618 Chapter 17
- Explain how the structure of the epithelial wall of the
proximal tubule and the distribution of Na^1 /K^1 pumps in
the epithelial cell membranes contribute to the ability of the
proximal tubule to reabsorb salt and water. - Describe how the thiazide diuretics, loop diuretics, and
osmotic diuretics work. - Identify where K^1 secretion occurs in the nephron,
and explain how this secretion is regulated to maintain
homeostasis of blood K^1 levels. Also, explain how loop
diuretics and thiazide diuretics can cause excessive K^1
secretion and hypokalemia. - Which diuretic drugs do not produce hypokalemia? How do
these drugs function as diuretics and yet spare blood K^1? - Explain the mechanisms that normally prevent glycosuria.
Can a person have hyperglycemia without having
glycosuria? Explain. - Explain how filtration, secretion, and reabsorption affect
the renal plasma clearance of a substance. Use this
information to explain how creatinine can be used to
measure the GFR. - What happens to urinary bicarbonate excretion when a
person hyperventilates? How might this response be helpful? - Describe the location of the macula densa and explain
its role in the regulation of renin secretion and in
tubuloglomerular feedback.
Test Your Analytical Ability
- The very high rates of urea transport in the region of the
collecting duct in the inner medulla are due to the presence of
specific urea transporters that are stimulated by ADH. Suppose
you collect urine from two patients who have been deprived of
water overnight. One has normally functioning kidneys, and
the other has a genetic defect in the urea transporters. How
would the two urine samples differ? Explain. - Two men are diagnosed with diabetes insipidus. One didn’t
have the disorder until he suffered a stroke. The other
had withstood the condition all his life, and it had never
responded to exogenous ADH despite the presence of normal
ADH receptors. What might be the cause of the diabetes
insipidus in the two men? - Suppose a woman with a family history of polycystic
kidney disease develops proteinuria. She has elevated blood
creatinine levels and a reduced inulin clearance. What might
these lab results indicate? Explain.
34. You love to spend hours fishing in a float tube in a lake,
where the lower half of your body is submerged and the
upper half is supported by an inner tube. However, you
always have to leave the lake sooner than you’d like because
you produce urine at a faster than usual rate. Using your
knowledge about the regulation of urine volume, propose an
explanation as to why a person might produce more urine
under these conditions.
35. You have an infection, and you see that the physician is
about to inject you with millions of units of penicillin. What
do you think will happen to your urine production as a
result? Explain. In the hope of speeding your recovery, you
gobble extra amounts of vitamin C. How will this affect your
urine output?
36. Explain how the different causes of incontinence could
be treated by (a) surgery, (b) a drug that blocks specific
muscarinic ACH receptors, and (c) a drug that blocks
the action of testosterone (by inhibiting its conversion to
dihydrotestosterone; see chapter 20).
37. Potassium is both reabsorbed and secreted by the nephron.
Explain this statement, and speculate about the possible
benefits of the nephron handling potassium in this way.
38. What are xenobiotics, and how are we able to quickly
eliminate them in the urine? Describe the carriers involved,
and how they can transport many different molecules.
Explain how this elimination of xenobiotics can sometimes
interfere with medical treatment.
Test Your Quantitative Ability
Refer to figure 17.22 and to the renal plasma clearance formula
on page 600 to calculate the answers to the following questions:- A woman who undergoes an inulin clearance test has an
inulin concentration in her urine of 20 mg/ml; an inulin
concentration in her blood of 0.70 mg/ml; and a rate of urine
formation of 4 ml/min. What is her GFR? - If 35% of her filtered urea is reabsorbed, what would be her
renal plasma clearance of urea? - If she is filtering exactly 20% of the total plasma flow rate
to her kidneys, what would be her renal plasma clearance of
PAH? - Suppose a substance has a renal plasma clearance of
300 ml/ min. What portion of its clearance is due to its
secretion across the wall of the tubules?
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