196 Questions
What is the primary characteristic of mannitol that makes it a suitable marker for ECF?
It is a large molecule that cannot cross cell membranes
What is the purpose of allowing the substance to equilibrate in the body?
To allow the substance to distribute evenly throughout the body fluid compartments
What is the formula used to calculate the volume of distribution of a substance?
Volume = Amount ÷ Concentration
What is the primary function of tritiated water in measuring body fluid compartments?
To measure the volume of TBW
What is the primary assumption about solutes such as NaCl and mannitol?
They do not cross cell membranes and are confined to the ECF
What is the purpose of Evans blue in measuring body fluid compartments?
To measure the volume of plasma
What happens to the substance during the equilibration period in the sample calculation?
10% of the substance is excreted in the urine
What happens to plasma protein concentration and hematocrit when there is an infusion of isotonic NaCI?
They decrease
What is the term for the addition of isotonic fluid to the ECF?
Isosmotic volume expansion
What happens to ECF osmolarity when there is an infusion of isotonic NaCI?
It remains unchanged
What is the term for the loss of isotonic fluid from the ECF?
Isosmotic volume contraction
What happens to arterial blood pressure when there is an infusion of isotonic NaCI?
It increases
What is the estimated plasma osmolarity if the plasma Na concentration is 140 mEq/L, plasma glucose concentration is 100 mg/dL, and blood urea nitrogen concentration is 20 mg/dL?
290 mOsm/L
What is the approximate percentage of total body weight that is total body water (TBW)?
60%
What is the volume of the interstitial fluid compartment if the plasma volume is 3.2 liters and the ECF volume is 14.1 liters?
10.9 liters
Which of the following markers is used to measure the volume of the intracellular fluid compartment?
None of the above
What is the concentration of solute particles that determines osmolarity?
Osmolarity
What is the ratio of the volume of the interstitial fluid compartment to the volume of the plasma compartment?
3:4
What happens to the ICF volume as a result of sweating in a desert?
It decreases due to the shift of water out of ICF
What is the effect of hyperosmotic volume contraction on plasma protein concentration?
It increases due to the decrease in ECF volume
Why does the hematocrit remain unchanged during sweating in a desert?
Water shifts out of the RBCs, decreasing their volume
What happens to the ECF volume in syndrome of inappropriate antidiuretic hormone (SIADH)?
It increases due to the retention of excess water
What is the effect of hyperosmotic volume contraction on the osmolarity of the ECF?
It increases due to the loss of water in the sweat
What is the effect of SIADH on the osmolarity of the ECF?
It decreases due to the retention of excess water
What is the equation that relates clearance to urine concentration, urine volume, and plasma concentration?
C = U × V/P
What is the effect of angiotensin II on renal arterioles at low concentrations?
Constriction of efferent arterioles and protection of GFR
What is the effect of ACE inhibitors on renal function?
Decrease in GFR and reduction of hyperfiltration
What is the effect of atrial natriuretic peptide (ANP) on renal arterioles?
Vasodilation of afferent arterioles and vasoconstriction of efferent arterioles
What is the percentage of cardiac output that is typically represented by renal blood flow (RBF)?
25%
What is the mechanism by which the kidney regulates renal blood flow (RBF)?
Changing renal vascular resistance
What is the primary reason why inulin is used to measure GFR?
Because it is freely filtered by the glomeruli
What is the formula used to calculate GFR using inulin?
GFR = [U] x V / [P]
What happens to the BUN/creatinine ratio in prerenal azotemia?
It increases to more than 20:1
What is the effect of age on GFR?
GFR decreases with age
What is the mechanism by which BUN and serum creatinine increase when GFR decreases?
Increased urea reabsorption in the proximal tubule
What is the purpose of measuring GFR using inulin clearance?
To estimate glomerular filtration rate
What percentage of renal plasma flow is normally filtered across the glomerular capillaries?
20%
What is the primary driving force for glomerular filtration?
Net ultrafiltration pressure across the glomerular capillaries
What is the effect of an increase in filtration fraction on the protein concentration of peritubular capillary blood?
Increased protein concentration
What is the equation that describes the relationship between glomerular filtration rate and the Starling forces?
GFR = Pgc - πgc
What is the direction of fluid movement favored by the net ultrafiltration pressure across the glomerular capillaries?
Out of the glomerular capillary
What is the percentage of renal plasma flow that leaves the glomerular capillaries by the efferent arterioles?
80%
What is the primary reason why substances with clearances equal to GFR are considered glomerular markers?
They are not reabsorbed or secreted
What is the effect of a high-K+ diet on the relative clearance of PAH?
It increases the relative clearance of PAH
What happens to the excretion of a weak acid when the urine pH is alkaline?
It increases
What is the effect of acidifying the urine on the excretion of a weak base?
It increases
What is the primary mechanism by which nonionic diffusion affects the excretion of weak acids and weak bases?
Back-diffusion
Which of the following substances has a clearance higher than GFR?
PAH
What is the effect of an increase in urine pH on the back-diffusion of a weak acid?
It decreases
What is the primary reason why the clearance of a substance is used to measure its excretion?
It is a measure of the substance's excretion rate
What does the TF/Pinull ratio correct for?
Water reabsorption
If TF/Pinull = 2.0, what percentage of filtered water has been reabsorbed?
50%
What is the value of TF/PNa+ in the tubular fluid of Bowman space?
1.0
If TF/P = 1.0, what can be concluded about the substance?
There has been no reabsorption or secretion of the substance.
If [TF/P]K+/[TF/P]inull = 0.3 at the end of the proximal tubule, what percentage of filtered K+ remains in the tubular fluid?
30%
What is the significance of TF/P > 1.0?
There has been secretion of the substance.
What is the primary site of Na+ reabsorption?
Entire nephron
What is the fate of most of the reabsorbed Na+?
Reabsorbed into the blood
What is the use of TF/P ratio in nephron terminology?
To compare the concentration of a substance in tubular fluid with the concentration in plasma.
What happens to TF/P as water is reabsorbed along the nephron?
TF/P increases.
What is the purpose of the double ratio [TF/P]K+/[TF/P]inull?
To calculate the fraction of filtered K+ reabsorbed
What is the result of the calculation: 1 - (1/TF/Pinull)?
Fraction of filtered H2O reabsorbed
What is the significance of inulin in nephron terminology?
It is a freely filtered substance that is not reabsorbed or secreted.
What does a TF/P ratio of 0.8 indicate?
The concentration of the substance in tubular fluid is 80% of the concentration in plasma.
What is the significance of TF/P < 1.0?
The concentration of the substance in tubular fluid is less than in plasma.
What is the advantage of using TF/P ratio in nephron terminology?
It allows for the comparison of the concentration of a substance in tubular fluid with the concentration in plasma.
What is the effect of a high-K+ diet on the principal cells?
It increases K+ secretion
What stimulates the a-intercalated cells to reabsorb K+?
H+, K+-ATPase
What is the effect of aldosterone on K+ secretion?
It increases K+ secretion
What is the effect of a low-K+ diet on the electrochemical driving force for K+?
It decreases the driving force
What is the effect of alkalosis on K+ secretion?
It increases K+ secretion
What is the effect of thiazide diuretics on K+ secretion?
It decreases K+ secretion
What is the effect of hyperaldosteronism on K+ secretion?
It increases K+ secretion
What is the effect of acidosis on K+ secretion?
It decreases K+ secretion
What is the primary use of K+-sparing diuretics in combination with other diuretics?
To reduce urinary K+ losses
What is the primary mechanism of urea secretion in the thin descending limb of the loop of Henle?
Simple diffusion
What is the effect of ADH on urea reabsorption in the inner medullary collecting ducts?
Increases urea reabsorption
What is the primary function of triamterene and amiloride in the nephron?
Act directly on principal cells
What is the percentage of filtered urea that is reabsorbed in the proximal tubule?
50%
What is the effect of an increase in luminal anions on K+ secretion in the nephron?
Increases K+ secretion
What is the primary site of urea secretion in the nephron?
Thin descending limb of the loop of Henle
How does urea excretion vary with urine flow rate?
Increases with increased urine flow rate
At high levels of water reabsorption, what happens to urea reabsorption?
It increases
What percentage of filtered phosphate is reabsorbed in the proximal tubule?
85%
What is the effect of parathyroid hormone (PTH) on phosphate reabsorption?
It decreases phosphate reabsorption
What is the fate of 15% of the filtered phosphate load?
It is excreted in urine
What is the effect of loop diuretics on urinary calcium excretion?
It increases urinary calcium excretion
What percentage of plasma calcium is filtered across the glomerular capillaries?
60%
What is the primary mechanism of calcium reabsorption in the proximal tubule?
Passive process coupled to sodium reabsorption
What is the effect of fibroblast growth factor 23 (FGF23) on phosphate reabsorption?
It decreases phosphate reabsorption
What is the primary mechanism by which aldosterone increases sodium reabsorption in the kidney?
By stimulating the synthesis of new sodium channels
What is the primary effect of antidiuretic hormone (ADH) on the kidney?
Increased water permeability in the collecting duct
What is the primary mechanism by which the kidney regulates potassium balance?
By adjusting potassium secretion in the collecting duct
What is the effect of aldosterone on the intercalated cells of the kidney?
Increased hydrogen ion secretion
What is the primary mechanism by which K+-sparing diuretics decrease potassium secretion?
By inhibiting the action of aldosterone
What is the effect of a shift of potassium from the intracellular fluid (ICF) to the extracellular fluid (ECF)?
Hyperkalemia
What is the primary mechanism by which the kidney regulates potassium excretion?
By adjusting potassium secretion in the collecting duct
What is the effect of aldosterone on potassium reabsorption in the kidney?
Increased potassium reabsorption
What is the effect of hyperaldosteronism on potassium secretion?
Increased K+ secretion
What occurs in response to acidosis in the principal cells?
H+ enters the cell, K+ leaves the cell
What is the effect of loop and thiazide diuretics on potassium secretion?
Increased K+ secretion
What is the primary mechanism by which loop and thiazide diuretics increase potassium secretion?
Increased Na+ delivery to the late distal tubule and collecting ducts
What is the effect of alkalosis on potassium secretion?
Increased K+ secretion
What is the primary mechanism by which K+-sparing diuretics decrease potassium secretion?
The mechanism is not specified in the text
What is the effect of acidosis on the intracellular potassium concentration?
Decreased intracellular K+ concentration
What is the primary reason why loop and thiazide diuretics cause hypokalemia?
Increased potassium secretion
What is the primary function of antidiuretic hormone (ADH) in the nephron?
Stimulation of water reabsorption in the distal tubule and collecting duct
What is the role of the vasa recta capillaries in the medulla?
Maintenance of the corticopapillary osmotic gradient
What is the effect of antidiuretic hormone (ADH) on the countercurrent multiplication in the loop of Henle?
Stimulation of sodium reabsorption in the thick ascending limb
What is the osmolarity of the glomerular filtrate in the proximal tubule?
300 mOsm/L
What percentage of the filtered water is reabsorbed isosmotically in the proximal tubule?
Two-thirds
What is the effect of antidiuretic hormone (ADH) on urea recycling in the medulla?
Stimulation of urea recycling
What is the primary function of ADH in the collecting ducts?
To increase the water permeability of the principal cells
What is the osmolarity of the final urine in the presence of ADH?
1200 mOsm/L
What is the result of low circulating levels of ADH or ineffective ADH?
Production of dilute urine
What is the effect of ADH on countercurrent multiplication and urea recycling?
ADH stimulates countercurrent multiplication and urea recycling
What is the osmolarity of the tubular fluid at the bend of the loop of Henle and the tip of the papilla?
1200 mOsm/L
What is the result of osmotic equilibration with the corticopapillary gradient in the presence of ADH?
TF/P > 1.0
What is the primary function of the thick ascending limb of the loop of Henle in the absence of ADH?
Reabsorbing NaCl without water, and making the tubular fluid dilute
What is the characteristic of the cells in the late distal tubule and collecting ducts in the absence of ADH?
Impermeable to water
What is the purpose of measuring free-water clearance (CH2O)?
To estimate the ability to dilute the urine
In which segments of the nephron is free water produced?
Thick ascending limb and early distal tubule
What is the minimum osmolarity of the final urine in the absence of ADH?
50 mOsm/L
What happens to the tubular fluid in the early distal tubule in the absence of ADH?
It becomes more dilute
What is the primary function of the thick ascending limb of the loop of Henle?
Reabsorbs NaCl and decreases plasma osmolarity
What is the effect of ADH on the principal cells of the late distal tubule?
Increases H2O permeability
What is the osmolarity of the tubular fluid at the end of the distal tubule?
300 mOsm/L
What is the primary function of the early distal tubule?
Reabsorbs NaCl and decreases plasma osmolarity
What is the reason for the decrease in urine osmolarity and increase in urine volume when ADH is inhibited?
Decreased water reabsorption in the late distal tubule
What is the effect of high ADH on the late distal tubule and collecting duct?
Increases water permeability
What is the effect of ADH on the free-water clearance (CH2O) in the kidneys?
It decreases CH2O by promoting water reabsorption in the collecting ducts.
What is the primary reason why urine cannot be diluted during high water intake or concentrated during water deprivation in the presence of a loop diuretic?
The loop diuretic inhibits NaCl reabsorption in the thick ascending limb, preventing the production of a corticopapillary osmotic gradient.
What is the formula used to calculate the free-water clearance (CH2O)?
CH2O = V - Co
What is the characteristic of urine produced during treatment with a loop diuretic?
It is isosmotic to plasma.
What is the effect of ADH on the urine osmolarity in central diabetes insipidus?
It has no effect on urine osmolarity as ADH is absent in central diabetes insipidus.
What is the primary difference between the urine produced during treatment with a loop diuretic and the urine produced in central diabetes insipidus?
The urine produced during treatment with a loop diuretic is isosmotic, while the urine produced in central diabetes insipidus is hypotonic.
What is the primary mechanism of action of PTH on the kidneys?
Stimulating Ca2+ reabsorption in the distal tubule
What is the effect of aldosterone on the kidneys?
Increasing Na+ reabsorption in the distal tubule
What is the primary function of ADH on the kidneys?
Increasing H2O permeability in the late distal tubule and collecting duct
What is the effect of angiotensin II on the kidneys?
Increasing Na+ reabsorption in the proximal tubule
What is the primary mechanism of action of ANP on the kidneys?
Decreasing GFR
What is the effect of PTH on phosphate reabsorption in the kidneys?
Decreasing phosphate reabsorption in the proximal tubule
What is the effect of hyperkalemia on NH3 synthesis?
It inhibits NH3 synthesis
What is the primary disturbance in metabolic acidosis?
Decrease in arteria I [HC03-]
What is the effect of hypokalemia on NH3 synthesis?
It stimulates NH3 synthesis
What is the respiratory compensation for metabolic acidosis?
Hyperventilation
What is the adaptive response in chronic metabolic acidosis?
Increased NH1 synthesis
What is the effect of a decrease in PCO2 on HCO3- reabsorption in the kidneys?
Decreased HCO3- reabsorption
What is the expected response to simple acid-base disorders?
The actual response equals the calculated response
What is the primary mechanism by which the kidneys excrete fixed H+?
Titratable acid and NH4+
What is the effect of ECF volume expansion on HCO3- reabsorption?
Decreased HCO3- reabsorption
What is the effect of angiotensin II on HCO3- reabsorption?
Increased HCO3- reabsorption
In the reabsorption of filtered HCO3-, what is the role of carbonic anhydrase?
To catalyze the dissociation of H2CO3 into H+ and HCO3-
What is the role of H+-ATPase in the excretion of H+ as titratable acid?
Secretes H+ into the lumen
What is the effect of increased PCO2 on the reabsorption of filtered HCO3-?
Increased reabsorption of HCO3-
What happens to the filtered load of HCO3- when the plasma HCO3- concentration becomes very high?
The reabsorptive capacity is exceeded, and HCO3- is excreted in the urine
What is the effect of aldosterone on H+-ATPase?
Increases H+-ATPase activity
What is the primary function of the Na+-H+ exchange mechanism in the luminal membrane?
To secrete H+ into the lumen
What is the result of the reabsorption of filtered HCO3- in the proximal tubule?
Net reabsorption of filtered HCO3-
What is the site of HCO3- reabsorption in the nephron?
Early proximal tubule
What is the primary function of the Hco,- buffer in the extracellular fluid?
To buffer excess H+ ions produced during metabolic activities
What is the term for the excretion of H+ ions as H2PO4- in the urine?
Titratable acid
What is the pH range within which the imidazole and α-amino groups of proteins have a buffering effect?
pH 7.35-7.45
What is the formula used to calculate the pH of a solution when a weak acid and its conjugate base are present?
pH = pK + log[A-]/[HA]
Which of the following buffers is most effective within 1.0 pH unit of its pK?
All of the above
What is the primary function of deoxyhemoglobin as a buffer?
To buffer excess H+ ions in the blood
Which hormone stimulates the reabsorption of Ca2+ in the distal tubule?
PTH
What is the mechanism of action of ADH on the late distal tubule and collecting duct principal cells?
V2 receptor, adenylate cyclase, and cAMP
Which of the following hormones increases the secretion of K+ in the distal tubule principal cells?
Aldosterone
What is the effect of ANP on glomerular filtration rate (GFR)?
Increases GFR
Which hormone stimulates the reabsorption of phosphate in the proximal tubule?
PTH
What is the effect of angiotensin II on blood volume?
Increases blood volume
What is the primary function of the major extracellular buffer in the human body?
To remove excess hydrogen ions from the blood
Which of the following is a minor extracellular buffer in the human body?
Phosphate
What is the pK of the CO2/HCO3- buffer pair?
6.1
What is the role of hemoglobin in intracellular buffering?
It is a major intracellular buffer in red blood cells
What is the purpose of the Henderson-Hasselbalch equation?
To calculate the pH of a solution
What is the role of organic phosphates in intracellular buffering?
They are major intracellular buffers in red blood cells
What is the effect of a decrease in PCO2 on the rate of HCO3- reabsorption?
Decreased rate of HCO3- reabsorption
What is the mechanism by which angiotensin II contributes to contraction alkalosis?
By stimulating Na+-H+ exchange
What is the fate of the H+ secreted into the lumen by the H+-ATPase?
It combines with HPO42- to form H2PO4-
What is the effect of ECF volume expansion on HCO3- reabsorption?
Decreased HCO3- reabsorption
What is the role of aldosterone in the excretion of titratable acid?
It stimulates the H+-ATPase
What is the term for the process by which the kidney regulates HCO3- reabsorption in response to changes in ECF volume?
Volume-mediated HCO3- reabsorption
What is the minimum urinary pH?
4.4
What is the product formed when H+ combines with NH3?
NH4+
What is the primary factor that determines the amount of NH4+ excreted?
Urine pH
What is the process by which NH3 diffuses from the cells into the lumen?
Diffusion trapping
What is produced in the intercalated cells from CO2 and H2O?
H+ and HC03-
What is the term for the process by which the kidneys excrete excess H+ ions?
Titratable acidity
What is the primary source of H+ ions that are secreted into the lumen via the Na+-H+ exchange mechanism?
C02 and H2O
What is the consequence of an increase in the filtered load of HCO3- on the rate of HCO3- reabsorption?
Increased rate of HCO3- reabsorption
What is the primary mechanism by which an increase in PCO2 increases the rate of HCO3- reabsorption?
Increased availability of intracellular H+ for secretion
What is the primary consequence of the reabsorption of filtered HCO3- in the proximal tubule?
Net reabsorption of HCO3- in the blood
What is the primary site of HCO3- reabsorption in the nephron?
Early proximal tubule
What is the primary role of brush border carbonic anhydrase in the reabsorption of filtered HCO3-?
Catalyzing the dissociation of H2CO3 into H+ and HCO3-
This quiz covers the distribution of tritiated water, mannitol, and Evans blue in the body, and their relation to total body water, intracellular and extracellular fluids.
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