05 Nephron Physiology

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• high to low concentration: no energy needed

• paracellular: between cells

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• osm: how much solute dissolved in water

• low osm: high concentration of water, vice versa

• water move from high concentration to low concentration

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PCT

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• work horse of nephron

• most absorption

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• use concentration of Na to drag glucose in

• K pump into cell, diffuse out and drag Cl with it, lower Cl concentration in cell

• Cl can then be pulled into cell in exchange for anion

• water reabsorbed paracellularly via high Na/Cl concentration in blood

Glucose Clearance

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• pellagra: B3 deficiency (niacin). Tryp converted to niacin

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Fanconi

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• proximal tubule disfunctional

• phosphate leads to growth failure

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Descending Loop

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• Cortex: water drawn out until lumen = 300

• medulla: continue drawn out

Ascending Limb

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• K leak into lumen, cause + charge and push cation in

• NKCC: Na, K, Cl, Cl

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• NaCl pulled out, leave water in, very dilute urine

• impermeable to water

Distal

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• PTH and thiazide diuretics increase Ca absorption

CD

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• Ang II most important

ADH

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• vasopressin: vasoconstriction

• supraoptic/paraventricular

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• AQP 3 and 4 always present: basolateral always permeable to water

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• water deprived: concentrate urine by pulling it out

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• water not absorbed, NaCl absorption dilute urine

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• high osmolarity in lumen at CD: less water leaving

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• water leaving causes urea in lumen to be more concentrated: urea leaves via gradient

• ADH promotes absorption of urea

• urea pushed out in distal CD

• urea needed in descending loop to draw water out

Misc

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• middle: pull more solute out than water, result = more dilute

• bottom: pull water more than solute

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• inulin/Cr: not absorbed, concentration rises

• Cl/urea/Na/K: not really changed, concentration a little higher

• glucose/aa/bicarb: absorbed, concentration decreases

• PAH: secreted