counterparts to extracellular Cl
and protein anions.
eat salty pretzels, your extracellular ﬂuid volume will expand even if you
don’t ingest ﬂuids. Tis is because water will ﬂow by osmosis from the in-
tracellular ﬂuid to the extracellular ﬂuid.
An increase in osmolality of the
plasma is most important for triggering thirst. Tis change is sensed by os-
moreceptors in the hypothalamus.
ADH cannot add water—it can only
conserve what is already there. In order to reduce an increase in osmolality
of body ﬂuids, the thirst mechanism is required.
(a) A loss of plasma
proteins causes edema. (b) Copious sweating causes dehydration. (c) Using
ecstasy (together with drinking lots of ﬂuids) could cause hypotonic hydra-
tion because it promotes ADH secretion, which interferes with the body’s
ability to get rid of extra water.
Insuﬃcient aldosterone would cause
Jacob’s plasma Na
to be decreased and his plasma K
to be elevated. Te
decrease in plasma Na
would cause a decrease in blood pressure, because
is directly related to blood volume, which is a major deter-
minant of blood pressure.
Te kidneys’ handling of K
can be summed
up as “Te kidneys reabsorb most of the ﬁltered K
in the proximal parts
of the kidney’s tubules and then secrete just the right amount in the distal
parts (collecting duct).”
Te major regulator of calcium in the blood is
parathyroid hormone. Hypercalcemia decreases excitability of neurons and
muscle cells and may cause life-threatening cardiac arrhythmias. Hypo-
calcemia increases excitability and causes muscle tetany.
Acidemia is an
arterial pH below 7.35 and alkalemia is a pH above 7.45.
A weak base
would be better at minimizing the shiF in pH caused by adding a strong
acid to a solution because its ability to loosely tie up H
allows it to act as
Te three major chemical buﬀer systems of the body are the
bicarbonate buﬀer system, the phosphate buﬀer system, and the protein
buﬀer system. Te most important intracellular buﬀer is the protein buﬀer
Joanne’s ventilation would be increased. Te acidosis caused
by the accumulated ketone bodies will stimulate the peripheral chemore-
ceptors, and this will cause more CO
to be “blown oﬀ ” in an attempt to
restore pH to normal.
Reabsorption of HCO
is always linked with se-
cretion of H
Te most important urine buﬀer of H
is the phosphate
Te tubule and collecting duct cells generate new HCO
either by excreting ammonium ion (NH
) or by excreting buﬀered H
Key features of an uncompensated metabolic alkalosis are an
increase in blood pH and an increase in blood HCO
. Key features of an
uncompensated respiratory acidosis are a decrease in blood pH and an
increase in blood P
Te kidneys compensate for respiratory acidosis
by excreting more H
and generating new HCO
to buﬀer the acidosis.
Infants’ immature kidneys are not as proﬁcient at concentrating urine.
In addition, they have a high metabolic rate, so they produce more meta-
bolic water and also have larger amounts of metabolic wastes and acids
that need to be excreted with water.
Review Questions 1.
a and b;
Case Study 1.
Mr. Heyden’s vital signs suggest that he is in hypovolemic
shock, which is probably due to an internal hemorrhage.
is a highly vascular organ due to its role as a blood-ﬁltering organ. Te
macrophages in Mr. Heyden’s liver and bone marrow will help com-
pensate for the loss of his spleen.
Elevation of renin, aldosterone,
and antidiuretic hormone indicate that Mr. Heyden’s body is trying to
compensate for his falling blood pressure and blood loss. Renin: released
when renal blood ﬂow is diminished and blood pressure falls. Te
angiotensin-aldosterone response is initiated by renin. Te formation
of angiotensin II leads to vasoconstriction, which will increase blood
pressure, and to the release of aldosterone. Aldosterone: increases Na
reabsorption by the kidney. Te movement of this reabsorbed Na
the bloodstream will promote the movement of water from the inter-
stitial ﬂuid, resulting in an increase in blood volume. Antidiuretic hor-
mone (ADH): released when the hypothalamic osmoreceptors sense an
increase in osmolality. ADH has two consequences: It is a potent vaso-
its concentration gradient.
Te reabsorption of Na
by primary active
transport drives reabsorption of amino acids and glucose by secondary
active transport. It also drives passive reabsorption of chloride, and re-
absorption of water by osmosis. Te reabsorption of water leaves behind
other solutes, which become more concentrated and can therefore be re-
absorbed by diﬀusion.
, creatinine, urea, and uric acid are
all substances that are secreted into the kidney tubules.
limb of the nephron loop is permeable to water and impermeable to NaCl.
Te ascending limb is impermeable to water and permeable to NaCl.
ADH is released from the posterior pituitary in response to hyperos-
motic extracellular ﬂuid (as sensed by hypothalamic osmoreceptors). ADH
causes insertion of aquaporins into the apical membrane of the principal
cells of the collecting ducts.
Te normal renal clearance value for amino
acids is zero. You would expect this because amino acids are valuable as
nutrients and as the building blocks for protein synthesis, so it would not
be good to lose them in the urine.
Te three major nitrogenous wastes
excreted in urine are urea, creatinine, and uric acid.
A kidney stone
blocking the ureter would interfere with urine ﬂow to the bladder. Te
pain would occur in waves that coincide with the peristaltic contractions
of the smooth muscle of the ureter.
Te trigone is a smooth triangular
region at the base of the bladder. Its borders are deﬁned by the openings
for the ureters and the urethra.
Te prostatic urethra, the intermediate
part of the urethra, and the spongy urethra are the three regions of the male
Te detrusor contracts in response to increased ﬁring of para-
sympathetic nerves. Te internal urethral sphincter opens.
Te three sets
of embryonic kidneys in the order that they develop are the pronephros,
mesonephros, and metanephros.
Both loss of bladder tone with age
and an increase in size of the prostate can contribute to urinary retention in
Review Questions 1.
Case Study 1.
Albumin is the smallest and most abundant plasma pro-
tein. More than trace amounts of albumin are not normally found in
urine, so its presence indicates damage to the ﬁltration membrane of the
Tese medications were prescribed to treat Mr. Boulard’s
hypertension. Both diabetes and hypertension can cause kidney dam-
age, and hypertension is a major cause of other cardiovascular diseases
such as heart failure and stroke. Albuminuria indicates that Mr. Boulard
already has damage to his kidneys, so it is important to protect his kid-
neys from further damage.
Tiazide diuretics increase urine output by
reabsorption in the DC±. Tis decreases blood volume,
which decreases blood pressure.
While Mr. Boulard still has hyperten-
sion, his main problem is that his blood K
is low. He is losing too much
in his urine. Tis is the underlying cause of his irregular heartbeat,
which could turn into a fatal arrhythmia if his hypokalemia is not cor-
Tiazide diuretics increase Na
excretion and decrease blood
pressure. ±o compensate for these thiazide eﬀects, Mr. Boulard’s renin-
angiotensin-aldosterone mechanism is activated. Aldosterone increases
reabsorption and K
secretion, resulting in hypokalemia (low blood
ACE inhibitors decrease blood pressure by blocking the action of
angiotensin converting enzyme and so reducing the amount of circulat-
ing angiotensin II. Because angiotensin II increases blood pressure in a
number of ways, including by increasing aldosterone release and causing
vasoconstriction (see ²igure 19.10 on p. 708), ACE inhibitors are very
eﬀective at lowering blood pressure. (ACE inhibitors also help minimize
kidney damage in diabetes.)
Yes. Te ACE inhibitors would have pre-
vented the formation of excess angiotensin II and the resulting release of
aldosterone. Tis would have lessened excess secretion of K
Check Your Understanding 1.
You have more intracellular than extra-
cellular ﬂuid and more interstitial ﬂuid than plasma.
is the major
cation in the EC² and K
is the major cation in the IC². Te intracellular