Review Questions 23. Nine hundred millimicrocuries of albumin labeled with radioactive iodine are injected intravenously into a lean, 70-kg man. If there is complete mixing in the plasma and no excre- tion of the albumin, what approximate plasma concentration of the labeled albumin do you expect to find 10 minutes after injection(assume normal plasma volume of about 3 L)? A <29 millimicrocuries/liter B. 60 millimicrocuries/liter C. 130 miLimicrocuries/liter D. 300 millimicrocuries/liter E. 500 millimicrocuries/liter 4. Which set of the following best illustrates the consequences of the infusion of plasma Intracellular Extracellular ExtracellularExtracellular Hematocrit Volume Osmolarity Sodium Conc. A. no change increase no change decrease B increase Lncrease no change C no change increase no change D increase Increase E no change no change no change Increase decrease 25. An excessive intake of tap water over a short period of time would be expected to produce which of the following: Extracellular Intracellular Extracellular Intracellular Volume Sodium Conc. Osmolarity A increase decrease decrease Increase Increas decrease decrease C. increase increase decrease crease crease Increase decrease uncease 26. Exposure to the sun in a hot desert environment for a prolonged period of time without adequate uid intake would produce: Intracellular Intracellular Extracellular Extracellular Urine volume Osmolarity Sodiurm Conc. Osmolarity Osmolarity A decrease Increase B decrease increase Increase crease Increasc C. increase Increase Increase Increase decrease D. decrease increase decrease Increase Increase E decrease decrease decrease decrease medical 27
ReviewQuestions 23. Nine hundred millimicrocuries of albumin labeled with radioactive iodine are injected intravenously into a lean, 70-kg man. If there is complete mixing in the plasma and no excretion of the albumin, what approximate plasma concentration of the labeled albumin do you expect to find 10 minutes after injection (assume normal plasma volume of about 3 L)? A. B. C. D. E. <29millimicrocuries/liter 60 millimicrocuries/liter 130 millimicrocuries/liter 300 millimicrocuries/liter 500 millimicrocuries/liter 24. Which set of the following best illustrates the consequences of the infusion of plasma: 25. An excessive intake of tap water over a short period of time would be expected to produce which of the following: Extracellular Intracellular Volume Volume A. increase decrease Extracellular Sodium Cone. decrease Intracellular Osmolarity increase 26. Exposure to the sun in a hot desert environment for a prolonged period of time without adequate fluid intake would produce: Intracellular Intracellular Extracellular Volume Osmolarity Sodium Cone. A. decrease decrease increase Extracellular Osmolarity increase Urine Osmolarity increase KAPLA d N'. me Ica I 27 Intracellular Extracellular Extracellular Extracellular Hematocrit Volume Volume Osmolarity Sodium Conc. A. no change increase no change no change decrease B. increase increase increase lllcrease no change C. no change lllcrease no change no change no change D. increase increase decrease decrease no change E. no change no change no change increase decrease B. increase decrease decrease increase C. increase increase decrease decrease D. increase increase increase decrease E. increase increase decrease increase B. decrease increase increase lllcrease lllcrease C. increase lllcrease increase lllcrease decrease D. decrease lllcrease decrease lllcrease increase E. decrease decrease decrease decrease decrease
USMLE Step 1: Physiolo 7. Five uCi of inulin and an unknown substance were injected simultaneously and intra venously as a bolus. Ten minutes later a plasma sample revealed equal activities of the two substances. Thereafter, the activity of the unknown substance decreased more rapidly than inulin. a possible explanation could be the unknown substance A. was filtered and partially reabsorbed by the kidney B. was weakly bound to plasma proteins C. had slowly ated capillary membrane E. was filtered and secreted by the kidney 28. A young man was found after wandering the arizona desert for several hours under a hot sun with no source of drinking water. Which of the following solutions given intra venously would best return the individual s intracellular volume toward normal A. Hypertonic saline E. Dextran in isotonic saline 9. A hypotensive young woman was admitted to the emergency room. Laboratory data revealed the following: Pla normal Osmolarity K Hematocrit Which of the following acute problems would be most consistent with the above? A. Hemorrhage C. Hypotonic diuresis E. Alcoholic-induced dehydration 28 medical
USMLEStep 1: Physiology 28 KAPLA~. meulCa I 27. Five f..lCiof inulin and an unknown substance were injected simultaneously and intravenouslyas a bolus. Ten minutes later a plasma sample revealedequal activities of the two substances. Thereafter, the activity of the unknown substance decreased more rapidly than inulin. A possible explanation could be the unknown substance A. B. e. D. E. was filtered and partially reabsorbed by the kidney was weaklybound to plasma proteins had slowlypenetrated capillary membranes had rapidly entered cellsand was metabolized was filtered and secreted by the kidney 28. A young man was found after wandering the Arizona desert for severalhours under a hot sun with no source of drinking water. Which of the following solutions given intravenously would best return the individual's intracellular volume toward normal? A. B. e. D. E. Hypertonic saline Isotonic saline Whole blood Plasma Dextran in isotonic saline 29. A hypotensive young woman was admitted to the emergency room. Laboratory data revealed the following: Plasma Na CI Osmolarity K Hematocrit normal normal normal decreased increased Which of the following acute problems would be most consistent with the above? A. Hemorrhage B. Diarrhea e. Hypotonic diuresis D. Water intoxication E. Alcoholic-induced dehydration
Review questions Answers 1. Answer: A. A 250 mOsm/L (or stated as just mOsm)solution of sodium chloride is a hypotonic solution, thus it has a higher water concentration than the red blood cell inte- rior. Water will thus diffuse into the red blood cell, and the cell's volume will increase 2. Answer: B. The " X"side has the lower solute concentration and thus the higher water con- centration, Water diffuses from X to Y, thus the level of side x decreases and the level of side y increases 3. Answer: D. Body water is approximately distributed as 2/3 intracellular fluid and 1/3 extracellular fluid 4. Answer: A Facilitated diffusion and simple diffusion are both passive processes driven by concentration gradients; however, facilitated diffusion has characteristics that apply to protein-mediated transport, e. g, exhibits saturation kinetics and chemical specificity 5. Answer: A. A 200 mOsm sodium chloride solution is hypotonic and thus has a greater water concentration than the red blood cell. Thus water diffuses into the cell and its vol ume increases 6. Answer: A. A 400 mOsm glycerol solution represents a solution with a lower water concen tration than in the red blood cell. The glycerol, however, will penetrate the red blood cell but does so slowly. Thus, initially water will leave the red blood cell and the cell will shrink However, the question says to ignore this initial effect and only consider the long-term changes. The glycerol will enter the cell until the concentration of glycerol in the red blood cell will equal the concentration of glycerol in the beaker. The problem is that there is ne nonpenetrating solute like Nacl in the beaker to balance the 300 mOsm of nonpenetrating solutes inside the red blood cell, thus the cell will swell Answer: C. The red blood cell was equilibrated in 150 mM Nacl which equals 300 mOsm and thus is an isotonic saline solution. A 300 mOsm CaCl solution is also an isotonic sol tion of a nonpenetrating solute, thus, there will be no change in red blood cell volume 8. Answer: B 200 mOsm Nacl is nonpenetrating but the 200 mOsm glycerol penetrates slowly. Initially the effective osmolarity of the solution is 400 mOsm, thus the ceul shrinks With time the glycerol penetrates and the final effective osmolarity of the solution is only 200 mOsm due to the Nacl. Thus as the glycerol penetrates, water moves into the red blood cell and the final volume will be greater than at time zero Curve B, which shows an initial shrinkage then overall swelling, is the best answer 9. Answer: C. Loss of pure water from the extracellular Quid would increase body osmolar ity and decrease extracellular volume. The increased extracellular osmolarity will cause some water to diffuse out of cells, decreasing intracellular volume 10. Answer: E. 300 mOsm NaCl is isotonic saline, thus there is no change in body osmolar- ty. The fuid will enter the extracellular compartment and the volume of this space will increase. Since no change occurred in osmolarity, there will be no net movement of water across the cell membrane. This means no change in intracellular volume 11. Answer: A. Infusing hypertonic saline will increase body osmolarity. Since fluid is given, the volume of the extracellular compartment will increase. The increased osmolarity of the extracellular fluid will cause water to diffuse out of cells, decreasing intracellular volume. medical 29
ReviewQuestions Answers 1. Answer: A. A 250 mOsm/L (or stated as just mOsm) solution of sodium chloride is a hypotonic solution, thus it has a higher water concentration than the red blood cell interior. Water will thus diffuse into the red blood cell, and the cell'svolume will increase. 2. Answer: B. The "X" side has the lower solute concentration and thus the higher water concentration. Water diffuses from X to Y, thus the level of side X decreases and the level of side Y increases. 3. Answer: D. Body water is approximately distributed as 2/3 intracellular fluid and 1/3 extracellular fluid. 4. Answer: A. Facilitated diffusion and simple diffusion are both passive processes driven by concentration gradients; however, facilitated diffusion has characteristics that apply to protein-mediated transport, e.g., exhibits saturation kinetics and chemical specificity. 5. Answer: A. A 200 mOsm sodium chloride solution is hypotonic and thus has a greater water concentration than the red blood cell. Thus water diffuses into the cell and its volume mcreases. 6. Answer: A. A 400 mOsm glycerol solution represents a solution with a lower water concentration than in the red blood cell. The glycerol, however, will penetrate the red blood cell but does so slowly. Thus, initially water will leave the red blood cell and the cell will shrink. However, the question says to ignore this initial effect and only consider the long-term changes. The glycerol will enter the cell until the concentration of glycerol in the red blood cell will equal the concentration of glycerol in the beaker. The problem is that there is no nonpenetrating solute like NaCl in the beaker to balance the 300 mOsm of nonpenetrating solutes inside the red blood cell, thus the cell will swell. 7. Answer: C. The red blood cellwas equilibrated in 150mM NaCl which equals 300 mOsm and thus is an isotonic saline solution. A 300 mOsm CaClzsolution is also an isotonic solution of a nonpenetrating solute, thus, there will be no change in red blood cellvolume. 8. Answer: B. 200 mOsm NaCl is nonpenetrating but the 200 mOsm glycerol penetrates slowly. Initially the effective osmolarity of the solution is 400 mOsm, thus the cell shrinks. With time the glycerol penetrates and the final effective osmolarity of the solution is only 200 mOsm due to the NaCl. Thus as the glycerol penetrates, water moves into the red blood cell and the final volume will be greater than at time zero. Curve B, which shows an initial shrinkage then overall swelling, is the best answer. 9. Answer: C. Loss of pure water from the extracellular fluid would increase body osmolarity and decrease extracellular volume. The increased extracellular osmolarity will cause some water to diffuse out of cells, decreasing intracellular volume. 10. Answer: E. 300 mOsm NaCl is isotonic saline, thus there is no change in body osmolarity. The fluid will enter the extracellular compartment and the volume of this space will increase. Since no change occurred in osmolarity, there will be no net movement of water across the cell membrane. This means no change in intracellular volume. 11. Answer: A. Infusing hypertonic saline will increase body osmolarity. Since fluid is given, the volume of the extracellular compartment willincrease.The increased osmolarity of the extracellular fluid will cause water to diffuse out of cells,decreasing intracellular volume. iiletlical 29 (
USMLE Step 1: Physiology 2. Answer: A. If a permeating solute is added to chamber X, the solute will diffuse across the membrane until its concentration is equal in X and Y. Since the solute concentration is equal in X and Y, there will not be a water concentration difference and thus no net dif- fusion of water. The fluid levels in X and Y will be equal. 3. Answer: E Simple diffusion and membrane transport are rapid over short distances When distances reach I cm or greater a significant movement can occur ony with pres- sure differences, which is also referred to as bulk ftow 14. Answer: B Infusion of distilled water would decrease body osmolarity and increase the volume of the extracellular fluid. The decreased extracellular osmolarity would cause water to diffuse into cells and raise intracellular volume 15. Answer: D. Answers A, B, and C are characteristics of all protein-mediated transport Facilitated diffusion is a passive process driven by a concentration gradient, thus is inde pendent of ATP 16. Answer: D. Intracellular fluid contains 2/3 of body water. Under steady-state conditions the intracellular osmolarity and extracellular osmolarity are equal. If there was a differ- ence, water would diffuse until they were equal. The intracellular compartment does have a higher concentration of organic anions, mainly proteins, than the extracellular fluid 7. Answer: A Low solute concentration means high water concentration and water diffuses from a higher water concentration. Even if no membrane was present the water would still diffuse down its concentration gradient. Diffusion depends upon a concentration gradi ent and is not an energy-demanding(ATP)process 8. Answer: 1, 5. If I liter of isotonic saline is injected it will disperse in the extracellular com partment which will increase in volume by I liter. Since it is isotonic, there will be no change in osmolarity and thus no change in intracellular volume. Nacl can cross capillary membranes and at least 3/4 of the I liter (750 ml)will enter the interstitial space. Less than 250 ml will remain in the vascular compartment. This will be in part due to the dilution of plasma proteins 19. Answer: 1, 4, 5. If plasma is infused it will remain almost entirely in the vascular space This is due to the fact that the plasma proteins cannot diffuse readily across the capillary membrane. Retention of the proteins in the vascular compartment will prevent the loss of water to the interstitium 20. Answer: 5. Urea can penetrate capillary membranes and almost all cell membranes in the body. Thus, the infused water and urea will distribute within the total body water, 2/3 inside celis and 1/3 outside cells 21. Answer: D. The y axis is the intracedlular concentration as a percentage of the extracellu lar concentration. At the origin there is nothing inside the cells. Moving up the y axis, intracellular concentration is increasing and when the 100 point is reached, the intracel lular and extracellular concentrations are equal above the 100 point, the intracellular concentration is greater than the extracellular concentration. Substance H moves into the cell down its concentration gradient, but once the concentration gradient is eliminated (100 point), net transport stops. This indicates that H is transported by a passive process Movement of G into the cell is also dependent upon a concentration gradient but it moves more slowly than H. F initially moves into the cell down its concentration gradient but continues to be transported into the cell after the concentration gradient is eliminated This indicates active transport is involved 30 medical
USMLEStep1: Physiology 30 KAPLA~. meulca I 12. Answer: A. If a permeating solute is added to chamber X,the solute will diffuse acrossthe membrane until ~s concentration is equal in X and Y.Since the solute concentration is equal in X and Y,there will not be a water concentration difference and thus no net diffusion of water. The fluid levelsin X and Y will be equal. 13. Answer: E. Simple diffusion and membrane transport are rapid over short distances. When distances reach 1 cm or greater a significant movement can occur only with pressure differences,which is also referred to as bulk flow. 14. Answer: B. Infusion of distilled water would decrease body osmolarity and increase the volume of the extracellular fluid. The decreased extracellular osmolarity would cause water to diffuse into cells and raise intracellular volume. 15. Answer: D. Answers A, B, and C are characteristics of all protein-mediated transport. Facilitated diffusion is a passive process driven by a concentration gradient, thus is independent of ATP. 16. Answer: D. Intracellular fluid contains 2/3 of body water. Under steady-state conditions the intracellular osmolarity and extracellular osmolarity are equal. If there was a difference, water would diffuse until they were equal. The intracellular compartment does have a higher concentration of organic anions, mainly proteins, than the extracellular fluid. 17. Answer: A. Low solute concentration means high water concentration and water diffuses from a higher water concentration. Evenif no membrane was present the water would still diffuse down its concentration gradient. Diffusion depends upon a concentration gradient and is not an energy-demanding (ATP) process. 18. Answer: 1,5. If 1liter of isotonic saline is injected it will disperse in the extracellularcompartment which will increase in volume by 1 liter. Since it is isotonic, there will be no change in osmolarity and thus no change in intracellular volume. NaCl can cross capillary membranes and at least 3/4 of the 1liter (750 rnI) will enter the interstitial space.Lessthan 250 rnl willremain in the vascular compartment. This willbe in part due to the dilution of plasma proteins. 19. Answer: 1, 4, 5. If plasma is infused it will remain almost entirely in the vascular space. This is due to the fact that the plasma proteins cannot diffuse readily across the capillary membrane. Retention of the proteins in the vascular compartment willprevent the loss of water to the interstitium. 20. Answer: 5. Urea can penetrate capillary membranes and almost all cell membranes in the body. Thus, the infused water and urea will distribute within the total body water, 2/3 inside cellsand 1/3 outside cells. 21. Answer: D. The y axis is the intracellular concentration as a percentage of the extracellular concentration. At the origin there is nothing inside the cells. Moving up the y axis, intracellular concentration is increasing and when the 100 point is reached, the intracellular and extracellular concentrations are equal. Above the 100 point, the intracellular concentration is greater than the extracellular concentration. Substance H moves into the cell down its concentration gradient, but once the concentration gradient is eliminated (100 point), net transport stops. This indicates that H is transported by a passiveprocess. Movement of G into the cellis also dependent upon a concentration gradient but it moves more slowly than H. F initially moves into the cell down its concentration gradient but continues to be transported into the cell after the concentration gradient is eliminated. This indicates activetransport is involved
Review Questions 22. Answer: B. Blood volume plasma volume 0.405L 3. Answer: D. Volume(v)x concentration(C)=amount of tracer(A) A 900 millicurie 3 liters 300 millicuries/liter 24. Answer: A. The infusion of plasma will add significant volume only to the vascular com- partment, which is part of the extracellular fluid. The protein present in the plasma pre vents fluid from crossing the capillary membrane into the interstitial compartment. However, because of a slight increase in capillary pressure a very small amount of Quid would be filtered to the interstitium, but this would be a minor effect (see cardiovascular) The infused plasma will have the same osmolarity and sodium concentration as the extra- ellular Quid, thus no change would occur in these variables. Since extracellular osmolar- ty will not change, intracellular osmolarity will not change. Plasma does not contain red blood cells. Thus, infusing plasma will dilute the red blood cells and decrease hematocrit 25. Answer: C Ingesting excessive amounts of tap water will increase the volume of the extra cellular fluid. Since tap water contains few if any electrolytes, it will dilute the extracellular sodium and reduce extracellular osmolarity. The decreased extracellular osmolarity will cause a diffusion of water into cells, increasing intracellular volume but reducing intracellular osmolarity. 26. Answer: B. Loss of hypotonic fluid from the skin(sweat) in this environment would cause a decrease in volume but an increase in extracellular fluid osmolarity. Since extracellular osmolarity is determined to a large part by sodium, sodium concentration should also rise. The increased extracellular osmolarity will cause a diffusion of water out of cells, decreasing intracellular volume but causing a rise in intracellular osmolarity. The dehydrated individual will form a small volume of highly concentrated urine 27. Answer: E. The same initial plasma activities indicated a similar initial volume of distri- bution, the extracellular space (ECF). The more rapid decrease in activity of the unknown substance with time indicates it was removed more rapidly from the ECF than inulin Inulin is filtered and excreted by the kidney. The addition of a net secretion by the kidney for the unknown substance would cause its plasma activity to decrease more rapidly than inulin. If the substance were reabsorbed by the kidney, its activity over time would exceed hat of inulin ( choice A). If it was weakly bound to plasma protein(choice B)or if it slow. ly penetrated capillary membranes(choice C), the initial activity would be greater than inulin, If the substance rapidly entered cells(choice E), its initial activity would be less than inulin 28. Answer: B. The loss of hypotonic fluid due to sweating would produce a hyperosmotic osmolarity and an extracellular and intracelluar contraction, given that isotonic saline would lower the individual's osmolarity and expand the intracellular space. Wbole blood (choice C), plasma(choice D), and dextran in isotonic saline(choice E)contain a solute (albumin, dextran) that does not penetrate a capillary membrane; thus, less fluid would enter the interstitial space. This is not the case with isotonic saline
ReviewQuestions 22. Answer: B. Blood volume = plasma volume 1 - Hct 3L 1 - 0.40 = 5 L 23. Answer: D. Volume (V) X concentration (C) =amount of tracer (A) C = A = 900 millicuries V 3 liters - 300 millicuries/liter 24. Answer: A. The infusion of plasma will add significant volume only to the vascular compartment, which is part of the extracellular fluid. The protein present in the plasma prevents fluid from crossing the capillary membrane into the interstitial compartment. However,because of a slight increase in capillary pressure a very small amount of fluid would be filtered to the interstitium, but this would be a minor effect (see cardiovascular). The infused plasma will have the same osmolarity and sodium concentration as the extracellular fluid, thus no change would occur in these variables. Since extracellular osmolarity will not change, intracellular osmolarity will not change. Plasma does not contain red blood cells.Thus, infusing plasma will dilute the red blood cells and decrease hematocrit. 25. Answer: C. Ingesting excessiveamounts of tap water will increase the volume of the extracellularfluid. Sincetap water contains few if any electrolytes,it will dilute the extracellular sodium and reduce extracellular osmolarity. The decreased extracellular osmolarity will cause a diffusion of water into cells, increasing intracellular volume but reducing intracellular osmolarity. 26. Answer: B. Lossof hypotonic fluid from the skin (sweat) in this environment would cause a decrease in volume but an increase in extracellular fluid osmolarity. Since extracellular osmolarity is determined to a large part by sodium, sodium concentration should also rise. The increased extracellular osmolarity will cause a diffusion of water out of cells, decreasing intracellular volume but causing a rise in intracellular osmolarity. The dehydrated individual will form a small volume of highly concentrated urine. 27. Answer: E. The same initial plasma activities indicated a similar initial volume of distribution, the extracellular space (ECF). The more rapid decrease in activity of the unknown substance with time indicates it was removed more rapidly from the ECF than inulin. Inulin is filtered and excretedby the kidney. The addition of a net secretion by the kidney for the unknown substance would cause its plasma activity to decrease more rapidly than inulin. If the substance were reabsorbed by the kidney, its activity over time would exceed that of inulin (choice A). If it was weaklybound to plasma protein (choice B) or if it slowly penetrated capillary membranes (choice C), the initial activity would be greater than inulin. If the substance rapidly entered cells (choice E), its initial activity would be less than inulin. 28. Answer: B. The loss of hypotonic fluid due to sweating would produce a hyperosmotic osmolarity and an extracellular and intracellular contraction, given that isotonic saline would lower the individual's osmolarity and expand the intracellular space. Whole blood (choice C), plasma (choice D), and dextran in isotonic saline (choice E) contain a solute (albumin, dextran) that does not penetrate a capillary membrane; thus, less fluid would enter the interstitial space. This is not the case with isotonic saline. iiieilical 31