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Histology of cartilage


Cartilage is a tough, flexible form of connective tissue, characterised by
extracellular matrix (ECM), with a high concentration of glycosaminoglycans
and proteoglycans which interact with collagen and elastic fibres



Cartilage consists of chondrocytes embedded in an extensive ECM
o
o

Chrondrocytes synthesize and maintain ECM components

o


Chondrocytes have low metabolic activity
Chondrocytes are located in matrix cavities called lacunae

Cartilage is avascular and receives nutrients by diffusion from capillaries in
adjacent connective tissue



Perichondrium (dense connective tissue) surrounds cartilage in most places
o

Also harbours cartilage’s vasculature supply, nerves and lymphatics

o

Articular cartilage lacks perichondrium

Taken from Mescher, Junqueira’s Basic Histology: Text and Atlas, Twelfth Edition


Variations in the composition of matrix components and cells produce three
types of tissue
o
o

Hyaline

Taken from Mescher, Junqueira’s Basic Histology: Text and Atlas, Twelfth Edition
Hyaline cartilage
Matrix


Most collagen is type II collagen



Aggrecan is the most abundant proteoglycan
o



These are bound to hyaluronic acid and to type II collagen fibres

Water bound to GAGs in the proteoglycans constitutes 60-80% of the weight
of fresh hyaline cartilage



Chondronectin binds to GAGs, type II collagen and integrins and mediates
the adherence of chondrocytes to the ECM



The molecular composition has local difference, the area around each
chondrocyte is richer in GAGs (these territorial matrixes stain differentially)

Taken from Mescher, Junqueira’s Basic Histology: Text and Atlas, Twelfth Edition

Chondrocytes


Young chondrocytes are found at the periphery of cartilage and have a long
elliptic shape



Deeper in the cartilage, chondrocytes may be rounder and appear in groups
of up to 8 cells – isogenous aggregates
o

As the cells become more active and secrete ECM components, they
are pushed apart



Respire under low-oxygen tension



Transport of water and solutes in the matrix is promoted by the pumping
action of iintermittent cartilage compression and decompression
o



Maximum thickness is limited by the limits of diffusion

Synthesis of sulphated GAGs and secretion of proteoglycans are accelerated
by hormones and growth factors
o

Somatotropin is a major regulator of hyaline cartilage growth

Perichondrium


Except in the articular joints, all hyaline cartilage is covered by perichondrium



Essential for growth and maintenance



Consists of type I fibres and fibroblasts (including chondroblasts that
differentiate into chondrocytes)

Cartilage formation, growth and repair


All forms of cartilage form from embryonic mesenchyme



Cartilaginous structures grow by mitosis of existing chondroblasts in lacunae
(interstitial growth or formation of new chondroblasts peripherally from
progenitor cells in the perichondrium (appositional growth)



Repair or replacement of injured cartilage is very slow and ineffective due in
part to the tissue’s avascularity and low metabolic rate

Hyaline cartilage

Elastic cartilage

Fibrocartilage

Main features of



Homogenous



Type II collagen



Type II collagen

ECM



Type II collagen



Aggrecan



Large areas of dense



Aggrecan (proteoglycan)



Elastic fibres

connective tissue with type I
collagen

Major cells

Chondrocytes


Typical



chondroblasts

Isolated or in small isogenous groups



Chondrocytes, chondroblasts

Usually in small isogenous groups

chondrocyte



Chondrocytes, fibroblasts

Isolated or in isogenous groups
arranged axially

arrangement
Presence of

Yes (except at epiphyses and articular

perichondrium

cartilage)

Main location



examples

Many components of upper

Yes


respiratory tract


Articular ends and epiphyseal

Main functions

External ear, external acoustic



Intervertebral discs, public

meatus, auditory tube


plates of long bones


No

symphysis, meniscus and

Epiglottis and certain other

certain other joints

laryngeal cartilages



Insertions of tendons

Foetal skeleton
Flexible shape and support of soft

Cushioning, tensile strength,

structural support for respiratory tract
Other notes

Smooth, low-friction surfaces in joints;

tissues

resists tearing/compression



Perichondrium is similar to that of



No distinct perichondrium

most hyaline cartilage



Scarcity of proteoglycans
means it is more acidophilic

Medical application








Many genetic conditions that cause defective cartilage, joint
deformities or short limbs are due to recessive mutations in genes
required for chondrocyte function
o e
...
collagen type II, the aggrecan core protein and the
sulphate transporter
Osteoarthritis involves the gradual loss or changed physical properties of
the hyaline cartilage that lines the articular ends of bones in joints
o Fragments released by wear-and-tear to the articular cartilage
trigger secretion of matrix metalloproteinases (MMPs)
o MMPs exacerbate damage and cause pain and inflammation
Inability of cartilage to regenerate or to be repaired fully may be
attributed to the chondrocytes immobility, low metabolic and mitotic
rates and avascularity
o In the event of injury, new tissue can be produced but function is
often impaired
Cells of cartilage can give rise to either benign (chondroma) or slowgrowing, malignant, rarely metastasising (chondrosarcoma) tumours in
which cells produce normal matrix components

Reference
1
...
Junquiera’s Basic Histology: text and Atlas
...




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