bursa

bursa , closed fibrous sac lined with a smooth membrane, producing a viscous lubricant known as synovial fluid. Bursas are found in regions where muscles or tendons rub against other muscles, tendons, or bones. The bursas function in two ways, lubricating points of friction, and dissipating force by distributing it through a fluid medium. Normally, the bursas produce just enough synovial fluid to reduce friction. However, constant irritation may lead to oversecretion and consequent enlargement of the bursa, a condition known as bursitis . In the hand and foot, the bursa assumes a tubular form. Called the synovial sheath, the structure encloses the tendons along their entire length.

bursa (pl. bursae) A sac of fibrous connective tissue lined with synovial membrane and filled with synovial fluid. Bursae are found between bones and other tissues, such as skin, ligaments, tendons, and muscles, where they reduce friction when one part moves over another.

bursa (ber-să) n. (pl. bursae) a small sac of fibrous tissue that is lined with synovial membrane and filled with fluid. Bursae help to reduce friction; they are normally formed round joints and in places where ligaments and tendons pass over bones.
—bursal adj.