What term is used to describe the removal of water from blood due to pressure gradient across the membrane?

The term that describes the removal of water from blood due to a pressure gradient across the membrane is ultrafiltration. This process occurs during hemodialysis, where a semipermeable membrane allows for the movement of water (and some solutes) from an area of higher pressure to an area of lower pressure. In hemodialysis, by creating a pressure difference, excess fluid can be efficiently removed from the blood of the patient.

Osmosis refers to the movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration, which is a different mechanism. Filtration generally describes the separation of solid particles from liquids based on size, but in the context of dialysis, it does not specifically capture the concept of pressure-driven water removal. Diffusion involves the movement of solutes from an area of higher concentration to an area of lower concentration and does not pertain to the removal of water through a pressure gradient. Therefore, ultrafiltration is the most accurate term for the process described, specifically focusing on the role of pressure in the removal of water.