next 30 minute
collection time, and adjust your calculations accordingly.
5. Analyze the urine from each collection, including the “control” for:
a) Volume: Measure the total volume with a graduated cylinder.
Express as ml/min excreted. (This is why it is important to know the time interval
between specimen collections.)
b) NaCl concentration:
i) Place 1ml of urine into a test tube.
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