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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