- The primary driving force for filtration across the glomerular capillaries in the kidney is the hydrostatic pressure within the glomerular capillaries.
- This pressure is generated by the blood flow entering the glomerulus and serves to push water and solutes out of the capillaries and into Bowman's space, initiating the process of urine formation.

- In contrast, oncotic pressure within the glomerular capillaries (Option 1) opposes filtration by pulling water back into the capillaries due to plasma proteins.
- The hydrostatic pressure in Bowman's space (Option 3) also opposes filtration by exerting pressure against the capillary filtration membrane.
- Lastly, the osmotic pressure in the peritubular capillaries (Option 4) mainly influences reabsorption downstream rather than glomerular filtration.

- Thus, the balance of these pressures is described by the Starling forces, where the dominant force favoring filtration at the glomerulus is the glomerular capillary hydrostatic pressure. - This allows plasma water and small solutes to be filtered efficiently, an essential step in urine production and kidney function.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th Edition, Chapter 26, Page 313-315