BIOL 330 - Chapter 7 Cartilage

Cartilage (definition)

A specialized connective tissue with a firm, hydrated extracellular matrix that provides structural support, flexibility, and low-friction surfaces in joints

Chondrocyte

Mature cartilage cell located in lacunae that synthesizes and maintains the extracellular matrix

Chondroblast

Immature cartilage cell that actively produces extracellular matrix and differentiates into chondrocytes

Lacuna

Small cavity within the cartilage matrix that houses a chondrocyte

Cartilage ECM composition

Consists of collagen fibers (type II or I depending on type) and proteoglycans that bind water for strength and compression resistance

Proteoglycans (cartilage)

Molecules (like aggrecan) that bind large amounts of water, giving cartilage its resilience and shock-absorbing ability

GAG function in cartilage

Attract and retain water, creating resistance to compression and allowing cartilage to be flexible yet strong

Cartilage vascularity

Cartilage is avascular and receives nutrients by diffusion from surrounding tissues or synovial fluid

Cartilage innervation

Cartilage lacks nerves and lymphatic vessels

Cartilage metabolism

Low metabolic activity, contributing to slow growth and repair

Cartilage healing

Slow and often incomplete due to lack of blood supply and low metabolic rate

Perichondrium

Dense connective tissue surrounding most cartilage that provides nutrients and allows for growth

Cartilage types

Hyaline cartilage, elastic cartilage, and fibrocartilage

Hyaline cartilage (definition)

The most common cartilage type with a smooth, glassy matrix composed mainly of type II collagen and proteoglycans

Hyaline cartilage ECM

Homogeneous, basophilic matrix rich in type II collagen and aggrecan with high water content (~75%)

Hyaline cartilage function

Provides smooth, low-friction surfaces in joints and structural support in respiratory passages

Hyaline cartilage locations

Articular surfaces of joints, nose, larynx, trachea, bronchi, costal cartilage, epiphyseal plates, and fetal skeleton

Articular cartilage

Hyaline cartilage covering joint surfaces that reduces friction and absorbs shock

Epiphyseal plate

Hyaline cartilage growth plate responsible for longitudinal bone growth

Hyaline cartilage matrix staining

Basophilic due to high GAG content

Territorial matrix

Region around lacunae with more proteoglycans and less collagen, staining darker than surrounding matrix

Chondrocyte arrangement (hyaline)

Cells occur singly or in small isogenous groups

Isogenous groups

Clusters of chondrocytes formed by mitotic division within lacunae

Hyaline cartilage perichondrium

Present except in articular cartilage and epiphyseal plates

Hyaline cartilage embryonic role

Forms temporary skeleton during fetal development

Hyaline cartilage ECM structure

Type II collagen fibrils interact with proteoglycans linked to hyaluronic acid forming a hydrated, cross-linked matrix

Elastic cartilage (definition)

Cartilage similar to hyaline but with abundant elastic fibers that provide increased flexibility

Elastic cartilage ECM

Contains type II collagen, proteoglycans, and elastic fibers visible with special stains

Elastic cartilage function

Maintains shape while allowing flexibility and repeated bending

Elastic cartilage locations

External ear (auricle), external acoustic meatus, auditory tube, epiglottis, and parts of the larynx

Elastic cartilage perichondrium

Always present

Elastic cartilage chondrocytes

Similar in arrangement to hyaline cartilage but embedded in elastic fiber-rich matrix

Fibrocartilage (definition)

Strong cartilage that combines features of hyaline cartilage and dense connective tissue

Fibrocartilage ECM

Contains type II collagen plus large amounts of type I collagen, giving high tensile strength

Fibrocartilage function

Provides resistance to compression, tension, and shear forces

Fibrocartilage locations

Intervertebral discs, pubic symphysis, menisci, and tendon insertions

Fibrocartilage structure

Thick bundles of collagen fibers with chondrocytes arranged in rows

Fibrocartilage chondrocyte arrangement

Cells are isolated or aligned in rows between collagen fibers

Fibrocartilage perichondrium

Absent

Annulus fibrosus

Outer layer of intervertebral disc made of type I collagen providing strength

Nucleus pulposus

Gel-like center of disc rich in hyaluronic acid providing shock absorption

Fibrocartilage staining

Acidophilic due to high collagen content

Hyaline cartilage ECM

Homogeneous matrix with type II collagen and aggrecan providing smooth surfaces

Elastic cartilage ECM

Type II collagen with abundant elastic fibers allowing flexibility

Fibrocartilage ECM

Combination of type II collagen and dense type I collagen for strength

Hyaline cartilage cells

Chondrocytes and chondroblasts

Elastic cartilage cells

Chondrocytes and chondroblasts

Fibrocartilage cells

Chondrocytes and fibroblasts

Hyaline cartilage chondrocyte arrangement

Isolated or in small isogenous groups

Elastic cartilage chondrocyte arrangement

Usually in small isogenous groups

Fibrocartilage chondrocyte arrangement

Isolated or arranged in rows along stress lines

Hyaline cartilage perichondrium

Present except at joints and growth plates

Elastic cartilage perichondrium

Present

Fibrocartilage perichondrium

Absent

Hyaline cartilage function

Smooth joint movement and structural support

Elastic cartilage function

Flexible support and shape maintenance

Fibrocartilage function

Shock absorption and resistance to tension and compression

Chondrogenesis

Process of cartilage formation from mesenchymal cells

Mesenchymal condensation

Early stage where mesenchymal cells cluster and differentiate

Chondroblast formation

Mesenchymal cells differentiate into matrix-producing chondroblasts

Chondrocyte formation

Chondroblasts become chondrocytes once surrounded by matrix

Isogenous aggregates

Groups of chondrocytes formed by mitosis

Cartilage maturation

ECM production increases, pushing cells farther apart

Interstitial growth

Growth from within cartilage via division of chondrocytes in lacunae

Appositional growth

Growth at surface from progenitor cells in perichondrium

Cartilage growth inhibitors

Cortisone slows cartilage growth

Cartilage growth stimulators

Thyroxine, growth hormone, and testosterone increase cartilage growth

Growth hormone mechanism

Stimulates liver to produce somatomedin C (IGF-1), promoting cartilage growth

Disc herniation

Protrusion of nucleus pulposus through annulus fibrosus, compressing spinal nerves

Chondroma

Benign cartilage tumor

Ollier disease

Disorder with multiple benign cartilage tumors near growth plates

Chondrosarcoma

Malignant tumor that produces cartilage matrix

Primary chondrosarcoma

Arises within bone, often in children

Secondary chondrosarcoma

Develops from pre-existing benign cartilage lesions