Which structure in the body is responsible for cushioning and lubricating joints?

• A. Ligaments
• B. Tendons
• C. Synovial fluid
• D. Cartilage

Answer: (C)

The correct answer is synovial fluid, which plays a crucial role in the functioning of joints within the body. This thick, viscous fluid is found within the synovial cavities of diarthrodial joints (freely movable joints) and serves two primary purposes: cushioning and lubrication.

Cushioning is vital because it helps absorb shocks and impacts that joints may experience during movement, thus protecting the surfaces of the bones and reducing wear and tear on the cartilage. Additionally, synovial fluid creates a slippery environment that allows for smooth movement between the joint surfaces, minimizing friction during activities such as walking, running, and bending.

In contrast, while cartilage does provide some cushioning at the joint surfaces, its primary function is to provide a smooth, low-friction surface for the movement of bones and to absorb impact. Ligaments and tendons, although essential for connecting bones to each other (ligaments) and muscles to bones (tendons), do not have a direct role in the cushioning or lubricating functions of joints. Thus, synovial fluid stands out as the key component specifically responsible for these vital functions.