Musculoskeletal 4 Flashcards
What is a disaccharide?
Two sugars
What is a repeating disaccharide unit called?
A glycosaminoglycans
Examples of a glycosaminoglycan?
Chondroitin (CS) and keratin sulphate (KS)
What is a proteoglycan?
Many glycosaminoglycans attached to a protein core
Example of a proteoglycan?
Aggrecan
Why do GAGs stand out like bristles on s brush on a proteoglycan?
Because the negative charges repel each other
What do proteoglycan attach to?
A long hyaluronic acid chain
What is a hyaluronic acid chain?
A large proteoglycan complex
What can extremely large hyaluronic acid chain molecules attach to?
Collagen fibre
What is recently unloaded cartilage like?
Has just had a compressive force taken away
What is the first stage of the loading cycle of articular cartilage?
Negative charges on the repeating disaccharide units cataract positive ions into the cartilage from the joint space; which increases ion concentration in the matrix
What mobile fluids enter the articular cartilage during the loading phase?
Ca k Na H2O Nutrients O2
How many glycosaminoglycans are attached to a core protein?
125 CS
50 KS
What’s the second phase of the articular cartilage loading cycle?
The increase in ion concentration creates an osmotic pressure/gradient which draws water into the matrix; the cartilage begins to swell with the influx of water
What is the third step of the loading cycle of articular cartilage?
As the cartilage swells the collagen is placed under increasing tension. Eventually the swelling force= the tensional forces, and the cartilage stops swelling. This is known as the unloaded equilibrium
What is the fourth step of the articular cartilage loading cycle?
When a load is introduced the fluid phase (water and positive ions- ie Ca, K, Na etc) is squeezes out of the cartilage and back into joint space and synovial fluid
What’s the last phase of the loading cycle of articular cartilage?
The loss of the fluid phase reduces the volume of cartilage (creep). This pushed the negative charges closer together. Eventually the compressive load will be supported by the solid phase and the repulsion of the negative charges. The cartilage will stop shrinking = loaded equilibrium
What are all synovial joints surrounded and enclosed by?
A joint capsule
What does the joint capsule form?
A “sleeve” around the joint connecting the ends of the contributing bones
What is the role of the articular capsule?
To not tightly hold the bones together, as this would restrict movement at the joint
Why does the capsule have to be suitably loose?
To permit the joint to function properly
When does the articular capsule become tight?
At the extreme limits of the natural range of joint motion, thereby protecting the joint from damage caused by excessive movement
What is the articular capsule perforated by and reinforced by?
Perforated by vessels and nerves, reinforced by ligaments
What are ligaments?
Dense regular connective tissue connecting bone to bone
What is the articular capsule comprised of?
Outer fibrous layer and inner synovial membrane
What is the fibrous layer of the articular capsule?
The outer layer of dense connective tissue with variable thickness
What is the fibrous layer comprised of?
Parallel but interlacing bundles of white collagen fibres that are continuous with the periosteum of bone
What are the thicker sections of the articular capsule sometimes called?
Capsular or intrinsic ligaments
What do articular capsule ligaments in the fibrous layer, along with the rest of the capsule, resist?
Tensional forces, and are designed to check excessive and abnormal joint movement
What does the fibrous layer support?
The synovial membrane
What does the synovial layer protect?
The synovial membrane and the whole joint
What is poorly vascularised but richly innervated?
The fibrous layer
Why does it hurt to sprain your joints?
Because the fibrous capsule is poorly vascularised but richly innervated
What is the synovial membrane?
An inner layer of loose connective tissue of variable thickness
What does the synovial membrane line?
All the non-articular surfaces inside the joint cavity, up to the edge of the articular cartilage
What histological layers can the synovial membrane be divided into?
The intima and the subintima
What is the synovial intima like physically?
Thin and normally only 1-3 cells thick
What are the cells in the synovial intima loosely called?
Synoviocytes
What do synoviocytes do?
Secrete some of the components found in synovial fluid
What is the subintima like?
Highly vascular and contains macrophages, fat cells and fibroblasts, which help maintain and protect the articular capsule during normal movement
What is the joint cavity?
A small area between the articulating surfaces
What are the peripheral margins of the joint cavity filled by?
The collapsing an in-folding of the synovial membrane (villi)
What is the “potential space” (joint cavity) filled with?
Synovial fluid
What does the amount of synovial fluid inside a healthy joint cavity really exceed?
1ml, even in large human joints like the knee
What is synovial fluid?
A clear or slightly yellowish fluid that is an ultrafiltrate of blood plasma that leaks out of the vessels in the synovial membrane (subintima)
What are the other components, besides blood filtrate, in synovial fluid secreted by?
Synoviocytes
What are other components of synovial fluid?
Hyaluronic acid, free cells in low concentration (such as monocytes, lymphocytes, macrophages and synoviocytes)
What is the function of synovial fluid?
Joint lubrication, shock absorption, chondrocyte metabolism and overall joint maintenance
