Urinalysis and Acid/Base Balance



Urinalysis and Acid/Base Balance

I. PURPOSE

This exercise is designed to familiarize the student with some of the physiological factors that are involved in kidney function.

II. PERFORMANCE OBJECTIVES

At the end of this exercise the student should be able to:

1. Describe the effects that drinking large volumes of water has on urine production.

2. Describe the effects that caffeine has on urine production.

3. Describe the normal color, odor and pH of urine.

4. Describe the main functions of the kidneys.

5. Describe the physical characteristics of normal urine.

6. Describe the role the kidneys have in the regulation of pH.

III. INTRODUCTION

The kidneys are the most important organs responsible for homeostatic control of blood and other body fluids. They move water and a variety of other substances out of the blood into the environment and in so doing establish a balance between removal and retention of essential and harmful materials. To this end, they help maintain osmotic pressure, electrolyte balance, pH and minimize nitrogenous wastes produced as a result of protein metabolism.

The human kidneys contain more than two million nephrons, the functional units of the kidney, that are responsible for the performance of these functions. Glomerular filtration, tubular reabsorption, and tubular secretion are involved in this process of urine formation. As the filtrate passes through the tubule segments of the nephron, the fluid is modified both in volume and composition as a result of these processes.

Water reabsorption is regulated by antidiurectic hormone (ADH) which is released from the posterior pituitary. Changes in the amount of fluid intake causes osmoreceptors to respond which results in a change in the production of ADH depending on the amount of fluid intake. The ADH has an effect upon kidney tubules to change urine output. For example, an increase in osmotic pressure brought about by a decrease in fluid intake stimulates the production of ADH with resultant retention of fluid and decreases in urine output.

Sodium and potassium regulation is taken care of by the kidneys through the secretion of aldosterone produced by the adrenal glands. Sodium passes in and out of the body and is maintained in the blood at constant levels. If the level becomes high, the kidney can excrete excess sodium. Regulation of sodium is closely related to fluid volume since retention of increased amounts of sodium will result in the retention of additional water. With increasing aldosterone, increased sodium, chloride, and water are retained.

To maintain acid-base balance, the kidneys can eliminate more hydrogen ions if the pH of the extracellular fluid goes down. If the pH goes up, the kidney will eliminate more bicarbonate ions to maintain this proper balance. Even with changing acidity or alkalinity of intake loads, the pH of the blood will remain 7.4 but urine pH will change to maintain this value.

In this experiment, some of the physiological principles mentioned will be demonstrated using your own kidneys as the subject for this investigation.

V. PROCEDURE

Food and water intake should be restricted for approximately two hours before starting this exercise. Persons with kidney abnormalities or problems should be eliminated from the ingestion of test solutions but should aid their group members in the analysis of urine samples.

1. Before drinking any of the test solutions each student should urinate and keep this sample for further analysis.

2. The students should work in groups of 3 or 4 depending on class size. All students in the group should be drinking the same experimental solution.

3. Students should drink all solutions quickly but without discomfort and should be divided up into the following groups:

Group A - drinks 800-1000 ml of water

Group B - drinks 300 ml of a 2.5% sodium bicarbonate

Group C - drinks 800-1000 ml of coffee or tea (without sugar)

4. Each student should urinate at 30 minute intervals , collect the urine and measure its pH, specific gravity, sodium chloride content, and glucosecontent using methods described in this exercise. If you are unable to void, a urine sample is taken at the next 30 minute interval.

5. Your urine sample from step 1 and those taken at 30 minute intervals shouldbe evaluated using the following procedures for urinalysis. All data should be recorded in the chart at the end of this laboratory exercise.

Color - Normal urine is straw to amber color. Observe the color of urine before ingestion of test solutions and note any changes that occur during the course of this experiment.

Volume - Measure the volume of the urine specimen by pouring it into a graduated cylinder.

Specific Gravity - The normal range for specific gravity is between 1.015 and 1.030. It is a measure of the relative amounts of solids in the urine.

To measure specific gravity, place the hydrometer (urinometer) in its cylinder filled 3/4 full of urine. Remove any bubbles on the surface of the urine by rotating the urinometer. Also make sure that the urinometer does not cling to the sides of the urinometer cylinder. Observe where the urine meniscus lines up with the lines engraved on the urinometer for the value of specific gravity. Specific gravity changes with temperature and should be corrected. Add .001 for every 3o C above 15o C. Use the same urinometer for all tests during the course of the experiment and make sure that it is washed, rinsed and dried after each use.

Glucose-

Use the test strips available to determine glucose

pH

Record the pH by either using pH paper, by dipping the paper into the urine and comparing a color chart provided or use a pH meter and follow procedures that your instructor will provide.

Sodium Chloride Determination

a. Measure 10 drops of urine into a small test tube

b. Add 1 drop of 10% potassium chromate

c. Add 2.9% silver nitrate 1 drop at a time and shake after each drop

d. Count the number of drops required to turn the solution from yellow to brown

e. Calculate the sodium chloride content as follows:

Na Cl (gm) = volume of specimen in ml 1 x drops silver nitrate

1000 ml

Proteins, ketones, blood, bilirubin

With your urine and a pathological urine if available, use multistix to determine protein, ketones, blood, and bilirubin.

Microscopic Examination

1. Obtain 10 ml of freshly voided urine from the first voided control sample.

2. Centrifuge for 10 minutes at 1600 rpm.

3. Place one drop of sediment on a clean glass slide.

4. Add one drop of sedi-stain and place a cover glass over specimen.

5. Under low power look for the presence of blood cells, salt crystals, epithelial cells, bacteria, yeast cells, parasites and casts (Figure 1).

6. Under high power (40x) count five fields and average the number of red and white cells found.

7. Enter your observations and data in the chart at the end of this laboratory exercise.

Disposal: glass pasteur pipettes, slides, coverslips( glass disposal box

gloves, towels, cups, urine test strips, straws ( trash

urinometers, beakers, flasks ( bleach bucket

MATERIALS (for part II)

2.5% sodium bicarbonate, 50% sucrose solution (Glucola) caffeinated coffee, tea, hot water, urine specimen containers, pH paper and pH meter, buffer (pH7), 500 ml graduated cylinders (100ml and 500 ml, urinometers or refractometers, thermometers, 10% potassium chromate, 2.9% silver nitrate, multistix, large test tubes, small test tubes, centrifuge tubes, 10 ml pipets, pipeting devices, test tube racks, test tube holders, microscopes, sedi-stain, cover slip, rubber gloves, centrifuge.

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Data Sheet

|General |Normal Urine | |0.5 hr |1.0 hr |1.5 hr |2.0 hr |2.5 hr |3.0 hr |

|Characteristics & | |Sample | | | | | | |

|Tests | | | | | | | | |

|Color |light yellow or | | | | | | | |

| |amber | | | | | | | |

|Odor |pungent | | | | | | | |

| |characteristic | | | | | | | |

|pH |4.5 - 8.0 | | | | | | | |

|Glucose |Neg | | | | | | | |

|Protein |Neg | | | | | | | |

|Volume |1 - 1.5 L/day | | | | | | | |

|Specific Gravity |1.001 - 1.030 | | | | | | | |

|Sodium Chloride |present | | | | | | | |

|Bilirubin | | | | | | | | |

|Ketones |neg | | | | | | | |

|Sediment | | | | | | | | |

|WBC's |neg | | | | | | | |

|RBC's |neg | | | | | | | |

|Epithelial Cells |present | | | | | | | |

|Casts |neg | | | | | | | |

|Crystals |neg | | | | | | | |

|Bacteria |neg | | | | | | | |

|Parasites |neg | | | | | | | |

|Yeast Cells |neg | | | | | | | |

Review Questions:

1. If the specific gravity of the urine specimen is high, what color would you expect the sample to be? Explain.

2. What specific conditions would result in urine of high specific gravity? Of low specific gravity?

3. List five examples of abnormal constituents in a urine sample (other than those you found in your unknown samples above) and describe what problems each might indicate

4. How do you account for the fact that saliva and urine may have a pH below 6.8 or above 7.8 in healthy individuals.

5. What exactly is a buffer? Which of the three solutions (water, bicarbonate, plasma) acted as the least effective buffer? Explain.

6. Compare the effects of acids and bases on the buffered and unbuffered solutions. How does the buffering ability of plasma or albumin compare with that of sodium bicarbonate?

1 Amount of urine produced at each test period

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