The kidneys filter roughly what proportion of the total resting blood volume each day?

1. The kidneys filter about 180 litres of blood in an average adult each day. 2. That is about 20 percent of the total resting volume. 3. Seeing that much of the circulation makes the kidney an ideal site for receptors that read oxygen saturation. 4. Low oxygen delivery to the kidney creates hypoxia in its tissue fluid. 5. Interstitial fibroblasts there respond by secreting erythropoietin, raising erythrocyte production. 6. About 45 percent is the erythrocyte fraction of blood rather than a filtration figure, which is why it reads plausibly and is the main trap. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 18 "The Cardiovascular System: Blood", section 18.3 Erythrocytes_