Introduction and objective: To report the hydrodynamic of a porous orifice (G) tube as replacement for the wrong Starling’s law.

Material and methods: Hydrodynamics of the G tube, based on capillary ultra-structure, were studied. The effect of changing G tube orifice diameter, proximal pressure and distal pressure on the side pressure and chamber (C) pressure were evaluated. The physiological proof that the capillary works as G tube not Poiseuille’s tube is provided.

Results: Hydrodynamics of the G tube showed that proximal, akin to arterial, pressure induces a negative side pressure gradient on the G tube wall, which is negative causing suction maximum near the inlet and turn positive near the exit causing filtration. This created the rapid, autonomous magnetic field like fluid circulation phenomenon between G and C. The physiological evidence on the hind limb of sheep proves that the capillary works as G tube.

Conclusion: Hydrodynamic of the G tube challenges the role attributed to arterial pressure as a filtration force in Starling’s law. A literature review shows that oncotic pressure does not work, and the law has failed to explain the capillary–ISF transfer. A concept based on the new hydrodynamic phenomenon of the G tube is proposed to replace Starling’s law. A rapid autonomous dynamic magnetic field-like G–C circulation occurs. Factors which initiate, regulate, and affect the G–C circulation, its physiological proof and relevance to clinical importance are given. Physiological evidence on capillary working as G tube not Poiseuille’s tube is provided.

Keywords: Capillary physiology, Starling’s law, Poiseuille’s tube, Hydrodynamics of the porous orifice (G) tube