1. Ultrafiltration
Definition: Ultrafiltration is the process of removing excess water from the blood by applying a pressure gradient across a semipermeable membrane.
Mechanism: Water moves from the blood into the dialysis fluid (or filtrate) due to hydrostatic pressure.
Clinical relevance: It’s used to control fluid overload in patients with kidney failure. 
2. Convection
Definition: Convection is the transport of solutes along with water (solvent) during ultrafiltration.
Mechanism: As water is “pushed” across the membrane, solutes dissolved in that water are dragged along. This is sometimes called solvent drag.
Key point: Larger molecules can be removed more effectively by convection than by diffusion.
3. Diffusion
Definition: Diffusion is the movement of solutes from an area of higher concentration to lower concentration across a semipermeable membrane.
Mechanism: Solutes move down their concentration gradient until equilibrium is reached.
Clinical relevance: Efficient for removing small molecules like urea, creatinine, and electrolytes.
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