What is the function of bursae in joints?

• A. Fluid-filled sacs that reduce friction between moving structures such as tendons and bones.
• B. Bones that are present in all joints.
• C. Muscle tissue inside joints.
• D. Cartilage that lines joint surfaces.

Answer: (A)

Bursae are small, fluid-filled sacs around joints that reduce friction between moving structures. They’re lined with a slippery synovial membrane and filled with synovial fluid, acting as cushions where tendons pass over bones or where ligaments and skin contacts bone. As joints move, these sacs help tendons and other tissues glide smoothly past each other, preventing wear and tear and making movement easier. If a bursae becomes inflamed, bursitis can occur, causing pain and restricted movement. The other options describe different structures: bones form the joint framework, muscle tissue inside joints isn’t how movement is lubricated, and cartilage lining joint surfaces provides a smooth bearing surface—not a cushion between moving parts.