The various vascular beds are arranged in parallel. In the kidney the blood passes through two consecutive capillary beds. Venous blood from the spleen and gastrointestinal organs passes through a second capillary network, the portal circulation, in the liver. The greater proportion of the blood volume resides within the venous side of the circulation. Velocity varies in a tube, being low near the wall and high near the center-line.
Viscosity is a molecular property of fluid.
Internal frictional force set up by interaction of molecules. The more interaction, the higher the viscosity. Layers of fluid do not slide so easily past each other for a given driving pressure. Increased viscosity gives increased resistance to flow, so R is directly proportional to viscosity . Velocity of fluid in contact with sides of the tube is zero.