What causes hydrostatic pressure in blood vessels?

Hydrostatic pressure in blood vessels is caused by the weight of the blood above it in the vessels.

Hydrostatic pressure is the pressure exerted by a fluid at a given point, due to the weight of the fluid above it.

Blood is a fluid, so blood has a hydrostatic pressure.

Increased elevation increases the amount of hydrostatic pressure.

For example, the veins and capillaries in our feet have about 100 mm Hg more pressure inside than those at heart level. In an upraised hand, the hydrostatic pressure is about 50 mm Hg less than at heart level.

Hydrostatic pressure is not the only pressure that exists in a blood vessel

We must consider also the hydraulic pressure caused by the pumping of the heart

Hydraulic pressure is the pressure that results from pushing a liquid through a pipe or other channel.

Osmotic pressure is also present. It depends on the relative concentrations of solutes on either side of the vessel walls.

So blood pressure has hydrostatic, hydraulic, and osmotic components.