3. Physiology
        3.12. Renal
3.12.4. Tubular transport mechanisms

Tubular transport mechanisms

[Ref: AV6:Chp4]


Transporters vs channels




Reabsorption via transcellular route

In proximal tubule

Step 1

Step 2

Step 3

Step 4



Reabsorption via paracelluar route

As water and sodium (and associated anions) get reabsorbed

--> Concentration of solutes not specifically transported via the transcellular route will become concentrated
* e.g. Urea, K, Cl-, Ca2+, Mg2+

--> Diffuse down the concentration gradient via the paracellular route



Electric charge of lumen


Tm vs gradient-limited system

Transport mechanism can be either

  1. Tubular maximum-limited (Tm), or
  2. Gradient-limited

Tm limited system

e.g. Glucose in proximal tubule

Gradient-limited system

e.g. Sodium in proximal tubule







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