Joints
- Joints are locations where bones connect to other bones or skeletal structures.
- Synarthroses are immovable joints composed of connective tissue, cartilage, or bone.
- First rib-to-sternum union is an example of a synarthrosis.
- Skull bone connections include synarthroses that help protect the brain by forming stable cranial joints.
- Diarthroses, also called synovial joints, permit maximal movement.
- Long bone articulation commonly occurs through synovial joints.
- Two-layered joint capsule surrounds synovial joints and encloses the articular cavity.
- Articular cavity is the space inside a synovial joint that contains synovial fluid.
- Synovial fluid is colorless, viscous joint fluid rich in hyaluronic acid and proteins.
- Hyaluronic acid helps make synovial fluid viscous and lubricating.
- External fibrous capsular layer is a tough dense connective-tissue layer around a synovial joint.
- Internal synovial capsular layer lines the joint capsule internally.
- Squamous to cuboidal synovial lining cells line the internal synovial layer.
- Type A synovial cells are intensely phagocytic cells in the synovial lining.
- Phagocytic synovial cells remove debris from the joint cavity.
- Type A synovial cells contain a well-developed Golgi complex, many lysosomes, and sparse rough endoplasmic reticulum.
- Type B synovial cells resemble fibroblasts and probably secrete synovial fluid.
- Type B synovial cells contain abundant rough endoplasmic reticulum, consistent with secretory activity.
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