What does the term "lumen" refer to in a needle?

The term "lumen" specifically refers to the hollow cavity inside of a needle. This cavity is crucial because it is the passage through which fluids or medications can flow when the needle is used for injections or drawing fluids. The size of the lumen can also affect the flow rate; a larger lumen allows for a faster flow of fluid. Understanding the concept of the lumen is essential for tasks such as selecting the appropriate needle size for various medical procedures, as different procedures may require different flow rates and volumes.