Supporting tissues. Part II

Cartilage, bone and ossification.

Cartilage

Cartilage is elastic, fibrous connective tissue covered by

perichondrium

Cartilage does not contain blood vessels, it is supplied by diffusion.

Basic types

- hyaline cartilage

- elastic cartilage

- fibrocartilage

Cartilage

extracellular

matrix

fibrilar

ground (amorphous)

substance

collagen

fibers (I, II)

chondrocytes

chondroblasts

cells

(water, ions, proteoglycan

aggregates, glycoprotein)

elastic fibers

1. Hyaline cartilage - localisation

in the wall of nose, epiphyseal plate and small

cartilage of larynx, in trachea, bronchi, ventral

ends of ribs, articular surfaces of movable joints

embryonal hyaline cartilage – temporary

skeleton

The chondrocytes become walled off into chambers or lacunae .

They are grouped into small clusters referred to as isogenous.

groups. Nuclei of chondrocytes are pale with nucleolus.

Cytoplasm contains glykogen, lipids, gER.

Hyaline cartilage - cells

The chondroblasts -flattened, elongate cells between the perichondrium and cartilage, more basophilic than chondrocytes.

chondrocytes

izogenetic

groups

chondroblasts

Perichondrium Is dense irregular connective tissue

consists of two separate layers:

1) the outer fibrous layer contains fibroblasts, which produce collagenous fibers

2) the inner chondrogenic layer contains cells

of the fibroblast line which have the potential

to differentiate into the

chondroblasts

blood vessels provide

nutrients to the cartilage.

2.

1.

Hyaline cartilage (trichrome)

perichondrium

ground (amorphous) substance

homogeneous material fills the spaces

in the meshwork of collagen fibers (II)

Hyaline cartilage (trichrom)

izogenetic

groups

teritorial matrix

interteritorial matrix – the amorphous substance

masks collagen fibers (II)

Hyaline cartilage (trichrome)- isogenous groups

izogenetic

groups

- chondrocytes

in lacunae

Hyaline cartilage (HE)

Hyaline cartilage (HE)

isogenous groups

2. Elastic cartilage, epiglottis (HE)localisation: auricle of ear, walls of

external auditory and Eustachian

tube, epiglottis, cuneiform

cartilage in larynx

chondrocytes arranged dispersly and

in not complet isogenous groups

Elastic cartilage, epiglottis (HE)

network of elastic fibers,

collagenic microfibrils

(collagen type II)

Elastic cartilage, epiglottis (orcein)

Elastic cartilage (orcein)

network of elastic fibers,

nuclei of chondrocytes

excentricaly

localised

3. Fibrocartilage

present in: attachment of certain ligaments,

symphysis ossium pubis and anulus

fibrosus (intervertebral discs)

structure intermediate between dense

connective tissue and hyaline cartilage

not identifiable perichondrium

Fibrocartilage (Trichrome)

chondrocytes - izogenous group

collagenic fibers (collagen type I ) form bundles

- predominant element.

chondrocytes - arranged in rows or occur solitary

Fibrocartilage (trichrome)

chondrocytes

collagen fibres

Bone

It is hard skeletal type of specialized connective

tissue with complex structure consisting of

minerals - mainly of calcium and phosphate

(hydroxyapatite), proteins and cells.

Inorganic component (50%) giving the bone

rigidity and strength.

Organic component includes proteins mainly

collagen (95%). Collagen fibrils form the soft

framework of the bone substance

Bone

cells

extracellular

matrix

fibrillar

ground

substance

collagen

fibers

osteoblasts

osteocytes

osteoklasts

osteoprogenitor

cells

anorganic

organic

Bone components

Cells of bone

Osteoprogenitor cells (mesenchymal stem cells) -

periosteal and endosteal region and perivascularly

in canals of

compact bone.

They can differentiate

into osteoblasts.

Cells of bone Osteoblast cells (immature bone cells) - “bone creators“

they synthetise osteoid and mediate bone mineralisation.

They are derived from osteoprogenitor cells. Active form

- cubic cells with short extensions and basofilic

cytoplasm.

Osteocytes evolve from osteoblasts

which become embedded in bone matrix

during the mineralization process.

They participate in homeostatic role

in blood calcium and other inorganic

substrate concentration.

Cells of bone .

Osteoclast cells – they resorb bone. Large

multinucleated phagocytic cells, located on bone

tissue in resorption pits (Howship lacunes). Into this

space they secrete acid phosphatase to dissolve the

bone mineral, and proteolytic enzymes to digest the

collagen. The cell membrane

closest to the bone has

multiple invaginations - "ruffled

border".

Basic types of bone tissue

Bone is generally classified into two types :

1) Vowen (immature, primary) bone

- typical during embryonal development

- disorganized structure with a high proportion of

osteocytes in young and in healing bone. Bone

tissue consists mostly of irregularly oriented

collagen fibres. Primary bone is not usually

found in adult people except for some specific

locations : the vicinity of sutures of flat bones

of the kranium, in tooth sockets, and some

tendon insertions.

Basic types of bone tissue

2) mature (lamellar, secondary) bone - two kinds:

Compact bone - also called denseor cortical bone.

Spongy bone - also called cancellous , trabecular ormedullary bone.

These two mature types are classified on the basis of porosity and the unit microstructure.

epiphysis

diaphysis

inner spongy bone

Lamellar bone

Compact,cortical bone

- the basic morphological

unit are osteons (Haversian

system) forming the

Haversian canals and

concentric lamellae that

surround them.

Trabecular,

spongy bone

Periost

Lamellar bone Trabecular, spongy bone

trabecular meshwork and

cavities containing bone marrow

The parallel lamellae can be replaced

by short sections of the Havers. system

Trabeculae are formed

by parallel lamellae

Each osteon contains concentric lamellae

separated by thin interlamellar layers

(cementing substance)

with osteocytes placed in

lacunae and central Haversian canal,

which contains blood vessels,

nerve fibers and loos

connective tissue.

Osteons communicate with

marrow cavity (endosteum),

the periosteum and to each other

via transversial Volkman´s canals.

Haversian systems (osteons)

outer circumferential

lamellae – at the outermost

aspect of compact bone

laid down of the

periosteum – layer of

condensed fibrous tissue

an outer 'fibrous layer' and an

inner 'cambium layer '‚

containing mainly progenitor

cells which can develop into

osteoblasts

Volkmann's canals

with vessels (VC)

Haversian canal (HC)

Lamellar bone

inner circumferential

lamellae – line inside

of the compact bone

where it abuts the

marrow cavity

Ground section ( rebore) of bone

Volkmann's canal

Haversian canal

Lamellar bone - osteocytesOsteocytes in lacunar spaces

are connected to each other

and to the central canal by

fine cellular extensions of

osteocytes placed in canaliculi.

Through these extensions,

nutrients are exchanged

between the osteocytes

and blood vessels.

lacunes

Ground section ( rebore) of bone

Bone development

The development of bone occurs in two ways:

1 - intramembranous ossification – direct

replacement of primitive mesenchyme by bone. The clavicle and the flat bones of the skull and face develop by this manner.

2 - enchondral ossification – involves the

replacement of hyaline cartilage with bony tissue. Formation of a growing embryoniccartilage model which is progressively replacedby bone. The weight-bearing bones of the axialskeleton (vertebrae, pelvis) and the bones of theextremities - most of the skeleton.

Intramembranous ossification

osteoblasts (3) after embedding in

their osteoid product are changing

to osteocytes.

Osteocytes (1) within the spicules,

that continuously calcifies.

osteoblasts (3). ---------------------------------------------------------------------------------------

Calcified osteoid (1), osteocytes (2)

within the spicules surrounded with

matrix secreted by osteoblasts (3)

Primary ossification center -

aggregation of mesenchyme cells

that differentiate into osteoblasts (2) –

secreting bone matrix - osteoid (3)

-------------------------------------------

Intramembranous

ossificationin mesenchyme

Skin

In flat boneinternal and external plates of compact arise. The central portion maintains spongy nature – diploe

Intramembranous ossification (trichrome)

spicul

osteoclast

osteoblasts

Intramembranous ossification (trichrome)

Intramembranous ossification (trichrome)

osteoclast

Resorption of the newly

formed primary bone tissue

by osteoclasts

mezenchyme matrix

trabecule

Intramembranous ossification (trichrome)

Several spicules fuse together, replacing the mesenchyme

to give the bone of spongy structure.

osteoclasts

Hypertrophy and destruction

of the chondrocytes in

primary ossification center

of the cartilaginous model.

Reduction of cartilage matrix.

Forming of bone collar

in the perichondrium –

intramembranous ossification

Osteoprogenitor cells along with blood vessels of osteogenic bud from

the periosteum penetrate cartilage toward the primary ossification center.

Endochondral ossification - the first phase

Resorption of cartilage

model by chondroclasts.

Osteoprogenitor cells give rise

to the osteoblasts that synthetise

bone matrix – osteoid over

the remnants of the calcified

cartilaginous septa –

- bone spiculae.

Diaphyseal ossification

Osteoclasts break down the

newly formed bone to open

up the primary medullary

cavity from ossification

center toward the epiphyses.

The cartilage of growth plate

outside the primary ossification

center simultaneously

proliferates..

Zone of cell hypertrophy

Zone of calcification

Ossification zones –

of cartilage removal

and bone deposition

Zone of reserve cartilage

Zone of cell proliferation

1. Resting zone) - hyaline cartilage

2. Zone of cell proliferation - the chondrocytes are arranged in columns (this is indicative of their intense mitotic activity.

3. Zone of hypertrophy -chondrocytes increase in size

4. Zone of calcification -small zone having basophilic staining The chondrocytes die in this zone.

5. Zones of cartilage removal and bone deposition (ossification zones) - osseous elements are present among the pieces of calcified cartilage.

cartilage zones

ossification

zones

Endochondral ossification (trichrome)

2.3.

4. 5.

spicule

Endochondral ossification - ossification zones (trichrome)

Spicule with

osteoblasts and osteocytes

Secondary ossification centres

will develop after birth at

the epiphyses.

The primary and secondary

centres are separated by

a cartilage (growth) plate.

This plate allows the bone

to grow in length.

Epiphyseal ossification

Secondary ossification – woven bone is remodelled by its resorption

and by appositional growth to form mature adult skeleton of lamellar

bone.

In this presentation, pictures from the

recommended literature for subject Histology

and Embryology were used.

Black and white pictures were taken from the

atlases from Krstič:

Die Gewebe des Menschen und der Säugetiere.

Springer1978,

Human Microscopic Anatomy . Springer1991.

The preparations presented were from our

archive.

Thanks for your attention