Which physical feature helps to reduce friction in synovial joints?

The feature that helps to reduce friction in synovial joints is synovial fluid. This lubricating fluid is produced by the synovial membrane that lines the joint capsule. It fills the joint cavity and acts as a lubricant between the articulating surfaces of the bones, allowing them to move smoothly against one another during joint actions. The presence of synovial fluid not only minimizes the wear and tear on the joint cartilage but also provides nourishment to the cartilage, which is avascular and relies on this fluid for delivering nutrients and oxygen.

In contrast, ligaments primarily serve to stabilize and support the joint by connecting bones to each other, but they do not play a direct role in reducing friction. Muscles contribute to joint movement and stability but are not involved in lubricating the joint surfaces. The articular capsule provides structural support and encases the joint but does not work to lessen friction like synovial fluid does. Thus, synovial fluid is essential in facilitating smooth movements and maintaining joint health.