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Saundra Swain
BIOL345-202
11/10/10
                 Regulation of Urine Volume and Salt Concentration in Humans

Abstract

        This experiment was carried out to determine what effect the volume and salinity of
water consumed had on the volume and salt concentration of the urine excreted. A class of
students was divided into three groups; group I consumed a large volume of non-saline water;
group II consumed a large volume of saline water; and group III consumed a small volume of
saline water. The volume and salt concentration of the excreted urine from each individual was
measured and recorded every 30 minutes over a 120 minute timespan. It was found that group I
produced a large volume of hyposmotic, or dilute, urine; group II produced a large volume of
isosmotic urine; and group III produced a large volume of hyperosmotic, or concentrated, urine.
The ability in mammals to osmoregulate, or control the volume and concentration of urine, is
important in water conservation. A terrestrial mammal in a hot, dry habitat would need to
produce very concentrated urine in small amounts in order to conserve water. A mammal in a
cool, wet habitat would not need to conserve as much water and could produce large volumes of
dilute urine.

Introduction

       Osmoregulation is the maintenance of a nearly constant osmotic pressure in the plasma,

resulting in no net movement of water between the intracellular fluid and the extracellular fluid.

Osmoregulation is important in the maintenance of cell volume. In humans, the kidneys play a

large role in osmoregulation; they are responsible for the regulation of salt and water volumes in

the body and controlling the excretion of water and solutes from the body. Human kidneys are

able to generate urine that can be modified to meet an organism’s need at a particular time by

filtering blood and modifying the filtrate so that it can vary depending on the body’s osmotic and

ionic needs at that time. The parts of the kidney responsible for this regulation are the nephrons

and the collecting ducts. Nephrons are made of up the Bowman’s capsule, the proximal

convoluted tubule, the loop of Henle, and the distal convoluted tubule. The Bowman’s capsule

filters the blood to generate primary urine, which is isosmotic to the plasma; the proximal

convoluted tubule causes selective reabsorption of water and solutes into the blood. The loop of
Henle is responsible for generating an osmotic pressure gradient in the medulla and is composed

of two limbs. The descending limb travels from the cortex to the medulla and is permeable to

water and solutes; salts pumped out of the ascending limb are cycled back to the descending

limb, creating high levels of solutes deep in the medulla. The ascending limb is not permeable to

water but is permeable to solutes, it pumps salts out and cycles them back to the descending

limb, causing the fluid leaving the loop of Henle to be hyposmotic to the plasma. The fluid then

enters the collecting duct, which is under hormonal control as to whether the fluid stays dilute or

is concentrated. To produce dilute urine, the collecting duct walls remain impermeable to water,

resulting in large quantities of dilute urine. If vasopressin is released, aquaporins are inserted into

the collecting duct’s walls, allowing water to be reabsorbed back into the blood. This would

result in a small amount of concentrated urine being produced (Hill 2008).

       This experiment tested human osmoregulation by having groups drink differing volumes

and salinities of water and measuring salinity and volume of the urine produced. It was expected

that the group drinking the large quantity of water would produce a large volume of hyposmotic

urine; the group drinking the large quantity of saline water would produce a large volume of

isosmotic urine, and the group drinking the small quantity of saline water would produce a small

volume of hyperosmotic urine.

Materials and Methods

       This experiment was carried out by dividing the class into three groups, each consisting

of 6 individuals. At the beginning of the experiment, group I quickly consumed 1 liter of water;

group II quickly consumed 100ml of water containing 6g of NaCl and then consumed 900ml of

water; group III quickly consumed 100ml of water containing 6g of NaCl. Before consuming the

solutions, each individual immediately collected a urine sample. Collection was carried out by
the individual urinating into a urine collection cup and measuring and recording the volume of

urine in the cup. Ten drops of urine were then transferred to a test tube using a disposable

pipette. Four drops of 5% Potassium Chromate were then added to the test tube and the test tube

was shaken. Finally, 2.9% Silver Nitrate was added dropwise to the test tube and the test tube

was shaken after each drop. The addition of Silver Nitrate stopped once the solution turned from

bright yellow to a reddish brown color and the number of drops necessary to achieve the color

change was recorded. After the first sample was collected, each individual drank the assigned

solution and the above steps for urine collection and testing were performed every 30 minutes for

a total of 120 minutes, resulting in 5 collections per individual.

       Each individual used a data sheet to record the volume of the urine excreted and the

concentration of NaCl in the urine. The data was then compiled and graphed to show

comparisons of the mean urine volume over time and mean urine NaCl concentration over time

for all three groups.

Results

       Analysis of the volume of urine excreted by all three groups is shown in Table 1 and the

means are graphed in Figure 1. Immediately before consuming the water, group I showed a mean

urine volume of 175mL; group II showed a mean urine volume of 84.17mL; and group III

showed a mean urine volume of 125mL. After 30 minutes, group I showed a mean urine volume

of 49.17mL; group II showed a mean urine volume of 76.67mL; and group III showed a mean

urine volume of 79.17mL. After 60 minutes, group I showed a mean urine volume of 201.67mL;

group II showed a mean urine volume of 200mL; and group III showed a mean urine volume of

25.33mL. After 90 minutes, group I showed a mean urine volume of 287.50mL; group II showed

a mean urine volume of 110mL; and group III showed a mean urine volume of 25mL. For the
final sample after 120 minutes, group I showed a mean urine volume of 240mL; group II showed

a mean urine volume of 30mL; and group III showed a mean urine volume of 23.33mL. This

data supported our hypothesis that groups I and II would generate large volumes of urine and

group III would generate a small volume of urine.

       Analysis of salt concentration of urine excreted by all three groups is shown in Table 2

and the means are graphed in Figure 2. Immediately before consuming the water, group I showed

a mean salt concentration of 10mg/ml; group II showed a mean salt concentration of

14.17mg/ml; and group III showed a mean salt concentration of 8.33mg/ml. After 30 minutes,

group I showed a mean salt concentration of 7.67mg/ml; group II showed a mean salt

concentration of 9.83mg/ml; and group III showed a mean salt concentration of 8.17mg/ml. after

60 minutes, group I showed a mean salt concentration of 2.33mg/ml; group II showed a mean

salt concentration of 4.17mg/ml; and group III showed a mean salt concentration of 11.50mg/ml.

After 90 minutes, group I showed a mean salt concentration of 1.83mg/ml; group II showed a

mean salt concentration of 7.5mg/ml; and group III showed a mean salt concentration of

13.50mg/ml. For the final sample after 120 minutes, group I showed a mean salt concentration of

2.67mg/ml; group II showed a mean salt concentration of 13.83mg/ml; and group III showed a

mean salt concentration of 15.17mg/ml. This data supported our hypothesis that group I would

generate hyposmotic urine, group II would generate isosmotic urine, and group III would

generate hyperosmotic urine.
Figure 1


                                                  Urine Volume
                                  350
     Urine Volume (ml)




                                  300
                                  250
                                  200
                                  150                                          Group 1
                                  100                                          Group 2
                                   50
                                                                               Group 3
                                    0
                                         0 min 30 min 60 min 90 min 120 min
                                                        Time




  Figure 2


                                                Salt Concentration
                                  16
     Salt Concentration (mg/ml)




                                  14
                                  12
                                  10
                                   8                                           Group 1
                                   6
                                   4                                           Group 2
                                   2                                           Group 3
                                   0
                                        0 min   30 min 60 min 90 min 120 min
                                                       Time




  Table 1

                                  Group I                Urine Volume (ml)
Name                              Rebecca     Hunter     Nick       katie                Amanda     Kristen         Mean
0 min                                     105        420        375              30            60              60        175
 30min                                     55     90             60              60            20              10   49.16667
60min                                     250        300        240             310            70              40   201.6667
90min                                     285        420        120             310           350             240      287.5
120min        240           270            40             240             320             330       240
       Group II                   Urine Volume (ml)
 Name Chelsea      Kimberly       Jennie      Brittnay          Heather         Delanie         Mean
0min            95          165           25               10              60             150   84.16667
30min         190            55           40               10              10             155   76.66667
60min         280           320           90               30             150             330        200
90min         150           120           50               70              20             250        110
120min          35           40           40               20              30              15         30
       Group III                  Urine Volume (ml)
 Name Ashley       Jennifer       Lauren      Christine         Cody            Logan           Mean
0min          250           210           75               10              35             170        125
30min         150           110          110               25              30              50   79.16667
60min           40           25           27               20              20              20   25.33333
90min           30           25           30               30              15              20         25
120min          25           20           30               40              15              10   23.33333




   Table 2

       Group I                    Concentration (mg/ml)
Name   Rebecca      Hunter        Nick         katie            Amanda          Kristen         Mean
 0 min            7           9           18                9              10               7         10
30min             6           2           10                5              13              10   7.666667
60min             2           1            3                1               4               3   2.333333
90min             3           1            3                1               2               1   1.833333
120min            2           1            9                1               2               1   2.666667
       Group II                   Concentration (mg/ml)
 Name Chelsea       Kimberly      Jennie      Brittnay          Heather         Delanie         Mean
0min              9          23          18                12              11              12   14.16667
30min             5           9          15                12               9               9   9.833333
60min             3           4           7                 5               1               5   4.166667
90min             3           9          15                 5               8               5         7.5
120min           15          17          12                13              11              15   13.83333
       Group III                  Concentration (mg/ml)
 Name Ashley        Jennifer      Lauren      Christine         Cody            Logan           Mean
0min              5          10           5                12               8              10   8.333333
30min             3           4           4                18              13               7   8.166667
60min            10          13          13                14               9              10        11.5
90min            12          15          12                14              13              15        13.5
120min           15          17          18                16              15              10   15.16667
Discussion

       The results of this experiment showed a peak in urine volume for group I after 90 minutes

and a peak in group II after 60 minutes. As expected, group III showed a dramatic decrease in

urine volume after 60 minutes. Group II showed a peak in salt concentration after 120 minutes,

group III showed a slight increase in salt concentration after 120 minutes, and group I showed a

dramatic decrease in salt concentration after 60 minutes. These results were as expected since a

consumption of large amounts of non-saline water will cause the collecting ducts to be

impermeable to water, causing the water in the collecting duct to not be reabsorbed into the

blood resulting in the hyposmotic fluid in the collecting duct to be excreted in a large volume.

The consumption of large amount of saline water also causes the collecting ducts to be

impermeable to water and results in the isosmotic fluid in the collecting duct to be excreted in a

large volume. The consumption of a small amount of saline water triggers the release of

vasopressin, which causes the collecting duct walls to become permeable to water, allowing the

water to be reabsorbed into the blood and conserved, resulting in the hyperosmotic fluid in the

collecting duct to be excreted in a small volume (Hill 2008). Dramatic water loss results in an

increase in salt concentration and may lead to dehydration. In a study examining cutaneous water

loss through sweating, it was found that plasma volume did not dramatically increase which

suggested that osmoregulation was maintaining the plasma volume to preserve cardiovascular

regularity. This was observed in a similar way in our experiment in group III, they had only a

small amount of water available and this resulted in the blood conserving the water volume

rather than excreting it (Shirreffs 2003).

       An experiment examining osmoregulation of marine mammals showed that pinnipeds,

sea otters, cetaceans, and manatees could produce urine more concentrated than the seawater
they live in. This experiment examined the structure of the marine mammal kidney, which is

different from that of a human, in that they are more specialized for living in habitats with

differing salinity levels. Some of the marine mammals had kidneys with hundreds of lobes; the

proximal convoluted tubules of marine mammals are able to store glycogen; there are more

bundles of blood vessels in the medulla than in humans, and there is a layer of tissue and muscle

that separates the cortex from the medulla. This study found that marine mammals could produce

urine more concentrated than that of humans, but less concentrated than that of desert mammals.

It is suggested that marine mammals rely on hormones to regulate urine concentration instead of

anatomical methods (Ortiz 2001).

       Animals that are not mammals, such as reptiles, amphibians and birds are not capable of

producing such concentrated urine as seen in out experiment. Reptiles completely lack a loop of

Henle; therefore they do not create the osmotic pressure gradient that is critical in the production

of concentrated urine. Birds have some nephrons that have a loop of Henle and some nephrons

that do not; thus they cannot produce a large concentration of urine. Desert mammals can

produce more highly concentrated urine than seen in our experiment; these mammals have very

long loops of Henle and thicker medullas which results in the generation of a very large osmotic

pressure gradient which allows them to conserve even more water (Hill 2008).

       The results of this experiment were as expected and support the hypothesis that group I

would generate a large volume of hyposmotic urine, group II would generate a large volume of

isosmotic urine, and group III would generate a small volume of hyperosmotic urine. A

suggestion for additions to this experiment would be measuring the levels of hormones

associated with osmoregulation, such as vasopressin; thirst level; and blood pressure in each
individual participating in this experiment before consuming the water and after each time

interval in which the urine was analyzed (McCormick 2006).

       In conclusion, the consumption of a large volume of non-saline water resulted in the

collecting ducts of the kidney to be impermeable to water and cause the excretion of a large

volume of hyposmotic, or dilute, urine. The consumption of a large volume of saline water also

resulted in the collecting ducts remaining impermeable to water which caused excretion of a

large volume of urine; the presence of salts in the consumed water caused an increase in the salt

concentration of the urine, causing it to be isosmotic. The consumption of a small volume of

saline water resulted in the release of vasopressin and the insertion of aquaporins in the

collecting duct, causing it to become permeable to water, thus allowing the water to be

reabsorbed into the blood; this resulted in the excretion of a small amount of hyperosmotic, or

concentrated, urine.



Literature Cited

Hill, Richard W., Gordon A. Wyse, and Margaret Anderson. 2008. Animal Physiology, 2nd ed.

   Sinauer Associates, Inc., MA: 663-748.

McCormick, SD and D Bradshaw. 2006. Hormonal control of salt and water balance in

   vertebrates. General and Comparative Endocrinology. 147: 3-8.

Ortiz, RM. 2001. Osmoregulation in marine mammals.The Journal of Experimental Biology.

   204: 1831–1844.

Shirreffs, S.M.. 2003. Markers of hydration status. European Journal of Clinical Nutrition. 57

   Suppl 2: S6–S9.

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Osmoregulation

  • 1. Saundra Swain BIOL345-202 11/10/10 Regulation of Urine Volume and Salt Concentration in Humans Abstract This experiment was carried out to determine what effect the volume and salinity of water consumed had on the volume and salt concentration of the urine excreted. A class of students was divided into three groups; group I consumed a large volume of non-saline water; group II consumed a large volume of saline water; and group III consumed a small volume of saline water. The volume and salt concentration of the excreted urine from each individual was measured and recorded every 30 minutes over a 120 minute timespan. It was found that group I produced a large volume of hyposmotic, or dilute, urine; group II produced a large volume of isosmotic urine; and group III produced a large volume of hyperosmotic, or concentrated, urine. The ability in mammals to osmoregulate, or control the volume and concentration of urine, is important in water conservation. A terrestrial mammal in a hot, dry habitat would need to produce very concentrated urine in small amounts in order to conserve water. A mammal in a cool, wet habitat would not need to conserve as much water and could produce large volumes of dilute urine. Introduction Osmoregulation is the maintenance of a nearly constant osmotic pressure in the plasma, resulting in no net movement of water between the intracellular fluid and the extracellular fluid. Osmoregulation is important in the maintenance of cell volume. In humans, the kidneys play a large role in osmoregulation; they are responsible for the regulation of salt and water volumes in the body and controlling the excretion of water and solutes from the body. Human kidneys are able to generate urine that can be modified to meet an organism’s need at a particular time by filtering blood and modifying the filtrate so that it can vary depending on the body’s osmotic and ionic needs at that time. The parts of the kidney responsible for this regulation are the nephrons and the collecting ducts. Nephrons are made of up the Bowman’s capsule, the proximal convoluted tubule, the loop of Henle, and the distal convoluted tubule. The Bowman’s capsule filters the blood to generate primary urine, which is isosmotic to the plasma; the proximal convoluted tubule causes selective reabsorption of water and solutes into the blood. The loop of
  • 2. Henle is responsible for generating an osmotic pressure gradient in the medulla and is composed of two limbs. The descending limb travels from the cortex to the medulla and is permeable to water and solutes; salts pumped out of the ascending limb are cycled back to the descending limb, creating high levels of solutes deep in the medulla. The ascending limb is not permeable to water but is permeable to solutes, it pumps salts out and cycles them back to the descending limb, causing the fluid leaving the loop of Henle to be hyposmotic to the plasma. The fluid then enters the collecting duct, which is under hormonal control as to whether the fluid stays dilute or is concentrated. To produce dilute urine, the collecting duct walls remain impermeable to water, resulting in large quantities of dilute urine. If vasopressin is released, aquaporins are inserted into the collecting duct’s walls, allowing water to be reabsorbed back into the blood. This would result in a small amount of concentrated urine being produced (Hill 2008). This experiment tested human osmoregulation by having groups drink differing volumes and salinities of water and measuring salinity and volume of the urine produced. It was expected that the group drinking the large quantity of water would produce a large volume of hyposmotic urine; the group drinking the large quantity of saline water would produce a large volume of isosmotic urine, and the group drinking the small quantity of saline water would produce a small volume of hyperosmotic urine. Materials and Methods This experiment was carried out by dividing the class into three groups, each consisting of 6 individuals. At the beginning of the experiment, group I quickly consumed 1 liter of water; group II quickly consumed 100ml of water containing 6g of NaCl and then consumed 900ml of water; group III quickly consumed 100ml of water containing 6g of NaCl. Before consuming the solutions, each individual immediately collected a urine sample. Collection was carried out by
  • 3. the individual urinating into a urine collection cup and measuring and recording the volume of urine in the cup. Ten drops of urine were then transferred to a test tube using a disposable pipette. Four drops of 5% Potassium Chromate were then added to the test tube and the test tube was shaken. Finally, 2.9% Silver Nitrate was added dropwise to the test tube and the test tube was shaken after each drop. The addition of Silver Nitrate stopped once the solution turned from bright yellow to a reddish brown color and the number of drops necessary to achieve the color change was recorded. After the first sample was collected, each individual drank the assigned solution and the above steps for urine collection and testing were performed every 30 minutes for a total of 120 minutes, resulting in 5 collections per individual. Each individual used a data sheet to record the volume of the urine excreted and the concentration of NaCl in the urine. The data was then compiled and graphed to show comparisons of the mean urine volume over time and mean urine NaCl concentration over time for all three groups. Results Analysis of the volume of urine excreted by all three groups is shown in Table 1 and the means are graphed in Figure 1. Immediately before consuming the water, group I showed a mean urine volume of 175mL; group II showed a mean urine volume of 84.17mL; and group III showed a mean urine volume of 125mL. After 30 minutes, group I showed a mean urine volume of 49.17mL; group II showed a mean urine volume of 76.67mL; and group III showed a mean urine volume of 79.17mL. After 60 minutes, group I showed a mean urine volume of 201.67mL; group II showed a mean urine volume of 200mL; and group III showed a mean urine volume of 25.33mL. After 90 minutes, group I showed a mean urine volume of 287.50mL; group II showed a mean urine volume of 110mL; and group III showed a mean urine volume of 25mL. For the
  • 4. final sample after 120 minutes, group I showed a mean urine volume of 240mL; group II showed a mean urine volume of 30mL; and group III showed a mean urine volume of 23.33mL. This data supported our hypothesis that groups I and II would generate large volumes of urine and group III would generate a small volume of urine. Analysis of salt concentration of urine excreted by all three groups is shown in Table 2 and the means are graphed in Figure 2. Immediately before consuming the water, group I showed a mean salt concentration of 10mg/ml; group II showed a mean salt concentration of 14.17mg/ml; and group III showed a mean salt concentration of 8.33mg/ml. After 30 minutes, group I showed a mean salt concentration of 7.67mg/ml; group II showed a mean salt concentration of 9.83mg/ml; and group III showed a mean salt concentration of 8.17mg/ml. after 60 minutes, group I showed a mean salt concentration of 2.33mg/ml; group II showed a mean salt concentration of 4.17mg/ml; and group III showed a mean salt concentration of 11.50mg/ml. After 90 minutes, group I showed a mean salt concentration of 1.83mg/ml; group II showed a mean salt concentration of 7.5mg/ml; and group III showed a mean salt concentration of 13.50mg/ml. For the final sample after 120 minutes, group I showed a mean salt concentration of 2.67mg/ml; group II showed a mean salt concentration of 13.83mg/ml; and group III showed a mean salt concentration of 15.17mg/ml. This data supported our hypothesis that group I would generate hyposmotic urine, group II would generate isosmotic urine, and group III would generate hyperosmotic urine.
  • 5. Figure 1 Urine Volume 350 Urine Volume (ml) 300 250 200 150 Group 1 100 Group 2 50 Group 3 0 0 min 30 min 60 min 90 min 120 min Time Figure 2 Salt Concentration 16 Salt Concentration (mg/ml) 14 12 10 8 Group 1 6 4 Group 2 2 Group 3 0 0 min 30 min 60 min 90 min 120 min Time Table 1 Group I Urine Volume (ml) Name Rebecca Hunter Nick katie Amanda Kristen Mean 0 min 105 420 375 30 60 60 175 30min 55 90 60 60 20 10 49.16667 60min 250 300 240 310 70 40 201.6667 90min 285 420 120 310 350 240 287.5
  • 6. 120min 240 270 40 240 320 330 240 Group II Urine Volume (ml) Name Chelsea Kimberly Jennie Brittnay Heather Delanie Mean 0min 95 165 25 10 60 150 84.16667 30min 190 55 40 10 10 155 76.66667 60min 280 320 90 30 150 330 200 90min 150 120 50 70 20 250 110 120min 35 40 40 20 30 15 30 Group III Urine Volume (ml) Name Ashley Jennifer Lauren Christine Cody Logan Mean 0min 250 210 75 10 35 170 125 30min 150 110 110 25 30 50 79.16667 60min 40 25 27 20 20 20 25.33333 90min 30 25 30 30 15 20 25 120min 25 20 30 40 15 10 23.33333 Table 2 Group I Concentration (mg/ml) Name Rebecca Hunter Nick katie Amanda Kristen Mean 0 min 7 9 18 9 10 7 10 30min 6 2 10 5 13 10 7.666667 60min 2 1 3 1 4 3 2.333333 90min 3 1 3 1 2 1 1.833333 120min 2 1 9 1 2 1 2.666667 Group II Concentration (mg/ml) Name Chelsea Kimberly Jennie Brittnay Heather Delanie Mean 0min 9 23 18 12 11 12 14.16667 30min 5 9 15 12 9 9 9.833333 60min 3 4 7 5 1 5 4.166667 90min 3 9 15 5 8 5 7.5 120min 15 17 12 13 11 15 13.83333 Group III Concentration (mg/ml) Name Ashley Jennifer Lauren Christine Cody Logan Mean 0min 5 10 5 12 8 10 8.333333 30min 3 4 4 18 13 7 8.166667 60min 10 13 13 14 9 10 11.5 90min 12 15 12 14 13 15 13.5 120min 15 17 18 16 15 10 15.16667
  • 7. Discussion The results of this experiment showed a peak in urine volume for group I after 90 minutes and a peak in group II after 60 minutes. As expected, group III showed a dramatic decrease in urine volume after 60 minutes. Group II showed a peak in salt concentration after 120 minutes, group III showed a slight increase in salt concentration after 120 minutes, and group I showed a dramatic decrease in salt concentration after 60 minutes. These results were as expected since a consumption of large amounts of non-saline water will cause the collecting ducts to be impermeable to water, causing the water in the collecting duct to not be reabsorbed into the blood resulting in the hyposmotic fluid in the collecting duct to be excreted in a large volume. The consumption of large amount of saline water also causes the collecting ducts to be impermeable to water and results in the isosmotic fluid in the collecting duct to be excreted in a large volume. The consumption of a small amount of saline water triggers the release of vasopressin, which causes the collecting duct walls to become permeable to water, allowing the water to be reabsorbed into the blood and conserved, resulting in the hyperosmotic fluid in the collecting duct to be excreted in a small volume (Hill 2008). Dramatic water loss results in an increase in salt concentration and may lead to dehydration. In a study examining cutaneous water loss through sweating, it was found that plasma volume did not dramatically increase which suggested that osmoregulation was maintaining the plasma volume to preserve cardiovascular regularity. This was observed in a similar way in our experiment in group III, they had only a small amount of water available and this resulted in the blood conserving the water volume rather than excreting it (Shirreffs 2003). An experiment examining osmoregulation of marine mammals showed that pinnipeds, sea otters, cetaceans, and manatees could produce urine more concentrated than the seawater
  • 8. they live in. This experiment examined the structure of the marine mammal kidney, which is different from that of a human, in that they are more specialized for living in habitats with differing salinity levels. Some of the marine mammals had kidneys with hundreds of lobes; the proximal convoluted tubules of marine mammals are able to store glycogen; there are more bundles of blood vessels in the medulla than in humans, and there is a layer of tissue and muscle that separates the cortex from the medulla. This study found that marine mammals could produce urine more concentrated than that of humans, but less concentrated than that of desert mammals. It is suggested that marine mammals rely on hormones to regulate urine concentration instead of anatomical methods (Ortiz 2001). Animals that are not mammals, such as reptiles, amphibians and birds are not capable of producing such concentrated urine as seen in out experiment. Reptiles completely lack a loop of Henle; therefore they do not create the osmotic pressure gradient that is critical in the production of concentrated urine. Birds have some nephrons that have a loop of Henle and some nephrons that do not; thus they cannot produce a large concentration of urine. Desert mammals can produce more highly concentrated urine than seen in our experiment; these mammals have very long loops of Henle and thicker medullas which results in the generation of a very large osmotic pressure gradient which allows them to conserve even more water (Hill 2008). The results of this experiment were as expected and support the hypothesis that group I would generate a large volume of hyposmotic urine, group II would generate a large volume of isosmotic urine, and group III would generate a small volume of hyperosmotic urine. A suggestion for additions to this experiment would be measuring the levels of hormones associated with osmoregulation, such as vasopressin; thirst level; and blood pressure in each
  • 9. individual participating in this experiment before consuming the water and after each time interval in which the urine was analyzed (McCormick 2006). In conclusion, the consumption of a large volume of non-saline water resulted in the collecting ducts of the kidney to be impermeable to water and cause the excretion of a large volume of hyposmotic, or dilute, urine. The consumption of a large volume of saline water also resulted in the collecting ducts remaining impermeable to water which caused excretion of a large volume of urine; the presence of salts in the consumed water caused an increase in the salt concentration of the urine, causing it to be isosmotic. The consumption of a small volume of saline water resulted in the release of vasopressin and the insertion of aquaporins in the collecting duct, causing it to become permeable to water, thus allowing the water to be reabsorbed into the blood; this resulted in the excretion of a small amount of hyperosmotic, or concentrated, urine. Literature Cited Hill, Richard W., Gordon A. Wyse, and Margaret Anderson. 2008. Animal Physiology, 2nd ed. Sinauer Associates, Inc., MA: 663-748. McCormick, SD and D Bradshaw. 2006. Hormonal control of salt and water balance in vertebrates. General and Comparative Endocrinology. 147: 3-8. Ortiz, RM. 2001. Osmoregulation in marine mammals.The Journal of Experimental Biology. 204: 1831–1844. Shirreffs, S.M.. 2003. Markers of hydration status. European Journal of Clinical Nutrition. 57 Suppl 2: S6–S9.