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90 Cards in this Set
- Front
- Back
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what occurs to reabsorbed substances once in the interstitial fluid
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net flow into peritubular capillaries due to osmotic and hydrostatic forces
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transport coupled directly to an energy source
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primary active transport; Na+/K+ pump
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transport associated indirectly to an an energy source (ion gradient)
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secondary active transport; glucose
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how is water reabsorbed
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passive physical mechanism (osmosis)
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where can solutes be reabsorbed across epithelial renal tubular cells
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transcellular or paracellular (btwn cells)
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where is water especially absorbed paracellularly
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proximal tubule
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what occurs when water is is reabsorbed paracellularly
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substances dissolves in the water are carried with it (K+, Mg+, Cl-)
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known ATPases workin gin kidneys
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sodium-potassium ATPase, hydrogen ATPase, hydrogen-potassium ATPase, calcium ATPase
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what net effects do Na+/K+ pumps in the basolateral membrane have
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1)passive diffusion of Na+ on luminal side 2) negative intracellular potential attracts Na+ from tubular lumen
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what is the effect of the extensive brush border in the proximal tubule on the luminal side
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multiplies SA by 20
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what drives aa and glucose to exit across basolateral membranes in tubular cells
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high concentration within cell
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what involves counter-transport of of substance with Na+ ions
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substances secreted into tubules; H+
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when is pinocytosis used
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reabsorb large moleules like proteins
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transport maximum
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due to saturation of specific transport systems
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threshold
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concentration at which some of a substance doesn't get reabsorbed
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glucose threshold vs transport max
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250 mg/min (plasma concentration of 200 mg/100 ml) versus 375 mg/min
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transport maximum for substances passively reabsorbed
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do not demonstate transport max; gradient-time transport
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what do substances passively reabsorbed depend on
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1) electrochemical gradient 2) permeability of membrane for substance 3) time fluid with substance remains in tubule
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why doesn't Na+ exibit a transport max in the proximal tubules
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other factors limit reabsorption rate: transport capacity of ATPase pump far greater than rate of net Na+ reabsorption
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what determines rate of sodium backleak
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1) permeability of tight jxns 2) interstitial forces
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what occurs with Na+ in more distal parts of tubule
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much tighter jxns and transport smaller amounts of Na+; exhibits transport maximum
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what can change sodium reabsorption in distal parts of tubule
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aldosterone
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why isn't there a huge concentration difference across tubular cells from lumen once substances reabsorbed
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water follows
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solvent drag
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water carries solvents with it as it goes from high to low concentration
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when does the tubule become less permeable to water and solutes
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beginning in loop of henle and extending through collecting tubule
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what can increase water permeability in distal and collecting tubules
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ADH
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diffusion of Cl-
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passively through paracellular pathway due to electrochemical gradient set up from Na+; also via secondary active trasnport with Na+ across luminal membrane
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Na+, Cl-, and water reabsoption percentage in proximal tubule
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65% filtered load of Na+ and water, slightly less Cl-
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secretion of H+ into lumen causes
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removal of bicarb ions from tubule
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first half of proximal tubule sodium reabsorption
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reabsorbed by co-transport along with glucose, aas, and other solutes
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second half of proximal tubule sodium reabsorption
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reabsorbed mainly with Cl-
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chloride concentration difference from first half to second half of proximal tubule
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140 mEq/L to 105
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why does sodium concentration across proximal tubule remain fairly constant
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water follow, amount of sodium on each side changes
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what organic acids and bases are secreted along proximal tubule
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bile salts, oxalate, urate, catecholamines
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what drugs does the kidney have an especial rapid clearance
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penicillin, salicylates
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para-aminohippuric acid (PAH)
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secreted so rapidly, a person clears about 90%
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what is PAH used for
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estimate renal plasma flow
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thin ascending and descending limbs
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no brush borders, few mitochondria, and minimal metabolic activity
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descending part of thin segment permeability
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highly permeable to water and moderately to most solutes
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ascending limb permeability
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impermeable to water; important for concentrating urine
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thick segment of loop of Henle
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high metabolic activity; active reabsorption of Na+, Cl-. K+ (also Ca+, bicarb, and Mg)
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what percent of filtered Na+, Cl-, and K+ are reabsorbed in thick ascending limb
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~25%
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important component of solute reabsorption in thick ascending limb
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Na+/K+ pump in basolateral membranes
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site of powerful loop diuretics
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thick ascending limb; furosemide, ethacrynic acid, bumetanide
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what do furosemide, ethacrynic acid, bumetanide inhibit
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action of sodium 2-chloride, potassium co-transporter
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what paracellular reabsorption occurs in thick ascending limb
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Mg++, Ca++, Na+, K+; due to slight positive charge of tubular lumen because of K+ leakage
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water permeability of thick ascending limb
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impermeable to water; fluid become dilute
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first part of distal tubule forms
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part of juxtaglomerular complex
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distal tubule
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sililar to thick ascending limb--diluting segment
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what percent of the filtered load of NaCl is reabsorbed in early distal tubule
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~5%
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thiazide diuretics
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inhibit Na+/Cl- co-transporter in early distal tubule
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when are thiazide diuretics used
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hypertension, heart failure
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second half of distal tubule and collecting tubule
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principle cells and intercalated cells
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job of principle cells
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absorb Na+ and water from lumen and secrete K+ into lumen
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intercalated cells job
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reabsorb K+ and bicarb and secrete H+ into tubular lumen
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site of action of potassium-sparing diuretics
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principal cells
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examples of K+ sparing diuretics
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spironolactone, eplereone, amiloride, and triamterene
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where does aldosterone act
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on principal cells
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sodium channel blockers
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directly inhibit entry of Na+ into sodium channels of luminal membranes; decrease urinary secretion of K+
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characteristics of late distal tubule and cortical collecting tubule
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1) impermeable to urea 2) reabsorb Na+ 3) secrete H+ 4) permeability controlled by ADH
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what is special about the intercalated cell secretion of H+
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primary active, not secondary active secretion; can secrete against large concentration gradient 1000:1
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what H+ concentration gradient can be achieved via secondary active transport
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4 to 10 fold
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epithelial celss in collecting ducts
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nearly cuboidal with smooth surfaces, few mitochondria
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special characteristics of medullary collecting ducts
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1)permeability controlled by ADH 2) permeable to urea 3) capable of secreting H+ against large gradient
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inulin
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not absorbed or secreted by renal tubules; changes in concentration purely dependent on water movement
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importartance of glomerlotubular balance
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prevents overload of distal tubular segments when GFR increases
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normal rate of peritubular capillary reabsorption
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124 ml/min
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equation for peritubular capillary reabsorption
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Kf times Net reabsorptive force
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normal peritubular capillary P average
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13 mmHg
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renal interstitial fluid hydrostatic P
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6 mmHg
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positive hydrostatic P gradient from peritubular capillaries to interstitial fluid
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about 7 mmHg which opposes fluid reabsorption
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plasma colloid osmotic P
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32 mmHg
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colloid osmotic P of interstitium
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15 mmHg
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net colloid osmotic P
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17 mmHg favoring reabsorption
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what is peritubular capillary hydrostatic P influenced by
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arterial P and resistances in efferent and afferent arterioles
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constriction of efferent artioles affects on glomerular and peritubular capillaries
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increases glomerular hydrostatic P and decreases peritubular hydrostatic P
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where is aldosterone secreted
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zona glomerulosa in adrenal cortex
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action and effect of aldosterone
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principal cells of cortical collecting tube; increase Na+ reabsorption and potassium secretion
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what mechanism of aldosterone causes increased Na+ absorbtion and K+ secretion
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stimulation of basolateral Na+/K+ ATPase pump and increasing Na+ permeability on luminal side of membrane
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what occurs with adrenal destruction or malfunction
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Addisons disease (lack of aldosterone)
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three main effects of angiotensin II
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1) stimulates aldosterone secretion 2) constricts efferent arterioles 3) directly stimulates sodium reabsorption in proximal tubules, loops of henle, distal tubules, and colleting ducts
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mechanism of angiotensin II dirct effects
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stimulate Na+/K+ ATPase pump on bastolateral membrane; stimulate H+/Na+ exchange in luminal membrane (especially proximal tubule)
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what does ADH bind
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specific V2 receptors in late distal tubules, collecting ducts, and collecting tubules increasing cAMP and activating protein kinases
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what does activation of protein kinases in ADH binding cause
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movement of aquaporin-2 to luminal side of membranes; ADP-2s cluster together and fuse with cell membrane by exocytosis to form water channels
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where does atrial natriuretic peptide act
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mostly inhibit reabsorption of Na+ and water in collecting ducts
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parathyroid hormone action in kidneys
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increase renal reabsorption of Ca2+ via distal tubules and some in loop of henle
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what other action can PTH have in kidney
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inhibition of phosphate reabsorption by proximal tubules and stimulation og Mg++ reabsorption by loop of henle
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clearance of drugs in kidney
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colume of plasma that would be necessary to supply the amount of substance excreted in urine per unit time
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equation for clearance
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urinary excretion rate/plasma concentration
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creatinine levels and GFR
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double plasma levels indicate 1/2 GFR; 4 times plasma levels indicate 1/4 GFR and so on
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