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