MCB 136 - Advanced Physiology


MCB 136 Review | Kidneys and Body Fluids | Body Fluids

Review Problems | Body Fluids

  1. 10 mg of inulin is injected into a subject; after 15 min the urine is voided and collected and a sample of plasma is collected. Analyses reveal 0.0005 mg inulin/ml of plasma and 300 ml of urine containing 0.005 mg inulin/ml. What is the "inulin space" for this individual? What is the estimated ECF? Would this volume of ECF be more likely that from a subject who weighed 15 kg, 70 kg or 150 kg? If you knew the hematocrit, could you calculate blood volume from these data?

  2. You have a sample of non-allergenic, fluorescently tagged, plasma protein and you wish to estimate the total blood volume of an individual. You inject 60 µg of the plasma protein into a vein. 10 min later you withdraw 1 ml sample of blood, centrifuge it, and find that the plasma layer, which consists of 60% of the blood sample, contains the tagged plasma protein at a concentration of 0.02 µg/ml. What is the plasma volume? What is the total blood volume?

  3. Given the results of problem #1 and #2, and assuming they were dervied from the same person, calculate the volume of the interstitial fluid for the individual.

  4. Radiolabeled tracers can be usefully applied to measure various body fluid compartments. For example, when mixed with a sample of blood or injected into the blood stream Na2CrO4 (labeled with radioactive 51Cr) irreversibly "tags" red blood cells, and is used as a diagnostic aid for blood volume determination or for a measure of red blood cell survival time. Inulin is a metabolically inert polysaccharide that readily permeates across capillary membranes but cannot penetrate cell membranes, thus it is a marker (labeled with 14C) of extracellular space (inulin is also useful to measure GFR). In this problem, a sample of blood was tagged with 51CrO4 and 14C-inulin. After assessing the concentration of radioactive label in an aliquot of the sample, 2 ml were injected into a 10 kg, nephrectomized dog (kidneys removed). After a two hour period blood samples were removed and again assayed for radioactivity. The following measurements were made:


    Pre-injection sample Two hour blood sample
       
    51Cr = 1 × 106 cpm/ml 51Cr = 2800 cpm/ml blood
    14C = 4 × 106 cpm/ml 14C = 2200 cpm/ ml blood
      Hematocrit = 0.5
       
        Calculate:
            (a) Cr space.   (To what does this correspond?)
            (b) Inulin space.   (What does this approximate?)
            (c) Volume of interstitial fluid.


  5. Calculate the concentration of NaCl in molarity for a solution of 0.9 gm%. What is the osmolarity of this solution if one assumes a complete dissociation of the salt?

  6. Normal blood plasma contains 10 mg% of Ca2+ and 2.2 mg% of Mg2+.
    Calculate the concentrations of these ions in mM and in mEq/L.

  7. The protein concentration is highest in ______ fluid, and lowest in ______ fluid. (T, interstitial; I, intracellular; P, plasma).

        a. P, T     b. I, P     c. T, I     d. P, I     e. I, T     f. T, P


  8. What will happen to red cell volume when placed in the following solutions? (i.e., swell, shrink, no change; why?)

    a. 0.15 M NaCl d. 0.15 M CaCl2 g. 0.3 M glycerol
    b. 0.15 M glucose e. 0.3 M urea h. 0.5 M NaCl
    c. 0.3 M sucrose f. 0.1 M MgCl2 i. 0.5 M glycerol
         
         

Functional Anatomy & Glomerular Filtration Problems

  1. Define the term renal clearance. What are its dimensions? What information does a clearance give concerning intrinsic renal mechanisms?

  2. What are the principle and method for measuring total renal GFR? What is meant by SNGFR? What experimental evidence suggests an involvement of the macula densa to regulate SNGFR?

  3. Show the formal identity between the clearance concept for PAH and the Fick Principal for measurement of blood flow.

  4. Consider three types of substances:

            (a) Substance x: handled by glomerular filtration alone;
            (b) Substance y: handled by glomerular filtration and active tubular reabsorption;
            (c) Substance z: handled by glomerular filtration and active secretion.

        For each substance, construct 3 curves showing:
          (1) relationship betwen filtered load (F) and plasma concentration (P),
          (2) relationship between rate of excretion (E) of substance and plasma concentration, and
          (3) relationship between reabsorption (T) or secretion and plasma concentration.
        Use abscissa for plasma concentration throughout.

        What is the relationship between Clearance (C) and plasma concentration for each substance? Graph each of these separately.


  5. Given the following data:

            Plasma glucose = 4.1 mg/ml plasma (410 mg %)
            Glomerular filtration rate = 125 ml/min
            Amount of glucose excreted = 190 mg/min
            Also given the fact that plasma [glucose] is significantly above the max saturation for glucose tubular reabsorption:

        (a) Calculate rate of glucose reabsorption.
        (b) Calculate the maximum rate for glucose reabsorption.
        (c) What would you expect the rate of urine flow to be in the subject compared to one with normal plasma glucose levels? Why?


  6. Given the following:

            Glomerular filtration rate = 125 ml/min
            Plasma clearance of urea = 75 ml/min
            Rate of excretion of urea in urine = 18 mg/min

        (a) What is the plasma concentration of urea?
        (b) What fraction of the urea entering the glomerular filtrate appears in the urine?


  7. Dextran is a high molecular weight polymer of maltose which can be prepared in a variety of sizes. They are huge water soluble molecules which do not permeate cell membranes and are neither reabsorbed nor secreted by the renal tubular epithelium. Using dextran with an approximate radius = 28 Å, the following data were obtained:

      Urine (mg/ml) Plasma (mg/ml)
         
    Inulin (radius = 14 Å) 165 3
    Neutral Dextran (radius = 28 Å) 15 0.4
    Sulfonated Dextan (radius = 28 Å) 6 0.9
         
    Urine flow = 2.2 ml/min    
         
     
      (a) Calculate:
          (i) GFR (glomerular filtration rate).
          (ii) Fractional filtration of neutral dextran (i.e., amount actually filtered as a fraction of that which would be filtered if the dextran were freely filtered).
          (iii) Fractional filtration of sulfonated dextran.

      (b) Interpret these results.


  8. Explain how a hypertonic urine is produced.

  9. What is the difference between a countercurrent exchanger and a countercurrent multiplier?

  10. The macula densa is a specialized group of sensory cells found in the ________ (E, efferent arteriole; D, distal tubule; P, podocytes) and forms part of the ________ (J, juxtaglomerular apparatus; L, lamina densa).

        a. E, J     b. E, L   c. D, J     d. D, L     e. P, J     f. P, L


  11. The glomerular filtration rate is unaffected by

        a. strenuous exercise
        b. tubular reabsorption and secretion mechanisms
        c. renal blood flow
        d. the concentration of inulin appearing in the urine


  12. For a normal person at rest, the kidneys receive about _______ (10%; 25%; 40%) of the cardiac output. It would be reasonable to suspect that during severe exercise, the fraction of cardiac output going to the kidney would _______ (I, increase; D, decrease; O, not change).

        a. 10%, I     b. 10%, O     c. 25%, I     d. 25%, O     e. 25%, D     f. 40%, I


  13. Which of the following would cause an increase in both GFR and RPF?

        A. high protein in blood
        B. an obstruction in the nephron
        C. dilation of the afferent arteriole
        D. dilation of the efferent arteriole
        E. constriction of the efferent arteriole

  14. In order, from the lowest to the highest, the plasma clearances for the following substances would be ________. (N, Na+; G, glucose; I, inulin; U, urea; P, para-amino hippuric acid)

        a. P,I,N,U,G    b. P,U,I,N,G    d. N,G,I,P,U    c. N,I,P,U,G    e. G,U,N,P,I    f. G,N,U,I,P


  15. A plasma concentration of 0.26 mg/ml, a urine flow of 1 ml/min, and a urine concentration of 1,820 mg%, correspond to a plasma clearance of a constituent of ______ ml/minute.

        a. 4.7     b. 47     c. 470     d. 7.0     e. 70     f. 700


  16. The proximal tubule reabsorbs 2/3 or more of each of the following except:

        a. glucose     b. sodium     c. bicarbonate     d. potassium     e. urea


  17. The thin ascending limb of the loop of Henle has ______ levels of metabolic activity and ______ levels of permeability to Na+ and Cl- as compared to other renal tubular segments. (H, high; L, low; S, about the same)

        a. H, L     b. L, H     c. L, L     d. L, S     e. S, H     f. S, L


  18. Given the values below, what glomerular capillary oncotic pressure would just prevent filtration?

          Glomerular capillary hydrostatic pressure = 47 mmHg
            Bowman's space hydrostatic pressure = 10 mmHg
              Bowman's space oncotic pressure = 0 mmHg

        a. 57 mmHg     b. 47 mmHg     c. 37 mmHg     d. 10 mmHg     e. 0 mmHg


Regulation of Salt & Water Balance Problems

  1. Define and know function of: insensible water loss; excretion, filtration, reabsorption and secretion; glomerulotubular balance; aldosterone, Addison's disease, roles of Na/K-ATPase and ENaC in action of aldosterone; regulation of aldosterone secretion by renin-angiotensin system, including angiotensinogen, converting enzyme, adrenal cortex, aldoseterone; obligatory water loss; ADH action at cellular level and control of release by osmoreceptors and baroreceptors; diuretics

  2. Describe the set of reactions that would occur in a person who had been lost on the desert and had lost 4 liters of sweat (hypotonic fluid). What would happen to ECF volume and [Na+], plasma [ADH], water permeability of collecting duct, and osmolarity of urine?

  3. A patient came to the doctor with the following symptoms: polydypsia (excessive drinking), polyuria (excessive urine production) abnormally high blood [glucose] and glucosuria (glucose in urine). Explain the symptoms.

  4. What would happen to urine production during treatment with

        a. amiloride (blocks ENaC)
        b. Furosemide (blocks NaKCl cotransporter)
        c. Overproduction and release of ADH by posterior pituitary
        d. Overproduction of aldosterone

  5. A patient with renal insufficiency has blood drawn and it is found that [Na+] is low, glucose is normal, urea is high and osmolarity is high. What is expected for plasma levels of [ADH]?

  6. A patient had increased levels of renin due to a tumor in the juxtaglomerular cells. Explain likely outcome in terms of Na+ transport by the kidney and circulating levels of aldosterone.

  7. If it were possible to treat only renal cells with inhibitors of protein synthesis, which of the following responses would be impaired by such treatment?

        a. ADH effect on collecting duct
        b. aldosterone effect on distal tubule

  8. During hemorrhage there is a reduced blood volume and blood pressure. Explain physiological mechanisms that would occur in kidney in response to these changes.

  9. Explain why the heart is an endocrine organ.

  10. How are renal effects of aldosterone and ANF antagonistic?

  11. Aldosterone has been implicated as playing a role in all of the following processes EXCEPT

        a. increased Na+ entry from tubular lumen to distal tubular cells
        b. increased NaCl and fluid retention by the kidney
        c. increased turnover of ATP in distal tubular cells
        d. increased levels of cyclic AMP in distal tubular cells
        e. increased Na/K-ATPase activity in distal tubular cells

  12. Secretion of antidiuretic hormone

        a. is decreased by hemorrhage
        b. causes an increased blood flow to the renal medulla
        c. increases the loss of water in the urine
        d. is increased by injection of hypertonic saline


  13. The more significant renal effect of antidiuretic hormone involves altered _____ (A, active transport; P, permeability) of epithelial cells of the _____ (T, proximal tubule; C, collecting duct; L, loop of Henle) to ______ (H20; Na+ )

        a. A, T, H20     b. A, C, Na+     c. A, L, H20     d. P, T, H20     e. P, C, H20     f. P, L, Na+

Salt, water and pH Problems

  1. A patient is suffering from primary hyperaldosteronism, that is, increased secretion of aldosterone, which is usually caused by an aldosterone-producing adrenal tumor. Is the plasma renin concentration in this patient higher or lower than normal? Why?

  2. Changes in response to congestive heart failure include

        A. increased release of renin.
        B. increased secretion of aldosterone.
        C. decreased glomerular filtration rate.
        D. increased permeability of collecting ducts to water.
        E. all of the above.

      Explain your answer.


  3. Why is it that the bicarbonate-carbonic acid buffer system is such an effective system in vivo despite the fact that it operates far from its pK?

  4. What are the stimuli mediating the hyperventilation of metabolic acidosis?

  5. What effect does respiratory compensation have upon blood pH in metabolic acidosis?

  6. What mechanisms does the kidney use to combat metabolic acidosis? Which is quantitatively the most significant in ridding the body of H+ ions?

        A. Acid pH of urine.
        B. Increased titratable acid excretion [T.A.].
        C. Increased ammonium excretion.

  7. What is the difference between H+ secretion and H+ excretion?

  8. Given the following data and the assumption that all bicarbonate is reabsorbed by exchange of Na+ for H+,

      Normal Hypothetical Metabolic Acidosis
         
    GFR 150 L/day 150 L/day
    Plasma HCO3- 25 mEq/L 10 mEq/L
    T.A. & NH4+ 30 mEq/day 300 mEq/day
    Urinary HCO3- 0 0
         
    carry out the following calculations:    
    Daily filtered load of HCO3- _____mEq/day _____mEq/day
    H+ secretion: for HCO3- _____mEq/day _____mEq/day
    For T.A. & NH4+ _____mEq/day _____mEq/day
    Total H+ secretion _____mEq/day _____mEq/day
    H+ excretion (T.A.+NH4+) _____mEq/day _____mEq/day
         
     
        Carry out similar calculations for other disturbances of Acid-Base Equilibrium, making reasonable assumptions for T.A. and NH4+ excretion.


  9. Given: one liter of solution at pH 7.4 containing 20 mM HCO3- and PCO2 equal to 33.3 torr (mmHg).   Take pKa = 6.1 and SCO2 = 0.03 mM CO2/liter/torr at 38`C.   What will the pH and [HCO3-] become if 10 mEq of HCl are introduced to the system, assuming:

        (a) The system is completely closed from the atmosphere.
        (b) The system is open to, and in equilibrium with, an atmosphere containing the same PCO2 as the original solution (33.3 torr).
        (c) The system is transferred to an atmosphere containing PCO2 of 16.6 torr.
        (d) What would be the physiological analogies for the above problem?

  10. The secretion of ammonia by renal tubules is regulated largely by the renal secretion of excess ________ (HCO3-; Cl-; H+), and is ________ (I, increased; D, decreased) in acidosis.

        a. HCO3-, D     b. Cl-, D     c. H+, D     d. HCO3-, I     e. Cl-, I     f. H+, I

  11. Renal bicarbonate excretion

        a. increases while ingesting a high protein diet
        b. increases during hyperventilation
        c. increases as blood pH decreases
        d. increases in respiratory acidosis

  12. The serum: Na+ = 139, K+ = 2.0, Cl- = 90, HCO3- = 40, pH = 7.6, PCO2 = 44. These findings are compatible with

        a. diabetic ketoacidosis (metabolic)
        b. excessive vomiting of gastric juice
        c. excessive ingestion of NH4Cl
        d. excessive administration of NaHCO3

  13. In partially compensated metabolic acidosis blood [HCO3-] is ______, arterial PCO2 is_____, and renal HCO3- production by distal tubule/collecting duct is______ (I, increased; D, decreased).

        a. I, I, D     b. D, D, I     c. I, D, D     d. D, I, I     e. D, I, D     f. D, D, D

  14. In respiratory acidosis blood [HCO3-] ______, arterial PCO2 ______, and renal HCO3- absorption by the distal tubule and collecting duct ______ (I, increases; D, decreases)

        a. I, I, D     b. I, I, I     c. I, D, D     d. D, I, I     e. D, I, D     f. D, D, D