A turbine rotor blade comprising: a platform, an airfoil extending span-wise radially outward from the platform, and comprising a pressure side and a suction side joined at a leading edge and at a trailing edge, a root extending radially inward from the platform for mounting the turbine rotor blade to a disc, and an integrated airfoil and platform cooling system, comprising: a first serpentine channel extending chord-wise in an aft-to-forward direction toward the leading edge of the airfoil, a second serpentine channel extending chord-wise in a forward-to-aft direction toward the trailing edge of the airfoil, wherein each of the first and second serpentine channels comprise; at least three flegs (32a, 32b, 32c, 42a, 42b, 42c) which are located at least partially within the airfoil, wherein serially adjacent legs of each serpentine channel (32, 42) conduct a coolant in alternating radial directions and are fluidly connected by a respective flow turn defined by a tip turn (34, 44) and a root turn (36, 46), wherein each root turn (36, 46) of the first serpentine channel and the second serpentine channel is located radially inboard of the platform, and characterized in that downstream of each root turn (36, 46), the respective serpentine channel (32, 42) comprises a respective flow passage (92, 102) that extends radially outboard and laterally into the platform, so as to direct a radially outboard flowing coolant to impinge on an inner side of a radially outer surface of the platform, wherein the inner side of the radially outer surface of the platform comprises turbulators in an impingement region defined within the lateral extension of both of the flow passages (92, 102) into the platform. a platform, an airfoil extending span-wise radially outward from the platform, and comprising a pressure side and a suction side joined at a leading edge and at a trailing edge, a root extending radially inward from the platform for mounting the turbine rotor blade to a disc, and an integrated airfoil and platform cooling system, comprising: a first serpentine channel extending chord-wise in an aft-to-forward direction toward the leading edge of the airfoil, a second serpentine channel extending chord-wise in a forward-to-aft direction toward the trailing edge of the airfoil, wherein each of the first and second serpentine channels comprise; at least three flegs (32a, 32b, 32c, 42a, 42b, 42c) which are located at least partially within the airfoil, wherein serially adjacent legs of each serpentine channel (32, 42) conduct a coolant in alternating radial directions and are fluidly connected by a respective flow turn defined by a tip turn (34, 44) and a root turn (36, 46), wherein each root turn (36, 46) of the first serpentine channel and the second serpentine channel is located radially inboard of the platform, and a first serpentine channel extending chord-wise in an aft-to-forward direction toward the leading edge of the airfoil, a second serpentine channel extending chord-wise in a forward-to-aft direction toward the trailing edge of the airfoil, wherein each of the first and second serpentine channels comprise; at least three flegs (32a, 32b, 32c, 42a, 42b, 42c) which are located at least partially within the airfoil, wherein serially adjacent legs of each serpentine channel (32, 42) conduct a coolant in alternating radial directions and are fluidly connected by a respective flow turn defined by a tip turn (34, 44) and a root turn (36, 46), wherein each root turn (36, 46) of the first serpentine channel and the second serpentine channel is located radially inboard of the platform, and characterized in that downstream of each root turn (36, 46), the respective serpentine channel (32, 42) comprises a respective flow passage (92, 102) that extends radially outboard and laterally into the platform, so as to direct a radially outboard flowing coolant to impinge on an inner side of a radially outer surface of the platform, wherein the inner side of the radially outer surface of the platform comprises turbulators in an impingement region defined within the lateral extension of both of the flow passages (92, 102) into the platform.