Albumin glomerular membrane permeability

These membranes are distinguished from Type 1 by the presence of pores, the size of which can be gauged from the size of the largest molecule which can penetrate them. As a homologous series is ascended, substances are obtained which penetrate Type 4 membranes less (and Type 1 membranes more) readily. One of the best-known examples of a Type 4 membrane is the glomerular tuft in Bowman s capsule of the kidney (see later). This tuft is permeable to all molecules smaller than albumin (mol. wt. 70000). The pore size is estimated as 3 nm, and inulin (mol. wt. 5000) passes through easily. Mammalian capillaries and liver parenchyma, too, have Type 4 membranes, which are not often met apart from these important examples. 

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