Now, what's an example of such a substance? Well, one example that is not naturally found in our body, but our doctors use to study the global filtration rate is known as insulin. So inulin or inulin is this polysaccharide that we can basically ingest into our body and which is basically follows this pathway as described. So it is completely filtered by our global illus. It can basically travel across freely, but it is not reabsorbed, nor is it actually secreted. So the global filtration rate, or GFR is equal to the filtration rate of this substance, our inulin.