Osteogenesis Flashcards
what 2 components of cartilage
- Cells
i. Chondrocytes ii. Chondroblast - Extra cellular matrix
i. ground substance
•
composed of proteoglycan (predominant), hyaluronic acid
& small amount of glycoprotein
ii. fibres
how the cartilage grow and regeneration
• i. Appositional growth - by spindle-shaped
cells from perichondrium
• ii.Interstitialgrowth
- by further division of chondrocytes in matrix & subsequent deposition of more matrix
why regeneration cartilage is limited ?
– Regeneration is limited partly because of poor blood supply of cartilage.
how does cartilage get nutrition
i. generally
Exchange of metabolites between. chondrocytes & surrounding tissue is by diffusion
Cartilage has no blood supply, no nerve supply or lymphatic drainage.
ii. for the sites where the cartilage is thick (eg. costal cartilage)-just for general knowledge
small blood vessels enter the centre of cartilage through the cartilage canals
list 3 type of cartilage
- Hyaline cartilage -most common type
-contains few fibres in extracellular matrix
• 2. Fibro cartilage
- where body is subjected to pulling force
- abundant coarse type I collagen fibre in matrix
• 3. Elastic cartilage
– more pliable & distensible
- contains elastic fibres in matrix
what characteristics hyaline cartilage
Appearance
Fresh hyaline cartilage is bluish-
white & translucent • Sites
– Respiratory system - Nasal septum
- Larynx
-Trachea & bronchus
– Skeletal system
- precursor of developing (long) bone
-covering articular surface most of the bones
-sternal ends of the ribs
-between manubrium sterni & 1st. Rib it forms the primary
cartilagenous joint (synchondrosis)
what microscopic of hyaline cartilage
• Cells
- few inactive fibroblasts with
parallel collagen fibres
- small chondroblasts
- clusters of chondrocytes :
- 2-4 cells (isogenous)
-Surrounded by amorphous ground substance (teritorial/capsular matrix)
• Matrix
-appears fairly amorphous
Matrix appear homogeneous Ground substance &
collagen (mostly type II) have similar refractive index
Chondrocytes
Nucleus.
dispersed chromatin
• surrounded by teritorrial./capsular matrix
Cytoplasm
- basophilic granules (rER.)
(active secretion of ground subst.& fibres)
What example clinical application
Hyaline cartilage of articular surfaces of joints has no perchondrium on the surface
- no regeneration after damage
Hyaline cartilages are more susceptible to degenerations
i. Calcification in matrix followed by death of chondrocytes
ii. Asbestiform degeneration
- localised aggregation of thick collagen fibres
Chondromas
-benign tumors of hyaline cartilage -site ; 1/3.bones of fingers
What is fibrocartilage characteristics
• Sites
• i. -forms secondary cartilagenous joint (Symphysis)
• In midline
• -intervertebral disc
(annulus fibrosus)
• -pubic symphysis
• -manubrosternal jt.
-symphysis menti in new born
• ii. articular cartilages of sterno-clavicular & acromio-clavicular joints.
• iii. articular discs
• including minisci of
knee jt.
& Tempromandibular jt
what is microscopic fibrocartilage
it has features of both cartilage & dense supporting t/s
• Thick layers of dense
coarse (type i.)collagen fibres alternating with cartilage cells
• Chondrocytes in lacunae -arrange in groups or rows
(between dense collagen layers)
• Note; there is no identifiable perichodrium in fibrocartilage
what clinical applications prolapse of inter-vertebral disc
nucleus polposus at the centre and annulus fibrosus at the periphery
-rupture of annulus fibrosus n protrusion of nucleus polposus
-may compress the spinal nerve
what gross appearance elastic cartilage and which site
Gross appearance - yellow due to elastin
• Sites
- auricle of External ear
- External auditory meatus (lat.1/3.)
- Eustachian tube
- Epiglottis
- Cuneiform cartilage
What histological/microscopic features of elastic cartilage
Similar to hyaline cartilage
– Perichondrium ( collagen & few elastic fibres )
• Matrix
– mainly collagen (Type II) fibres
– With numerous bundles of elastic fibres in the matrix
(therefore more pliable)
– networks of elastic fibres are particularly dense in vicinity of the chondrocytes
Bone composed of ?
Is a specialized connective tissue.
Every individual bone is an organ, composed of bone cells &
calcified intercellular matrix
(with type I collagen predominant) Organic component and inorganic
component [Calcium, Phosphorus]
• bones are lined by layers of connective
tissue.
(containing osteogenic cells)
- periosteum from outside - endosteum from inside
what 5 functions of bone
- support (bones of axial skeleton)
- protection (eg. skull & bones of Thorax)
- locomotion (lower limb)
- formation of blood cells
- storage & regulation of calcium & other ions
what gross appearance bones
– Compact bone
– Spongy bone [cancellous]
what microscopic bones
• Microscopic
– Primary [immature or woven]
• Usually temporary except in a very few places
• Irregular array of collagen fibers, low mineral content, higher osteocytes than secondary bone.
– Secondary [mature or lamellar]
• Usually found in adults
• Characteristically collagen fibers arranged in lamellae that are parallel to each other or concentrically around the vascular canal
What is cellular components of bone
Composed of 1. Osteoblast
-bone forming cell
2. Osteocyte -assists in nutrition & maintenance of matrix
3. Osteoclast together with osteoblast
bone resorption & remodelling
• Origin
- osteoblast & osteocyte from osteoprogenitor cell - osteoclast from macrophage-monocyte cell line
what is location and function osteoblast
exclusively at the surface of bony tissue.
-in a sheet like arrangement resembling simple cuboidal /columnar epithelium
Quiescent osteoblast are flattened
When active become cuboidal nucleus pushed to one side cytoplasm – become more basophilic
- with abundant rER, Golgi, & secretory vesicles
Function
- secrete Osteoid
what is osteoid
Osteoid
Newly formed (uncalcified) matrix
(with predominantly type I collagen)
Subsequently calcium salt is deposited into the osteoid
what is the location osteocytes
almond shaped bone cells trapped within the calcified matrix
Lacunae
-are the spaces in bony matrix containing osteocytes - one lacuna contains only one osteocyte
Canaliculi
- minute canals interconnecting adjacent lacunae
- it contain fine cytoplasmic extesions of osteocytes
- thro these canaliculi exchange of metabolites b/t. Osteocytes & blood capillaries takes place
- Osteocytes are long living cells
- actively involved in maintenance of bony matrix
how to detect osteoclast in microscopic
large multinuclear motile cells
containing many nuclei
what is the location, origin and function of osteoclast
Location
-in areas of bone resorption
Osteoclasts lie within the depression known as .Howship’s lacunae
Origin
- derived from fusion of bone marrow derived mononucleated cells
Function
Active osteoclast has microvilli forming ‘ruffled border’ in Electron Microscopy. - secretes i.organic acid.
ii.proteolytic enzymes - It has phagocytic property
- Capable of eroding/resorption of bone
- Play important role in remodeling of bone
- Also participate in controlling blood calcium
- (parathyroid hormone stimulate Osteoclastic resorption & release of calcium ion from.bone)
- Calcitonin inhibit osteoclastic activity
Medical applications of osteoclasts
-Osteoclast hyperactivity
• i. Giant cell tumor (Osteoclastoma) - locally aggressive
- commonly in epiphysial end of long bone in adult ,more than1/2.in knee
ii. In Hyperparathyroidism
-Increase osteoclastic activity leads to
-excessive bone erosion (brown t/m.)
& prone to fracture
-.hypercalcaemia as serious side effect
• Unbalance activities of Osteoclast & Osteoblast Paget’s disease
haphazard excessive osteoclastic bone erosion followed by distorted bone formation
• Osteoclast hypoactivity
Osteopetrosis /Marble bone (bone resemble solid but brittle like a chalk) - Osteoclasts lacking ruffled border
- defective bone resorption
bony matrix consists of ?
• Composed of 1.Ground substance & 2. Fibers 1. Ground substance
i. Organic matter includes
- proteoglycan
- several glycoprotein
ii. Inorganic matter
- mainly calcium (99% of body calcium)& phosphorus(80% of body phosporus)
- others include bicarb., citrate, magnesium, potassium & sodium
2. fibers
- almost all collagen type 1
Note: inorganic – 70%, organic – (mainly collagen) 30%
- inorganic matters (minerals) - Rigidity & strength (Hardness)
- organic matters (collagen) - Resist breaking
what are medical applications of bony matrix
• Osteoporosis
- reduction in bone mass most often in elderly
- predisposes to fractures particularly femoral neck, wrist & vertebrae. DEXA= Bone density determination test
• Osteomalacia [painful condition]
-bone is soft & prone to fracture
-failure of mineralisation of Osteoid -maybe due to inadequate intake in diet
- malabsorption
- kidney disease in which loss of phosphate in urine
• Osteogenesis imperfecta (brittle bone disease)
- skeletal fragility
-deficiencies in synthesis of type I collagen
what are the connective tissue covering and lining the bone
• Periosteum & endosteum
-outer dense fibrous
connective tissue
- inner cellular containing osteogenetic cells
function
-nutrition of osseous
-provision of continuous supply of nee osteoblast for bone growth and repair
wht is division of periosteum
i.
Outer layer - collagen fibres & fibroblasts
Sharpey’s fibres
-bundles of collagen fibres penetrate the bone matrix
-binds periosteum to bone
-Inner layer
more cellular
-composed of Osteoprogenitor cells
(fibroblast like) with potential to divide & differentiate into osteoblasts
Note ;
Osteoprogenitor cells play important role in bone growth & repair
what characteristics endosteum
It lines
-inner surfaces of bone
(marrow cavity),
- the vascular canals
- & trabeculae (of spongy bone)
- composed of single layer of Osteoprogenitor cells & very small amount of connective tissue
what type of bone (according to maturity)
• A. Primary/ immature /woven or fetal bone
- is formed either directly from mesenchymal t/s.(membranous ossification) or from cartilagenous model (endochondral ossification)
• Woven bone
- has collagen fibres arranged randomly
Woven bone is later replaced by mature or lamella bone
B. Secondary/ mature or Lamella bone
- by remodeling (by resorption & appositional growth )
What is the histological feature of immature or woven bone
Histological feature Collagen - arranged randomly Mineral contents – lower Osteocytes – in higher proportion
Site
normal
i. during fetal bone formation
ii. near the sutures of flat bones iii. in tooth sockets
iv. at insertions of some tendons
pathological conditions
where bone are forming rapidly
i. in healing of fracture ii. Paget’s disease
what characteristics of mature bone
Secondary or Lamellar bone
matureChararecteristic -Collagen fibres are arranged in
lamellae
which are
i. parallel to each other or ii.concentrically around a vascular canal
Macroscopically Classified into
1. Spongy
2. Compact bone
where is the site if spongy bone
Site
• in long bones
- at the ends (epiphysis)
- in interior (medullary)part
of the shaft (diaphysis)
in flat bone
eg.vault of skull
- in diploe (marrow space)
b/t.outer & inner tables
in short bone -at the central core
what are the gross appearance n texture spongy bone
Composed of trabeculae spicules of bone
Jutting out fr. Internal surface of compact bone into medullary cavity
forming
- network of trabeculae &
- numerous
interconnecting cavities
what microscopic feature of spongy bone
• Microscpic feature
• Trabeculae
- oriented either parallel to the long - axis of trabecula or
- in irregular plates
there is
no Haversian system
- lacunae & osteocytes are scanty
• -have thin external coating of endosteum containing
• flat inactive osteoblasts
• -between the trabeculae of bone are the marrow spaces
where is compact bone site
• In long bone
in the shaft
-forms thick ,outer part at the end of long bone
-forms a thin outer layer that covering the spongy bone
• In Flat bones
-forms outer & inner tables
• In short bone
- completely surrounding the core of spongy bone
what histological features of compact bone
Composed of thin layers of bony lamellae
• Lamellae are of 4 types
i. concentric lamellae of Haversian system
- Osteon
• ii. inner circum.lamellae
- Concentric lamellae lining the inside
of compact bone
• iii. Outer circum.lamellae
- Concentric lamellae at the outermost
aspect of compact bone
• iv. Interstitial lamellae
- Lamellae found b/t.Haversian systems - Old Haversian system left during
• the process of growth/remodelling
what is haversian system and osteon
-Column of long cylinder of bony t/s.
-running parallel to longitudinal axis of a (usually ) compact bone
-Consist of a Central canal
-surrounded by concentric lamellae (4-20) of bony tissue
-Haversian canal
- central canal of Haversian system
lined by endosteum
it contains blood vessels, lymphatics & nerves
Note ;
lacunae containing the osteocytes usually lie b/t.
lamellae canaliculi
–minute canals interconnected lacunae & have connection with H.canal.
- it contains cytoplasmic extensions of Osteocytes
what is volkmanns canal
Communicates
• Haversian canals to
• i. one another
• ii. with marrow cavity
• iii. & also with periosteum
• Pierce lamellae
• run oblique or
right angle to H.canal
what 2 types of ossification
- Intramembranous
- Endochondral
what is intramembraneous ossification
– formation of bone directly from mesenchymal t/s
– flat bones
exp: vault of the skull
maxilla
cavicle
what intramembraneous ossification histological or process
i. condensation of mesenchymal tissue
(from mesoderm or neural crest)
from mesenchymal tissue forms
ii. Osteoprogenitor cells
- these cells differentiate into
iii. Osteoblasts
-secrete matrix osteoid
-osteoblasts trapped inside the lacunae b/c
iv. Osteocytes
v. Mineralisation of matrix & bone forming centres (ossification centres)
are formed
vi.
• Ossification centres
grow radially
• & finally fused together
what is endochondral ossification
- formation of Primary ossification centre 2. formation of Secondary ossification centre
• Formation of bone from (continuously growing) cartilage model
• by deposition of bony matrix on preexisting cartilage matrix
• eg. long bones
• base of the skull
•vertebrae
-pelvis
what endochondral ossification process
• i. Formation of hyaline
cartilagenous model
a. mesenchyme begins.to condense & cells differentiate to form cartilage cells
• •
b. by the end of 6th.wk.
hyaline cartilage model is formed by the chondrocytes
ii. Mineralisation of cartilagenous matrix
at the central (diaphysis) portion of cartilage model
a. Chondrocytes enlarge & degenerate.
b. followed by
calcification of cartiilage matrix
iii. Formation of bone collar
• - mean while a thin layer of bone
(bone collar) is formed around surface of the shaft
• by osteoprogenitor cells of perichondrium
(ie. by intramembranous ossification)
iv. Formation of spaces (alternating) with calcified cartilagenous matrix
• now instead of solid hyaline cartilage
the central portion of developing bone is filled with
a. remnants of calcified cartilagenous matrix &
• b. interconnecting spaces left by degenerated chondrocytes
v. Invasion of blood vessel into the spaces left by dead cartilage cells & Osteoblasts formation
a. blood vessels with primitive mesenchymal cells (fr. perichondrium) penetrate through bone collar
&
b. invade the spaceleft by degenerated cartilage cells
c. Primitive mesenchymal cells differentiate into Osteoblasts
& blood forming cells of bone marrow
V.
d. Osteoblasts adhere to calcified matrix
vi. Formation of Primary ossification centre - bony matrix formation & calcification
-Osteoblasts adhered to
calcified cartilagenous matrix
a. lay down the bony matrix
b. followed by calcification
-& thus form Primary/woven bone around the calcified cartilage matrix
-the osteoblasts trapped in calcified bony matrix b/c osteocytes
Endochondral ossification, Secondary ossification centre
Secondary ossification centres appear at the ends (epiphyses) of long bone with
• regressive changes in Cartilage
• & bone formation
• similar to diaphysis.
• Generally secondary ossification centres appear after birth [within the first 5 years]
Mature bone formation
the woven/primary bones & calcified carti.matrix are later replaced by lamellar bones
• by remodelling so that mature
• bone finally consists of
• Compact outer layer &
• medulla of spongy bone in adult
what is the result of calsification of cartilage matrix
the centre of hyaline cartilage model solid hyaline cartilage is replaced by
a.Calcified matrix
b.Spaces left by dead Chondrocytes
what epiphysial plate do
ii. epiphysial plate
responsible for growth in length of
the bone by proliferation of new cartilage cells
-On reaching maturity
hormonal changes inhibit further proliferation of cartilage cells &
-epiphysial growth plate is finally replaced by bone & no more growth in length
Age determination in medicolegal cases [ X Ray]
generally It is complete about the age of 20.
what body organ that perform regulatory functions have a direct effect on bone
– Kidneys
• Determinesbloodcomposition
– Digestive system
• Via proteins, Vitamin A, D, C
– Female reproductive system
• Pregnancy can alter bones [hormonal levels]
– Liver
• Enzymes-alkaline phosphatase, glycogen
what hormone effect bone
– Pituitary [GH-growth hormone]
– Thyroid hormone-osteogenesis/osteolysis [bone destruction]
– Androgens and Oestrogens of gonads- bone growth and closure of epiphyseal plates
– Unbalanced cortisol and calcitonin may cause osteoporosis
6 zones of epiphysial growth plate
Zone of Reserve cartilage
-hyaline cartilage with small clusters of chondrocytes
Zone of Proliferation
-cartilage cells proliferate by mitosis & form columns of chondrocytes
Zone of Maturation
-chondrocytes enlarge
- no more cell division
Zone of Hypertrophy & calcification
-chondrocytes b/c.vacuolated
-stop secretion of collagen & proteoglycan -instead it secretes alkaline phosphatase
& matrix calcified
Zone of Degeneration
-chondrocytes degenerate, creating cavities in lacunae
-lacunae of calcified matrix invaded by capillaries
Osteogenic zone
-Osteogenic cells differentiate into
-Osteoblasts which adhere to the surface
of Calcified cartilage spicules & start to form bone
how the growing bone increase in length
• Cartilage cells in epiphysial plate proliferate continuosly
• Chondrocytes b/c mature as they move toward the centre of diaphysis
• (& epiphysial growth plates are pushed further apart) thus increases in length
• Cells become larger &
• Degenerate as they approach the central part of diaphysis
• Degenerating zone of cartilage is finally replaced by bone
