1 Discuss whether or not sweat should be considered as an excretory
product. Suggest
arguments both for and against.
(A)
2 Undigested food has never been used in your cells; it has merely
passed through the
alimentary canal. For this reason, egestion
of faeces is not usually included under the heading
of excretion. However, at least one
component of the faeces could be considered as an excretory product. Name this
component, say where it comes from and why its removal can be regarded as
excretion.
(A)
3 The heart pumps about 5 litres of blood per minute. At rest, about
one-quarter of the heart's output passes through the kidneys. About180 litres
of blood-derived liquid (glomerular filtrate) passes out of the glomeruli, into
the renal capsules each day.
Use
these figures to calculate the percentage volume of blood that is filtered by
the kidneys. (I)
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subject after drinking a litre of water.
(a) What is the approximate rate of urine
production in normal circumstances?
(b) What was the maximum rate of urine
output in the course of the experiment?
(c)
How long did it take to reach the
maximum rate of urine output?
(d)
How long did the subject take to get.
rid of the excess water? (I)
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line) and concentration (broken line) of
urine produced in one
day.
(a) In general, what is the relationship
between the volume and the
concentration of urine?
(b) Suggest what might have happened
between 12 noon and 2 p.m. to cause
both the volume and the concentration
to increase.
(c) What might have happened between
4 p.m. and 6 p.m. to cause a rise in
volume but decrease in concentration?
(d)
Why do you think the concentration
increases so much during the night?
(I)
(NOTE. Water has a specific gravity of 1.
Values
above this represent an increase in
concentration
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Excretion and the Kidneys - exercises and discussion (continued)
6 The following table shows the
concentration of certain ions in plasma and
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Plasma / g per 100 cm3
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Urine/ g per 100 cm3
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Water
Sodium
Potassium
Calcium
Chloride
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90-93
0.32
0.02
0.01
0.37
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95
0.6
0.15
0.015
0.6
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in urine. The percentage volume of water is
also shown.
Plot the figures for the ions on a bar
chart.
Put the values for the plasma and urine
concentrations on the same chart in order
to show the changes clearly.
(a) Are the ions more concentrated in
plasma or in urine?
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have come about simply by removal of
water. What evidence is there
for this?
(c)
Which of the ions has increased its
concentration the most?
(d)
In what ways might the kidneys
increase .the concentration of ions in
urine?
(I)
7 The table shows the survival rate of kidney patients on different
forms of treatment.
(NOTE. Records do not go beyond 3years in this
study which was conducted some years ago.
The figures in all categories will have
improved significantly)
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Treatment
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Sample size
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% survival
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Dialysis in hospital
Dialysis at home
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27,495
4,518
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1 year
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2 years
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3 years
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87.5
95.3
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77.0
90.7
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68.0
84.3
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Kidney transplant
from living donor
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833
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87.5
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82.2
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79.4
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Kidney transplant from dead donor
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5,782
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81.1
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74.9
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70.6
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(a) Which set of figures do you think is the most reliable? Why do you
think so?
(b) It seems surprising that the survival rate for dialysis in hospital
is lower than for
dialysis at home. Suggest a simple explanation for this difference,
(c) Why, do you think, is the survival rate for transplants greater when
the kidney is taken
from a living donor?
(d) Discuss which treatment might be most cost-effective. (I/A)
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Excretion
and the kidneys - exercises and discussion (continued)
8 Read the following passage:
Two factors could increase the potential
demand for transplants. First the relaxation of age
and fitness criteria for first
transplantation (many units have an upper age limit of 55, but this
may change). The second, and very important,
factor is the survival rate of transplantees. If
patient survival were to rise but graft
survival were to remain the same, the potential demand
for second, third and even subsequent
transplants could be very considerably increased.
©
Office of Health Economics
Explain, in your own words, the two
possible causes of an increased demand for donor
kidneys. Invent examples of age, patient
survival and graft survival to illustrate your explanations.
(C)
9 A physiologist wants to find out the rate of filtration in the
glomeruli of the kidneys. The
best experimental design would be inject a
substance which
(a) cannot pass through the glomerular capillaries
(b) can pass through the glomerular capillaries but is totally
reabsorbed in the renal
tubules
(c) can pass through the glomerular capillaries and is partially
reabsorbed in the renal tubules
(d) can pass through the glomerular capillaries and is not reabsorbed in
the renal tubules. (E/A)
10 A researcher wants to find out if a drug affects the volume of
urine produced. Suggest an experimental procedure to find out if this is
so.
(E)
It is nicely represented.
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