Department of Physiology

PHY2021Body Systems Physiology

Water DiuresisWorksheet

Due Date: Noon (12 pm) Friday May 31

Pre-prac reading: Vander’s Human PhysiologyChapter 11 Section B (the first few pages on the posterior pituitary)Chapter 14, section B.4 (Renal Water Regulation)

TOTAL MARKS = 75

1) What does the word ‘diuresis’ refer to?

The word diuresis by any means the excessive discharge of water in the urine, which might be due to the

increased intake of liquid or effects of diuretic drug.

2) What are the particular characteristics of a ‘water diuresis’?

Water diuresis by any means the increase in urinary output following extensive intake of water. Some of

the characteristic features of water diuresis are: water diuresis starts at 15 minutes after intake of water

and reaches its maximum at 40 minutes, urinary output may increase to 20Litres per day and urine

discharged is diluted. It is resulted from inhibition of ADH secretion, causing low water permeability

in distal tubule and collecting duct. As a result, excess water is discharged but there are little or no change

in the concentration of solute.

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)

Subject Treatment Sex Body Weight

(kg)

Volume of

Water Ingested

(litres)

A Exercise F 42.5 0.510

B Control F 60.5 0.726

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 concentration or 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 in terms of the treatment group (ie Control, Exercise or ADH)

(b) Urine osmolality versus time (for those subject for which osmolarity was measured).

(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)

Subject:     A

Treatment:   Exercise

Sample 1 Drink Sample 2 Sample 3 Sample 4 Sample 5 Sample 6

Time of day

Time interval (min)

0 20 40 60 80 100

Urine volume (ml) 35.61 49.44 42.52 48.42 12.88 8.11

Urine flow (ml/min)

Na+ conc’n (mmol/litre)

Na+ excretion rate (mol/min)

Subject:     B

Treatment: Control  

Sample 1 Drink Sample 2 Sample 3 Sample 4 Sample 5 Sample 6

Time of day

Time interval (min)

0 20 40 60 80 100

Urine volume (ml) 41.53 51.60 46.41 41.43 53.75 44.70

Urine flow (ml/min)

Na+ conc’n (mmol/litre)

Na+ excretion rate (mol/min)

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6) What is meant by the term ‘osmolality’?(1 mark)

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)

(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)

(c) Describe and explain what happens to the urine sodium and osmolar excretion rates in the control and desmopressin subjects.(4 marks)

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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)

9) Describe the mechanisms by which severe exercise or emotion could affect the diuresis produced by a water load.(4 marks)

10) Briefly account for the effects of administered desmopressin on the diuresis (subject B).(4 marks)

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)

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)

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13) Fill in the following table (where applicable the an arrow or the word increase, decrease or unchanged is sufficient)

Stimulus Type/Site of Receptors

ADH ResponsePhysiological response on Urine Volume

Physiological response on

Blood Volume

Increased osmolality (dehydration)

Decreased osmolality

Increased blood volume

Decreased blood volume

(8 marks)(0.5 for each ‘box’ = 0.5 x 16 = 8)

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