What is the purpose of the fluid-filled sac known as a bursa?

The bursa is a small, fluid-filled sac located in various areas of the body, particularly around joints. Its primary function is to alleviate friction and pressure between moving parts, such as bones and soft tissues like muscles, tendons, and ligaments. When joints move, particularly during activities that involve repetitive motions, the bursa acts as a cushion, allowing these structures to glide smoothly without causing damage or discomfort. This protective mechanism is vital for the proper functioning of joints and helps maintain mobility and flexibility.

The other choices do not accurately describe the function of a bursa. For instance, bursa do not serve as storage for cartilage or have a role in inter-bone communication or the nourishment of blood vessels. Instead, their specialized structure and fluid content specifically cater to reducing friction and protecting against wear and tear in areas where movement occurs. Thus, the role of the bursa is crucial in maintaining healthy joint mechanics and overall musculoskeletal function.