noun, plural: joint capsules
A sac-like fibrous tissue that envelopes a synovial joint
Synovial joints are movable joints that enable abduction, adduction, extension, flexion, and rotation. It is comprised of a sac-like fibrous joint capsule, a synovial cavity filled with a synovial fluid, and a layer of articular cartilage.
The joint capsule is a sac-like fibrous capsule continuous with the periosteum of the articulating bones. This capsule is made up of two layers: (1) an outer fibrous membrane comprised chiefly of ligaments and (2) an inner synovial membrane. The synovial membrane, in turn, is generally comprised of subintima (an outer layer of connective tissue) and intima. The intimal layer is the inner layer of the synovial membrane with two types of cells: fibroblast-like (type B) synovial cells and macrophage-like (type A) synovial cells. The type B synovial cells release components of the synovial fluid into the synovial cavity. The synovial membrane, therefore, is involved in secreting components for the synovial fluid that fills the synovial cavity. The synovial fluid is the clear, viscid fluid that functions by lubricating the articulating joints, supplying nutrients and oxygen, and removing metabolic wastes.
The joint capsule lacks blood and lymph vessels and therefore receives nutrition by diffusion or by convection.
- articular capsule