The chief force pushing water and solutes out of the blood across the filtration membrane is .

The chief force pushing water and solutes out of the blood across the filtration membrane is the glomerular hydrostatic pressure (glomerular blood pressure).

Explanation:

The Glomerular hydrostatic pressure, is part of the Glomerular filtration forces which are part of the urine system. We are considering here how the blood is filtrated, and this is the main function of the glomerulus. This glomerular hydristatic pressure is the pressure exerted by fluid on the capillary walls of the glomerulus or the walls of the Bowman's capsule.

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