Here's a breakdown:

* Carbon atoms: The ring structure is formed by five carbons from the glucose molecule: carbons 1, 2, 3, 4, and 5.

* Oxygen atom: The oxygen atom (O) is incorporated into the ring when the aldehyde group on carbon 1 reacts with the hydroxyl group on carbon 5.

This creates a six-membered ring, which is called a pyranose ring, resembling the structure of pyran.