0617 - Structure of joints and tendons Flashcards
What is a joint? What are the three subtypes?
Space or connection or junction between two bones.
Synarthroses - Interlocking suture line between adjacent bones (e.g. skull)
Amphiarthroses - Fibrocartilage between adjacent bones (e.g. costal cartilage in rib cage)
Diarthrodial (synovial) - Have cavity with synovial fluid, with a thin synovial membrane, and a fibrous capsule surrounding.
What are the three types of diarthrodial joint?
Hinge (e.g. Elbow)
Ball and socket (e.g. hip joint)
Saddle (Base of thumb)
What are the characteristics of synovium? (location, composition)
Internal lining of joint, that doesn’t cover cartilage or meniscus
2 layers - lining and intima.
-Lining - synoviocytes (3 cells thick), secrete hyaluronic acid
-Subintima - Fibroblasts
Stroma of collagen fibrils and proteoglycans.
What are the characteristics of synovial fluid? (Composition, appearance, location, function)
Ultrafiltrate of blood, with added hyaluronic acid from synoviocytes to increase viscosity
Clear to pale yellow, relatively acellular.
Covers surface of synovium and cartilage.
Lubricant, nutrient transport functions
How does the synovium change in synovitis?
Early - thickened, oedematous, with more vascular and hyperplastic projections
Late - becomes ‘pannus’ - destructive enzymes destroy cartilage and bone. Becomes fibrovascular granulation tissue.
What are the 5 types of cartilage?
Growth plate
Articular (synovial joints)
Fibrocartilage - attaches tendons and ligaments to bone
Elastic cartilage - Auricles, nose, epiglottis, trachea
Fibroelastic - intervertebral disks and intra-articular menisci (load bearing and shock absorption).
What are the characteristics of articular cartilage? (location, composition, function)
Covers ends of bones in synovial joints, function as a shock absorber.
Chondrocytes synthesise the ECM
80% water, remainder collagen and proteoglycans.
Collagen is mainly type 2 - provide framework and tensile strength.
Proteoglycans serve to bind water and regulate compressibility, stiffness, and resilience.
Has no blood vessels or nerves. Nutrition given by diffusion, and it will not regenerate to normal.
What is the structure of articular cartilage?
Chondrocytes all the way through
Collagen fibres - superficial are horizontal, intermediate are oblique, deep are vertical and link into calcified cartilage (tidemark on H&E), which is related to the bones.
Briefly outline proteoglycans (Function, composition, structure)
Important shock absorber of the cartilage.
Components of the ground substance, secreted by chondrocytes and exist among collagen fibrils.
15-40% of dry weight of cartilage.
Hydrophilic. Core protein plus side chains of GAGs (chondroitin and keratin sulfate)
Aggregated to hyaluronic acid filaments (orange in picture)
What is collagen?
Fibres produced by fibroblasts, chondroblasts, and osteoblasts.
28 types (90% type 1) - all composed of three chains arranged like a rope.
Type 1 - Skin, fascia, tendon, ligaments, bone, scar tissue
Type 2 - all forms of cartilage
Type 3-5 not important
What does collagen do? (5)
Determines tensile strength of tissues
Provides a framework
Limits movement of other tissue components
Induces platelet aggregation and clot formation
Regulates hydroxyapatite deposition in bone.
Briefly outline osteoarthritis as it relates to cartilage
Cartilage degeneration with an inflammatory component. Affects cartilage by:
- Fibrillation, erosion and cracking, and final full-thickness loss.
- Reduced water content and loss of collagen network via collagenase release
- Chondrocyte necrosis and hyperplastic synovium.
Outline the meniscus (Location, structure, composition, function(
An intra-articular cartilage body. (cartilage body inside joint)
Cup-shaped. Function to deepen articular surfaces
Fibrocartilage - Type 1 collagen and proteoglycans with fibroblasts and chondrocytes
In the knee, peripheral 25% is vascular, possibly for repair.
What is a ligament? (Description, Micro, Composition, function, injury)
A dense collagenous structure that links bone to bone.
Similar composition to tendon, but more collagen.
Rows of fibroblasts within an ECM of mainly type 1 collagen.
Elastin to allow stretch, monitored by deformation curve.
Function is to prevent excessive movement of a joint.
Injury to a ligament is a sprain, or rupture if beyond 10% stretch.
What is a tendon? (Location, composition, structure, function, injury)
Dense collagenous structure that links muscle to bone.
Collagen fibrils embedded in ground substance (matrix of proteoglycans, GAGs, structural glycoproteins)
More collagen (65-75% dry mass) and less ground substance than ligaments
86% type 1 collagen, some elastin (2% dry mass). Very linear collagen arrangements.
Fibroblasts (tenocytes)
Function - carry tensile force and store energy
Injury - tear or degeneration. TendinOPATHY/tendinOSIS, NOT tendonitis (no inflammatory cells, but degenerative change).
