Nephron Function

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 (

<SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='HCO3−’>HCO−3

HCO3−

HCO 3 −
Reabsorption)

Nephron Segment	Mechanism	Regulation
Proximal tubule	Na ⁺-H ⁺antiporter, H ⁺-ATPase	↑ Filtered load of <SPAN role=presentation tabIndex=0 id=MathJax-Element-2-Frame class=MathJax style="POSITION: relative" data-mathml='HCO3−’>HCO−3 HCO 3 − (+) ↓ ECF volume (+) ↑ P co ₂(+) ↓ Plasma [ <SPAN role=presentation tabIndex=0 id=MathJax-Element-3-Frame class=MathJax style="POSITION: relative" data-mathml='HCO3−’>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 [ <SPAN role=presentation tabIndex=0 id=MathJax-Element-4-Frame class=MathJax style="POSITION: relative" data-mathml='HCO3−’>HCO−3 HCO 3 − ] (+)
Early distal tubule	Na ⁺-H ⁺antiporter, H ⁺-ATPase	↑ P co ₂(+) ↓ Plasma [ <SPAN role=presentation tabIndex=0 id=MathJax-Element-5-Frame class=MathJax style="POSITION: relative" data-mathml='HCO3−’>HCO−3 HCO 3 − ] (+) Angiotensin II (+) Endothelin (+) Glucocorticoid (+)
Late distal tubule and collecting duct	H ⁺-ATPase, H ⁺-K ⁺-ATPase	↑ P co ₂(+) ↓ Plasma [ <SPAN role=presentation tabIndex=0 id=MathJax-Element-6-Frame class=MathJax style="POSITION: relative" data-mathml='HCO3−’>HCO−3 HCO 3 − ] (+) Aldosterone (+) Angiotensin II (+) Endothelin (+) Glucocorticoid (+)