File:Components of an Adalimumab-Humira pen - annotated.jpg

English: Components of a Adalimumab-Humira pen separated out and annotated for ease of identification.

1 = protective lower cap that covers the needle 2 = protective upper cap that shields the firing button 3 = main plastic outer chassis of the autoinjector pen housing. Note the window above the directional arrow marking. 4 = firing spring 5 = plunger - firing spring sits on top of collar. Yellow bar acts as indicator to patient. When plunger descends and is visible in the window of #3 the injection has completed. 6 = glass syringe vial that holds the drug to be administered. 7 = piston that's pushed down by the plunger. This is in direct contact with the drug. As the plunger is pushed down the piston pushes the drug through the needle, administering the medication.

8 = hypodermic needle.