Composition of the glomerular filtrate: ultrafiltrate of plasma, due to size-selective filtration: nonselectively permeable to small particles but not very permeable to larger particles, such as blood cells and plasma proteins
In other words, all small particles (inorganic ions, glucose, amino acids, etc.) enter Boman's space at exactly the same concentration as in blood plasma
1. filtration barriers
a. capillary endothelium: fenestrated capillaries with relatively large pore size (1000 A); not a major barrier to filtration
b. basement membrane: negatively charged meshwork of glycoproteins and collagen
c. epithelial cells with foot processes (podocytes) separated by slits (240 A wide)
Note: the basement membrane and podocytes are the major filtration barrier, passing particles depending on size and charge
2. Effect of particle charge: because of the negative charge on the membrane pores, the size cutoff is smaller for negative particles (such as plasma proteins) than for neutral or positive particles.
In kidney inflammation, the membrane charge is reduced or lost, permitting plasma proteins to enter the tubule in larger amounts