Chapter 19 review questions

Question 1

Level 1:
List and explain the significance of the five characteristics of urine that can be found by physical examination.

Answer 1

color (concentration), odor (infection or excreted substances), clarity (presence of cells), taste (presence of glucose), and froth (presence of proteins)

Question 2

List and explain the six major kidney functions.

Answer 2

regulation of extracellular fluid volume (to maintain adequate blood pressure), regulation of osmolarity, maintenance of ion balance (neuron function), regulation of pH (proteins denature if pH not maintained), excretion of wastes and foreign substances (to prevent toxic effects), and production of hormones (that regulate RBC synthesis, Ca2+, and Na+ balance)

Question 3

At any given time, what percentage of cardiac output goes to the kidneys?

Answer 3

20-25%

Question 4

List the major structures of the urinary system in their anatomical sequence, from the kidneys to the urine leaving the body. Describe the function of each structure.

Answer 4

nephrons through ureters to urinary bladder (storage), leaving through the urethra

Question 5

Arrange the following structures in the order that a drop of water entering the nephron would encounter them:
a. afferent arteriole
b. Bowman’s capsule
c. collecting duct
d. distal tubule
e. glomerulus
f. loop of Henle
g. proximal tubule
h. renal pelvis

Answer 5

(a), (e), (b), (g), (f), (d), (c), (h)

Question 6

Name the three filtration barriers that solutes must cross as they move from plasma to the lumen of Bowman’s capsule. What components of blood are usually excluded by these layers?

Answer 6

Glomerular capillary endothelium, basal lamina, and epithelium of Bowman’s capsule. Blood cells and most plasma proteins are excluded.

Question 7

What force(s) promote(s) glomerular filtration? What force(s) oppose(s) it? What is meant by the term net driving force?

Answer 7

Capillary hydrostatic pressure promotes filtration. Fluid pressure in Bowman’s capsule and colloid osmotic (oncotic) pressure of plasma oppose it. Net driving force is the sum of these pressures.

Question 8

What does the abbreviation GFR stand for? What is a typical numerical value for GFR in milliliters per minute? In liters per day?

Answer 8

GFR—glomerular filtration rate. 125 mL/min or 180 L/day.

Question 9

Identify the following structures, then explain their significance in renal physiology:
a. juxtaglomerular apparatus
b. macula densa
c. mesangial cells
d. podocytes
e. sphincters in the bladder
f. renal cortex

Answer 9

(a) Found where distal tubule passes between afferent and efferent arterioles. Composed of macula densa cells in the distal tubule and granular cells in arteriole wall. (b) Macula densa paracrine signals control autoregulation of GFR and renin secretion. (c) Alter the size of filtration slits. (d) Specialized epithelial cells that surround glomerular capillaries. Changes in slit size alter GFR. (e) An internal smooth muscle sphincter that is passively contracted and an external skeletal muscle sphincter that is tonically (actively) contracted. (f) Outer layer of the kidney that contains renal corpuscles, proximal and distal tubules, and parts of the loop of Henle and collecting ducts.

Question 10

In which segment of the nephron does most reabsorption take place? When a molecule or ion is reabsorbed from the lumen of the nephron, where does it go? If a solute is filtered and not reabsorbed from the tubule, where does it go?

Answer 10

70% occurs in the proximal tubule. Reabsorbed molecules go into the peritubular capillaries and the systemic venous circulation. If filtered and not reabsorbed, a molecule is excreted in the urine.

Question 11

Match each of the following substances with its mode(s) of transport in proximal tubule reabsorption.
a. Na+
b. glucose
c. urea
d. plasma proteins
e. water

1. simple diffusion
2. primary active transport
3. indirect active transport
4. facilitated diffusion
5. movement through open channels
6. endocytosis
7. paracellular movement

Answer 11

(a) 2, 3, 5; (b) 3, 4; (c) 4, 7; (d) 6; (e) 5, 7

Question 12

List three solutes secreted into the tubule lumen.

Answer 12

penicillin, K+, and H+

Question 13

What solute that is normally present in the body is used to estimate GFR in humans?

Answer 13

creatinine

Question 14

What is micturition?

Answer 14

urination

Question 15

Level 2:
Define, compare, and contrast the items in the following sets of terms:
a. filtration, secretion, and excretion
b. saturation, transport maximum, and renal threshold
c. probenecid, creatinine, inulin, and penicillin
d. clearance, excretion, and glomerular filtration rate

Answer 15

(a) Filtration and secretion both move material from blood to tubule lumen, but filtration is a bulk flow process while secretion is a selective process. Excretion is also bulk flow but involves movement from the kidney lumen to the outside world. (b) Saturation—all transporter binding sites are occupied by ligand. Transport maximum—the maximum rate at which carriers are saturated by substrate. Renal threshold—plasma concentration at which saturation occurs. (c) Creatinine and inulin—compounds used to determine GFR. Penicillin and probenecid—xenobiotics that are secreted. (d) Clearance—rate at which plasma is cleared of a substance (mL plasma cleared of substance X/min). GFR—filtration rate of plasma (mL plasma filtered/min). Excretion—removal of urine, mL urine/min.

Question 16

What is the advantages of a kidney that filters a large volume of fluid and then reabsorbs 99% of it?

Answer 16

Allows rapid removal of foreign substances that are filtered but not reabsorbed.

Question 17

If the afferent arteriole of a nephron constricts, what happens to GFR in that nephron? If the efferent arteriole of a nephron constricts, what happens to GFR in that nephron? Assume that no autoregulation takes place.

Answer 17

Afferent arteriole constricts, GFR decreases. Efferent arteriole constricts, GFR increases.

Question 18

Diagram the micturition reflex. How is this reflex altered by toilet training? How do higher brain centers influence micturition?

Answer 18

See Fig. 19.15. Toilet training allows higher brain centers to inhibit the reflex until an appropriate time. Higher brain centers can also initiate the reflex.

Question 19

Antimuscarinic drugs are the accepted treatment for an overactive bladder. Explain why they work for this condition.

Answer 19

Bladder smooth muscle contracts under parasympathetic control, so blocking muscarinic receptors decreases bladder contraction.

Question 20

Level 3:
Draw a section of renal tubule epithelium showing three cells joined by cell junctions. Label the apical and basolateral membranes, the tubule lumen, and the extracellular fluid. Use the following written description of proximal tubule processes to draw a model cell.
The proximal tubule cells contain carbonic anhydrase, which promotes the conversion of CO2 and water H+ and HCO3-. Sodium is reabsorbed by an apical Na+ -H+ antiporter and a basolateral Na+ -K+ -ATPase. Chloride is passively reabsorbed by movement through the paracellular pathway. Bicarbonate produced in the cytoplasm leaves the cell on a basolateral Na+ -HCO-3 symporter.

Answer 20

See Fig. 19.8. Place transporters as described. Cl- moves between the cells.

Question 21

You have been asked to study kidney function in a new species of rodent found in the Amazonian jungle. You isolate some nephrons and expose them to inulin. The following graph shows the results of your studies. (a) How is the rodent nephron handling inulin? Is inulin filtered? Is it excreted? Is there net inulin reabsorption? Is there net secretion? (b) On the graph, accurately draw a line indicating the net reabsorption or secretion. (Hint: excretion = filttration - reabsorption + secretion)

Answer 21

(a) Inulin is filtered, secreted, and excreted. No evidence for reabsorption is presented. (b) The line indicating net secretion will be close to the filtration line until the slope changes, after which the secretion line is horizontal (no further increase in rate due to saturation).

Question 22

Read the box on hemodialysis on p. 603 and see if you can create a model system that would work for dialysis. Draw two compartments (one to represent blood and one to represent dialysis fluid) separated by a semipermeable membrane. In the blood compartment, list normal extracellular fluid solutes and their concentrations (see the table with normal values of blood components inside the back cover of this book). What will happen to the concentrations of these solutes during kidney failure? Which of these solutes should you put in the dialysis fluid, and what should their concentrations be? (Hint: Do you want diffusion into the dialysis fluid, out of the dialysis fluid, or no net movement?) How would you change the dialysis fluid if the patient was retaining too much water?

Answer 22

Dialysis fluid should resemble plasma without waste substances, such as urea. This will allow diffusion of solutes and water from the blood into the dialysis fluid, but diffusion will stop at the desired concentration. To remove excess water from the blood, you can make the dialysis fluid more concentrated than plasma.

Question 23

Graphing question: You are given a chemical Z and told to determine how it is handled by the kidneys of a mouse. After a series of experiments, you determine that (a) Z is freely filtered; (b) Z is not reabsorbed; (c) Z is actively secreted; and (d) the renal threshold for Z secretion is a plasma concentration of 80 mg/mL plasma, and the transport maximum is 40 mg/min. The mouse GFR is 1 mL/min. On a graph similar to the one in question 22, show how filtration, secretion, and excretion are related. One axis will be plasma concentration of Z (mg/mL) with a range of 0–140, and the other axis will show rates of kidney processes (mg/min) with a range of 0–140.

Answer 23

Filtration line: Use several plasma concentrations of Z (0-140 mg Z/mL plasma) x GFR. The line will be a straight line beginning at the origin and extending upward to the right. Secretion reaches its maximum rate of 40 mg/min at 80 mg Z/mL plasma. Plot that point. Draw the secretion line from the origin to that point. Above the renal threshold, secretion rate does not change, so the line becomes horizontal. Excretion line: Add the filtration rate and secretion rate at a number of plasma concentrations of Z.