What is the purpose of the plunger in a syringe?

The plunger in a syringe serves an essential role in the process of administering or withdrawing fluids. It is designed to create a vacuum or pressure within the barrel of the syringe, allowing the user to draw in medication or fluid when pulling the plunger back and to expel the fluid when pushing the plunger forward. This mechanism is fundamental to the functionality of the syringe, making it an indispensable tool in various medical procedures, including those in radiology practice where precise delivery of contrast agents or medications is required.

Other options, while related to the operation of a syringe, do not encompass the primary function of the plunger. For instance, holding the syringe steady is typically a function of the user’s grip, and measuring liquids is a feature of the graduated markings along the syringe barrel. Securing the needle pertains to the connection between the needle and the syringe but does not involve the plunger's movement or purpose. Thus, the primary purpose of the plunger is to facilitate the drawing and expelling of fluids, making it a critical component in syringe operation.