Vanders Renal Questions and Key Comments

Question 1

Ch 1 Key Concept. In addition to excreting waste, the kidneys perform many necessary functions in partnership with other body organ systems.

Question 2

Ch 1 Key Concept. The kidneys regulate the excretion of many substances at a rate that balances their input, thereby maintaining appropriate body content of those substances.

Question 3

Ch 1 Key Concept. A major function of the kidneys is to regulate the volume and osmolality of extracellular fluid volume.

Question 4

Ch 1 Key Concept. The kidneys are composed mainly of tubules and closely associated blood vessels.

Question 5

Ch 1 Key Concept. Each functional renal unit is composed of a filtering component (glomerulus) and a transporting tubular component (the nephron and collecting duct).

Question 6

Ch 1 Key Concept. The tubules are made up of multiple segments with distinct functions.

Question 7

Ch 1 Key Concept. Basic renal mechanisms consist of filtering a large volume, reabsorbing most of it, and adding substances by secretion, and, in some cases, synthesis.

Question 8

1-1 Renal corpuscles are located
a. along the cortico-medullary border.
b. throughout the cortex.
c. throughout the cortex and outer medulla.
d. throughout the whole kidney.

Answer 8

1�1. (b) Renal corpuscles are distributed throughout the cortex, which
includes the region just above the cortico-medullary border
(i.e., the juxtamedullary region). None are in the medulla.

Question 9

1-2 Relative to the number of glomeruli, how many loops of Henle,
and how many collecting ducts are there?
a. Same number of loops of Henle; same number of collecting
ducts.
b. Fewer loops of Henle; fewer collecting ducts.
c. Same number of loops of Henle; fewer collecting ducts.
d. Same number of loops of Henle; more collecting ducts.

Answer 9

1�2. (c) Each glomerulus is associated with a nephron, which includes a
loop of Henle. Each collecting duct is formed from the
coalescence of several nephrons.

Question 10

1-3 It is possible for the body to be in balance for a substance when
a. the amount of the substance in the body is constant.
b. the amount of the substance in the body is higher than normal.
c. the input of the substance into the body is higher than normal.
d. in all of these situations.

Answer 10

1�3. (d) Balance implies that input equals output, which can occur at
normal or abnormal levels of amounts in the body, or normal or
abnormal input, so long as the inputs are matched by equal
outputs.

Question 11

1-4 The macula densa is a group of cells located in the wall of
a. Bowman�s capsule.
b. the afferent arteriole.
c. the end of the thick ascending limb.
d. the descending thin limb.

Answer 11

1�4. (c) The macula densa cells are located in the tubule where it passes
between the afferent and efferent arterioles. This location is at
the end of the thick ascending limb of the loop of Henle just
before it becomes the distal tubule.

Question 12

1-5 The volume of fluid entering the tubules by glomerular filtration
in one day is typically
a. about three times the renal volume.
b. about the same as the volume filtered by all the capillaries in
the rest of the body.
c. about equal to the circulating plasma volume.
d. more than the total volume of water in the body.

Answer 12

1�5. (d) A healthy young 70-kg person contains about 42 L of water
(~60% of body weight), and filters up to 180 L of plasma each
day.

Question 13

1-6 In the context of the kidney, secretion of a substance implies that
a. it is transported from tubular cells into the tubular lumen.
b. it is filtered into Bowman�s capsule.
c. it is present in the final urine that is excreted.

Answer 13

1�6. (a) Secretion implies transport from tubular cell to the lumen. Most
often the substance entered the cell from the blood, but it could
also be synthesized and then transported.

Question 14

Ch 1 Key Note. We use the term �reabsorption� to describe the movement of filtered substances
back into the blood because they are re-entering the blood. �Absorption� describes
the original entrance of consumed substances from the GI tract into the blood.

Question 15

Ch 2 Key Concept. The kidneys have a very large blood flow relative to their mass that is regulated for functional reasons rather than
metabolic demand

Question 16

Ch 2 Key Concept. Glomerular capillary pressure is determined by the
relative resistances of afferent arterioles, which precede
the glomerulus, and efferent arterioles, which follow it.

Question 17

Ch 2 Key Concept. Glomerular filtration proceeds through a three-layered
barrier that restricts filtration of large macromolecules
such as albumin.

Question 18

Ch 2 Key Concept. Negative surface charge on the filtration barrier restricts
filtration of negatively charged solutes more than positively
charged solutes.

Question 19

Ch 2 Key Concept. The glomerular filtration rate (GFR) is determined by the
permeability of the filtration barrier and net filtration
pressure (NFP).

Question 20

Ch 2 Key Concept. Net filtration pressure (NFP) varies mainly with
hydrostatic and oncotic pressures in the glomerular
capillaries.

Question 21

Ch 2 Key Concept. Control of the resistances of the afferent and efferent
arterioles permits independent control of glomerular
filtration rate and renal blood flow.

Question 22

Ch 2 Key Concept. Autoregulation of vascular resistances keeps GFR within
limits in the face of large variations in arterial pressure.

Question 23

2-1. Blood enters the renal medulla immediately after passing through
which vessels?
a. Arcuate arteries
b. Peritubular capillaries
c. Afferent arterioles
d. Efferent arterioles

Answer 23

2�1. (d) Most efferent arterioles feed peritubular capillaries, but those
associated with juxtamedullary glomeruli feed vascular bundles
that descend into the medulla.

Question 24

2-2. Which cell type is the main determinant of the filterability of
plasma solutes?
a. Mesangial cell.
b. Podocyte.
c. Endothelial cell.
d. Vascular smooth muscle.

Answer 24

2�2. (d) While various factors affect how much plasma is filtered, the
glycocalyx, basement membrane, and particularly the slit
diaphragms bridging the foot processes of podocytes, all of
which are extracellular, are the key determinants of what is
filtered.

Question 25

2-3. Which one of the following is NOT subject to physiological
control on a moment-to-moment basis?
a. Hydrostatic pressure in glomerular capillaries.
b. Selectivity of the filtration barrier.
c. Filtration coefficient.
d. Resistance of efferent arterioles.

Answer 25

2�3. (a) Rapid control is exerted over the contractile properties of
vascular smooth muscle that in turn affects hydrostatic pressure
in glomerular capillaries.

Question 26

2-4. A substance is freely filtered and has a certain concentration in
peripheral plasma. You would expect the substance to have
virtually the same concentration in
a. the glomerular filtrate.
b. the afferent arteriole.
c. the efferent arteriole.
d. all of these places.

Answer 26

2�4. (d) Other than larger molecules that are only partially or slightly
filtered, the plasma concentrations of a small freely filtered
substance are not altered by filtration because water and the
substance in question are filtered in the same proportions.

Question 27

2-5. In the face of a 20% decrease in arterial pressure, GFR decreases
by only 2%. What could account for this finding?
a. The resistances of the afferent and efferent arterioles both
decrease equally.
b. Glomerular mesangial cells contract.
c. Efferent arteriolar resistance increases.
d. Afferent arteriolar resistance increases.

Answer 27

2�5. (c) The lowering of pressure upstream from the glomerulus is offset
by contraction of the efferent arteriole, an action that by itself
raises glomerular capillary pressure. The net effect leaves
glomerular capillary pressure almost unchanged.

Question 28

2-6. The hydrostatic pressure within the glomerular capillaries
a. is much higher than in most peripheral capillaries.
b. is about the same as in the peritubular capillaries.
c. decreases markedly along the length of the capillaries.
d. is generally lower than the oncotic pressure in the glomerular
capillaries.

Answer 28

2�6. (a) Glomerular capillary pressure starts at about 60 mm Hg and
falls very little along the length of the capillaries. This value is
far higher than in most peripheral capillaries.

Question 29

Ch 3 Key Concept. Clearance expresses the rate at which a substance is
removed from the plasma and excreted in the urine (renal
clearance), or removed by all mechanisms combined
(metabolic clearance rate), and is always quantified in
units of volume per time.

Question 30

Ch 3 Key Concept. Renal clearance of any substance is calculated by a
clearance formula relating urine flow to urine and plasma
concentrations.

Question 31

Ch 3 Key Concept. Inulin clearance is the best measure GFR because inulin is
freely filtered and neither secreted nor reabsorbed.

Question 32

Ch 3 Key Concept. Para-aminohippurate clearance can be used as an
estimate of renal blood flow.

Question 33

Ch 3 Key Concept. Creatinine clearance is used as practical measure of GFR.

Question 34

Ch 3 Key Concept. Plasma creatinine concentration and/or cystatin C is used
clinically as an indicator of the GFR.

Question 35

Ch 3 Key Concept. Renal scintigraphy assesses the function of each kidney
separately.

Question 36

3-1. We can calculate the renal clearance of any substance if we know
which pair of values?
a. Urine flow rate and urine concentration
b. Plasma concentration and urine concentration
c. GFR and urinary excretion rate
d. Plasma concentration and urinary excretion rate

Answer 36

3�1. (d) The excretion rate of a substance divided by its plasma
concentration yields the clearance.

Question 37

3-2. A drug X has a short plasma half-life and must be administered
frequently to maintain therapeutic levels. The urinary
concentration of X is much higher than the plasma concentration.
A substantial amount of X also appears in the feces. What can we
say about the renal clearance of X compared with the metabolic
clearance rate of X?
a. The metabolic clearance rate is higher than the renal
clearance.
b. The renal clearance is higher than the metabolic clearance
rate.
c. The two clearances are the same.
d. There is insufficient information to answer the question.

Answer 37

3�2. (a) The metabolic clearance rate represents the sum of all clearance
routes. Since there are two major routes of clearance (kidneys
and feces) the metabolic clearance must be higher than either
one alone. The fact that the drug has a higher urinary
concentration than plasma concentration mainly reflects the
reabsorption of water.

Question 38

3-3. Inulin clearance is measured twice; the first time at a low inulin
infusion rate, and the second time at a higher infusion rate that
results in a higher plasma inulin concentration during the test.
Assuming the kidneys behave the same in both cases, which
measurement will yield a higher inulin clearance?
a. The first
b. The second
c. Both measurements are the same.
d. There is insufficient information to answer the question.

Answer 38

3�3. (c) In the second test both the plasma concentration and filtered
load (and hence rate of excretion) are increased, yielding
offsetting effects on the calculation.

Question 39

Which of the following indicates correct relative renal
clearances?
a. Sodium clearance is greater than urea clearance.
b. PAH clearance is greater than inulin clearance. c. Urea clearance is greater than PAH clearance.
d. Creatinine clearance is greater than PAH clearance.

Answer 39

3�4. (b) Normally the relative clearance rates are: PAH > creatinine ?
inulin > urea > sodium.

Question 40

3-5. An acute poisoning episode destroys 80% of a patient�s nephrons.
If the plasma urea concentration prior to the episode was 5
mmol/L, and assuming dietary protein remains the same, what is
the expected value of plasma urea now?
a. 4 mmol/L
b. 6.25 mmol/L
c. 25 mmol/L
d. Continuously rising

Answer 40

3�5. (d) Anything that increases the removal of a substance from the
blood, whether by increased filtration, increased metabolism, or
less reabsorption, increases clearance.

Question 41

Ch 4 Key Concept. Flux from lumen to interstitium can be transcellular, using
separate transport steps in the apical and basolateral
membranes, or paracellular, around the cells through tight
junctions.

Question 42

Ch 4 Key Concept. The kidneys move solutes across membranes by multiple transport mechanisms, including channels, uniporters,
multiporters, and primary active transporters.

Question 43

Ch 4 Key Concept. The kidneys regulate excretion by regulating channels and
transporters in epithelial cell membranes.

Question 44

Ch 4 Key Concept. Water crosses epithelial barriers by movement down
osmotic gradients (from regions of lower to higher
osmolality).

Question 45

Ch 4 Key Concept. Volume reabsorption is a multistep process involving
transport across epithelial membranes from lumen to
interstitium, and bulk flow from interstitium to peritubular
capillaries driven by Starling forces.

Question 46

Ch 4 Key Concept. The reabsorption of water concentrates all remaining
tubular solutes, increasing the driving force for their
passive reabsorption by diffusion.

Question 47

Ch 4 Key Concept. All reabsorptive processes have a limit on how fast they
can occur, either because the substance leaks back into the
lumen (gradient-limited systems) or because the
transporters saturate (Tm systems).

Question 48

4-1. A healthy patient has a normal plasma osmolality (close to 300
100 mOsm/kg). If 100 mmol of solutes are reabsorbed iso-osmotically
from the proximal tubule, approximately how much water is
reabsorbed with the solute?
a. 100 mL
b. 300 mL
c. 333 mL
d. 1000 mL

Answer 48

4�1. (c) 100 mmol is the amount of solute in one-third of a kilogram of
filtrate (333 mL), so this much water accompanies the
reabsorbed solute.

Question 49

4-2. Quantitatively, most sodium enters proximal tubule cells by:
a. paracellular diffusion.
b. transcellular diffusion.
c. the Na-K-ATPase.
d. antiport with hydrogen ions.

Answer 49

4�2. (d) Sodium enters the cells across the apical membrane by several
pathways, the major one being the NHE3 antiporter.

Question 50

4-3. The tight junctions linking proximal tubule cells permit passive
diffusion of:
a. glucose.
b. sodium.
c. all filtered solutes.
d. no filtered solutes.

Answer 50

4�3. (b) Tight junctions exhibit selectivity just as membrane transporters
do. The proximal tubule tight junctions are leaky to sodium and
a number of other solutes, but not glucose.

Question 51

4-4. In the proximal tubule, water can move through
a. apical membranes of proximal tubule cells.
b. basolateral membranes of proximal tubule cells.
c. tight junctions.
d. all of these.

Answer 51

4�4. (d) In the proximal tubule water is reabsorbed both transcellularly
and paracellularly.

Question 52

4-5. A drug X is secreted into the proximal tubule by a Tm-limited
system. This implies that:
a. X cannot easily diffuse by the paracellular route.
b. all the X that enters the renal vasculature will be secreted.
c. the rate of X secretion is independent of the plasma
concentration.
d. X is not filtered at the glomerulus.

Answer 52

4�5. (a) A substance moving by a Tm-limited system cannot move
paracellularly. It moves transcellularly via transporters that
have an upper limit to their capacity to transport.

Question 53

4-6. All multiporters do what?
a. Simultaneously move several molecules of a given solute (e.g.,
three sodium ions or two glucose molecules).
b. Simultaneously move two or more different solute species.
c. Use ATP to energize the transport.
d. Move transported solutes in the same direction.

Answer 53

4�6. (b) By definition multiporters move two or more different solute
species simultaneously, either in the same direction
(symporters) or the opposite direction (antiporters).

Question 54

Ch 5 Key Concept. Important organic metabolites are reabsorbed almost
completely (saved), whereas waste products are for the
most part excreted.

Question 55

Ch 5 Key Concept. Most organic solutes are transported only in the proximal
tubule, usually by a combination of multiporters.

Question 56

Ch 5 Key Concept. Normal filtered loads of glucose are completely
reabsorbed in the proximal tubule, but in conditions of
pathological hyperglycemia the transport saturates,
leading to the appearance of glucose in the urine.

Question 57

Ch 5 Key Concept. Peptides are reabsorbed either by endocytosis or as
individual amino acids following enzymatic degradation on
the brush border of the proximal epithelium.

Question 58

Ch 5 Key Concept. Some organic solutes, when converted to neutral forms by
changes in tubular pH, can be reabsorbed passively in the
distal nephron.

Question 59

Ch 5 Key Concept. Urea is reabsorbed proximally and recycled between the
collecting ducts and loops of Henle in the medulla,
resulting in a net excretion of about half the filtered load.

Question 60

5-1. When plasma glucose reaches such high levels that substantial
amounts of glucose appear in the urine (glycosuria):
a. glucose is leaking back into the tubule through tight junctions.
b. there is not enough luminal sodium to move in symport with
glucose.
c. all the glucose transporters are working at their maximum
rate.
d. the glucose transporters are being inhibited by the high levels
of glucose.

Answer 60

5�1. (c) The large filtered load presents more glucose than the
reabsorptive Tm-limited transporters can handle. Under all
conditions there is always far more filtered sodium than
glucose and sodium is never rate-limiting.

Question 61

5-2. Useful small organic metabolites that should not be excreted are:
a. generally not filtered.
b. reabsorbed paracellularly.
c. taken up by endocytosis and degraded.
d. reabsorbed transcellularly.

Answer 61

5�2. (d) Small useful organic solutes are freely filtered. They are
reabsorbed transcellularly by a Tm system. The normal filtered
load is below the Tm.

Question 62

5-3. Organic anion secretion:
a. involves a step of active influx across the basolateral
membrane.
b. is passive and paracellular.
c. occurs via simple diffusion through the tubular membranes.
d. utilizes the same nonspecific transporters as organic cation
secretion.

Answer 62

5�3. (a) Anions that are secreted must enter the cell against a negative
membrane potential, and usually against a concentration
gradient as well; thus, they are actively transported.

Question 63

5-4. A high urinary pH favors:
a. low excretion of drugs that are weak acids.
b. active reabsorption of drugs that are weak bases.
c. low excretion of drugs that are weak bases.
d. high passive permeability of drugs that are weak acids.

Answer 63

5�4. (c) Drugs that are weak bases are usually neutral (unprotonated) at
high pH. This favors their passive reabsorption by simple
diffusion, and therefore low excretion.

Question 64

5-5. The tubular concentration of urea
a. exceeds the plasma concentration at the hairpin turn of the
loop of Henle.
b. decreases to below the plasma concentration by the end of the
loop of Henle.
c. decreases to below the plasma concentration by the end of the proximal tubule.
d. reaches its highest value in the cortical collecting duct.

Answer 64

5�5. (a) Urea becomes concentrated above plasma levels in the proximal
tubule by the loss of water, and further concentrated in the
descending thin limb by secretion. It is therefore quite
concentrated at the hairpin turn. Its concentration reaches its
highest value in the inner medullary collecting duct where little
water remains.

Question 65

5-6. Urea is secreted into the tubules
a. in proximal tubules.
b. in the thin descending limbs.
c. in medullary collecting ducts.
d. at any of these sites depending on hydration status.

Answer 65

5�6. (b) Urea is secreted in the deep descending thin limbs where the
interstitial concentration is high.

Question 66

Ch 5 Key Note. Plasma urea concentration is usually expressed as blood urea nitrogen (BUN) in
units of milligrams per deciliter. Each molecule of urea contains 2 atoms of
nitrogen, so 1 mmol of urea contains 2 mmol of nitrogen, with a combined weight
of 28 mg. Thus, the normal levels of plasma urea are expressed as BUN values
ranging from 8.4 to 25.2 mg/dL. We use units of millimoles per liter because we
can then directly convert to osmolality

Question 67

Ch 6 Key Concept. Most of the body consists of fluid compartments divided
into the intracellular fluid (ICF), all the cytosolic volumes
collectively, and the extracellular fluid (ECF), consisting
mostly of interstitial fluid and blood plasma.

Question 68

Ch 6 Key Concept. The reabsorption of most of the filtered water, anions
(primarily chloride and bicarbonate), and osmotic content
is linked directly to the active reabsorption of sodium.

Question 69

Ch 6 Key Concept. In all conditions, the vast majority (roughly two-thirds) of
the sodium, chloride, bicarbonate, and filtered volume is
reabsorbed iso-osmotically in the proximal tubule.

Question 70

Ch 6 Key Concept. The loop of Henle reabsorbs some water and
proportionally even more sodium, thereby diluting the
tubular fluid.

Question 71

Ch 6 Key Concept. The distal tubule continues the reabsorption of sodium
without water and, along with the loop of Henle, is
considered a �diluting segment.�

Question 72

Ch 6 Key Concept. Reabsorption of water in the distal nephron (connecting
tubule and collecting ducts) is highly variable depending
on hydration status, allowing the kidneys to excrete large
amounts of water or to conserve almost all of it.

Question 73

Ch 6 Key Concept. Levels of ADH determine whether the hypo-osmotic fluid
entering the distal nephron is excreted largely as is or
subsequently reabsorbed.

Question 74

Ch 6 Key Concept. The conservation of water and concentration of the urine
requires the reabsorption of water into the high osmolality
medullary interstitium.

Question 75

Ch 6 Key Concept. The medullary osmotic gradient is created by (1) transport
of salt with little or no water into the medullary interstitium
by the thick ascending limb, (2) low-volume countercurrent
blood flow in the vasa recta, and (3) recycling of urea.

Question 76

6-1. Chloride reabsorption parallels sodium reabsorption mainly
because:
a. most chloride transport is via a symporter with sodium.
b. chloride is the most abundant negatively charged species
available to balance the reabsorption of the positive charge
on sodium.
c. chloride has such a high passive permeability.
d. chloride and sodium are both part of the sodium chloride
molecule and cannot be separated.

Answer 76

6�1. (b) Reabsorbed sodium must be balanced by reabsorbed anions.
Once most of the bicarbonate is reabsorbed, only chloride
exists in high enough concentration to match the continued
reabsorption of sodium.

Question 77

6-2. The obligatory water loss in the kidney:
a. is another name for insensible loss of water.
b. occurs because there is always at least some excretion of
waste solutes.
c. occurs because there is an upper limit to how fast aquaporins
can reabsorb water.
d. is the amount of water that accompanies sodium excretion.

Answer 77

6�2. (b) So long as there is filtration there is excretion of organic waste
which obligates water to be excreted also.

Question 78

6-3. Which region of the tubule secretes water?
a. The descending thin limb.
b. The cortical collecting duct.
c. The medullary collecting duct (when ADH is absent).
d. No region secretes water.

Answer 78

6�3. (d) Osmotic conditions in all tubule regions favor water
reabsorption.

Question 79

6-4. If the thick ascending limb stopped reabsorbing sodium, then the
final urine would be:
a. iso-osmotic with plasma in all conditions.
b. dilute.
c. concentrated.
d. dilute or concentrated, depending on ADH.

Answer 79

6�4. (a) The tubular fluid entering the medulla is iso-osmotic. If the
tubules did not separate salt from water, the medullary
interstitium would remain iso-osmotic. The luminal fluid would
also remain iso-osmotic because there would be no osmotic
gradient to either dilute it or concentrate it.

Question 80

6-5. If a healthy young person drinks a large amount of water, which
of the following is unlikely to happen?
a. A decrease in osmolality of the cortical interstitium.
b. An increase in water permeability in the medullary collecting
ducts.
c. A decrease in interstitial osmolality in the inner medulla.
d. A decrease in the urea concentration in the final urine.

Answer 80

6�5. (b) After drinking a large amount of water there would be a decline in ADH, which would decrease water permeability in the ADHsensitive regions of the tubule.

Question 81

6-6. A healthy young person drinks a large amount of water. Over the
next several hours most of the water filtered by the glomerulus is
a. excreted.
b. reabsorbed in the proximal tubule.
c. reabsorbed in the loop of Henle.
d. reabsorbed in the cortical collecting-duct system.

Answer 81

6�6. (b) Under all conditions the majority of filtered water
(approximately two-thirds) is reabsorbed in the proximal
tubule.

Question 82

Ch 6 Key Note. Besides the sodium dissolved in the body fluids there is a considerable amount of
sodium in the mineral component of bone that is not osmotically active. In
addition, the polysaccharides of connective tissue loosely bind sodium in nonosmotic form.

Question 83

Ch 6 Key Note. The obligatory solute excretion explains why a thirsty sailor cannot drink sea
water, even if the urine osmolality is slightly greater than that of the sea water. To
excrete all the salt in 1 L of sea water (to prevent a net gain of salt) plus the
obligatory organic solutes produced by the body, the volume of urine would have to be much greater than 1 L.

Question 84

Ch 6 Key Note. For simplicity and clarity we have chosen to describe the medullary osmotic
gradient without some of the vocabulary found in most texts and discussions, such
as �countercurrent multiplier,� �single effect,� and �passive mechanism.� These
are terms developed in historical models of the renal medulla that may be
supplanted by more recent findings, such as the events in local microenvironments
created by the anatomic clustering of tubular and vascular elements.

Question 85

Ch 7 Key Concept. Sodium and water excretion are regulated primarily to
meet the needs of the cardiovascular system via
preservation of vascular volume and plasma osmolality.

Question 86

Ch 7 Key Concept. The macula densa blunts changes in GFR via
tubuloglomerular feedback.

Question 87

Ch 7 Key Concept. Extracellular volume varies directly with sodium content.

Question 88

Ch 7 Key Concept. Baroreceptors at various sites inform the kidneys of vascular pressures and volume status.

Question 89

Ch 7 Key Concept. The renin-angiotensin system is the major controller of
sodium excretion.

Question 90

Ch 7 Key Concept. Angiotensin II, produced by local and systemic reninangiotensin systems, is a crucial regulator of sodium
excretion and blood pressure via its actions in the kidneys,
peripheral vasculature, and adrenal glands.

Question 91

Ch 7 Key Concept. Aldosterone (in the presence of AII) stimulates sodium
reabsorption by NCC in DCT cells and by ENaC in
principal cells in the distal nephron.

Question 92

Ch 7 Key Concept. Sympathetic stimulation is a major controller of sodium
excretion.

Question 93

Ch 7 Key Concept. Intrarenal dopamine plus several other mediators limit
sodium reabsorption (increase excretion).

Question 94

Ch 7 Key Concept. Water excretion varies in proportion to solute excretion
and inversely with urine osmolality.

Question 95

Ch 7 Key Concept. ADH secretion is regulated by plasma osmolality via
osmoreceptors in the circumventricular organs, and by
blood pressure via the baroreceptor-vasomotor center
system.

Question 96

Ch 7 Key Concept. Most cases of heart failure and hypertension involve
hyperactivation of the RAAS and are commonly treated
with drugs that block components of the RAAS.

Question 97

Ch 7 Key Note. As an example of this variation, some patients experience �white coat
hypertension,� an elevation of blood pressure that is manifested in response to the
stress of being in a doctor�s office.

Question 98

Ch 7 Key Note. Arterial pressure is one among many physiological variables regulated around a
set point, for example, body temperature, partial pressure of carbon dioxide, or
plasma concentration of glucose. While much is known about the mechanisms that
keep these variables close to their set-points, the question of �what sets their setpoints� remains unclear.

Question 99

Ch 7 Key Note. In most secretory processes, for example, in nerve terminals, secretion of
materials stored in secretory granules is stimulated by a rise in intracellular
calcium. However, in jg cells, calcium inhibits secretion.

Question 100

Ch 7 Key Note. In contrast to atrial pressures that are high, arterial pressure is usually within the
normal range, and heart failure cannot be diagnosed based on arterial blood
pressure.

Question 101

7-1. Which of the following cell types are not nerve cells?
a. Pituitary cells that secrete ADH
b. Baroreceptors located in pulmonary vessels
c. Baroreceptors located in the arch of the aorta
d. Intrarenal baroreceptors

Answer 101

7�1. (d) Intrarenal baroreceptors are modified smooth muscle cells in
the afferent arteriole.

Question 102

7-2. In the production of aldosterone, the rate-limiting step is:
a. the production of angiotensin I.
b. the production of angiotensinogen.
c. the activity of angiotensin-converting enzyme.
d. the responsiveness of the adrenal gland to angiotensin II.

Answer 102

7�2. (a) The action of renin to produce angiotensin I is the rate-limiting
step because (1) there is excess substrate (angiotensinogen) and
(2) almost all angiotensin I is converted to angiotensin II by
angiotensin-converting enzyme (ACE).

Question 103

7-3. A person eats a large bag of very salty potato chips with no
beverage. Which response is most likely to ensue?
a. Movement of aquaporins into the apical membrane of cortical
collecting duct principal cells.
b. Enhanced activity of Na-H antiporters in the proximal tubule.
c. Enhanced activity of Na-K-ATPase pumps in collecting duct
principal cells.
d. Decreased levels of natriuretic peptides in the blood.

Answer 103

7�3. (a) Consumption of salt without water concentrates the ECF and
triggers secretion of ADH. A key action of ADH is to cause
insertion of aquaporins into the luminal membrane of cortical
collecting duct principal cells.

Question 104

7-4. In response to a major hemorrhage:
a. The afferent arteriole vasodilates.
b. ADH secretion is reduced.
c. Granular (juxtaglomerular) cells are stimulated by neural
input.
d. Neural baroreceptor firing rate increases.

Answer 104

7�4. (c) Loss of blood volume and likely ensuing drop of arterial
pressure both reduce the inhibition of sympathetic outflow (i.e.,
sympathetic outflow increases). A prime target of sympathetic
outflow in the kidneys is the juxtaglomerular cells.

Question 105

7-5. The macula densa generates signals that directly regulate
a. smooth muscle in afferent arterioles.
b. tubular water permeability.
c. ADH secretion.
d. all of these.

Answer 105

7�5. (a) Signals from the macula densa act in a paracrine manner (travel
by diffusion to nearby cells) to regulate afferent arteriole
smooth muscle, and thus GFR.

Question 106

7-6. Which one of the following will decrease sodium excretion?
a. Decreased activity in the renal sympathetic nerve.
b. Decreased levels of dopamine in the kidneys.
c. Decreased levels of AII in the kidneys.
d. Decreased levels of ADH in the kidneys.

Answer 106

7�6. (b) The blocking of agents that stimulate sodium reabsorption leads
to increased sodium excretion. Since dopamine is a natriuretic
agent (increases sodium excretion), blocking it will decrease
sodium excretion.

Question 107

Ch 8 Key Concept. Potassium is distributed predominantly in the intracellular
compartment, and the extracellular concentration may not
be a good indicator of total-body potassium status.

Question 108

Ch 8 Key Concept. On a short-term basis, uptake and release of potassium by
muscle stabilizes extracellular potassium concentration.

Question 109

Ch 8 Key Concept. Almost all filtered potassium is reabsorbed, with secretion
by distal convoluted tubule and cortical tubule cells in the
distal nephron determining the amount excreted.

Question 110

Ch 8 Key Concept. The rate of potassium secretion is set by active influx
across the basolateral membrane and apical channel
activity.

Question 111

Ch 8 Key Concept. Potassium secretion (and thus excretion) is increased by
high sodium delivery to the distal nephron, particularly
when this is caused by diuretics acting upstream.

Question 112

Ch 8 Key Concept. AII with aldosterone inhibits potassium secretion;
aldosterone in the absence of AII stimulates potassium
secretion.

Question 113

Ch 8 Key Note. Intense activity of the Na-K-ATPase hyperpolarizes the cells and prevents what
otherwise would be a dangerous depolarization due to the high extracellular
potassium.

Question 114

Ch 8 Key Note. Large loads of sodium or potassium cause transient increases in the excretion of
the other, but over time proper balance is reestablished for each one.

Question 115

Ch 8 Key Note. This effect is mediated by a complex signaling pathway dependent on membrane
potential. Depolarization of distal tubule cells leads to the shutting down of a
kinase that stimulates sodium reabsorption via the sodium-chloride symporter.

Question 116

8-1. Potassium excretion is controlled mainly by controlling the rate
of:
a. potassium reabsorption in the proximal tubule.
b. potassium reabsorption in the distal nephron.
c. potassium secretion in the proximal tubule.
d. potassium secretion in the distal nephron.

Answer 116

8�1. (d) The distal nephron both reabsorbs and secretes potassium.
Quantitatively the main control is exerted over the rate of
secretion.

Question 117

8-2. In the thick ascending limb:
a. the net amounts of potassium and sodium that are reabsorbed
are about the same.
b. the major pathway for moving potassium from lumen to cell is
via the Na-K-ATPase.
c. most of the potassium that is reabsorbed into the cells leaks
back into the lumen via potassium channels.
d. the major pathway for moving potassium from cell to
interstitium is via the Na-K-2Cl multiporter.

Answer 117

8�2. (d) The uptake of potassium from the lumen is an active process via
the Na-K-2Cl multiporter, energetically driven by the sodium
gradient.

Question 118

8-3. For which substance is it possible to excrete more than is
filtered?
a. Sodium
b. Potassium
c. Chloride
d. It is not possible to excrete any of these ions in amounts
greater than the filtered loads.

Answer 118

8�3. (b) Even under conditions of major natriuresis, most of the filtered
sodium and chloride is reabsorbed, but with a high potassium
load, high secretion in the distal nephron can lead to more
potassium excretion than filtration.

Question 119

8-4. After a potassium-rich meal, the key action of insulin that
prevents a large increase in plasma potassium is to:
a. decrease absorption of potassium from the GI tract.
b. increase uptake of potassium by tissue cells.
c. increase the filtered load of potassium.
d. increase tubular secretion of potassium.

Answer 119

8�4. (b) A large dietary load of potassium is absorbed from the GI tract
and taken up by tissue cells (mostly muscle), stimulated by
insulin, before being released slowly and excreted.

Question 120

8-5. A key role of �BK� potassium channels in the kidney is to
a. reabsorb potassium when the body is depleted of potassium.
b. recycle potassium in the thick ascending limb.
c. secrete potassium when distal nephron flow rate is very low.
d. help the body excrete potassium in response to very large
loads.

Answer 120

8�5. (d) BK potassium channels in the distal nephron are activated
during excretion of large potassium loads.

Question 121

8-6. Which of the following has the effect of reducing the excretion of
potassium?
a. The actions of angiotensin II on the kidney.
b. The actions of aldosterone on the kidney.
c. Decreased sodium reabsorption in the loop of Henle.
d. Activation of BK channels in principal cells.

Answer 121

8�6. (a) Angiotensin II reduces potassium secretion by principal cells.