Cartilage+and+Joints


 * 06 September 2006**
 * Cartilage and Bone**
 * Dr. Robert Crissman, Ph.D.**

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=**Cartilage**=


 * Supportive CT
 * CT that makes up skeletal framework of body
 * Consists of cartilage and bone
 * Provide support for other soft tissues

**Cartilage**

 * Three type: hyaline, elastic, fibrocartilage
 * Names based on the predominant fiber present in the extracellular matrix
 * Hyaline cartilage
 * Made of type II cartilage
 * Found where needed for weight bearing but some flexibility required
 * Elastic cartilage
 * Made of elastic fibers
 * Fibrocartilage
 * Made of type I collagen

=**Hyaline Cartilage**=


 * Most common type of cartilage
 * Condrocytes
 * **Diagnositic Characteristic**: Large round cells well separated from other cells, avascular
 * Lots of extracellular matrix
 * Surrounded by perichondrium – dense irregular CT

**Chondrocytes**

 * Reside in lacunae
 * Artifact: Cell shrinks away from matrix, leaving a “lake” during slide making; normally, cells are right up against matrix
 * Maintains extracellular matrix
 * Does not divide

**Chondroblasts**

 * Two cells in one lacunae
 * **Diagnostic Characteristic**: Divides
 * Produces additional new matrix
 * Two cells in one lacunae push each other apart as new matrix is being laid down

**Cartilage Growth**

 * Interstitial growth
 * “Growth from within”
 * Add new matrix within cartilage because extracellular matrix is flexible enough
 * Appositional growth
 * Growth on the perimeter or sides of cartilage

**Perichondrium**

 * Two layers
 * Fibrous Layer
 * Outer layer of dense irregular CT
 * Vascular
 * Chondrogenic layer
 * Differentiating into chondroblasts
 * Appositional growth
 * Lots of proteoglycans so that H2O diffusion can occur
 * However, prevents wandering cells from going into cartilage

**Ground Substance**
-
 * Abundant, amorphous gel
 * Rich in proteoglycans
 * Territorial matrix (a.k.a. capsular matrix)
 * Immediately around cell
 * Darker staining due to chondroitin sulfate
 * Few collagen fibrils
 * Interterritorial matrix
 * Between cells
 * Lighter staining matrix between cells because of lower condroitin sulfate content

**Proteoglycans**

 * Aggrecan aggregates are what provides cartilage its characteristic structure and gel-like character
 * More organized than CT proper
 * Aggrecan aggregate is a hyaluronic acid with 100 aggrecan molecules attached
 * Diffusion of nutrients and H2O
 * Resists compression
 * Slippery
 * Mother nature’s Teflon

**Glycoproteins**

 * Adhesion molecules
 * Chondronectin
 * Attaches cell membrane to ECM
 * Chondrocalon
 * Binds Ca2+ to the ECM

**Extracellular Fibers**

 * Type II collagen doesn’t aggregate together to form fibrils or fibers
 * Cannot be seen at light microscopy level
 * Fine microfibers at electromicroscope level
 * Pericellular capsule visible adjacent to cell
 * Thought to protect cells form mechanic stress

**Hyaline Cartilage Location**

 * Costal cartilage
 * Trachea, bronchi of lungs
 * Larynx, nasal cartilage
 * Articular cartilage of synovial joints
 * Fetal skeleton
 * Allow flexibility during birth
 * Cartilage grows faster than bone
 * Has both appositional and interstional growth (bone is only appositional growth)

**Functions of Hyaline Cartilage**

 * Provide structural support
 * Elastic firmness that is resilient yet fairly rigid
 * Withstand pressure and shear forces
 * Acts as shock absorber
 * Due to proteoglycan aggregates being full of water
 * Slippery
 * 80% of weight is water
 * Due to proteoglycans
 * Capable of rapid growth

**Cartilage Formation**

 * Can be formed directly from Mesenchyme
 * Areas of low O2 content causes formation of chondroblasts
 * In areas of high O2 content causes differentiation to bone
 * Called procartillage
 * Chondroblasts secretes matrix interstitially, pushing away from each other to form cartilage

=**Elastic Cartilage**= ---¬-
 * Chondrocytes
 * Large round cells, widely scattered
 * Principal fiber
 * Elastic fibers
 * Collagen Type II
 * Both fibers secreted by condrocyte
 * Special stain required to visualize elastic fibers
 * Ground Substance
 * Same as hyaline cartilage
 * Lots of aggrecan aggregates
 * Location
 * Auricle and epiglottis
 * Function
 * Resilient support
 * **Diagnositic Characteristics**: large, round chondrocytes, widely scattered cells, dark stained elastic fibers on light microscope
 * Has perichondrium and chondrogenic layer with few elastic fibers

=**Fibrocartilage**=


 * Collagen Type I, densely packed
 * Almost looks like dense regular CT
 * **Diagnostic Characteristic**: Has large round chondrocytes
 * Not a lot of ground substance, replaced with type I collagen
 * Chondrocytes secrete collagen and ground fibers
 * Don’t have to be epithelium to secrete
 * Functions:
 * Pubic symphysis
 * Junction at attachment between tendon and bone

**Intervertebral discs**

 * Fibrocartilage functions as a shock absorber
 * Annulus fibrosis – fibrocartilage
 * Nucleus pulposis – gelatinous matrix in the center
 * Herniated disk
 * Fibrocartilage fails and nucleus pulposis is extruded, putting pressure on spinal cords and causing pain
 * Treated by keeping patient off his/her feet so that nucleus pulposis will suck back in
 * Wait for fibrocartilage to reform

=**Joints**=


 * Function in articulation
 * Definition
 * Junction between two or more bones
 * Typically allows movement between bones

**Functional Classificaiton**

 * Based on degree of movement
 * Synarthroses – immovable
 * Amphiarthroses – slightly movable
 * Diathroses – freely moveable, most common

**Structural Classification**

 * Based on type of tissue between bones
 * Fibrous joints
 * Think layer of fibrous CT between bones
 * No cavity
 * Sutures – immovable bones in skull, synarthroses
 * Syndesmoses – articulating bones separated by dense fibrous tissue, amphiarthroses
 * Gomphoses – cone shaped socket; articulating bones separated by periodontal ligament, synarthroses
 * Cartilagenous joints
 * United by cartilage
 * No cavity
 * Synchondroses – connected by hyaline cartilage, synarthroses
 * Symphyses – connecting material is a broad, flat disk of fibrocartilage, amphiarthroses
 * Synovial joints
 * Ends of bone are covered by articular cartilage
 * Have a cavity
 * Gliding, hinge, pivot, ellipsoidal, saddle, ball-and-socket joints

=**Synovial Joints**=


 * Five common characteristics
 * Synovial cavity
 * Articular cartilage lines ends of bones
 * Have articular capsule
 * Synovial membrane
 * Synovial fluid is present within synovial membrane
 * Contains hyaluronic acid, lubricant
 * Nutrient supply to articular cartilage

**Articular Cartilage**

 * Modified hyaline cartilage
 * Functions to promote smooth movement between bones
 * Structurally designed to do so by lacking perichondrium on the surface
 * Naked cartilage on naked cartilage
 * Nutrients from synovial fluid produced by the synovial membrane that lines the cavity
 * Not really efficient at diffusing nutrients, but it does, slowly
 * Teflon function
 * Made of type II collagen that does form arched fibers like canes
 * Help resists shear stress forces
 * Additional support: cartilage near bone, away from articular cartilage is calcified
 * Subchondral bone layer – increases strength

=**Repair of Joint Cartilage**=


 * Difficult to do:
 * Nutrient supply is poor
 * Articular cartilage doesn’t undergo mitosis
 * To repair:
 * Allow condroprogenitor cells to enter fracture
 * Inject or drill holes to bone marrow
 * Move joint continuously to stimulate cartilage formation
 * Strap you to a machine that slowly moves you all the time
 * Repaired tissue is fibrocartilage
 * Not as smooth as before
 * Other forms of repair:
 * Subchondral bone grafts
 * Autologous bone grafts
 * Autologous tissue culture grafts
 * Injection of hyaluronic acid

=**Osteoarthritis**=


 * Degenerative arthritis affecting synovial joints
 * Most common type of arthrisis
 * Non-inflammatory and progressive deterioration of articular cartilage
 * Characterized by:
 * Fibrillation of articular cartilage
 * Loss of ground substance and retention of fibers
 * Proliferation of cartilage at periphery
 * Replacement of cartilage spur with bone tissue to form bone spurs which reduce degree of movement

=**Rheumatoid Arthrisis**=


 * Inflammatory autoimmune disease
 * Antibodies attack own joint cartilage and synovial membrane
 * Primary inflammation of synovial membrane
 * Joints will be swollen
 * Synovial membrane thickens and synovial fluid secretion increases
 * Joint swell up even more
 * Pressure due to increased amounts of synovial fluid causes pain and tenderness
 * //Pannus// of tissue forms across cartilage and erodes away cartilage
 * Bone exposed and eventually fuses across joint