Nephron Function - Clinical Tree

Summary By Transport Process

TABLE C.1

Na ⁺ and Cl ⁻ Reabsorption

Nephron Segment	Mechanism	Regulation
Proximal tubule	Na ⁺ -H ⁺ antiport, Na ⁺ -solute symporters, Cl ^– -HCO ₃ ^– antiporter, Na ⁺ -glucose symporters, paracellular	↓ ECF volume (+), ↑ ECF volume (–) Angiotensin II (+) Sympathetic nerves (+) Epinephrine (+) Dopamine (–) Starling forces (+/–)
Henle’s loop Thin descending limb Thin ascending limb Thick ascending limb	None Paracellular Na ⁺ -K ⁺ -2Cl ⁻ symporter, Na ⁺ -H ⁺ antiporter, Cl ^– -HCO ₃ ⁺ antiporter	Aldosterone (+) Sympathetic nerves (+)
Early distal tubule	Na ⁺ -Cl ⁻ symporter	Aldosterone (+)∗ Sympathetic nerves (+) Angiotensin II (+)
Late distal tubule and collecting duct (ASDN)	Na ⁺ channel	Aldosterone (+) Sympathetic nerves (+) Angiotensin II (+) ANP, BNP, urodilatin (–)

ANP, Atrial natriuretic peptide; ASDN, aldosterone-sensitive distal nephron; BNP, brain natriuretic peptide; ECF, extracellular fluid; (+), stimulation; (–), inhibition; (∗), indirect effect.

TABLE C.2

K ⁺ Reabsorption

Nephron Segment	Mechanism	Regulation
Proximal tubule	Paracellular	↓ ECF volume (+) ↑ ECF volume (–)
Henle’s loop Thin descending limb Thin ascending limb Thick ascending limb	None None Na ⁺ -K ⁺ -2Clˉ symporter	Aldosterone (+)
Early distal tubule	None
Late distal tubule and collecting duct	H ⁺ -K ⁺ -ATPase	Dietary K ⁺ depletion (+)

ATPase, Adenosine triphosphatase; ECF, extracellular fluid; (+), stimulation; (–), inhibition.

TABLE C.3

K ⁺ Secretion

Nephron Segment	Mechanism	Regulation
Proximal tubule	None
Henle’s loop Thin descending limb Thin ascending limb Thick ascending limb	None None None
Early distal tubule	None
Late distal tubule and collecting duct	K ⁺ channels, K-Cl ^– symporter	Plasma [K ⁺ ] (+) Aldosterone (+) AVP (+) Flow rate (+) Acid-base balance (+/–) Glucocorticoids (+)

AVP, Arginine vasopressin; (+), stimulation; (–), inhibition.

TABLE C.4

H ⁺ Secretion (

{HCO}_{3}^{-}

${HCO}_{3}^{-}$ Reabsorption)

Nephron Segment	Mechanism	Regulation
Proximal tubule	Na ⁺ -H ⁺ antiporter, H ⁺ -ATPase	↑ Filtered load of ${HCO}_{3}^{-}$ ${HCO}_{3}^{-}$ (+) ↓ ECF volume (+) ↑ P co ₂ (+) ↓ Plasma [ ${HCO}_{3}^{-}$ ${HCO}_{3}^{-}$ ] (+) Endothelin (+) Glucocorticoid (+) Angiotensin II (+)
Henle’s loop Thin descending limb Thin ascending limb Thick ascending limb	None None Na ⁺ -H ⁺ antiporter, H ⁺ -ATPase	↑ P co ₂ (+) ↓ Plasma [ ${HCO}_{3}^{-}$ ${HCO}_{3}^{-}$ ] (+)
Early distal tubule	Na ⁺ -H ⁺ antiporter, H ⁺ -ATPase	↑ P co ₂ (+) ↓ Plasma [ ${HCO}_{3}^{-}$ ${HCO}_{3}^{-}$ ] (+) Angiotensin II (+) Endothelin (+) Glucocorticoid (+)
Late distal tubule and collecting duct	H ⁺ -ATPase, H ⁺ -K ⁺ -ATPase	↑ P co ₂ (+) ↓ Plasma [ ${HCO}_{3}^{-}$ ${HCO}_{3}^{-}$ ] (+) Aldosterone (+) Angiotensin II (+) Endothelin (+) Glucocorticoid (+)

ATPase, Adenosine triphosphatase; ECF, extracellular fluid; (+), stimulation; (–), inhibition.

TABLE C.5

{HCO}_{3}^{-}

${HCO}_{3}^{-}$ Secretion

Nephron Segment	Mechanism	Regulation
Proximal tubule	None
Henle’s loop Thin descending limb Thin ascending limb Thick ascending limb	None None None
Early distal tubule	None
Late distal tubule and collecting duct	H ⁺ -ATPase, Clˉ- ${HCO}_{3}^{-}$ ${HCO}_{3}^{-}$ antiporter	Metabolic alkalosis (+)

ATPase, Adenosine triphosphatase; (+), stimulation; (–), inhibition.

TABLE C.6

Water Reabsorption

Nephron Segment	Mechanism	Regulation
Proximal tubule	AQP water channel	Starling forces (+/–)
Henle’s loop Thin descending limb Thin ascending limb Thick ascending limb	AQP water channel None None
Early distal tubule	None
Late distal tubule and collecting duct	AQP water channel	AVP (+) ANP, BNP, and urodilatin (–)

ANP, Atrial natriuretic peptide; AQP, aquaporin; AVP, arginine vasopressin; BNP, brain natriuretic peptide; (+), stimulation; (–), inhibition.

TABLE C.7

P _i Reabsorption

Nephron Segment	Mechanism	Regulation
Proximal tubule	3Na ⁺ -P _i symporter, 2Na ⁺ -P _i symporter	PTH P _i depletion (+) ↓ ECF volume (+) Acidosis (–) Glucocorticoids (–) FGF-23 (–)
Henle’s loop Thin descending limb Thin ascending limb Thick ascending limb	None None None
Early distal tubule	None
Late distal tubule and collecting duct	None

ECF, Extracellular fluid; FGF, fibroblast growth factor; P _i , inorganic phosphate; PTH, parathyroid hormone; (+), stimulation; (–), inhibition.

TABLE C.8

Ca ⁺⁺ Reabsorption

Nephron Segment	Mechanism	Regulation
Proximal tubule	Ca ⁺⁺ channel Paracellular	PTH (–) ↓ ECF volume (+), ↓ plasma [P _i ] (+)
Henle’s loop Thin descending limb Thin ascending limb Thick ascending limb	None None Paracellular	PTH (+) ↓ plasma [P _i ] (+) CaSR (–)
Early distal tubule	Ca ⁺⁺ channel	PTH (+) Calcitriol (+) ↓ Plasma [P _i ] (+) Acidosis (–) CaSR (–)
Late distal tubule and collecting duct	None

CaSR, Calcium-sensing receptor; ECF, extracellular fluid; Pi, inorganic phosphate; PTH, parathyroid hormone; (+), stimulation; (–), inhibition.

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Summary By Transport Process

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