An apparatus comprising: a cassette for controlling movement of blood and separated blood components during an extracorporeal treatment session; and a centrifuge bowl comprising a rotational axis; the cassette comprising: a rigid plastic housing having a top section and a bottom section, the top section and bottom sections together forming an internal space; a hub within the internal space; flexible tubes connected to the hub; loops (1120, 1121, 1122, 1123, 1124) formed of flexible tubes, each of the loops adapted to engage a peristaltic pump head (1301, 1302, 1303, 1304, 1305); an aperture; and a flexible tube section comprising tubing (1114, 1106, 1109), other than the loops (1120, 1121, 1122, 1123, 1124), traversing the aperture so that fluid flow through the flexible tube section (1114, 1106, 1109) can be closed off by pressure exerted on the flexible tube section (1114, 1106, 1109); the centrifuge bowl comprising: an outer housing, a connection sleeve, a top core, a bottom core, and a housing floor, wherein the outer housing is constructed of a biocompatible clear plastic material so that the top and bottom cores (200A, 201A) are visible there through, wherein the outer housing is attached to the housing floor, the housing floor comprising protrusions for locking the bowl into a rotational device, wherein the top core and the bottom core are separate components and where a bottom surface of the top core is in direct contact with a top surface area of the bottom core, wherein a space between the outer housing and each of the top core and the bottom core defines a separation volume, and wherein a first flow channel proceeds through the top core and fluidly interconnects with at least one channel that is located between the top core and the bottom core and that extends radially relative to the rotational axis and to the separation volume, the apparatus further comprising a plurality of inlet tubes (1107, 1108) and an outlet tube for coupling the cassette to the centrifuge bowl, wherein one of the inlet tubes delivers lower density blood components from the centrifuge bowl back to the cassette, wherein another of the inlet tubes delivers higher density blood components from the centrifuge bowl back to the cassette, and wherein the outlet tube delivers whole blood from the cassette to the centrifuge bowl and is fluidly connectable with the separation volume by the first flow channel and the at least one channel. a cassette for controlling movement of blood and separated blood components during an extracorporeal treatment session; and a centrifuge bowl comprising a rotational axis; the cassette comprising: a rigid plastic housing having a top section and a bottom section, the top section and bottom sections together forming an internal space; a hub within the internal space; flexible tubes connected to the hub; loops (1120, 1121, 1122, 1123, 1124) formed of flexible tubes, each of the loops adapted to engage a peristaltic pump head (1301, 1302, 1303, 1304, 1305); an aperture; and a flexible tube section comprising tubing (1114, 1106, 1109), other than the loops (1120, 1121, 1122, 1123, 1124), traversing the aperture so that fluid flow through the flexible tube section (1114, 1106, 1109) can be closed off by pressure exerted on the flexible tube section (1114, 1106, 1109); a rigid plastic housing having a top section and a bottom section, the top section and bottom sections together forming an internal space; a hub within the internal space; flexible tubes connected to the hub; loops (1120, 1121, 1122, 1123, 1124) formed of flexible tubes, each of the loops adapted to engage a peristaltic pump head (1301, 1302, 1303, 1304, 1305); an aperture; and a flexible tube section comprising tubing (1114, 1106, 1109), other than the loops (1120, 1121, 1122, 1123, 1124), traversing the aperture so that fluid flow through the flexible tube section (1114, 1106, 1109) can be closed off by pressure exerted on the flexible tube section (1114, 1106, 1109); the centrifuge bowl comprising: an outer housing, a connection sleeve, a top core, a bottom core, and a housing floor, wherein the outer housing is constructed of a biocompatible clear plastic material so that the top and bottom cores (200A, 201A) are visible there through, wherein the outer housing is attached to the housing floor, the housing floor comprising protrusions for locking the bowl into a rotational device, wherein the top core and the bottom core are separate components and where a bottom surface of the top core is in direct contact with a top surface area of the bottom core, wherein a space between the outer housing and each of the top core and the bottom core defines a separation volume, and wherein a first flow channel proceeds through the top core and fluidly interconnects with at least one channel that is located between the top core and the bottom core and that extends radially relative to the rotational axis and to the separation volume, the apparatus further comprising a plurality of inlet tubes (1107, 1108) and an outlet tube for coupling the cassette to the centrifuge bowl, wherein one of the inlet tubes delivers lower density blood components from the centrifuge bowl back to the cassette, wherein another of the inlet tubes delivers higher density blood components from the centrifuge bowl back to the cassette, and wherein the outlet tube delivers whole blood from the cassette to the centrifuge bowl and is fluidly connectable with the separation volume by the first flow channel and the at least one channel.