NAME: Gina Tolomei

NAME: Gina Tolomei

LAB SECTION: 5-7pm

LAB 4: URINARY HOMEOSTASIS

I. INTRODUCTION

A chief physiological function of the body is to maintain homeostasis, or an essentially constant internal chemical and physical environment. Our body temperature is typically 32°C, our blood pressure averages 120/80, and we have about 65-105 mg/dl of glucose in our blood. These values can change for a variety of reasons. During exercise our blood pressure goes up as the heart works harder to pump oxygenated blood to our muscles. When we have a bacterial infection, our body temperature is elevated to combat this invasion. After a meal, our body digests and absorbs nutrients into the blood and our blood glucose levels increase. Eventually, however, these systems return to their homeostatic normal values.

The kidneys are one of our most important homeostatic organs; they insure that our blood chemistry is held constant by removing excess water, salts, and metabolic wastes from the body in the form of urine. Nephrons are the microscopic, tubular structures within the kidneys that produce urine from the blood.

Urine production occurs in four steps, 1) filtration, 2) reabsorption, 3) secretion, and 4) excretion. To begin, blood passing through the kidneys is filtered by the nephron to remove water, salt, glucose, and metabolic wastes. The fluid (called ultrafiltrate – the fluid is not called urine until it has been fully processed by the kidneys) produced by this process is considerable, about 120 ml/minute, or 180 L (~45 gallons) per day. Given that there is only ~5.5 L of blood in the body we would literally urinate to death within minutes if all of this fluid was excreted.

Fortunately this does not occur. About 99 % of the ultrafiltrate is reabsorbed back into the blood as the ultrafiltrate moves through the nephron. Interestingly, 100% of the glucose in the ultrafiltrate is reabsorbed back into the blood in a normal, healthy individual. Presence of glucose in the urine suggests glucose levels are abnormally high, possibly due to diabetes.

In addition to reabsorption, materials can be secreted into the ultrafiltrate if necessary to “fine-tune” the chemistry of the urine. Once this is complete, the fluid (now called urine) can be excreted from the body.

When humans sweat, they lose both water and salts. Since one of the jobs of the kidneys is to maintain salt concentrations in the blood, rehydrating with water alone will lead to dilution of the salts in the blood, leading the kidneys to excrete MORE water. In other words, if you only drink water when exercising and sweating, you will not retain water. One potential solution is to add salts to the water you drink to replace the salts in the blood. The kidneys should respond by keeping more water in the body to maintain the blood’s salts concentration. This is the function of “sports drinks,” they aim to replenish both water and salts, thus helping the body to retain water.

During this lab, we will examine how kidney function is affected by adding a large volume of liquid. To do so, we will look at the difference in kidney response to the ingestion of water and a sports drink. To do this, you will each consume a large volume (~800 ml) of water or a sports drink and study the effect of this on 1) urine volume and 2) urine chloride concentration (chloride is one salt, abbreviated Cl). Based on the information you have been given thus far, answer the following questions.

PRE-LAB QUESTIONS

Answer in complete sentences!

1. Write a testable hypothesis for the question, "What will happen to urine volume over time after drinking two large glasses of water?"

· HYPOTHESIS 1: After drinking two large glasses of water, the urine volume will increase.

2. Remember, chloride is one salt of blood, sweat and urine (tears too)! Write a testable hypothesis for the question “What will happen to amount of chloride in urine over time after drinking two large glasses of water?”

· HYPOTHESIS 2: The amount of chloride in urine will decrease.

3. Write a testable hypothesis for the question, “How will urine volume over time differ for those who drink a sports drink compared to those who drink water?”

· HYPOTHESIS 3: The urine volume will be lower when one drinks a sports drink compared to one who drinks water.

4. Write a testable hypothesis for the question, “How will amount of chloride over time differ for those who drink a sports drink compared to those who drink water?”

· HYPOTHESIS 4: The amount of chloride will increase.

II. PROCEDURE

1. Begin by voiding your urine.

2. Following this, get a cup and drink 800 mL of water or sports drink (about 2 cups full) within five minutes (if you start to feel sick, drink only as much as you feel comfortable consuming but note how much you drank!).

3. Record the time at which you finish drinking the water or sports drink. IMPORTANT: DO NOT drink anything else until the lab is finished.

4. You will now void your urine into a new cup every 15 min. for the next 60 min. (four measurements total), collecting data on urine volume and chloride concentration for each sample (as described below). A good way to keep from losing track of your sampling times is to write the time next to the appropriate row on the Individual Data table. For example, if you finish drinking at 1:30, the next time to collect a sample will be 1:45 so write this next to the “15 minute” row and so on.

5. If you are unable to void, wait and try again at the next 15-minute interval. Record all data in the “Individual Data” table below and on the Excel file. If you are recording data in an Excel file and if you do not have data, put in ND for not determined!

6. Dispose of your urine sample in the bathroom after testing your urine.

7. When the class finishes gathering data, calculate the class average data for the experiments and record in the “Class Average” data table below.

TEST METHODS:

Measuring urine volume

1. In the bathroom, pour your urine sample into a graduated cylinder to measure the volume.

2. Record urine volume, return the sample to the cup, and rinse out cylinder.

Measuring chloride concentration

1. In the bathroom, add 10 drops of urine sample to a test tube and bring the test tube of urine back to the lab. The extra urine in the cup can be discarded in the toilet.

2. Add one drop of 20% potassium chromate (yellow liquid).

3. Add 2.9% silver nitrate solution, one drop at a time while continuously shaking the test tube. Count the minimum number of drops needed to change the solution from yellow to a uniform reddish-brown.

4. Calculate the chloride concentration using the following equation:

(# of drops) x 0.61 mg Cl/ml = chloride concentration in mg Cl/ml

5. Record the chloride concentration and dump out the sample in the beaker provided.

6. Rinse the test tube with water and keep it at your desk to re-use during the lab. When the lab is over, rinse again and put it in the dirty test tube bin for washing!

III. DATA

I DRANK TWO CUPS OF: Gatorade

Individual Data:
Time / Volume (mL) / Chloride (mg Cl/mL)
0 min. / 0 / 0
15 min. / 96 / 6.71
30 min. / 10 / 6.71
45 min. / 16 / 6.1
60 min. / 29 / 6.71

IV. TAKE HOME ASSIGNMENT

1. Remember when graphing:

· X-axis is for data representing the INDEPENDENT VARIABLE

· the Y-axis is for data representing the DEPENDENT VARIABLE, a value you are actually measuring

Using MS Excel, create a scatter plot for all the lab sections average for urine volume with water and all the lab sections average for urine volume with sports drink. THEN create a second graph with a plot for the chloride data.

This means you will have TWO EXCEL graphs printed to hand in (one for volume and one for chloride), each graph will have TWO LINES (e.g. two series).

2. Answer the following questions using complete sentences based on your graphed data:

· Based on the average data from all lab sections, do you accept or reject each of your hypotheses? Make sure to include a brief explanation of WHY you accept/reject your hypothesis!

I accept each of my hypotheses on volume because after consuming the water the volume was higher than the sports drink volume. However, I reject my hypotheses on chloride because my graph shows after a period of time the chloride content decreases instead of increases.

· Are you more confident in the results from your lab section or all lab sections combined? Why?

I am a lot more confident in the results from all of the lab sections rather than my lab section because the more data present, the more likely the data is going to be more accurate.

· Did the sports drink have its intended affect? A yes or no answer is not sufficient!

The sports drink did have its intended effect on this lab because the consuming the sports drink allows to keep water in the body so there is less in the urine and refills the lost salts.

· As you did the experiment, you probably noticed that individual results varied widely. What other variable(s) that we did not consider might have affected an individual’s results? Why?

Variables like the amount of physical activity and diet can affect an individual’s results. Physical activity, like being an athlete, requires more consumption of water and salts. A person’s diet could affect the results depending on how much more or less one meets its body’s needs.

3. Gout is a condition with elevated uric acid circulating in the blood. As a result, crystals of uric acid get deposited in articulating joints causing acute arthritis. You notice that people who drink cherry juice have a reduced occurrence of gout. Design an experiment to test if cherry juice has any effect on gout. Make sure you write a hypothesis and state your independent, dependent, and standardized variables.

Hypothesis: Consuming the cherry juice will decrease the amount of gout in the body.

Variables: the number of people, time, and amount of water and cherry juice consumed

Control: water

Experimental: cherry juice

There will be two random groups for this experiment, one group drinking the cherry juice and the other drinking water. Both will be tested for which will have any effect on gout.