A surgical system can include a first instrument defining a first channel and a second instrument receivable by the first channel. The second instrument can include a second channel. A valve coupled to the first instrument controls fluid flow through the first channel. The valve has at least two positions and in one position, the impedance of fluid flow through the valve into the first channel (when the second instrument is not received in the first channel) is substantially the same as when the valve is the other position and the first channel partially blocked by the second instrument. In another aspect, a surgical system can include an outer member and the first instrument can be received within the outer member to define a second channel there between. The first instrument can include a visualization system and an illumination system.