Department of Physiology BMS2031 Body Systems Physiology Water Diuresis Worksheet
Due Date: 2 pm Friday 25thMay
Joson Joy 1)
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What does the word ‘diuresis’ refer to?
Diuresis refers to the overproduction of urine, or excess urine flow. To be classed as dieresis, the flow rate needs to be more than twice the normal flow rate of urine.
2)
What are the particular characteristics of a ‘water diuresis’?
Water dieresis refers to the condition where there is increased outflow of water through urinary output And little or no solute excretion.
3)
In the table below record the details for each of the subjects in your group. If there were only 3 subjects in your group draw a line through the last row (Subject D). (2 marks) Volume of
Subject
Treatment
Sex
Body Weight
Water Ingested
(kg)
(litres)
A
Control
M
64
768
B
Exercise
M
91
1092
C
ADH (Desmopressin) – Ion
M
77
920
M
69
820
analyser D
ADH (desmopressin) Osmometer
4)
Complete the data tables on the next two pages. There should be one table completed for each subject in your group. Each subjects will have data for urine Sodium Ion concentrationor osmolality. If there were only 3 subjects in your group write ‘no subject available’ across the last data table. (12 marks)
5)
For the subjects in your group plot graphs showing the effects of the various treatments on: (a) Rate of urine production (ml/min) versus time. Plot the data for all subjects on the one graph. Make sure you identify each subject (b) Urine osmolality versus time. (c) Urine sodium concentration versus time. (d) Sodium excretion rate versus time.
For graphs (b) to (d) there will be a variable number of subjects depending on whether sodium concentration or osmolality was determined. Attach these four graphs to this Worksheet.
(4 marks for each graph = total of 16 marks)
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Subject: Alex Treatment: Control
Sample 1
Drink
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6
Time of day (pm)
2:17
2:38
2:58
3:18
3:38
3:58
Time interval (min)
0:00
20
20
20
20
20
Urine volume (ml)
140
50
160
180
50
30
Urine flow (ml/min)
2.33
2.5
8
9
2.5
1.5
+
155
68
27
31
74
123
+
361.15
170
216
279
185
184.5
Na conc’n (mmol/litre) Na excretion rate (mol/min) Urine osmolality (mOsm/kg H2O) Osmolar excretion rate (Osm/min)
Subject: Joson Treatment: Exercise
Sample 1
Drink
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6
Time of day (pm)
2:25
2:48
3:08
3:28
3:48
4:08
Time interval (min)
0;00
20
20
20
20
20
Urine volume (ml)
50
20
20
60
95
35
Urine flow (ml/min)
0.833
1
1
3
4.75
1.75
+
70
39
40
15
8
15
+
58.31
39
40
45
35
26.25
Na conc’n (mmol/litre) Na excretion rate (mol/min) Urine osmolality (mOsm/kg H2O) Osmolar excretion rate (Osm/min)
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Subject: Jesse Treatment: Demopressin – Ion Analyser
Sample 1
Drink
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6
Time of day (pm)
2:25
2:48
3:08
3:28
3:48
4:08
Time interval (min)
0;00
20
20
20
20
20
Urine volume (ml)
309
0
19
0
0
0
Urine flow (ml/min)
5.15
-
0.95
-
-
-
+
97.8
-
84.3
-
-
-
+
503.67
-
80.9
-
-
-
Na conc’n (mmol/litre) Na excretion rate (mol/min) Urine osmolality (mOsm/kg H2O) Osmolar excretion rate (Osm/min)
Subject: Nathan Treatment: ADH- Osmometer
Sample 1
Drink
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6
Time of day (pm)
2:25
2:48
3:08
3:28
3:48
4:08
Time interval (min)
0;00
20
20
20
20
20
Urine volume (ml)
118
10
10
10
25
10
Urine flow (ml/min)
1.97
0.5
0.5
0.5
1.25
0.5
Urine osmolality (mOsm/kg H2O)
1021
1545
1085
Inconclusive
1639
Inconclusive
Osmolar excretion rate (Osm/min)
2011.37
772.5
542.5
-
2048.75
Inconclusive
+
Na conc’n (mmol/litre) +
Na excretion rate (mol/min)
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6) What is meant by the term ‘osmolality’?(1 mark) Osmolality is a measure of the number of osmoles of solute per kilogram of water present in a sample. It is used to describe bodily fluids, which contain osmotically active solutes.
7) The average data from all subjects in the entire class (all days) will be posted on the PHY2021 WebCT site. Use this class data to answer the following: (a) Describe what happens to the rate of urine production in the 3 different treatment groups.(4
marks) As seen in Figure 1, it is evident that urine production varied for subject with different treatments. The control subject had a steady increase in urinary output. It is noteworthy that the urinary output Increased markedly 30 mins after drinking water, accounting for the lag period that occurs while water is being absorbed by the body. It is also evident that subjects who underwent exercise also showed flow rates similar to that of the control until after exercise. A notable downward trend in urinary output can be seen at the 80 minute mark. Subjects treated with the desmopressin had urinary output which decreased over the duration of the practical.
(b) Compare what happens to the urine osmolarity in the control subject and the desmopressin subject. Comment on the relationship between urine flow rate and solute concentration.(4 marks) Under normal circumstances, increase water diuresis causes a decrease urine osmolarity due to an Increased solute concentration. However, desmopressin causes an anti-diuretic effect and causes the Osmolarity to increase. It is evident that as urine flow increases, the solution becomes more dilute.
(c) Describe and explain what happens to the urine sodium and osmolar excretion rates in the control and desmopressin subjects.(4 marks) It is evident that the control subject had lower urine sodium concentration. This was due to a higher flow of liquid. Despite the higher fluid volume flow, solute excretion remained unchanged. Since the water that was ingested had little or no salt, the increased volume of water caused a change in sodium concentration of urine. On the other hand, increased reabsorption caused by the desmopressin meant that solute concentration increased and hence osmolar excretion rate increased.
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8) Why is there a delay in the onset of the diuresis after water loading in the control subject? (4 marks) The delay is mainly caused by the time it takes for water to be absorbed by the GI tract into the body. Once absorbed, there is an increase in extracellular fluid volume and consequently a lower osmolality. Initially, after being absorbed into the bloodstream, baroreceptors in the carotid sinuses detect blood volume expansion. They send signals to the medullary cardiovascular centre to initiate parasympathetic activity, resulting in vasodilation of blood vessels to the kidneys and other renal organs. This increases renal plasma flow leading to an increase in the Glomerular Filtration Rate (GFR). There is also an inhibitory effect on the release of ADH from the posterior pituatory. This means that there is lower levels of plasma ADH resulting in lower permeability of the collecting duct and hence lower reabsorption of water. Due to the several processes, the end result is only produced after an initial delay.
9)
Describe the mechanisms by which severe exercise or emotion could affect the diuresis produced by a water load.(4 marks) As stated above, it is evident that after exercise, urinary output decreased. During exercise, it is likely the subject would lose water through sweat and also be used for other bodily function relating exercise. This means that osmolality increases and this change is detected by the osmoreceptors in the anterior pituatory, which signals the release of more ADH from the posterior pituatory. The consequent increase in plasma ADH acts on the epithelial cells of the kidney, increasing water reabsorption. Furthermore, the
elevated levels of plasma adrenaline increases sympathetic activity causing vasoconstriction, resulting in lower renal blood flow. Both these effects combine to produce the effect of lower urinary output.
10) Briefly account for the effects of administered desmopressin on the diuresis (subject B).(4 marks) For the subjects administered with desmopressin, urinary output decreased significantly. Desmopressin is a synthetic drug which mimics some effects of the Anti-Diuretic Hormone (ADH) produced in the body. Desmopressin only affects the V2 receptors on the epithelial cells of the kidney collecting ducts. By acting on the V2 receptors, it causes a cascade of signalling pathways which results in the fusing of vesicles containing aquoporin to the luminal membrane, increasing water reabsorption and thus less flow
11) If a control subject was dehydrated at the beginning of the class, how would you expect this to affect his or her response to the water load?(4 marks) If the subject was dehydrated before the experiment it is likely that he/she would produce a smaller volume for the first sample than that of the control subject. This is because dehydration causes a higher expression of embedded aquoporins on the luminal membrane, which re-absorb greater amount of fluids.
12) What effect does alcohol have on water diuresis? (You might like to think about your own personal experience!) What is the mechanism of action of alcohol on water diuresis? ? (4 marks) Alcohol has an inhibitory effect on the part of the posterior pituatory which controls the release of ADH. It does so by causing an inhibition of the voltage gated channels which means that there is little or no release of ADH. This reduction in the levels of ADH increases osmolar flow rate and hence increases
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diuresis. This also means there is reduced water re-absorption. This leads to the onset of dehydration which stimulates an increased release of ADH causing the almost universal feeling of a hangover.
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13) Fill in the following table.
Stimulus
Increased osmolality (dehydration)
Decreased osmolality
Increased blood volume
Decreased blood volume
Type/Site of Receptors
ADH Response
Physiological response on Urine Volume
Physiological response on Blood Volume
Osmoreceptors/ Hypthalamus
Increase
decrease
Increase
Osmoreceptors/ Hypthalamus
decrease
Increase
decrease
Baroreceptors/
Decrease
decrease
decrease
increase
Increase
Increase
Carotid + Aortic
Baroreceptors/ Carotid + Aortic
(8 marks)(0.5 for each ‘box’ = 0.5 x 16 = 8)
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