Evaluating Kidney
Functions
Fluid, Electrolyte and pH Balance
Steven Le
Group: Harvey
Members’ Names: Jeffrey Lam, Darren Lee, Waseem Bader
Section 6
TA: Ailsa Dalgliesh
December 3, 2014
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Introduction
The kidneys are important for bodily homeostasis as they regulate fluid volume,
electrolytes and pH. This is done through the functional and structural unit of the kidney: the
nephron. There are over one million nephrons in each kidney and they each contribute to
controlling bodily homeostasis through glomerular filtration, tubular reabsorption and tubular
secretion (Marieb and Hoehn 963). In this lab the functions of the kidneys will be evaluated in
four subjects; control, hypotonic, isotonic and alkalosis subjects. Creatinine clearance, sodium
clearance, urine specific gravity and urine pH will be examined in these subjects.
Glomerular filtration is the process by which blood from the glomerulus passes through
barriers between the glomerulus and Bowman’s capsule, in order to form filtrate. Next is tubular
reabsorption, which is the process in which substances from the filtrate are moved back into the
blood and body. It occurs in order to retrieve substances that the body needs, such as electrolytes
and water for electrolyte and fluid balance. Lastly, tubular secretion occurs when substances
from the blood are sent out into the filtrate. This is generally done in order to remove unwanted
substances, such as in the case of acid base balance in order to regulate pH in the body. In
addition, excess electrolytes, fluids, waste and other metabolites are excreted as well. (Marieb
and Hoehn 963)
The nephron is broken down into two parts, the renal corpuscle and the renal tubule. The
former is responsible for glomerular filtration while the latter is responsible for tubular
reabsorption and tubular secretion. After the filtrate passes through the renal corpuscle and renal
tubule, it will enter the collecting duct, which will be the last time that water and electrolytes
(e.g. Na+) will be able to be reabsorbed into the body. Once the filtrate passes through the
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collecting duct, it will finally be called urine and will empty into the ureter. The ureter serves as
a connection to send urine from the kidneys to the bladder. (Marieb and Hoehn 963)
The renal system is affected by intrinsic controls and extrinsic controls. Intrinsic control
is called renal autoregulation, which includes myogenic mechanism and tubuloglomerular
feedback mechanism. It is done in order to maintain a constant glomerular filtration rate (GFR)
through controlling the diameter of the afferent arteriole, which diverges into the glomerulus.
Extrinsic control is done through neural and hormonal mechanisms. This includes sympathetic
nervous system controls and the Renin angiotensin aldosterone system (RAAS). This is done in
order to maintain systemic blood pressure. (Marieb and Hoehn 966- 968) Atrial natriuretic
peptide is another hormone that contributes to blood pressure regulation and it has the opposite
effects of aldosterone; meaning it promotes Na+ and water excretion.
In this lab, creatinine clearance, sodium clearance, urine specific gravity and urine pH
will be evaluated in four different subjects: control, hypotonic, isotonic and alkalosis subject.
Our hypothesis is that hypotonic and isotonic subjects will experience higher creatinine clearance
due to increased blood pressure from excessive fluid intake. Isotonic and control lower will
experience lower creatinine clearance due to lower blood pressure from little to no fluid intake.
For sodium clearance, it is expected that the hypotonic subject will have decreased sodium
clearance due to not consuming any sodium in the fluids, leading to sodium retention. The
control subject will also experience sodium retention indirectly as a result of water reabsorption.
Isotonic and alkalosis subjects should experience increased sodium clearance due to the
consumption of sodium. For specific gravity, is it expected that the control and hypotonic subject
will have a higher specific gravity due little to no consumption of water, which would lead to
more concentrated urine. Hypotonic and isotonic subjects should have less concentrated urine
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due to excess consumption of water, which would dilute the urine. For pH, it is expected that
isotonic, hypotonic and control subjects’ pH should remain the same, while pH should increase
for alkalosis subject due to the secretion of bicarbonate in the urine
Materials and Methods
Specific details of procedures can be found in NPB 101L Physiology Lab Manual 2nd
Edition under exercise seven The Role of the Kidney in Fluid Balance (Bautista and Korber, 6574). All subjects should come to class well hydrated, without exercising beforehand or
consuming any caffeine. In this lab, four values will be evaluated: creatinine clearance, sodium
clearance, urine specific gravity and urine pH. These values will be evaluated in four subjects:
control, hypotonic, isotonic and alkalosis.
Prior to drinking their fluids, all subjects must empty their bladders and collect their urine
samples; this will be recorded as Time 0 and will serve as that subject’s own control. After this
is done, each subject will consume their corresponding fluids. The control subject will not drink
anything in order to observe the effects of dehydration. The hypotonic subject will consume
distilled water in order to see the effects of excess fluid consumption without added electrolytes.
The isotonic subject will consume a saline solution in order to observe the effects of excess fluid
and salt consumption. Lastly, the alkalosis subject will consume a sodium bicarbonate solution in
order to observe the effects it will have on pH. After consumption of these fluids, each subject
will empty their bladder every 30 minutes, for a total of 4 times. These will be labeled as Time
30, 60, 90 and 120. In between urine sample collections, measurements and calculations were
done in order to analyze the effects that these different solutions will have on the renal functions
of each subject.
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It is important to note that our isotonic subject consumed caffeine beforehand and our
alkalosis subject was not able to urinate after Time 30. These factors affected and may have
skewed our data collection.
Results
The first task was to calculate the flow rate (VUrine) for each subject at every 30 minute
interval. The flow rate value is important because it will be to calculate creatinine clearance,
sodium clearance, creatinine concentration and sodium expected. Each subject: control,
hypotonic, alkalosis and isotonic urinated and collected urine volumes a total of five times each
at Time 0, 30, 60, 90 and 120. From these urine volume data, the flow rate was calculated as
urine volume is divided by the time elapsed since the last urination.
In Figure 1, it is seen that each subject started out at similar flow rates at Time 0, all
below 1 mL/min. The control subject maintained a constant flow rate of 0.33 mL/min to 0.4
mL/min. There were no exceptional changes in the control subject’s flow rate. This should also
be true for the alkalosis subject as well (No data). The opposite can be seen in the isotonic and
hypotonic subjects. Both subjects had increases in flow rate at Time 30 and at Time 60. The
isotonic subject had a flow rate that went up to 6.93 ml/min, while the hypotonic subject had a
flow rate that went up to 10 mL/min. After Time 60, the isotonic subject declined more rapidly
in flow rate, dropping to 1.2 mL/min, while the hypotonic subject’s flow rate remained relative
high at 9.5 mL/min. All subjects reached similar flow rates at Time 120, in which all flow rates
are around the same value of 2 mL/min or less.
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Flow Rate (mL/min)
12
10
8
6
Control
4
Isotonic
2
Hypotonic
0
0
30
60
90
120
Time (minutes)
Figure 1 Depicted is the flow rate of each subject observed over time. It can be seen that isotonic and
hypotonic subjects had increase in high flow rates over time. This is contrasted with the control subject,
who seemed to have a relatively low flow rate. The alkalosis subject should have a low flow rate as well.
Next, the specific gravity of each urine sample from each subject was measured, as can
Specific Gravity
be seen in Figure 2.
1.035
1.03
1.025
1.02
1.015
1.01
1.005
1
0.995
Control
Isotonic
Hypotonic
Alkalosis
0
30
60
90
Time (minutes)
120
Figure 2 The specific gravity of each subject were measured over time. It can be seen that the control had
a slight decrease in specific gravity over time, while the alkalosis subject had a slight increase in specific
gravity over time. This is contrasted with the isotonic and hypotonic subjects, whose specific gravity
declined initially and then increased towards the end.
Each subject started out with specific gravities around similar ranges: 1.02 (Hypotonic),
1.025 (Alkalosis), 1.026 (isotonic), and 1.03 (control). The control subject maintained the highest
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specific gravity with a slight decrease over time. The alkalosis subject had the second highest
specific gravity measurements, with measurements similar to that of the control subject, except
there was slight increase over time. The isotonic and hypotonic subjects both experienced a
decrease in specific gravity. The isotonic subject experienced his lowest specific gravity at Time
60, which was measured at 1.002. The hypotonic subject, on the other hand, experienced his
lowest specific gravity at Time 90, which measured at 1.001. Both subjects’ specific gravities
then started to increase afterwards.
Next, urine pH was measured for each subject. As can be seen in Figure 3, the pH of the
control, isotonic and hypotonic subjects remained relatively constant over time. Although each
subject started out at different pH, levels they stayed constant in their respective range. The
control subject’s pH ranged from 5.29 to 5.19; the isotonic subject’s pH ranged from 6.35 to 6.86
and the hypotonic subject’s pH ranged from 6.52 to 6.9. The alkalosis subject on the other hand
did not maintain a constant pH, as pH was increasing from the start. The initial pH of the
alkalosis subject started out at 7.18 and peaked at Time 60, with a value of 8.01. After that there
was a slight decline to 7.79 at Time 120.
9
pH
8
7
Control
6
Isotonic
5
Hypotonic
Alkalosis
4
0
30
60
90
120
Time (minutes)
Figure 3 The pH of urine was measured for each subject for all urine samples. It can be seen that for the
isotonic, hypotonic and control subjects, their pH remained relatively stable, with slight decreases towards
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the end. The alkalosis subject on the other hand showed an increase in pH, plateauing at Time 60, and
then slightly decreasing afterwards.
Next, urine Na+ concentration was found from values collected from the Na+ meter. The
Na+ meter will give us voltage readings, in which we will use to calculate the Na+ concentration
from the equation Y= 24.364 ln(x)-127.4. As can be seen in Figure 4, the control subject is the
only subject in which Na+ concentration remained relatively constant over time with a range of
56.76 mEq/L to 64.19 mEq/L. (Alkalosis subject should either experience similar results to that
of the control or a slight increase over time.) The hypotonic and isotonic subjects on the other
hand experienced a dramatic decrease in Na+ concentration. Both subjects started out at similar
Na+ concentration and showed similar declination rates as well. The hypotonic subject started
out at 171.9 mEq/L, and then continuously decreased until the minimum was reached at Time 90,
with a value of 9.72 mEq/L. After that, Na+ concentration went up. As for the isotonic subject,
he started out with a Na+ concentration of 171.9 mEq/L. The minimum concentration was
reached at Time 60, with a value of 17.26 mEq/L. Afterwards, there was a sharp increase in Na+
Urine Na+ Concentration
(mEq/L)
concentration of up to 135.38 mEq/L at Time 120.
200
150
Control
100
Hypotonic
50
Isotonic
0
0
30
60
90
120
Time (minutes)
Figure 4 Measurements of Na+ concentration over time. Urine Na+ concentration was calculated from
values collected from Na+ meters. The control subject is the only subject in which urine Na+
concentration remained constant. For the hypotonic and isotonic subjects, they experienced a sharp
decrease in Na+ concentration, followed by increases in Na+ concentration afterwards. (Alkalosis subject
should experience a constant or slight increase in Na+ concentration)
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After sodium concentration was found, those values were used in order to calculate Na+
clearance. As can be seen in Figure 5, the control subject appeared to have a relatively constant
urine Na+ clearance over time. (Alkalosis subject should have similar results to the control. No
data.) The isotonic subject had a sharp increase in Na+ clearance from 0.41 mEq/L at Time 0 to
0.867 mEq/L at Time 30. After that, Na+ clearance started to decrease. The hypotonic subject on
the other hand, experienced a decrease in Na+ clearance. This subject had an initial Na+
clearance of 1.037 mEq/L at Time 0 and continuously declined until he reached 0.68 mEq/L Na+
concentration at Time 120.
Urine Na+ Clearance
(mL/min)
1.2
1
0.8
0.6
Control
0.4
Hypotonic
0.2
Isotonic
0
0
30
60
90
120
Time (minutes)
Figure 5 Urine Na+ clearance was measured over time. All subjects appeared to have different effects on
Na+ clearance. The control subject remained relatively constant for Na+ clearance. Isotonic subject had
an increase in Na+ clearance, followed by a slight decrease. The hypotonic subject on the other hand
continuously decreased in Na+ clearance.
Next, creatinine clearance was calculated in order to estimate glomerular filtration rate.
However, in order to find creatinine clearance, we must first find creatinine concentration, which
is obtained through the spectrophotometer. The spectrophotometer will give us absorbance
values, in which we will to calculate creatinine concentration from the equation
Y=6.4378x+0.0229. As can be seen in Figure 6, creatinine clearance decreased from Time 0 to
Time 60 for both the isotonic and control subjects. However the isotonic subject experienced a
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greater decrease in creatinine clearance than the control subject. The hypotonic subject
experienced a slight increase in creatinine clearance from 0.137 mL/min to 0.187 mL/min.
(Alkalosis subject should either display a slight decrease in creatinine clearance or remained the
Creatinine Clearance
(mL/min)
same.)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Control
Isotonic
Hypotonic
0
60
Time (minutes)
Figure 6 Creatinine clearances at Time 0 and 60. The control and isotonic subjects displayed a decrease
in creatinine clearance at Time 60. The hypotonic subject on the other hand, seems to have experienced a
slightly higher creatinine clearance at Time 60.
Next, expected water secretion was compared to actual water excretion. Expected water
excretion was calculated by multiplying the flow rate (VUrine) at Time 0 by 120 min. This will be
used as a control to see the effects of the consumption of various fluids and fluid volumes.
Actual water excretion was calculated by adding all the volumes excreted from Time 30 to Time
120. As depicted in Figure 7, the control subject was the only subject in which actual water
excretion matched with expected water excretion. While both the isotonic and hypotonic subjects
had actual water excretion being far greater than expected water excretion. The hypotonic subject
had the biggest disparity in size, as expected volume is 105 mL, while actual volume was 694
mL. The isotonic subject had an expected water volume of 42 mL, while actual water volume
was 322 mL.
Next, expected Na+ excretion was compared to that of actual Na+ excretion. The results
were similar to that of data collected for water excretion. As can be seen in Figure 8, the control
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subject’s actual Na+ excretion (0.059g) matched with his expected Na+ excretion (0.058g). The
isotonic and hypotonic subjects had actual Na+ excretion levels far greater than their expected
excretion levels. The hypotonic subject showed the greatest change, from 0.42 g (expected) to
2.74 g (actual). The isotonic subject had a change from 0.17 g (expected) to 1.27 g (actual).
Water Excretion (mL)
800
600
400
Expected
200
Actual
0
Control
Isotonic
Hypotonic
Test Subjects
Na+ Excretion (g)
Figure 7 Expected water excretion versus actual water excretion in control, isotonic and hypotonic
subjects. The control subject is the only subject in which expected water excretion matched with actual
water excretion. For the isotonic and hypotonic subjects, their actual water excretion was a lot higher than
that of their expected water excretion.
3
2.5
2
1.5
1
0.5
0
Expected
Actual
Control
Isotonic
Hypotonic
Test Subjects
Figure 8 Expected water excretion versus actual water excretion. The control subject was the only subject
in which expected Na+ excretion matched with actual Na+ excretion. The isotonic and hypotonic subjects
had far higher actual Na+ secretion than expected excretion
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Discussion
The kidneys play a vital role in keeping the body in homeostasis as it regulates fluid
balance, bodily pH and electrolytes in the body. This is done so through activities of the
nephrons, which are the structural and functional units of the kidneys. The three main functions
of the nephrons include glomerular filtration, tubular reabsorption and tubular secretion.
Glomerular filtration rate (GFR) is the rate at which plasma is filtered through the
glomerulus and into Bowman’s capsule. Although GFR cannot be measured directly, it can be
estimated through other means such as by measuring the clearance rate of a substance. Clearance
is the rate at which a substance is cleared from a volume of plasma from the glomerulus. The
substance that will be used in this lab is creatinine, which is a byproduct of muscle metabolism
that is produced at a constant rate. It is a good candidate for GFR estimation because it is filtered
out and not reabsorbed. However, it is also secreted, so it will not perfectly estimate GFR, but it
does come close. (Marieb and Hoehn, 966)
The results of this lab often conflicted with what was expected and this may be due to
experimental errors such as failing to properly empty the bladder, exercising beforehand and
consuming caffeinated beverages. In addition, our alkalosis subject was not able to fully
complete this experiment; therefore we had to use another group’s data for the alkalosis subject,
which was also incomplete.
In this study, the flow rates of four different subjects were measured: control, isotonic,
hypotonic and alkalosis. Flow rate is directly proportional to creatinine clearance. In fact, it was
used to calculate creatinine clearance. This means that an increase in flow rate will correspond to
an increase in creatinine clearance and vice versa. Fluid consumption will directly affect flow
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rate. Increases in fluid consumption will lead to an increase in blood volume, which would cause
increases in blood pressure and therefore cause an increase in flow rate and creatinine clearance
(Marieb and Hoehn 966-967). This can be seen in Figure 1, as the hypotonic and isotonic
subject who consumed an excess amount of water had increases in flow rate due to the
mechanisms described earlier. Since flow rate is directly proportional to creatinine clearance, we
should expect the hypotonic and isotonic subject to display increases in creatinine clearance as
well. However this was only seen in the hypotonic subject as seen in Figure 6. The isotonic
subject experienced a decrease in creatinine clearance possibly due to experimental errors.
The opposite effects should have been seen in the control and alkalosis subject; they
should have experienced a decrease in flow rate due to little to no consumption of water. This is
due to decreased blood volume (through excretion of urine over time), which would lead to
lower blood pressure and therefore flow rate (Marieb and Hoehn 966). From the data collected as
seen in Figure 1, the control subject only displayed a slight decrease in flow rate at Time 0 to
Time 30, but increased slightly afterwards possibly due to errors. However, in Figure 6, it is
seen that creatinine clearance decreased at Time 60 for the control subject, which is expected. No
data was collected on the alkalosis subject, but similar findings should be expected. Due to the
low water volume consumption, this would lead to dehydration and therefore lower flow rate and
creatinine clearance; this is also demonstrated in the literature (Gellai, et al. F100).
Excessive fluid consumption will often lead to diuresis. Diuresis is a mechanism used to
help maintain fluid balance by excreting excess water out of the body. This parameter was tested
as we measured expected water excretion versus actual water excretion. In Figure 7, it is seen
that the hypotonic and isotonic subjects, had actual fluid excretion that was a lot higher than
expected fluid excretion. This is expected because in hydrated individuals such as the hypotonic
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and isotonic subjects, due to the increased fluid intake there will be an increase in mean arterial
pressure. This increase in pressure will be sensed by the granular cells (of the juxtaglomerular
complex), which would inhibit the activation of RAAS and therefore aldosterone will not be
released, which means less water will be reabsorbed (Marieb and Hoehn 968). RAAS also
stimulates the release of ADH, but since it is inhibited there will be decreased aquaporin
presence in the DCT and collecting duct, therefore decreasing water reabsorption (Marieb and
Hoehn, 994-995). In addition to this, the increase in fluid volume or Na+, will lead to the release
of atrial natriuretic peptide (ANP). ANP has the opposite effects of aldosterone and will inhibit
ADH and aldosterone, thereby promoting Na+ and water excretion. (Baxter, et al. 529)
Although the data did not support this in the control subject, the opposite effects should
be seen in dehydrated individuals such as the control and alkalosis subject. These individuals
consumed little to no water and urinated every 30 minutes, so this would decrease blood volume
and therefore cause an increase in plasma osmolality. This increase will be sensed by the
osmoreceptors (of hypothalamus) and ADH will be released from the posterior pituitary gland.
(Marieb and Hoehen 994) Once ADH is released into the system, it will bind to receptors in the
DCT or collecting duct and will cause the insertion of aquaporin 2 in the apical membrane,
which would contribute to water reabsorption from the filtrate. On the basolateral membrane
there will be aquarporin 3 and 4, which would allow water to re-enter the blood (Sherwood 544).
In addition, little fluid consumption would lead to a decrease in blood pressure (sensed by
macula cells) and therefore RAAS will be activated, leading to water and sodium reabsorption.
Therefore less water will be excreted, leading the subject to have more concentrated urine.
Plasma osmolality not only affects water reabsorption, but it will also affect electrolyte
reabsorption such as sodium (Na+) as seen earlier. In addition, filtrate osmolality will play a role
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in Na+ reabsorption as well. RAAS is one of the main regulators of Na+ excretion, as it will
cause reabsorption of Na+ due to the effects of aldosterone and angiotensin II (Hall 962). This
parameter was looked at when we compared actual Na+ excretion to expected sodium excretion.
As seen in Figure 8, the isotonic subject excreted more Na+ than the expected value. This is due
to the excess consumption of saline solution, leading to higher Na+ excretion in order to
maintain electrolyte homeostasis. Since the isotonic subject consumed a large amount of fluid,
this will cause an increase in GFR, as explained earlier. The increase in GFR will cause more
Na+ to remain in the filtrate and therefore more Na+ will be excreted, as there is less time for
reabsorption (Marieb and Hoehn 966). In addition, since there is a high concentration of Na+ in
the filtrate, rennin will not be released by the juxtaglomerular cell, which means there will be no
aldosterone to increase Na+ reabsorption (Sherwood 561). In addition, the effects of ANP will be
seen as described earlier, which further promotes Na+ and water excretion (Baxter, et al. 529).
The alkalosis subject should experience a slight increase in Na+ excretion due to the
same factors as the isotonic subject. The slight increase is due to the consumption of sodium in
the form of sodium bicarbonate. However, the Na+ content of the solution may also have been
negligible, which could lead Na+ excretion to be constant. This will be due to the fact that blood
osmolality will not increase because Na+ consumption was not excessive and it will not decrease
in osmolality because fluid consumption was not excessive. Therefore ADH should neither be
upregulated or inhibited and Na+ excretion should be the same.
Although the data did not support this, the opposite effects can be seen in the hypotonic
and control subjects. The hypotonic subject consumed an excess amount of water, leading to
decreased osmolality in the blood and therefore in the filtrate as well. Since this subject
consumed a large amount of water, the RAAS system will not be activated because this subject’s
P a g e | 15
blood pressure is already elevated. However, Na+ reabsorption will still take effect and this
could be done without the reabsorption of water. Na+ reabsorption will of course take place in
the PCT (proximal convoluted tubule) through active transport (water reabsorption will take
place here as well), and loop of Henle (through active transport and passive transport by
following a gradient). At the DCT and collecting duct Na+ reabsorption is usually controlled by
hormones such as aldosterone. However, at the DCT, there are also amiloride-blockable Na+
channels, which reabsorbs Na+ without water according to the body’s needs. (Eaton, et al. 941)
This mechanism will help the hypotonic subject reabsorb Na+ without reabsorbing water. In
addition, it will help with Na+ reabsorption despite the high GFR, which would tend to lower
Na+ reabsorption. Lastly, there will be autoregulations in which the myogenic mechanism will
cause the afferent arteriole to constrict in response to the stretching of the arteriolar walls due to
increased plasma volume. This constriction will decrease GFR by restricting blood flow,
therefore allowing for more Na+ reabsorption, resulting in decreased Na+ excretion.
In the control subject, no liquids were consumed, so this would cause a decrease in blood
pressure. Therefore the body will want to reabsorb water and Na+ in order to restore blood
pressure to normal. Na+ is reabsorbed because water generally follows Na+ and higher solutes in
the blood equates to higher blood pressure. The juxtaglomerular cells will respond to this
decrease in blood pressure and will cause the release of renin. The same pathways will be
activated like that of the hypotonic subject leading to Na+ and water reabsorption. In addition,
since there was a decrease in blood pressure, that will lead to a lower GFR, which would lead
Na+ to stay in the filtrate for a longer time, which would allow for greater reabsorption. (De
Alvarez 931)
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The Na+ excretion values were then used to calculate Na+ clearance. Na+ clearance is
directly proportional to Na+ excretion. An increase in Na+ excretion equates to higher Na+
clearance and a decrease in Na+ excretion would equate to lower Na+ clearance. In the
hypotonic subject, it can be seen from Figure 5 that this subject displayed a constant decrease in
Na+ clearance as expected due to consumption of excess water. This would lead to decreased
osmolality in the blood and therefore in the filtrate as well, which would result in Na+
reabsorption from actions of amiloride-blockable Na+ channels. (Eaton 941) This would then
cause Na+ excretion to decrease and therefore cause lower Na+ clearance. The control subject
should also have the same results, because this subject is reabsorbing Na+ in order to reabsorb
water due to dehydration. This would lead to lower Na+ excretion and therefore lower Na+
clearance.
The isotonic subject experienced an increase in Na+ clearance as expected due to the
excess Na+ consumption. Since Na+ consumption is high, blood osmolality will be high and
therefore filtrate osmolality as well. In addition, since this subject also consumed a large amount
of water, GFR will increase, which would also lead to greater Na+ in the filtrate. This increase in
filtrate osmolality, will suppress the release of aldosterone and Na+ will not be reabsorbed.
(Marieb and Hoehn 968) This should lead to higher Na+ excretion and therefore higher Na+
clearance. In addition, this subject will also have a high GFR, which would contribute to higher
Na+ excretion as well, leading to higher Na+ clearance.
Lastly, the alkalosis subject could also experience similar effects to that of the isotonic
subject (increased Na+ clearance) due to the consumption of Na+ in the form of sodium
bicarbonate, but this amount may have been negligible, leading to a constant Na+ clearance. It
P a g e | 17
could be constant because there will not be increased osmolality in the filtrate from excess Na+
and there will not be decreased osmolality due to the consumption of Na+ in the solution.
Another Na+ parameter that was looked at was urine Na+ concentration. For the
hypotonic subject, since there was high water excretion (due to high GFR) combined with low
Na+ excretion, there should be dilute urine Na+ concentration as can be seen in Figure 4. For the
control subject, since there was low water output combined with low Na+ excretion, the urine
Na+ concentration should be constant over time; this is supported by the data. The alkalosis
subject should have similar results to the control subject due to very little water consumption.
However, salt was consumed in the form of bicarbonate, so this may lead to more concentrated
urine due to Na+ excretion. For the isotonic subject, there should be increased water output, as
well as Na+, therefore the urine will not be as concentrated due to the overwhelming amount of
water excreted; the data collected supports this finding, as Na+ concentration quickly raised after
Time 60.
The last parameter measured was pH, which is controlled by acid base balance. As seen
in Figure 3, all subjects except the alkalosis subject had a relatively constant pH. This is
expected because pH is mainly affected by hydrogen ions (H+) or bicarbonate (HCO3-), and
since these subjects did not consume H+ or HCO3-, there should be minimal changes in pH in
those three subjects. The alkalosis subject on the other hand, experienced an increase in pH as
expected, due to acid base regulation, which occurs in the proximal convoluted tubule (PCT).
There are two types of intercalated cells that regulate acid base balance: Type A and Type B.
Type A secretes H+ and reabsorbs HCO3-; Type B absorbs H+ and secretes HCO3-. (Kim, et al
1) If enough HCO3- is consumed, then the excess will be excreted from the body; low amounts
will generally lead to reabsorption because the body likes to conserve HCO3- (Pitts, et al. 35).
P a g e | 18
Since HCO3- was consumed, there will be excess in the body, which will cause the intercalated
Type B cells to secrete HCO3- and reabsorb H+ in order to maintain bodily pH. In addition, once
HCO3- is filtered out of the plasma and goes into the filtrate, there will be less reabsorption of
HCO3- due to the excess in the plasma. H+ instead, will be reabsorbed in order to balance pH.
The kidney was evaluated in terms of three functions: fluid, electrolyte and pH balance.
The parameters used to test these functions included: pH, specific gravity, creatinine clearance,
Na+ clearance, flow rate, water excretion and Na+ excretion. It was found that blood pressure
heavily influences flow rate, which is directly proportional to creatinine clearance, which also
correlates to water excretion. Next is plasma and filtrate osmolality, affects Na+ clearance and
excretion, which in turn would affect specific gravity. Lastly, pH is regulated by acid base
balance, in which excess HCO3- or H+ would be secreted.
P a g e | 19
Sample calculations
All sample calculations will be done for control at time 0, except fluid intake volume needed to
drink, which will be done for the hypotonic subject.
Fluid intake volume
Fluid intake = body weight (kg) * 14mL
Body weight = 150 lb =68 kg
Fluid intake= 68 kg* 14 mL=952 mL
Vurine (Flow rate)
Vurine= Urine volume (mL)/ Elapsed Time (min)
Urine volume= 28 mL
Elapsed time =75 min
Vurine= 28mL/ 75 min= 0.373 mL/min
UCr estimate
UCr= (CCr *PCr)/ VUrine
Ccr given: 125 mL/min
Pcr given: 12 mg/L for males and 10 mg/L female
UCr= (125 mL/min*12 mg/L)/ 0.373 mL/min
UCr= 4021.45 mg/L
Dilution Factor (DF)in
DF= UCr/50
UCr= 4021.45 mg/L
- 4021.45 mg/L/50 =80
Creatinine Concentration
UCr= sample [Cr]* DF
Sample [Cr] derived from creatinine spectrometer B equation
- Y=6.4738x+0.0229
o Y= Spectrometer Reading
o X= Sample [Cr]
Y= 0.975; solve for X
0.975= 6.4738x+0.0229
X=0.147 mg/L
Creatinine Clearance
CCr= UCr*VUrine/ PCr
P a g e | 20
UCr= 0.147 mg/L* 80= 11.766 mg/L
- (11.766 mg/L* 0.373 mL/min)/ 12 mg/L= 0.366 mL/min
Water Expected
WaterExpected= Vurine(at time 0) *120
.373 mL/min*120 min= 45 mL
Water Actual
WaterActual= sum of urine volume from T=30 to T=120
10mL+11mL+12mL+12 mL= 45 mL
Sodium Concentration
Na+ Meter 2:
Y= 24.364 ln(x)-127.4
Y= -29
-29=24.364 ln(x)-127.4
X=56.76 mEq/L =UNa
Sodium Clearance
CNa= UNa*Vurine/PNa
VUrine= 0.373 mL/min
PNa= 145 mEq/L
UNa=56.76 mEq/L
CNa= 56.76 mEq/L *0.373 (mL/min)/145 mEq/L= 0.146 mL/min
Sodium Expected
NaExpected= 2.76[(gr-min)/mEq]* Vurine(mL/min)*UNa(mEq/L)
NaExpected= 2.76[(gr-min)/mEq]* 0.373(mL/min)*56.76(mEq/L)*(1L/1000mL)
= 0.05848 grams Na+
Sodium Actual
NaActual=Σ[0.023(g/mEq)*UNa(mEq/L)*Urine Volume (L)]
Use data from T=30 to T=120
NaActual= [0.023(g/mEq)*56.76(mEq/L)*.01(L)] +[0.023(g/mEq)*56.76(mEq/L)*.011(L)] +
[0.023(g/mEq)*56.76(mEq/L)*.012(L)] + [0.023(g/mEq)*56.76(mEq/L)*.012(L)]
=0.0587 grams
P a g e | 21
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