Blood separation systems and methods introduce blood into an annular separation channel between a low-G wall and a high-G wall while rotating the separation channel about an axis, for separation of the blood into blood components. The annular separation channel has an annular boundary wall. The systems and methods direct a first blood component into a constricted channel along the low-G wall. The systems and methods remove the first blood component through a first path that communicates with the separation channel through an opening that adjoins the constricted channel adjacent the low-G wall. The systems and methods direct a second blood component along a surface that extends generally in an axial direction along the high-G wall toward the annular boundary wall. The systems and methods collect the second blood component through a second path that communicates with the separation channel through an opening that adjoins the surface adjacent the high-G wall axially spaced from the annular boundary wall.
