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
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
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