Chapter 20 review questions

Question 1

What is an electrolyte? Name five electrolytes whose concentrations must be regulated by the body.

Answer 1

Electrolytes are ions, which can conduct electric current through a solution. Examples: Na+, K+, Ca2+, H+, HPO42-, and HCO3-.

Question 2

List five organs and four hormones important in maintaining fluid and electrolyte balance.

Answer 2

Organs: kidneys, lungs, heart, blood vessels, digestive tract. Hormones: vasopressin or antidiuretic hormone (AVP or ADH), aldosterone, atrial natriuretic peptides (ANP), RAS pathway.

Question 3

Compare the routes by which water enters the body with the routes by which the body loses water.

Answer 3

Entry: ingested and a small amount from metabolism. Loss: exhaled air, evaporation and perspiration from skin, excreted by kidneys, and in feces.

Question 4

List the receptors that regulate osmolarity, blood volume, blood pressure, ventilation, and pH. Where are they located, what stimulates them, and what compensatory mechanisms are triggered by them?

Answer 4

See Tbl. 20.1 and Fig. 20.15.

Question 5

How do the two limbs of the loop of Henle differ in their permeability to water? What makes this difference in permeability possible?

Answer 5

Descending limb: permeable to water but lacks transporters for salts. Ascending limb: impermeable to water but reabsorbs NaCl.

Question 6

Which ion is a primary determinant of ECF volume? Which ion is the determinant of extracellular pH?

Answer 6

ECF volume— Na+ ; pH – H+

Question 7

What happens to the resting membrane potential of excitable cells when plasma
K+ concentrations decrease? Which organ is most likely to be affected by changes in
K+ concentration?

Answer 7

More K+ leaves the cell, and membrane potential becomes more negative (hyperpolarizes). The heart is most likely to be affected.

Question 8

Appetite for which two substances is important in regulating fluid volume and osmolarity?

Answer 8

salt and water

Question 9

Write out the words for the following abbreviations: ADH, ANP, ACE, ANG II, JG apparatus, P cell, I cell.

Answer 9

ADH = antidiuetic hormone, ANP = artial natriuretic peptide,
ACE = angiontensis II, JG (apparatus) = juxtaglomerular, P cell = principal cell, I cell = intercalated cell

Question 10

Make a list of all the different membrane transporters in the kidney. For each transporter, tell (a) which section(s) of the nephron contain(s) the transporter; (b) whether the transporter is on the apical membrane only, on the basolateral membrane only, or on both; (c) whether it participates in reabsorption only, in secretion only, or in both.

Answer 10

Use Figs. 19.8, 19.12, 20.5c, 20.7d, 20.9b, 20.17, and 20.18.

Question 11

List and briefly explain three reasons why monitoring and regulating ECF pH are important. What three mechanisms does the body use to cope with changing pH?

Answer 11

pH alters protein structure (enzyme activity, membrane transporters, neural function). Buffers, renal and respiratory compensation.

Question 12

Which is more likely to accumulate in the body, acids or bases? List some sources of each.

Answer 12

Acids from CO2, metabolism, and food are more likely. Sources of bases include some foods.

Question 13

What is a buffer? List three intracellular buffers. Name the primary extracellular buffer.

Answer 13

A molecule that moderates changes in pH. Intracellular: proteins, HPO42-, and hemoglobin. Extracellular: HCO3-

Question 14

Name two ways the kidneys alter plasma pH. Which compounds serve as urinary buffers?

Answer 14

Kidneys excrete or reabsorb
or HCO3-. Ammonia and phosphates.

Question 15

Write the equation that shows how
is related to pH. What enzyme increases the rate of this reaction? Name two cell types that possess high concentrations of this enzyme.

Answer 15

CO2 + H2O <—-> H+ HCO3-. Carbonic anhydrase. High in renal tubule cells and RBCs.

Question 16

When ventilation increases, what happens to arterial PCO2? To plasma pH? To plasma H+ concentration?

Answer 16

Arterial PCO2 decreases, pH increases and plasma H+ concentration decreases.

Question 17

Level 2:
Concept map: Map the homeostatic reflexes that occur in response to each of the following situations:
a. decreased blood volume, normal blood osmolarity
b. increased blood volume, increased blood osmolarity
c. normal blood volume, increased blood osmolarity

Answer 17

Use the information in Tbl. 20.1 and compile multiple pathways into a single map similar to Fig. 20.13. Include all steps of the reflex.

Question 18

Figures 20.15 and 20.18a show the respiratory and renal compensations for acidosis. Draw similar maps for alkalosis.

Answer 18

Combine information from Figs. 20.15 and 20.18b.

Question 19

Explain how the loop of Henle and vasa recta work together to create dilute renal filtrate.

Answer 19

See Fig. 20.7.

Question 20

Diagram the mechanism by which vasopressin alters the composition of urine.

Answer 20

See Fig. 20.6

Question 21

Make a table that specifies the following for each substance listed: hormone or enzyme? steroid or peptide? produced by which cell or tissue? target cell or tissue? target has what response?
a. ANP
b. aldosterone
c. renin
d. ANG II
e. vasopressin
f. angiotensin-converting enzyme

Answer 21

(a) ANP—peptide from atrial myocardial cells. Causes Na+ and water excretion; inhibits ADH secretion. (b) Aldosterone—steroid from adrenal cortex. Increases distal nephron Na+ reabsorption and
K+ excretion. (c) Renin—an enzyme from JG cells. Converts plasma angiotensinogen to ANG I. (d) ANG II—peptide hormone made from ANG I. Increases blood pressure by actions on arterioles, brain, and adrenal cortex. (e) Vasopressin—hypothalamic peptide. Increases distal nephron water reabsorption. (f) ACE—enzyme on vascular endothelium. Converts ANG I to ANG II.

Question 22

Name the four main compensatory mechanisms for restoring low blood pressure to normal. Why do you think there are so many homeostatic pathways for raising low blood pressure?

Answer 22

Vasoconstriction, increased cardiac output, water conservation by kidneys, and increased thirst. If blood pressure falls too low, oxygen supply to the brain will decrease, resulting in damage or death.

Question 23

The interstitial fluid in contact with the basolateral side of collecting duct cells has an extremely high osmolarity, and yet the cells do not shrivel up. How can they maintain normal cell volume in the face of such high ECF osmolarity?

Answer 23

The cells concentrate organic solutes to increase their internal osmolarity.

Question 24

Compare and contrast the terms in each set:
a. principal cells and intercalated cells
b. renin, ANG II, aldosterone, ACE
c. respiratory acidosis and metabolic acidosis, including causes and compensations
d. water reabsorption in proximal tubule, distal tubule, and ascending limb of the loop of Henle
e. respiratory alkalosis and metabolic alkalosis, including causes and compensations

Answer 24

(a) Both are in the distal nephron. P cells are associated with aldosterone-mediated Na+ reabsorption; I cells are involved with acid-base regulation.
(b) All are parts of the RAS system. Renin and ACE—enzymes; ANG II and aldosterone—hormones.
(c) In both, body pH falls below 7.38. Respiratory—results from CO2 retention (from any number of causes); metabolic—results from excessive production of metabolic acids. Respiratory compensation—renal H+ excretion and HCO - retention. Metabolic compensation—increased ventilation, renal H+ excretion, and HCO3 retention. Respiratory—arterial PCO2 is elevated; metabolic—PCO2 usually decreased.
(d) Proximal tubule—not regulated; distal nephron—regulated by vasopressin. Ascending limb—impermeable to water.
(e) Both—pH goes above 7.42. Metabolic—may be caused by excessive ingestion of bicarbonate-containing antacids or vomiting; respiratory—hyperventilation. Metabolic compensation—decrease ventilation, excretion, increased HCO3 - excretion. Respiratory compensation—decreased renal H+ excretion, increased HCO - excretion decreased renal H+

Question 25

Level 3:
A 45-year-old man visiting from out of town arrives at the emergency room having an asthma attack caused by pollen.
a. Blood drawn before treatment showed the following: HCO3- = 30 mEq/L (normal: 24), PCo2 = 7-mm Hg, pH = 7.24. What is the man’s acid-base state? Is this an acute or a chronic situation?

b. The man was treated and made a complete recovery. Over the next 10 years, he continued to smoke a pack of cigarettes a day. A year ago his family doctor diagnosed chronic obstructive pulmonary disease (emphysema). The man’s most recent blood test showed the following: HCO3- = 45 mEq/L, PCO2 = 85 mm Hg, pH = 7.34. What is the man’s acid-base state now? Is this an acute or a chronic situation?
c. Explain why in his second illness his plasma bicarbonate level and PCO2, are higher than in the first illness but his pH is closer to normal.

Answer 25

(a) acute respiratory acidosis, (b) chronic respiratory acidosis, (c) Renal compensation has increased his pH by H+ excretion and HCO3 reabsorption. His PCO2 is elevated because of his emphysema.

Question 26

The U.S. Food and Drug Administration has now approved a new class of drugs called vasopressin receptor antagonists. Predict the effect these drugs would have on renal function and describe some clinical situations or diseases in which these drugs might be useful.

Answer 26

These drugs decrease ADH-mediated water reabsorption. Useful in people who secrete too much vasopressin (SIADH, or syndrome of inappropriate ADH secretion) or in hyponatremia.

Question 27

Karen has bulimia, in which she induces vomiting to avoid weight gain. When the doctor sees her, her weight is 89 lb and her respiration rate is 6 breaths/min (normal 12). Her blood HCO3- is 62 mEqE/L (normal: 24–29), arterial blood pH is 7.61, and PCO2 is 61 mm Hg.
a. What is her acid-base condition called?
b. Explain why her plasma bicarbonate level is so high.
c. Why is she hypoventilating? What effect does this have on the pH and total oxygen content of her blood? Explain your answers.

Answer 27

(a) Metabolic alkalosis, partially compensated. (b) After vomiting acid
(H ), her body was left with HCO3 . (c) Hypoventilation increases
PCO2, HCO3 , and H. Increased H decreases pH (compensation). Hypoventilation also decreases arterial PO2 and decreases the total oxygen content of blood

Question 28

Hannah, a 31-year-old woman, decided to have colonic irrigation, a procedure during which large volumes of distilled water were infused into her rectum. During the treatment, she absorbed 3000 mL of water. About 12 hours later, her roommate found her in convulsions and took her to the emergency room. Her blood pressure was 140/90, her plasma
Na+ concentration was 106 mEq/L (normal: 135 mEq/L), and her plasma osmolarity was 270 mOsM. In a concept map or flowchart, diagram all the homeostatic responses her body was using to attempt compensation for the changes in blood pressure and osmolarity.

Answer 28

Blood pressure is high, plasma
Na+ and osmolarity are low. Use Tbl. 20.1 to select reflex pathways for the map.

Question 29

Liddle’s syndrome is an inherited defect of apical ENaC sodium channels in P cells. It is characterized by high blood pressure and hypokalemia.
a. Are the defective ENaC channel proteins increasing or decreasing apical
Na+ movement? Explain and relate your answer to the characteristic hypokalemia.
b. Liddle’s syndrome is considered a form of pseudohyperaldosteronism {pseudo-, false}. What test(s) would you run to distinguish Liddle’s syndrome from primary or secondary hyperaldosteronism?

Answer 29

(a) ENaC activity is increased, bringing more Na+ into the cell. This increases the activity of the Na+ -K+ -ATPase, which pumps K+ into the cell. The K+ then leaks out the apical channels into the urine, resulting in increased excretion of K+ and hypokalemia.
(a) Run aldosterone and ANG II levels. They will both be normal in Liddle’s syndrome.