ABSTRACT
Synovial fluid in a joint facilitates movement of the adjoining bones by providing lubrication. For example, while a person is running, the cartilage in the knee joint can show an increase in thickness of about 10%, brought about in a short time by synovial fluid seeping into it from the underlying bone marrow cavity. Similarly, fluid seeps into the spinal disks (which are composed of fibrous cartilage) when they are not compressed, for example, while lying down to sleep. This makes them more pliable directly after getting up than during the day, when the fluid is “squeezed out” by the load of body masses and their accelerations. Thus, immediately after bed rest, one stands taller than after a day’s effort.
