The BBC News Universal Wonders short video Why water is one of the weirdest things in the universe says after
Water molecules can float upwards against the force of gravity. That’s because they love to stick to each other. They’re so good at it that they can actually pull each other up through tiny channels, such as the tiny blood vessels in your body. That’s how oxygen and nutrients reach the edges of your brain.
The same process, called capillary action, allows plants to move water from deep below the ground to nourish the leaves and branches that grow in the sunshine.
We learn about the importance of capillary action in water transport in plants, but I'd never heard that it was important for blood transport in Humans.
Question: How much does capillary action contribute to maintaining blood flow to the human brain? Is it a small effect compared to the difference between arterial and venous blood pressures, is it a substantial contributor?