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211 Cards in this Set
- Front
- Back
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Clearance equation
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C = (urinary conc x urinary flow) / plasma conc
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How much of the CO is the RBF?
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20%
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What are some things that vasodilate the renal arterioles?
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PGE2
PGI2 Bradykinin NO Dopamine |
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Over what range of arterial pressures does autoregulation occur?
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80-200 mmHg
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What are the mechanisms for autoregulation of RBF?
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Myogenic mechanism: afferent arteriole constricts in response to stretch
TGF mechanism: increased flow across the macula densa constricts the afferent arteriole |
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What substance is used to calculate RPF?
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PAH, because it is filtered and secreted
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How close is calculated RPF to actual RPF?
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It underestimates actual RPF by 10%
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What is the formula for RBF?
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RBF = RPF / (1-hematocrit)
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What substances are used to calculate GFR?
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Inulin or creatinine, because they are filtered but are not secreted or reabsorbed
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What happens to the BUN/creatinine ratio during azotemia (hypovolemia)?
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It increases (greater than 20:1)
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What happens to GFR as we age?
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Decreases
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What is the equation for filtration fraction?
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FF = GFR / RPF
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What is the normal value for the filtration fraction?
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20% (that is, 20% of RPF is filtered)
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If the FF is increased, what effect does this have on reabsorption in the proximal tubule? What if it is decreased?
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Increases and decreases proximal tubule reabsorption, respectively
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What is the formula for GFR?
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GFR = Kf [(Pgc - Pbs) - (PIgc - PIbs)]
Note that PIbs is typically 0 because there should be no protein in Bowman's space |
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How does the glomerular barrier contribute to Kf?
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Kf is the filtration coefficient, and it is maintained by the size barrier and the charge barrier (anionic glycoproteins inhibit the passage of negatively charged plasma proteins)
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What happens to Kf in glomerular disease?
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It decreases because the anionic charges on the barrier are lost, resulting in proteinuria
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What is the principal determinant of Pbs (hydrostatic pressure of Bowman's space)?
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Constriction of the ureters
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What happens to the glomerular capillary oncotic pressure as we go along the length of the capillary?
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It increases because as water is filtered out, the protein concentration is increased
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What is the equation for filtered load?
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Filtered load = GFR x plasma conc
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What is the equation for excretion rate?
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Excretion rate = urine flow rate x urine conc
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What is the equation for reabsorption rate?
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Reabsorption rate = filtered load - excretion rate
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What is the equation for secretion rate?
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Secretion rate = excretion rate - filtered load
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How can you tell if a substance is reabsorbed? Excreted?
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If it is reabsorbed, excretion rate is lower than filtered load. If it is secreted, excretion is higher than filtered load
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What is the conversion factor between ml and dl?
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100 ml = 1 dl
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How is glucose reabsorbed?
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Na-glucose cotransport in the proximal tubule reabsorbs Na and glucose from the lumen. Note that the number of these cotransporters is limited
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What is the transport maximum?
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The reabsorptive rate at which all available transporters are saturated and no further reabsorption can occur, so excess solute will be excreted in the urine
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What is the Tm for glucose?
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Under 250 mg/dl, all filtered glucose is reabsorbed because there are plenty of carriers. Over 350 mg/dl, the carriers are entirely saturated, so increased plasma concentration doesn't result in increased reabsorption. The threshold (where glucose first begins to appear in the urine) is about 250 mg/dl
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What is "splay?"
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The region of the solute titration curve (Tm curve) between threshold and Tm. It represents the excretion of solute in the urine before saturation of reabsorption occurs
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How can you promote excretion of weak acids?
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Alkalinization of the urine will deprotonate the acid (that is, you'll have the A- form instead of the HA form), which is less able to diffuse from the urine to the blood
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What does it mean if TF/P > 1?
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There has been secretion, so the concentration in the tubular fluid is higher than that in the plasma
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What is the significance of TF/Pinulin, and what is the equation?
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Marker for water absorption
% of filtered water that is reabsorbed = 1 - [1 / (TF/Pinulin)] |
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How much filtered Na is reabsorbed?
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Over 99% (less than 1% of filtered load is in the urine)
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How much Na is reabsorbed in the proximal convoluted tubule?
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67%
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How much Na is reabsorbed in the thick ascending limb of the loop of Henle?
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25%
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How much Na is reabsorbed in the distal convoluted tubule?
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5%
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How much Na is reabsorbed in the collecting duct?
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3%
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How much filtered water is reabsorbed in the proximal tubule?
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67%
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What is glomerulotubular balance?
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The same FRACTION of solute is reabsorbed at all times, for all concentrations (that is, for any concentration, X% is always reabsorbed)
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What part of the nephron is the site of glomerulotubular balance?
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The proximal tubule
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What does it mean for proximal tubule Na and water reabsorption to be isosmotic?
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The reabsorption of both Na and water in this region are exactly proportional, so osmolarity is maintained (both Na and water have TF/P ratios of 1.0 here)
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How is Na reabsorbed in the early proximal tubule?
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Na-Glucose cotransporter
Na-solute cotransport with various solutes Na-H symporter |
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How and where do carbonic anhydrase inhibitors work?
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By inhibiting CA, the reabsorption of HCO3 is decreased. These inhibitors (like acetazolamide) act in the proximal tubule, where H is secreted via Na-H antiport
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How is Na reabsorbed in the late proximal tubule?
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Na-Cl symport
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How does extracellular fluid volume influence Na reabsorption?
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If ECFV decreases, reabsorption is increased
If ECFV increases, reabsorption is decreased |
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How is Na reabsorbed in the thick ascending limb of the loop of Henle?
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Na-K-2Cl cotransporter
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What inhibits the Na-K-2Cl cotransporter?
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Loop diuretics such as furosemide, ethacrynic acid, and bumetanide
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Is the thick ascending limb of the loop of Henle permeable or impermeable to water?
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Impermeable, so in this region, NaCl is reabsorbed without water. Therefore, this segment is known as the diluting segment.
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What sort of potential difference is observed in the thick ascending limb of the loop of Henle?
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Lumen-positive
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How is Na reabsorbed in the early distal tubule?
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Na-Cl cotransporter
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What inhibits the Na-Cl cotransporter of the early distal tubule?
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Thiazide diuretics
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Is the early distal tubule permeable or impermeable to water?
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Impermeable
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What do the principal cells of the late distal tubule and collecting duct do?
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Reabsorb Na and water
Secrete K |
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What effect does aldosterone have upon Na and K transport?
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Increases Na reabsorption and K secretion in the late distal tubule and collecting duct
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What effect does ADH have upon water permeability?
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It increases water permeability in the collecting duct by inducing the insertion of aquaporin 2 into the apical membrane. In the absence of ADH, the principal cells of the collecting duct are virtually impermeable to water.
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What are K-sparing diuretics?
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Spironolactone, tiramterene, amiloride -- these decrease K secretion
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How is Na reabsorbed in the late distal tubule and collecting duct?
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Amiloride-sensitive Na channels
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What do the intercalated cells of the late distal tubule and collecting duct do?
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Secrete H via an H-ATPase that is induced by aldosterone
Reabsorb K via an H-K-ATPase |
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What body compartment is the majority of K found in?
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The intracellular fluid
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How do K shifts contribute to hypo/hyperkalemia?
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A shift of K OUT of the cells causes hyperkalemia
A shift of K INTO the cells causes hypokalemia |
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Is K filtered by the nephron? Secreted? Reabsorbed?
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Yes to all three
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How do we achieve K balance?
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When urinary excretion is exactly equal to dietary intake
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What are some causes of hyperkalemia (K shift out of cells)?
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Insulin deficiency
B-adrenergic antagonists Acidosis Hyperosmolarity Na-K ATPase inhibitors Exercise Cell lysis |
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What are some causes of hypokalemia (K shift into cells)?
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Insulin
B-adrenergic agonists Alkalosis Hyposmolarity |
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How much can K excretion vary?
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A lot! 1-110% of filtered load, depending upon dietary intake, aldosterone levels, and acid-base status
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How much K is reabsorbed in the proximal tubule?
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67%
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How much K is reabsorbed in the thick ascending limb of the loop of Henle?
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20%
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How is K reabsorbed in the thick ascending limb of the loop of Henle?
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The Na-K-2Cl cotransporter
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How do the distal tubule and collecting duct handle K transport?
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They either reabsorb OR secrete it, depending upon dietary intake
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How is K reabsorbed in the distal tubule and collecting duct?
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H-K ATPase in the apical membrane of alpha intercalated cells
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Under what conditions is K reabsorbed in the distal tubule and collecting duct?
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Low K diet (K depletion). It is under these conditions that K excretion is 1% of filtered load
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How is K secreted in the distal tubule?
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The Na-K ATPase imports K into the cell across the basolateral membrane
K channels export K across the apical membrane into the lumen |
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What drives K transport in the distal tubule?
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Chemical and electrical driving forces
Things that increase intracellular K (or decrease luminal K) will increase the driving force for K secretion |
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What specific things increase distal K secretion?
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High dietary K (increases intracellular K)
Aldosterone (stimulation of the Na-K ATPase) Alkalosis Thiazide and loop diuretics Luminal anions |
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What affect does hyperaldosteronism have upon K secretion?
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It increases K secretion and causes hypokalemia
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What affect does hypoaldosteronism have upon K secretion?
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It decreases K secretion and causes hyperkalemia. The Na-K ATPase is no longer stimulated to remove K from the interstitium.
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What effect does pH have upon K secretion?
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Alkalosis increases K secretion
Acidosis decreases K secretion H and K are effectively exchanged for each other across the basolateral membrane, so if the blood has excess H (acidosis), that H displaces K inside the cell such that K is no longer available for secretion |
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How do thiazide and loop diuretics affect K secretion?
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They increase flow rate through the distal tubule, which dilutes the K concentration within the lumen and creates a driving force for K secretion
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How do K-sparing diuretics affect K secretion?
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They decrease K secretion, and can cause hyperkalemia if not used in conjunction with thiazide or loop diuretics (which would reduce urinary K loss)
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How do luminal anions affect K secretion?
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Excess anions in the lumen increase the negativity of the lumen, which favors K secretion
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Where in the nephron is urea reabsorbed?
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50% is passively reabsorbed in the proximal tubule
The rest is reabsorbed in the inner medullary collecting duct upon ADH stimulation |
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How does ADH affect urea reabsorption?
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It increases the permeability of the inner medullary collecting duct
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How does urea contribute to the corticomedullary osmotic gradient?
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ADH causes urea to be reabsorbed from the collecting duct to the interstitium, which creates an osmotic gradient that increases as you go deeper into the medulla
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How does urine flow rate affect urea excretion?
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At low flow rates, more urea is reabsorbed and less is excreted, whereas at high flow rates, urea tends to be excreted
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Where is phosphate reabsorbed (and how much)?
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Proximal tubule; 85%
The remaining 15% is excreted in the urine |
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How is phosphate reabsorbed in the proximal tubule?
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Na-phosphate cotransport
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How does PTH affect phosphate reabsorption?
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It inhibits it by generating cAMP and inhibiting Na-phosphate cotransport. Since phosphate reabsorption is decreased, PTH causes phosphaturia
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Where is Ca reabsorbed (and how much)?
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Proximal tubule and thick ascending limb of the loop of Henle (90%)
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How much of the plasma Ca is filtered across the glomerular membrane?
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60%
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How do loop diuretics (eg furosemide) affect Ca excretion?
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They increase urinary Ca excretion because Na and Ca reabsorption in the loop of Henle are linked. Therefore, if the volume lost by the diuretic is replaced, loop diuretics can be used to treat hypercalcemia
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How does PTH affect Ca transport?
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It increases reabsorption in the distal tubule
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How do thiazide diuretics affect Ca transport?
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They increase reabsorption in the distal tubule, so they can be used to treat hypercalciuria
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Where in the nephron is Mg reabsorbed?
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Hahaha! Pretty much everywhere -- proximal tubule, thick ascending limb, distal tubule
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How do calcium imbalance disorders affect Mg transport?
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In the thick ascending limb, Mg and Ca compete for reabsorption, so if you are hypercalcemic, Mg reabsorption is inhibited and Mg is excreted (likewise, hypermagnesemia increases Ca excretion by inhibiting Ca reabsorption)
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What hormone is responsible for the production of concentrated urine?
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ADH
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When is ADH produced?
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Water deprivation
Hemorrhage (depleted ECFV) Increased plasma osmolarity |
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What hormone is responsible for the generation of the corticomedullary osmotic gradient?
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ADH
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What is the corticomedullary osmotic gradient?
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As you go from the cortex to the medulla, the osmolarity increases from 300 mOsm/L to 1200 mOsm/L. It is established by countercurrent multiplication and urea recycling, and is maintained by countercurrent exchange in the vasa recta
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What compounds create the corticomedullary osmotic gradient?
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NaCl and urea
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How does ADH affect NaCl reabsorption?
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It increases reabsorption in the thick ascending limb of the loop of Henle, which augments the corticomedullary osmotic gradient
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What role do the vasa recta play in the corticomedullary osmotic gradient?
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They act as osmotic exchangers, meaning they osmotically equilibrate with the interstitial fluid of the medulla
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How does ADH rectify water deprivation?
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Water deprivation
Increased plasma osmolarity Stimulation of hypothalamus osmoreceptors Secretion of ADH from anterior pituitary Increased water permeability of late distal tubule and collecting duct Increased water reabsorption Increased urine concentration Decreased plasma osmolarity |
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How does the osmolarity of glomerular filtrate compare to that of plasma?
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They are equal (300 mOsm/L)
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What is the TF/Posm along the length of the nephron?
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Proximal tubule: 1
Thick ascending limb: < 1 (because of dilution) Late distal tubule: 1 Collecting duct: > 1 in the presence of ADH (because of water reabsorption), < 1 in the absence of ADH |
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What is the water permeability in the various segments of the nephron?
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Proximal tubule: permeable
Thick ascending limb: impermeable Early distal tubule: impermeable Late distal tubule: permeable in response to ADH Collecting duct: permeable in response to ADH |
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How does ADH alter the magnitude of the corticomedullary osmotic gradient?
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Increases it
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What is free-water clearance (Ch2o)?
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It is used to estimate the kidney's ability to concentrate or dilute the urine. Free water is the solute-free water produced in the diluting segments where NaCl is reabsorbed and water is left behind in the lumen
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How does ADH affect the sign of Ch2o?
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In the absence of ADH, Ch2o is POSITIVE (solute-free water is excreted)
In the presence of ADH, Ch2o is NEGATIVE (solute-free water is reabsorbed in the late distal tubule and collecting duct) |
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What is the formula for Ch2o?
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Ch2o = urine flow rate x osmolar clearance
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What does it mean when Ch2o is equal to 0?
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Urine is isosmotic (isosthenuric) to plasma
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How do loop diuretics contribute to a Ch2o of 0?
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They inhibit NaCl reabsorption in the thick ascending limb and abolish the corticomedullary osmotic gradient. Therefore, urine cannot be diluted (because the diluting segment is inhibited) or concentrated (because there is no longer an osmotic gradient)
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What does it mean when Ch2o is positive?
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Urine is hyposmotic to plasma (low ADH conditions)
This occurs during high water intake (supressed ADH release) and during central and nephrogenic diabetes insipidus (inadequate response to ADH) |
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What does it mean when Ch2o is negative?
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Urine is hyperosmotic to plasma (high ADH conditions)
This happens when you are water-deprived (stimulates ADH release) or overproduce ADH (SIADH) |
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What stimulates PTH secretion?
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Decreased plasma Ca
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What effect does PTH have upon the kidney?
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Decreases phosphate reabsorption in the proximal tubule
Increases Ca reabsorption in the distal tubule |
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What stimulates ADH secretion?
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Increased plasma osmolarity
Decreased blood volume |
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What effect does ADH have upon the kidney?
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Increases water permeability of the late distal tubule and collecting duct
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What stimulates aldosterone secretion?
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Decreased blood volume (via the RAS)
Increased plasma K |
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What effect does aldosterone have upon the kidney?
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Increased Na reabsorption in the distal tubule principal cells
Increased K secretion in the distal tubule principal cells Increased H secretion in the alpha intercalated cells |
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What stimulates ANP release?
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Increased atrial pressure
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What effect does ANP have upon the kidneys?
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Increases GFR
Decreases Na reabsorption |
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What stimulates angiotensin II production?
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Decreased blood volume (via renin)
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What effect does angiotensin II have upon the kidneys?
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Increased Na reabsorption
Increased HCO3 reabsorption |
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What types of acids are produced by the body?
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Volatile (CO2) and non-volatile acids
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How are volatile acids produced?
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Carbonic anhydrase catalyzes the reversible reaction of H and HCO3 to give CO2 and water
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What non-volatile acids are produced, and is this normal or pathological?
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Normal: sulfuric, phosphoric acid
Bad: ketoacids, lactic acid, salicylic acid |
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What are buffers?
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The prevent a change in pH when H+ is added or removed from solution. They are most effective when they are within 1.0 pH unit of the pK of the buffer (within the linear portion of the titration curve)
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What is the major physiological buffer?
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HCO3/CO2. The pK of the buffer pair is 6.1
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What role does phosphate play as a buffer?
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It is a minor extracellular buffer, and the pK of H2PO4/HPO4 is 6.8. It is an important urinary buffer and as such contributes to the excretion of titratable acid
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What are some intracellular buffers?
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Organic phosphates (AMP, ADP, etc)
Proteins (hemoglobin, deoxyhemoglobin) |
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What is the overall Henderson-Hasselbalch equation?
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pH = pK + log [A-/HA]
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What does it mean when the pH of a solution equals the pK?
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The concentrations of HA and A- are equal
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Where does bicarbonate reabsorption occur?
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Primarily in the proximal tubule
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How is bicarbonate reabsorbed in the proximal tubule?
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H is secreted via the Na-H exchanger
Carbonic anhydrase catalyzes the reaction of that H with HCO3 in the lumen to give CO2 and water CO2 and water go into the cell Carbonic anhydrase converts them back to H and HCO3 The H is recycled into the lumen and the HCO3 is reabsorbed into the blood |
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How does filtered load affect HCO3 reabsorption?
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It increases it until the reabsorptive capacity, at which point excess HCO3 will be excreted in the urine
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How does PCO2 affect HCO3 reabsorption?
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Increased PCO2 results in increased HCO3 reabsorption because there is more intracellular H available for secretion (this is the mechanism for renal compensation for respiratory acidosis)
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How does ECFV affect HCO3 reabsorption?
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ECFV expansion decreases HCO3
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How does angiotensin II affect bicarbonate reabsorption?
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It increases it by stimulating Na-H exchange
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How is acid excreted in the kidneys?
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It is excreted as titratable acid or NH4
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What is titratable acid?
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It is acid that is buffered by urinary buffers. To determine how much titratable acid there is, you titrate the urine with NaOH until you get to 7.4, and the amount of base you need to add is equal to the amount of titratable acid
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How does aldosterone increase H secretion?
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It stimulates the H ATPase
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What does the excretion of titratable acid represent?
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A net secretion of acid and a net reabsorption of HCO3
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What is the minimum urinary pH?
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4.4
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What determines the amount of H+ excreted as titratable acid?
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The amount of urinary buffer and the pK of the buffer
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What determines the amount of H+ excreted as NH4?
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The amount of NH3 synthesized by renal cells and urine pH
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How is NH3 produced in renal cells?
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Glutamine is converted to HCO3 and NH3
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How is NH4 produced in the urine?
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NH3 diffuses down its concentration gradient from the cells to the lumen
Secreted H+ reacts with it to form NH4 The NH4 is excreted; this is known as diffusion trapping |
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How does pH affect the relative amount of NH4 in the urine?
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The lower the pH of the tubular fluid, the more H+ will be excreted as NH4. This is because during acidosis there is an adaptive increase in NH3 synthesis
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How does hyperkalemia inhibit H+ excretion as NH4?
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It inhibits the synthesis of NH3
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What is metabolic acidosis?
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Overproduction or ingestion of non-volatile acid, or loss of base
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Why does arterial HCO3 decrease in metabolic acidosis?
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It is used to buffer the excess acid
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What is the respiratory compensation for metabolic acidosis?
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Hyperventilation
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What is the renal response to metabolic acidosis?
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Increased excretion of H+ as titratable acid and NH4 (this is facilitated by an adaptive increase in NH3 synthesis)
Increased reabsorption of HCO3 (replenishes the HCO3 that is used to buffer excess H) |
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What is the formula for the serum anion gap?
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Na - (Cl + HCO3)
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What does the serum anion gap represent?
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It represents unmeasured anions in the serum. The normal value is 12 mEq/L
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How does the serum anion gap change in metabolic acidosis?
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HCO3 is consumed in acidosis, so to maintain electroneutrality, the concentration of another anion must increase. The gap increases if the anion is unmeasured, and is normal if the anion is Cl
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What is metabolic alkalosis?
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Loss of non-volatile acid or gain of base
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How does vomiting contribute to metabolic alkalosis?
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H+ is lost from the stomach
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What is the respiratory compensation for metabolic alkalosis?
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Hypoventilation
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What is the renal response to metabolic alkalosis?
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Increased HCO3 excretion, because the filtered load of HCO3 exceeds the reabsorptive capacity
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What is contraction alkalosis?
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If metabolic alkalosis is accompanied by ECFV contraction (as in the case of vomiting), the RAS is activated, which promotes H secretion and exacerbates the alkalosis
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What is respiratory acidosis?
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Decreased respiration rate results in CO2 retention and elevates PCO2. Elevated CO2 results in an increase in H and HCO3
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What is the respiratory compensation for respiratory acidosis and alkalosis?
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NONE!!!! hahahahaha
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What is the renal response to respiratory acidosis?
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Increased H excretion as titratable and NH4
Increased reabsorption of HCO3 This is facilitated by the increased PCO2, which provides more H to the renal cells for secretion |
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What is the difference between acute and chronic respiratory acidosis? (note that this is also the case with respiratory alkalosis)
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In acute, renal compensation hasn't occurred yet, so the pH is more acidic
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What is respiratory alkalosis?
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Increased respiration rate results in loss of CO2. This results in decreased production of H and HCO3
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What is the renal response to respiratory alkalosis?
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Decreased H+ excretion
Increased HCO3 reabsorption This is aided by the low PCO2, which decreases the availability of H in the renal cells for secretion |
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Why is hypocalcemia a symptom of respiratory alkalosis?
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H and Ca compete for binding sites on plasma proteins, so if there isn't enough H, more Ca will bind to proteins, which decreases free ionized Ca
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What are the effects of hypoaldosteronism on the kidney?
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Decreased Na reabsorption
Decreased K and H secretion This results in ECFV contraction, hyperkalemia, and metabolic acidosis |
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Why do patients with hypoaldosteronism have orthostatic hypotension?
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There is an ECFV contraction, and the decreased arterial pressure produces an increased pulse pressure
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Why is ADH secreted in hypoaldosteronism?
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There is an ECF volume contraction
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How does hypoaldosteronism cause hyperpigmentation?
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Adrenal insufficiency decreases the production of cortisol, which increases secretion of ACTH, which has pigmenting effects
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How does vomiting cause metabolic alkalosis?
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H+ is lost
Cl is also lost, resulting in hypochloremia and ECF volume contraction |
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Why is aldosterone secretion increased during vomiting?
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There is an ECF volume contraction, which results in decreased renal perfusion pressure. This causes renin secretion, which activates the RAS
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Why is hypokalemia observed during vomiting?
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Increased aldosterone secondary to ECFV contraction promotes K secretion
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How is vomiting treated?
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NaCl infusion to correct the ECF volume contraction
Administration of K to replace urinary K loss |
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How does diarrhea cause metabolic acidosis?
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You lose bicarbonate
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Why is the anion gap normal in diarrhea?
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To maintain electroneutrality, the HCO3 that is lost is replaced by increased Cl
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Why is pulse rate increased in diarrhea?
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There is an ECF volume contraction, which decreases blood volume and arterial pressure. This decreased pressure activates the baroreceptor reflex, which increases heart rate via sympathetic stimulation to the SA node
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Why does diarrhea result in hypokalemia?
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ECF volume contraction activates the RAS, and the aldosterone increases distal K secretion
K is also lost in the diarrhea fluid |
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How is diarrhea treated?
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Replacement of fluid and electrolytes
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Approximately, how much of your body weight is water?
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60%
This is known as total body water (TBW) |
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What sort of people have the highest percent TBW?
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Newborns
Adult males |
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What sort of people have the lowest percent TBW?
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Adult females
People with lots of adipose tissue |
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What are the two compartments of the TBW?
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Intracellular fluid (ICF) -- 2/3 of TBW
Extracellular fluid (ECF) -- 1/3 of TBW |
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What are the major cations of the ICF?
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K and Mg
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What are the major anions of the ICF?
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Protein
Organic phosphates (ATP, ADP, AMP) |
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What are the two compartments of the ECF?
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Interstitial fluid -- 3/4 of ECF
Plasma -- 1/4 of ECF |
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What is the major cation of the ECF?
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Na
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What are the major anions of the ECF?
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Cl
HCO3 |
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What are Prions? What are they resistant to?
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-misfolded proteins make others misfold, accumulate in brain tissue
-boiling, baking, radiation, disinfectants |
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What is the 60-40-20 rule?
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TBW is 60% of body weight
ICF is 40% of body weight ECF is 20% of body weight |
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What is the dilution method?
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A known about of indicator is administered
This indicator must distribute throughout the compartment of interest The substance equilibrates The concentration of the substance is measured Volume = amount / concentration |
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What are indicators for TBW?
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Tritiated H2O
D2O |
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What are indicators for ECF?
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Sulfate
Inulin Mannitol |
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What are indicators for plasma?
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RISA
Evan's blue |
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What is a marker for interstitial fluid?
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There is no real marker
ECF - plasma volume (indirect calculation) |
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What is a marker for ICF?
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There is no real marker
TBW - ECF (indirect calculation) |
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How do ECF and ICF osmolarity compare at steady state?
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They are equal
To achieve this, water shifts between the compartments It is assumed that osmotically active solutes like NaCl don't cross the cell membranes |
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What type of volume change is observed when you infuse isotonic NaCl?
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Isosmotic fluid expansion
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What characterizes an isosomotic fluid expansion?
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ECF volume increases
ECF osmolarity stays the same No water shifts to the ICF Plasma protein concentration and hematocrit decrease because you are diluting the blood RBCs do not shrink or swell Arterial blood pressure increases |
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What type of volume change is observed when you have diarrhea?
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Isosmotic volume contraction
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What characterizes an isosmotic volume contraction?
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ECF volume decreases
ECF osmolarity doesn't change No water shift Plasma protein concentration and hematocrit increase RBCs do not shrink or swell Arterial blood pressure decreases |
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What type of volume change is observed when you have excessive NaCl intake?
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Hyperosmotic volume expansion
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What characterizes a hyperosmotic volume expansion?
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ECF osmolarity increases
Water shifts from ICF to ECF until ICF and ECF osmolarity are equal ECF volume increases, ICF volume decreases Plasma protein concentration and hematocrit decrease |
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What type of volume change is observed when you sweat out a lot of water?
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Hyperosmotic volume contraction
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What characterizes a hyperosmotic volume contraction?
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The osmolarity of the ECF increases because sweat is hyposmotic
ECF volume decreases Water shifts from ICF to ECF until the osmolarities are equal Plasma protein concenration increases Hematocrit does not change because water shifts out of the RBCs and decreases their volume |
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What type of volume change is observed when you have SIADH (syndrome of inappropriate antidiuretic hormone)?
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Hyposmotic volume expansion
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What characterizes a hyposmotic volume expansion?
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The osmolarity of ECF decreases because excess water is retained
ECF volume increases Water shifts from ECF to ICF Plasma protein concentration decreases Hematocrit stays the same because water shifts into the RBCs |
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What type of volume change is observed when you have adrenocortical insufficiency and lose a lot of NaCl (not enough aldosterone)?
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Hyposmotic volume contraction
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What characterizes a hyposmotic volume contraction?
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The osmolarity of the ECF decreases
ECF volume decreases Water shifts from ECF to ICF Plasma protein concentration and hematocrit increase Arterial blood pressure decreases |
