05 Nephron Physiology

• high to low concentration: no energy needed

• paracellular: between cells

• osm: how much solute dissolved in water
• low osm: high concentration of water, vice versa
• water move from high concentration to low concentration

PCT

• work horse of nephron
• most absorption

• 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

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

Fanconi

• proximal tubule disfunctional
• phosphate leads to growth failure

Descending Loop

• Cortex: water drawn out until lumen = 300
• medulla: continue drawn out

Ascending Limb

• K leak into lumen, cause + charge and push cation in
• NKCC: Na, K, Cl, Cl

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

Distal

• PTH and thiazide diuretics increase Ca absorption

CD

• Ang II most important

ADH

• vasopressin: vasoconstriction
• supraoptic/paraventricular

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

• water deprived: concentrate urine by pulling it out

• water not absorbed, NaCl absorption dilute urine

• high osmolarity in lumen at CD: less water leaving

• 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

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

• 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