Question

if a substance in the blood does not become part of the filtrate what happens to it? How do the substances exit the glomerulus?

Answer 1

In the glomerular capillaries depending on the electric charge and molecular size,the substances are filtered,preferably small sized and positively charges substances are easily filtered across (since the glomerulus is negatively charged),the unfiltered substances exit the glomerulus via the efferent artery which then supplies blood to the Renal tubules where some substances like vasopressin (the ADH hormone) are secreted into the tubules and the ones that are neither filtered in the glomerulus nor secreted into the tubules are returned back to the systemic circulation via the Renal vein.

The substances that are not filtered or secreted are the ones that are essential for the body and are not to be excreted,like Albumin,globulins, complement proteins etc and are kept in the blood.