Materials Included In Kit

Additional Materials Required

Prelab Preparation

Either precut the dialysis tubing into 5" pieces, or have students do so before beginning the lab. To save time, preheat hot water baths (approx. 200 mL of tap water in a 250-mL beaker) to boiling for the Benedict’s test. The baths are needed on both the first and second days of this activity. Decide how the simulated blood samples will be split among students—half the class should use Sample A and half Sample B.

Before students begin this laboratory activity demonstrate the initial salt test. Construct a model kidney before class as instructed in steps 2–11. Once students arrive place the model kidney into the cup or beaker containing water. Dip the salt testing strip into the water of the cup and hold for two seconds. Remove the stick and place it on a paper towel pad side up. After one minute compare the pad color with the color chart on the side of the bottle. Inform the students of the initial salt concentration. The initial concentration should be zero.

Prepare one or more boiling water baths.

Safety Precautions

The simulated blood solutions are irritating to the skin and eyes and will stain skin and clothing. Benedict’s qualitative solution may also be a skin and eye irritant. Instruct students to wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Simulated blood, simulated urine, and Benedict’s solutions may be disposed of according to Flinn Suggested Disposal Method #26b. Dialysis tubing and clips may be thrown away in the regular trash.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. Setting up the model and initial tests can reasonably be completed in one 50-minute lab period. The second round of testing will require additional time the next lab period.
• Since the test tubes containing the Benedict’s solution will be very hot, test tube tongs or insulated gloves will be required to remove the tubes from the hot water bath.
• A piece of string may be tied to the top of the dialysis tubing and hung from a stirring rod resting on the rim of the cup to keep the model upright.
• Keep the salt test strips dry, except when in use, and out of direct sunlight at all times.
• Additions may be made to the simulated urine solutions in order to create different conditions. For example, adding a few drops of acid or base to the solutions can represent varying diets.

Teacher Tips

• The simulated blood solutions contain no real blood or blood products.
• The salt testing strips used in the lab only test for the presence of sodium chloride. Other commons salts found in urine are calcium carbonate, calcium oxalate, calcium phosphate, hippuric acid, magnesium ammonium phosphate, and uric acid.
• The simulated urine will test negative for glucose in kidney models filled with blood sample A representing a “normal” urine sample and will test positive in models containing simulated blood B. A negative test will remain royal blue in color and a positive test will change from the original color and typically will have an orange/brown precipitate. Glucose testing strips may be used in place of Benedict’s solution to save time.
• A kidney model, such as Flinn Catalog No. FB0764, or a preserved kidney, such as a pig kidney available from Flinn Catalog No. PM4025, are a great aid for discussing kidney parts and function.
• A related follow up to this activity for further discussion of urinalysis is the Simulated Urinalysis Kit available from Flinn Scientific (Catalog No. FB0438).

Answers to Prelab Questions

1. What is the signifigance of running the urinalysis testing on tap water the first day?

   These tests are used as a control.

2. What are the primary function of the kidneys?

   To filter out excess water and wastes from the blood.

3. Explain in your own words the term homeostasis, and how this relates to kidney function.

   Homeostasis refers to a system that is chemically balanced. The kidneys maintain a stable environment in the body by keeping toxins in an acceptable range for the all body systems to function normally.

4. Describe the function and location of nephrons in the kidney.

   The nephron is the functional unit of the kidney where the filtering processes are actually carried out. Most of the nephron is located in the cortex, although the loop of Henle extends down into the medulla.

Sample Data

Answers to Questions

1. True or False: Urinalysis is typically used to diagnose health problems. If false, explain why.

   False. Urinalysis provides a preliminary indication of possible health problems and would always be followed up with other appropriate tests for specific conditions by a physician. Urinalysis testing alone cannot diagnose any medical condition.

2. Describe the color and clarity of the simulated urine sample and what this, if anything, could possible indicate in a real world scenario.

   The color of the simulated urine is likely to be perceived as yellow (or a 3), and the clarity as clear. These are both considered to be normal reading. If students have a sample they perceive as bright yellow (or a 4), this could indicate dehydration or excessive vitamin intake.

3. Was the pH of the simulated urine acidic, neutral, or basic? If this were a real sample, what possible dietary factors may have been responsible for this pH level?

   This is dependent on the pH of the tap water in your area. If the simulated urine is acidic, possible dietary factors may include a high protein diet, a very low fat diet, metabolic acidosis, poisoning or other metabolic disorders. If it is basic, this person is likely to have a diet high in vegetables.

4. Is it likely that under microscopic investigation salt crystals would be observed in this sample?

   Yes. As stated in the Background section at salt concentrations over 500 ppm crystals may be present. Students are likely to find salt concentrations in the range of 2000–3000 ppm in their samples.

5. Did your simulated urine sample test positive or negative for glucose? Explain what your findings may indicate if this were a real sample.

   If the simulated urine sample tested positive (simulated blood sample A) for glucose, answers may include that the patient has glycosuria indicating they may be diabetic, pregnant, engaged in strenuous activity or have renal tube damage. If the simulated urine sample tested negative (simulated blood sample B), this would be considered normal in a clinical test.

6. Certain components of the simulated blood remained inside the nephron model (dialysis tubing) and did not pass through to the urine. Compare this to actual kidney function using terms from the Background section.

   Both the dialysis tubing and the Bowman’s capsule work as semipermeable membranes in which only small molecules may pass through. Blood cells and other large substances will not pass from the capillaries in the glomerulus through the Bowman’s capsule to the loop of Henle.

References

Scott, Ann Senisi.; Fong, Elizabeth. Body Structures and Functions, 10th edition; Delmar Learning; Clifton Park, NY (2004).

Introduction

Create a model of the nephron—the filtering, or functional, unit of the kidney. The model can be used filter out “wastes” from simulated blood, and the simulated urine produced by the model can be analyzed using common urinalysis tests.

Concepts

• Urinary/excretory system
• Urinalysis
• Homeostasis

Background

The kidney is a complex organ of the excretory system with unique characteristics. Kidneys are bean-shaped organs positioned in the lower back, with one located on each side of the vertebral column (spine). The right kidney is lower than the left due to the location of the liver. The primary function of the kidneys is to filter wastes out of the blood. Examples of wastes that must be removed include the products of metabolic reactions, excess water, and salts that the body does not need. The kidneys are constantly filled with blood, which gives rise to their dark color, and actually filter all the blood in the body hourly. Once the wastes have been filtered out of the blood, the waste products are transferred through the ureters to the urinary bladder, where they remain until they are excreted in the urine (see Figure 1).

The nephron is referred to as the functional unit of the kidney. Each kidney contains more than one million nephrons and over 140 miles of tiny tubes! Most of the nephron is located in the cortex, which lies just beneath the renal capsule, or the outer protective layer of the kidney. Under normal conditions only a fraction of the nephrons actually function. If one kidney is diseased or fails, however, the other kidney will compensate for the loss by utilizing an increased number of nephrons. Because of this excess “capacity,” doctors often do not detect kidney problems until the kidneys are functioning at 10% or less of the normal rate. Blood to be filtered enters the kidney via the renal artery and flows into the glomerulus, a ball of capillaries surrounded by the Bowman’s capsule. Water and wastes flow out of the blood through the Bowman’s capsule, which serves as a semipermeable membrane. This means large substances such as blood cells and proteins do not flow through the membrane and thus remain in the blood. Much of the water that passes through is reabsorbed via osmosis through the capillary net that surrounds the winding loop of Henle.

The loop of Henle extends down into the medulla (inner layer, consists of the cone-shaped renal pyramids) where it meets the collecting tubules. Collecting tubes then carry waste to the ureter where it is transferred to the urinary bladder to be held until excretion (see Figure 2). The kidney functions to help maintain a chemical balance, or homeostasis, in the body. When the body’s metabolism becomes abnormal, many substances not normally found in the urine may appear in varying amounts, while normal constituents may appear in abnormal amounts. Urinalysis is the analysis of the physical and chemical properties of urine and is a vital tool in diagnosing physiological health conditions. Urine test results, however, offer only a preliminary indication of possible health problems, and will usually be followed up with other appropriate tests for specific conditions. Urinalysis testing alone cannot diagnose any medical condition. Common urinalysis tests include color, clarity, density, pH, salt crystals, glucose, protein, ketones, bilirubin, and blood cells. Bright yellow urine is often an indication of dehydration or excessive vitamin intake. Yellow to clear amber samples are considered normal, and nearly colorless urine often means a person has consumed lots of excess liquid. Urine is often rated for color on a scale from 1 to 4: 4—Bright or dark yellow; 3—Yellow; 2—Clear amber; 1—Nearly colorless. Clarity simply refers to how transparent the urine sample is. Cloudy samples are often indicative of bacterial infection or blood cells in the sample. Clarity is often described as clear, slightly cloudy, cloudy, and very cloudy.

The normal pH of urine ranges from 4.6 to 8.0 and averages about 6.0. The pH of urine is strongly affected by diet. High protein diets cause a lowering of the pH, while a mostly vegetable diet increases the pH of the urine. Consistent acidic urine is a sign of metabolic acidosis, poisoning, or other metabolic disorders. Metabolism of fats produces more acidic waste products than the metabolism of carbohydrates. Starvation or excessive dieting and the resulting utilization of stored body fat will produce ketosis and acidic urine.

The major salt crystals found in urine are calcium carbonate, calcium oxalate, calcium phosphate, hippuric acid, magnesium ammonium phosphate, and uric acid. All of these salts form water insoluble precipitates and cause urinary tract problems. At concentrations of 0.05 g/100 mL (around 500 ppm) crystals may form in the urine. Some salt crystals may be visible by the naked eye, whereas others may only be visible microscopically.

Urine typically contains such small amounts of glucose (blood sugar) that glucose is considered to be absent in “normal” urine samples. The presence of glucose in significant amounts is called glycosuria. The most common cause of high blood sugar resulting in elevated glucose levels in simulated the urine, is the disease diabetes mellitus. Other conditions, such as pregnancy, excessive strenuous activity, or renal tube damage in the kidneys, may also result in elevated glucose in the urine.

Experiment Overview

The purpose of this activity is to build a nephron model and to investigate the ability of the model to filter simulated urine out of simulated blood. Urinalysis tests will first be performed on tap water and then on a simulated urine sample obtained after one day “filtration” using this model. The simulated urine will be tested for color, clarity, pH, salt crystals and glucose.

Materials

Prelab Questions

1. What is the signifigance of running the urinalysis tests on tap water the first day?
2. What are the primary functions of the kidneys?
3. Explain, in your own words, the term homeostasis and how this relates to kidney function.
4. Describe the function and location of nephrons in the kidney.

Safety Precautions

The simulated blood solution is irritating to the skin and eyes and will stain skin and clothing. Benedict’s qualitative solution may also be a skin and eye irritant. Avoid all contact of all chemicals with eyes and skin and wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

1. Observe your teacher’s demonstration and record the initial salt concentration in the data table on the worksheet.
2. Write the group members’ initials and simulated blood sample (A or B as assigned by your instructor) on the bottom of an empty plastic cup using a marker or wax pencil.
3. Fill the cup about three-quarters full with tap water.
4. Obtain a 5" piece of dialysis tubing and, using forceps to hold it, soak the tubing in the cup of water for approximately one minute.
5. Remove the tubing from the water and twist one end of the tubing three times about one inch from the end (see Figure 3A).
   {10814_Procedure_Figure_3}
6. Place one of the dialysis tubing clamps near the base of this “twist.”
7. Hold the tubing upright (with the clip-side pointing down) carefully open up the opposite end using a gloved hand or forceps. The tubing only needs to be separated enough to fit the tip of a pipet inside.
8. Fill the pipet with simulated blood and insert the tip of the pipet into the dialysis tubing. Squeeze the pipet bulb to empty the solution into the tubing (see Figure 3B).
9. Repeat step 7 twice more to fill the tubing 1–2 cm from the top.
10. Twist the top (open end) of the tubing three times and place the clamp on the twist (see Figure 3C).
11. Rinse the dialysis tubing (the nephron model) under the faucet. If any leaks are observed, the model will need to be discarded and remade.
12. Place the model into the cup of tap water (step 2).
13. Observe the initial color of the solution in the cup. Record the appropriate number or color description in the data table (4—bright yellow; 3—yellow; 2—pale yellow; 1—colorless).
14. Observe the initial clarity of the solution in the cup and record observations in the data table.
15. Dip the end of a piece of pH paper into the solution in the cup. Set the wet strip on a paper towel and observe the color of the wet area after 30 seconds. Compare the color of the pH paper with the color chart on the side of the bottle and record the pH value in the data table.
16. Obtain 5 mL of Benedict’s qualitative solution (test for glucose) in a test tube.
17. Add 8 drops of the solution surrounding the dialysis tubing to the same test tube.
18. Place the test tube in a boiling water bath for four minutes.
19. Remove the test tube using tongs or insulated gloves and place in a test tube rack.
20. Record all observations on the data table.
21. Store the model according to your teacher’s instructions.

Steps 22–31 are to be completed the next lab period.

22. Observe the color of the simulated urine solution in the cup that has diffused through the dialysis tubing. Record the appropriate number according the color in the data table (4—bright yellow, 3—yellow, 2—pale yellow, 1—clear).
23. Observe the clarity of the simulated urine and record observations in the data table.
24. Dip the salt testing stick into the solution in the cup. Hold the stick in the solution for about two seconds. Remove the stick and place it on a paper towel pad side up. Do not blot or tap off excess solution.
25. After one minute compare the pad color with the color chart on the side of the bottle and record the salt concentration in ppm in the data table.
26. Dip the end of a piece of pH paper into the solution in the cup. Set the wet strip on a paper towel and observe the color of the wet area after 30 seconds. Compare the color of the pH paper with the color chart on the side of the bottle and record the pH value in the data table.
27. Obtain 5 mL of Benedict’s qualitative solution (test for glucose) in a test tube.
28. Add 8 drops of the solution surrounding the dialysis tubing to the same test tube.
29. Place the test tube in a boiling water bath for four minutes.
30. Remove the test tube using tongs or insulated gloves and place in a test tube rack.
31. Record all observations on the data table.
32. Dispose of all materials as directed by your teacher.

Student Worksheet PDF

10814_Student1.pdf