This graph shows how molecular size and charge influence the degree to which a molecule is filtered through the glomerular filtration barrier. Notice that for molecules of similar size, addition of positive charge (blue line) significantly enhances filtration and, conversely, addition of negative charge (red line) significantly reduces filtration. Fraction filtered refers to the fraction of the total circulating amount that moves from the lumen of the glomerular capillaries through the glomerular filtration barriers to enter the Bowman's space and ultimately the nephron lumen. Neutral molecules are represented by the black line, positively charged molecules by the blue line, and negatively charged molecules by the red line. Neutral molecules with a radius larger than about 42 Å are not filtered. This corresponds to an upper molecular size limit of about 40,000 Daltons (40 kDa) for neutral molecules. Not shown in this graph is the influence of molecular shape on filtration, such that for molecules of similar size and charge, elongated molecules tend to be filtered more readily than globular molecules.