Nephrons and filtration work because the fluid going into the nephron capsule is under pressure than the fluid outside the capsule.

Answer

Hydrostatic pressure

Explanation:

Filtration occurs as pressure forces fluid and solutes through a semipermeable barrier with the solute movement affected by particle size. Hydrostatic pressure is the pressure produced by a fluid against a surface. The blood inside the glomerulus creates glomerular hydrostatic pressure which forces fluid out of the glomerulus into the glomerular capsule. The fluid in the glomerular capsule creates pressure pushing fluid out of the glomerular capsule back into the glomerulus, opposing the glomerular hydrostatic pressure. This is the capsular hydrostatic pressure. These fluids exert pressures in opposing directions. Net fluid movement will be in the direction of the lower pressure.

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