Chapter 79 - Synovial joint biology Flashcards
What primary anatomical feature provides frictionless contact surfaces in a synovial joint?
Articular cartilage
Figure 79-1. A normal synovial joint (left), including articular cartilage,
synovial fluid, and synovial membranes, together with changes seen in
a joint with osteoarthritis (right). In an osteoarthritic joint, the following
abnormalities can be present: a, capsular fibrosis; b, synovitis; c, cartilage
failure; d, depolymerized hyaluronic acid; e, osteophytes; f, subchondral
cysts; g, vascular engorgement.
Figure 79-4. Synovial and joint capsule laxity or tension based on the anatomic position of the joint. The dorsal aspect of the joint capsule is lax in fetlock extension (A) and under tension in flexion (B). This figure also illustrates the change in joint congruity thought to occur during loading. In an unloaded position (B), it is thought that joints are not completely congruous, but as load is applied, a more congruous joint is formed. (Adapted from McIlwraith CW. Diseases of joints, tendons, ligaments, and related structures.
Name the two layers of the synovial membrane.
Intimal and subintimal
How are joints functionally classified based on movement?
Synarthroses (immovable), amphiarthroses (slightly movable), diarthroses (movable)
What structure attaches the synovial membrane to bone and stabilizes the joint?
Fibrous joint capsule
Which type of joint is most common in the body and facilitates skeleton movement?
Diarthrodial joints
What are the three major structural categories of joints?
Fibrous, cartilaginous, synovial
Which layer of the synovial membrane is responsible for synovial fluid content?
Intimal layer
What distinguishes the intimal layer from other tissues regarding its structure?
It lacks a basement membrane.
What cell types are responsible for phagocytosis in the intimal layer?
Type A synoviocytes
Which additional synoviocyte type represents a transition between types A and B?
Type C synoviocytes
What cell type in the intimal layer is involved in protein secretion?
Type B synoviocytes
List two substances secreted by synoviocytes that are found in synovial fluid.
Hyaluronan and lubricin
What process allows molecules like glucose and oxygen to enter the synovial fluid from plasma?
Ultrafiltration through the subintima
How is hyaluronan clearance achieved in the body?
Through the synovium and lymphatics
What is the term for the mechanism that excludes large molecules from the synovial cavity?
Steric exclusion (or steric hindrance)
What primary function do hyaluronan and lubricin serve in synovial fluid?
Boundary lubrication
How is hyaluronan’s half-life measured in the joint?
By tracking radiolabeled hyaluronan degradation and clearance
What cell count in synovial fluid is generally considered normal?
Less than 500 cells/μL
Which tissue layer has a strong blood supply and innervation within the synovial membrane?
Subintimal layer
What is the role of matrix metalloproteinases (pro-MMPs) secreted by synoviocytes?
They contribute to joint metabolism and tissue remodeling
what is the main role of the synovial membrane?
The cellular population of the intimal layer is based on two basic functions: phagocytosis and protein secretion
regulate the composition of synovial fluid
Synoviocytes are responsible for the secretion of proteins that compose the synovial fluid, name them
hyaluronan,
collagen,
lubricin,
matrix prometalloproteinases (pro-MMPs),
interleukins,
nd eicosanoids (e.g., prostaglandin E2).
The components of the plasma are less than ____ kDa size
Components of the plasma, such as glucose, oxygen, carbon dioxide, and proteins, typically less than 10 kDa in size,
Exogenous hyaluronan is cleared within __ hours through the synovium and lymphatics
It appears that the majority of exogenous hyaluronan is cleared within 48 hours through the synovium and lymphatics, with degradation occurring in both the synovium and
the liver
What structures primarily provide stability to synovial joints?
Periarticular ligaments, fibrous joint capsule, and surrounding muscles.
What effect does suprascapular nerve desensitization have on the shoulder joint?
It leads to subluxation of the shoulder joint.
How does the contribution of stability structures vary by location in the limb?
Higher limb joints rely more on muscles; lower limb joints rely on joint contour and capsule stability..
In the lower limb, which two structures are crucial for joint stability?
Joint surface contour and joint capsule stabilit
How does capsular tension in the metacarpophalangeal joint change between extension and flexion?
In extension, there is capsular redundancy; in flexion, the capsule is under tension.
What is the primary organizational structure of collagen in ligaments?
Parallel fascicles with fibrocytes and blood vessels.
What percentage of organic solids in ligaments and the joint capsule is type I collagen?
75%
To what are most joint innervations associated?
Sharpey fibers.
What happens to ligament tissues in response to increased activity?
They undergo hypertrophy.
What term is used to describe collagen fibers that course through fibrocartilage to the bone?
Sharpey fibers.
How does immobilization affect ligaments at a microscopic level?
It affects microscopic, enzymatic, and biomechanical properties.
What type of cartilage connects the subchondral bone to articular cartilage?
Calcified cartilage.
How does the vascularization of subchondral bone compare to that of articular cartilage?
Subchondral bone is abundantly vascularized; articular cartilage is avascular.
How is the Haversian system oriented in subchondral bone relative to the joint surface?
Parallel to the joint surface.
What range of thickness was found in the subchondral bone plate of the distal tarsal in horses?
2 to 4 mm.
How does the flexibility of the subchondral bone plate in humans compare to the cortical shaft?
It is approximately 10 times more deformable than the cortical shaft.
What effect does osteoarthritis have on the subchondral bone plate?
It can lead to remodeling or stiffening, which is detrimental to joint function.
What is the main component of articular cartilage’s extracellular matrix?
Water.
What is the approximate water content of articular cartilage in adult animals?
About 70% in adults.
Which cell type is primarily responsible for creating the extracellular matrix in articular cartilage?
Chondrocytes.
What percentage of cartilage volume is typically made up by chondrocytes?
1% to 12%.
Name the three main components of the extracellular matrix in cartilage.
Collagens, proteoglycans, and water
What structure marks the transition between calcified and noncalcified cartilage?
Tidemark.
Which layer of articular cartilage contains the highest density of chondrocytes?
The superficial (tangential) zone.
What unique structure has been found in the superficial zone of articular cartilage?
The lamina splendens.
How do the chondrocytes in the intermediate zone differ in shape from those in the superficial zone?
They are larger and more ovoid to round.
In which direction are collagen fibrils oriented in the deep zone of articular cartilage
Perpendicular to the joint surface.
What is the primary function of collagen in articular cartilage?
To provide a framework and resist tensile stress.
How does collagen orientation differ between the superficial and deep zones of articular cartilage?
Superficial zone collagen is parallel to the surface; deep zone collagen is perpendicular.
How many types of collagen have been identified in mammals?
At least 16.
Why is the slow turnover of type II collagen significant in cartilage repair?
It limits cartilage’s ability to repair itself.
What is the primary type of collagen in articular cartilage?
Type II collagen.
What cell type produces type II collagen in articular cartilage?
chondrocytes