Urinalysis

Introduction

Homeostasis is the maintenance of constant conditions within the internal environment of the body in order to sustain health and functioning, despite changes in the external environment. The kidney, a principal regulator of the internal environment of the body, establishes homeostasis by regulating the concentration of ions, water and blood volume, pH balance of plasma, and through the elimination of the waste products of metabolism (Tilley, 2003).

The functional unit of the kidney, the nephron, is composed of two key structures: the glomerulus and the renal tubule. The afferent and efferent arterioles supply blood to the glomerulus. As a network of capillaries, the glomerulus acts as a filtering unit by keeping normal proteins and cells in the blood while allowing the filtrate, which contains particles such as ions, sugars, and ammonia, to pass through to the glomerular capsule and exits into the renal tubule (Tilley, 2003).

Glomerular filtration is regulated by blood pressure and osmosis. A decrease in blood pressure results in the release of renin by renal juxtaglomerular cells, which is transformed into angiotensin, ultimately causing vasoconstriction. Vasoconstriction results in the increase of blood pressure, thus powering filtration (Ira, 2009).

There are four distinct regions of the renal tubule through which the filtrate is modified prior to becoming urine: the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule, and the collecting duct (Crowder, 2010). The proximal convoluted tubule reabsorbs a large majority of the filtrate via active and passive transport. By means of a countercurrent multiplication mechanism, the loop of Henle is able to concentrate the fluid (Tilley, 2003). In response to the release of anti-diuretic hormone (ADH) from the posterior pituitary gland, water is reabsorbed in the distal convoluted tubule and the collecting duct. Eventually, the solutes and fluid that remain in the renal tubule are excreted as urine (Crowder, 2010).

An analysis of urine can provide a clear indication of not only the health of the kidney, but the overall health of the body as well.

Hypotheses

Four experiments were conducted to examine the production of urine under the following treatments: water, water and exercise, coffee, and V8.

In subjects undergoing the water treatment, the results should reveal an increased volume, a light color, an increase in pH, and a decrease in specific gravity. Excessive water in the body causes an imbalance of sodium and water content in the body, resulting in more dilute extracellular fluid and lowered osmotic pressure. This decrease in pressure is detected by osmoreceptors in the hypothalamus, inhibiting the release of ADH, and prevents the reabsorption of water which is excreted in the urine (Ira, 2009). The loss of water from the body into the urine causes the urine to become more dilute, thus lighter in color. Also, when the water levels present in the urine increase, the concentration of H+ ions will decrease. This causes the pH of the urine to increase. The specific gravity of the urine will decrease because the urine is more dilute.

In subjects undergoing the water and exercise treatment, the results should reveal a decreased volume, a darker color, a decrease in pH, and an increase in specific gravity. The sympathetic division of the autonomic nervous system is activated during physical exercise, causing the blood vessels that supply the kidneys to constrict. This constriction causes the glomerular filtration rate to decrease, which results in the production of less urine. Also, the constriction of the blood vessels supplying the kidneys produces a reduced blood supply to the kidneys, causing the release of renin and consequently the renin-angiotensin-Aldosterone cascade occurs (Ira, 2009). The Aldosterone acting on the kidneys promotes the retention of sodium which stimulates the release of ADH and causes the kidneys to retain water. When the water levels present in the urine decrease, the concentration of H+ ions will increase (Ira, 2009). This causes the pH of the urine to decrease. The specific gravity of the urine will increase because the urine is more concentrated.

In subjects undergoing the coffee treatment, the results should reveal increased volume, a light color, an increase in pH, and a decrease in specific gravity. Caffeine is chemically similar to adenosine, and therefore competitively binds to the same neurotransmitter, inhibiting the vasoconstriction effect of adenosine (Tilley, 2003). This allows an increase in the blood supply to the kidneys, increases the glomerular filtration rate, and results in the production of more urine. Also, caffeine works by inhibiting the release of ADH. When the release of ADH is inhibited, the reabsorption of water is prevented and the water is excreted in the urine (Ira, 2009). The loss of water from the body into the urine causes the urine to become more dilute, thus lighter in color. Also, when the water levels present in the urine increase, the concentration of H+ ions will decrease (Ira, 2009). This causes the pH of the urine to increase. The specific gravity of the urine will decrease because the urine is more dilute.

In subjects undergoing the V8 treatment, the results should reveal a decreased volume, a darker color, a decrease in pH, and an increase in specific gravity. V8 contains a high salt content. An increase in sodium serum concentration results in an increased osmolarity of the extracellular fluid, which in turn stimulates the release of ADH from the posterior pituitary gland. The release of ADH causes the kidneys to retain water (Ira, 2009). When the water levels present in the urine decrease, the concentration of H+ ions will increase. This causes the pH of the urine to decrease. The specific gravity of the urine will increase because the urine is more concentrated.

Materials and Methods

Four experiments were conducted to examine the production of urine under the following treatments: water, water and exercise, coffee, and V8. Subjects were assigned a single, specific treatment and drank 1000 mL of the assigned beverage. After 20 minutes, the initial urine sample was obtained. Volume was read and measured using the scale on the side of the urine cup. A refractometer was used to measure specific gravity. In order to use the refractometer, a small sample was placed on the meter and upon placing the subject’s eye on the eyepiece the specific gravity was clearly displayed. Using pH strips, the pH of the urine was measured. Also, the color of the sample was observed and compared to a scale in which 0 was considered to be clear and each subsequent number was a slightly darker shade. Each experimental value was recorded in a Data Collection Record.

The above procedure was repeated every 20 minutes for a total of 6 sets of data.

Results Figure 1 displays the Total Volume of the Experiment for each substance consumed. The following figures present a comparison of each specific treatment; Figure 2: pH; Figure 3: Volume; Figure 4: Specific Gravity; Figure 5: Color.

Figure 1. Total Volume of Experiment

Figure 2. Comparison of pH versus Time

Figure 3. Comparison of Volume versus Time

Figure 4. Comparison of Specific Gravity versus Time

Figure 5. Comparison of Color versus Time

Discussion

In subjects undergoing the water treatment, the results should reveal an increased volume, a lighter color, an increase in pH, and a decrease in specific gravity. Excessive water in the body causes an imbalance of sodium and water content in the body, resulting in more dilute extracellular fluid and lowered osmotic pressure. This decrease in pressure is detected by osmoreceptors in the hypothalamus, inhibiting the release of ADH, and prevents the reabsorption of water which is excreted in the urine (Ira, 2009). The loss of water from the body into the urine causes the urine to become more dilute, thus lighter in color. Also, when the water levels present in the urine increase, the concentration of H+ ions will decrease. This causes the pH of the urine to increase. The specific gravity of the urine will decrease because the urine is more dilute. As evidenced by Figure 2, the results revealed an unexpected trend: subjects undergoing the water treatment experienced a decrease in pH over time. However, Figure 3 reveals expected results: subjects experienced a rapid increase in urine volume. Over time, the volume did begin to decrease after the initial rapid increase. Figure 4 shows an initial decrease in specific gravity, yet a gradual increase. This shows expected results because after the initial rapid increase of volume, the volume decreased, thus causing the specific gravity to increase. As evidenced by Figure 5, the color of the urine obtained from the subject undergoing the water treatment started out darker and gradually got lighter over time. A lighter color was expected, and was realized.

In subjects undergoing the water and exercise treatment, the results should reveal a decreased volume, a darker color, a decrease in pH, and an increase in specific gravity. The sympathetic division of the autonomic nervous system is activated during physical exercise, causing the blood vessels that supply the kidneys to constrict. This constriction causes the glomerular filtration rate to decrease, which results in the production of less urine. Also, the constriction of the blood vessels supplying the kidneys produces a reduced blood supply to the kidneys, causing the release of renin and consequently the renin-angiotensin-Aldosterone cascade occurs (Ira, 2009). The Aldosterone acting on the kidneys promotes the retention of sodium which stimulates the release of ADH and causes the kidneys to retain water. When the water levels present in the urine decrease, the concentration of H+ ions will increase (Ira, 2009). This causes the pH of the urine to decrease. The specific gravity of the urine will increase because the urine is more concentrated.
As evidenced by Figure 2, the results revealed expected results: decrease in pH over time. Figure 4 shows a decrease in specific gravity. While this does not match the expected hypothesis, it is understandable due to the unexpected increase in volume evidenced by Figure 3. Interestingly, the color gradually became darker over time, which matches the expected hypothesis, yet does not correspond to the experimentally measured increase in volume.

In subjects undergoing the coffee treatment, the results should reveal increased volume, a light color, an increase in pH, and a decrease in specific gravity. Caffeine is chemically similar to adenosine, and therefore competitively binds to the same neurotransmitter, inhibiting the vasoconstriction effect of adenosine (Tilley, 2003). This allows an increase in the blood supply to the kidneys, increases the glomerular filtration rate, and results in the production of more urine. Also, caffeine works by inhibiting the release of ADH. When the release of ADH is inhibited, the reabsorption of water is prevented and the water is excreted in the urine (Ira, 2009). The loss of water from the body into the urine causes the urine to become more dilute, thus lighter in color. Also, when the water levels present in the urine increase, the concentration of H+ ions will decrease (Ira, 2009). This causes the pH of the urine to increase. The specific gravity of the urine will decrease because the urine is more dilute. As expected, Figure 2 shows an increase in pH and Figure 5 reveals a lighter color over time. However, Figure 3 provides evidence of a decrease in volume, which is unexpected. In Figure 4 it is seen that the specific gravity increases, rather than decreasing as expected. While this is against the hypothesis, it corresponds to the decrease in volume experienced.

In subjects undergoing the V8 treatment, the results should reveal a decreased volume, a darker color, a decrease in pH, and an increase in specific gravity. V8 contains a high salt content. An increase in sodium serum concentration results in an increased osmolarity of the extracellular fluid, which in turn stimulates the release of ADH from the posterior pituitary gland. The release of ADH causes the kidneys to retain water (Ira, 2009). When the water levels present in the urine decrease, the concentration of H+ ions will increase. This causes the pH of the urine to decrease. The specific gravity of the urine will increase because the urine is more concentrated. The pH of the urine showed very slight changes in Figure 2, and stayed almost constant around a single value, so there was no true increase or decrease as expected. As evidenced by Figure 3, volume did not fluctuate either; therefore the specific gravity displayed in Figure 4 was also fairly constant. Because the volume and specific gravity was consistent, the color of the urine did not change either. These results were unexpected.

While many of the results of each experiment were expected, the unexpected results could be explained by many possibilities. The experiment was not conducted until 2:00 in the afternoon, so the activity and food/beverage consumption of the subjects prior to consuming the specified treatment can not be factored into the experiment with any degree of certainty. Also, some of the subjects recorded the volume of urine in ounces while the experiment was examined in milliliters. Though for examining the results the ounces could be simply converted to milliliters, the accuracy of the measurement in ounces is in question. In one subject, the volume was listed as 6.5 ounces several times in a row. It is highly unlikely that the volume was exactly 6.5 ounces every time, so perhaps the subject rounded. If a standard measurement of milliliters was used by all subjects, the volume could have been more accurately measured. Faulty equipment could also contribute to unexpected results. At times one of the refractometers used to measure specific gravity did not work properly and had to be adjusted in order to achieve results. Another source of error could have come from the timing of obtaining samples. The samples were to be obtained every 20 minutes, but because this timing was the responsibility of each individual subject, it possible that each sample was not obtained at the exact same time difference.

As experimenters that obtained unexpected results, the next step is to perform an experiment in a manner that could compensate for the errors discussed above. The experiment could be conducted first thing in the morning, with the requirement that all subjects fast from 6:00 the night before until the test. A single experimenter could perform each test on the urine sample in order to prevent discrepancies in the use of the equipment.

References

Crowder, Thomas D. 2010. Lab 12 – Urine Analysis Lab. Biology 460 Course Handout. University of South Carolina, Columbia, SC.

Ira, S. (2009). Human Physiology (Eleventh Edition). New York, NY: McGraw-Hill Companies, Inc.

Tilley, W. 2003. Introduction to Urinalysis. Biology 1345 Course Handout. Cornell University, Ithaca, NY.