Answer: Depends on the balance between blood pressure and osmotic pressure.
Explanation:
The capillaries are part of the microcirculation that transports nutrients to the tissues and removes cell excreta. The walls of the capillaries are extremely thin, constructed of single - layer, highly permeable endothelial cells. Therefore, water, cell nutrients and cell excreta can all interchange quickly and easily between the tissues and the circulating blood.
The tissues of the body is made up of soo many capillaries which helps to deliver blood and it's contents to it. The hydrostatic pressure in the capillaries tends to force fluid and it's dissolved substances through the capillary pores into the interstitial spaces. Conversely, osmotic pressure caused by the plasma proteins( called COLLOID OSMOTIC PRESSURE) tends to cause fluid movement by osmosis from the interstitial spaces into the blood. This osmotic pressure excreted by the plasma proteins normally prevents significant loss of fluid volume from the blood into the interstitial spaces.
Therefore, a balance between hydrostatic pressure in the capillaries which is influenced by blood pressure and osmotic pressure in order for a net flow of fluid into or out of a capillary to occur.
