Renal Regulation of Blood Osmolarity

Topics: Kidney, Sodium, Renin-angiotensin system Pages: 7 (2553 words) Published: July 18, 2010
The experiment was done to demonstrate the effect of ADH on the volume and concentration of urine in order to demonstrate the control of ADH over blood plasma osmolarity. Since non-invasive methods were preferred the volume and concentration of urine was used in place of drawing blood. The results that we our anticipating are that ADH levels in the group of subjects that ingested the 6 gm. Of NaCl would increase over time in response to the increased osmolarity of the blood from all of the salt. Urine output would decrease and eventually the body would stabilize.

In this experiment, renal regulation of osmolarity will be demonstrated through the use of urinalysis.

Materials and Methods:
In this experiment, we assigned two groups. The first group was given 800ml of distilled to drink and the second was given 6mg of NaCl dissolved in a small amount of water. Both groups were instructed to note the time each time they voided from waking up until the control urine that was obtained just prior to the beginning of the experiment. They also were not to deviate from their normal activities of food and liquid consumption on this day. The control urine was the last urine prior to the experiment and was taken in a large specimen cup. The osmolarity of blood plasma is within normal range at 275-295 mosmol/L of blood. Due to the fact that urine is the end product of our filtered plasma, it was an appropriate and noninvasive vehicle to demonstrate how ADH secretion works in regulating osmolarity.

The experiment began when the groups drank the entire solutions and the time was noted for that. Once the experiment was in progress, the groups were instructed not to ingest anything until the lab was complete. During the 30 minute waiting periods between voiding there were three tests to perform on the urine samples. The control urine was used for the first set of data and time was measured since last void. The total amount of time to complete the experiment was 120 minutes, giving four test urines and five sets to examine and chart. The first test performed was to determine urinary output. The urine was poured completely into a beaker and measured in milliliters. That measurement was put into the formula x ml/y min. Minutes were measured from the time of previous void until the current void. The second test was to determine the specific gravity. Normal specific gravity is 1.003-1.030 and measures the number of solutes in the solution. Therefore, if the number of solutes is increased the concentration of the urine is increased. We placed a drop of each test urine, including the control urine, on the tip of a refractometer and used the number shown. The final test was to measure the sodium ion concentration in the urine. Ten drops of urine were placed into a test tube and first mixed with one drop of 20% potassium chromate turning the urine bright yellow. The urine is then mixed with 2.9% silver nitrate drop by drop while shaking the test tube. Once the solution turned a orange brown color then the number of drops was recorded. The number of drops of 2.9% silver nitrate was for the purpose of our experiment equal to one mg NaCl/ml. The amount of sodium in the plasma changes the irritability of neurons and cell membranes action potentials making it an important solute to test. Each member of the experiment tracked their data and entered it into a spreadsheet. All the values for the four different labs were combined and averaged according to group to produce a larger sample size. The averages were graphed based on each test measured against time. The data, averages, and graphs are all included in the results section of this report. Theory:

The experiment was based upon correct functioning of the hypothalamic osmoreceptors located in the supra-optic nucleus of the hypothalamus to sense a change in blood osmolarity. This change should increase or decrease the amount...
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