616 Chapter 17
Test Your Knowledge
- Which of these statements about the renal pyramids is false?
a. They are located in the medulla.
b. They contain glomeruli.
c. They contain collecting ducts.
d. They empty urine into the calyces.REVIEW ACTIVITIES
Match the following items:- Active transport of sodium;
water follows passively - Active transport of sodium;
impermeable to water - Passively permeable to
water only - Passively permeable to
water and urea
a. Proximal tubule
b. Descending limb of loop
c. Ascending limb of loop
d. Distal tubule
e. Medullary collecting
ductB. The reabsorption of most of the remaining water occurs as a
result of the action of the countercurrent multiplier system.
- Sodium is actively extruded from the ascending limb,
followed passively by chloride. - Because the ascending limb is impermeable to water,
the remaining filtrate becomes hypotonic. - Because of this salt transport and because of
countercurrent exchange in the vasa recta, the interstitial
fluid of the medulla becomes hypertonic. - The hypertonicity of the medulla is multiplied by a
positive feedback mechanism involving the descending
limb, which is passively permeable to water and perhaps
to salt.
C. The collecting duct is permeable to water but not to salt. - As the collecting ducts pass through the hypertonic
renal medulla, water leaves by osmosis and is carried
away in surrounding capillaries. - The permeability of the collecting ducts to water is
stimulated by antidiuretic hormone (ADH).
17.4 Renal Plasma Clearance 598
A. Inulin is filtered but neither reabsorbed nor secreted. Its
clearance is thus equal to the glomerular filtration rate.
B. Some of the filtered urea is reabsorbed. Its clearance is
therefore less than the glomerular filtration rate.
C. Since almost all the PAH in blood going through the kidneys
is cleared by filtration and secretion, the PAH clearance is a
measure of the total renal blood flow.
D. Normally all of the filtered glucose is reabsorbed.
Glycosuria occurs when the transport carriers for glucose
become saturated as a result of hyperglycemia.
17.5 Renal Control of Electrolyte and Acid-Base
Balance 604
A. Aldosterone stimulates sodium reabsorption and potassium
secretion in the late distal tubule and cortical collecting duct.
B. Aldosterone secretion is stimulated directly by a rise in
blood potassium and indirectly by a fall in blood volume.
1. Decreased blood flow and pressure through the kidneys
stimulates the secretion of the enzyme renin from the
juxtaglomerular apparatus.
2. Renin catalyzes the formation of angiotensin I, which is
then converted to angiotensin II.
3. Angiotensin II stimulates the adrenal cortex to secrete
aldosterone.
C. Aldosterone stimulates the secretion of H^1 , as well as
potassium, into the filtrate in exchange for sodium.
D. The nephrons filter bicarbonate and reabsorb the amount
required to maintain acid-base balance. Reabsorption of
bicarbonate, however, is indirect.
1. Filtered bicarbonate combines with H^1 to form carbonic
acid in the filtrate.
2. Carbonic anhydrase in the membranes of microvilli in
the tubules catalyzes the conversion of carbonic acid to
carbon dioxide and water.
3. Carbon dioxide is reabsorbed and converted in either
the tubule cells or the red blood cells to carbonic acid,
which dissociates to bicarbonate and H^1.
4. In addition to reabsorbing bicarbonate, the nephrons
filter and secrete H^1 , which is excreted in the urine
buffered by ammonium and phosphate buffers.17.6 Diuretics and Renal Function Tests 611
A. Diuretic drugs are used clinically to increase the urine
volume and thus to lower the blood volume and pressure.
1. Loop diuretics and the thiazides inhibit active Na^1
transport in the ascending limb and early portion of the
distal tubule, respectively.
2. Osmotic diuretics are extra solutes in the filtrate that
increase the osmotic pressure of the filtrate and inhibit
the osmotic reabsorption of water.
3. The potassium-sparing diuretics act on the distal tubule
to inhibit the reabsorption of Na^1 and secretion of K^1.
B. In glomerulonephritis, the glomeruli can permit the leakage
of plasma proteins into the urine.
C. The technique of hemodialysis is used to treat people with
renal insufficiency.