Skeletal Flashcards
How does cartilage receive nutrients?
Diffusion
What are the two means of cartilage growth and development?
Appositional growth
Interstitial growth
Describe appositional growth of cartilage
New cartilage is added to the surface of the older cartilage by chondroblasts from the deep perichondrium.
The chondroblasts then become more chondrocytic over time.
Describe interstitial growth of cartilage
New cartilage is formed within older cartilage by chondrocytes that divide and produce new matrix.
What are the three cartilage types?
Hyaline
Fibrous
Elastic
How does cartilage underpin long bone growth?
Hyaline cartilage present in the epiphysial plates of the long bones
New cartilage forms on the epiphysis side of the epiphysial plate and its ossifies into bone on the diaphysis side.
Describe how events at epiphysial plates lead to long bone growth?
Chondrocytes proliferate in the upper plate and arrange into vertical stacks, the cells hypertrophy lower down before they die and are ossified into the bone matrix.
What is bone tissue made of?
Tissue made up if several cells and connective fibres
What are functions of bone?
Load bearing
Protection (e.g. skull)
Attachment for muscles
Storage of calcium + phosphate
Contains bone marrow
What does bone consist of?
Cellular component and ECM mineralised by deposition of hydroxyapatite
What happens to the ECM in bone?
Mineralised by desposition of hydroxyapatite
2 features of bone
Resistant to tensile and compressive forces
What happens in rickets?
Lack of Vitamin D3 so failure to absorb calcium -bones bend
What happens as you add acid to bone, why?
Lose compressive strength
Becomes flexible as demineralised
What happens as you heat bone, why?
Collagen denatures and bone shatters when tensile force (but can deal with compressive forces)
What gives compressive strength to bone?
Hydroxyapatite crystals
What gives tensile strength to bone?
Collagen
What do calcium hydroxyapatite crystals attach to?
Collagen fibres
What 2 things does bone remodelling allow?
Bone shape maintenance during growth and fracture healing.
What are osteogenic cells derived from?
Mesenchyme
What are osteogenic cells?
Undifferentiated, pluripotent stem cells which can produce bone forming cells
Where are osteogenic cells found in adults?
Periosteum and endosteum in adults
Why are osteogenic cells important?
Remodelling, growth and repair of bones by providing new osteoblasts (when required)
What do osteoblasts do?
Secrete osteoid, make new bone
What happens to osteoid after secreted from osteoblasts?
Initially uncalcified but then mineralsed as it moves away from osteoblasts by deposition of hydroxyapatite
When are osteoblasts recruited?
When bone needs to grow
What do osteoclasts do?
Bone removal
What do osteoclasts allow?
Bone remodelling
Describe structure of osteoclasts?
Multinucleated marcophages
How do osteoclasts remove bone?
Acid and protease secretion, forming Howship’s lacunae
What are Howship’s lacunae?
Depression of bone surface where resorption has occured
How are osteoclasts anchored to bone?
Attach via integrins to matrix protein osteopontin in the bone matrix.
What do osteocytes do?
Preserve bone matrix, sitting in lacunae (surrounding bony matrix)
What are two types of bone formation?
Intramembranous and endochondral
Which bones form from intramembranous ossification?
Flat skull bones, mandible, maxilla and clavicle
Describe intramembranous ossification?
Bone formation from connective tissue not cartilage
What are 4 steps of intramembranous ossification?
1) Osteogenic progenitor - osteoblasts - ossification centre
2) Osteoid secreted, mineralised by hydroxyapaptie deposition. Osteoblasts trapped in matrix - osteocyte
3) Spongy bone formed: trabeculae form around blood vessels, blood vessel outside spongy bone condenses -periosteum
4) Peripheral osteoid condenses - compact bone
What is definition of endochondral ossification?
Initial hyaline cartilage model continues to grow then is calcified by chondrocytes
What is osteoid?
Unmineralized, organic portion of the bone matrix that forms prior to the maturation of bone tissue.
Gelatinous substance made up of collagen, a fibrous protein, and mucopolysaccharide, an organic glue
What forms around hyaline cartilage in endochondral ossification?
Periosteum
Are bones vascular?
Yes
What does ECM of bone consist of?
Collagen, hydroxyapatite, proteoglycans
What happens in endochondral ossification?
Osteoblasts secrete osteoid outside cartilage -forming compact bony collar
Inner cartilage ossifies -primary ossification centre in diaphysis
Vessels in periosteum pass through bony collar, via nutrient foramen to inner cartilage (osteoblasts and osteoclasts can pass)
Remaining cartilage broken down by osteoblasts
Osteoblasts secrete osteoid forming trabeculae
What happens to diaphysis and medullary cavity in endochondral ossification?
Undergoes elongation and appositional growth
When and where do secondary ossification centres form?
Before birth, at epiphysis
How does secondary ossification centre ossify differently to primary?
Spongy bone formed not compact.
Layer of hyaline cartilage remains on end of bone
Epiphysial growth plates do not mineralise until maturity (so long bone growth until adult hood.)
What is epiphysial plate made of and what happens to it?
Cartilage, it grows and divides so more cells on underside laid down and bone shaft left increases
What are the stages of growth of long bone?
Resting cartilage Proliferation Hypertrophy Calcification Ossified bone
What happens in the zone of resting cartilage?
Cartilage attaches to epiphysis
What happens in the zone of proliferation at a epiphysial plate?
New cartilage made on epiphysial side of plate as chondrocytes divide form stacks of cells
What happens in the zone of hypertrophy?
Chondrocytes mature and enlarge
What happens in the zone of calcification?
Cartilage matrix digested by osteoclasts and calcified + ossified by osteoblasts
What happens to chondrocytes in zone of calcification?
Chondrocytes die (don’t receive enough nutrients)
What happens in osteoporosis?
Bone breakdown > bone formation.
i.e. too much osteoclast activity or too little osteoblast activity
What does growth plate extend?
Diaphysis
What becomes more likely in osteoporosis?
Hip fractures
Describe the process of bone remodelling?
Force/stimulus to remodel perceived by osteocyte
Osteoclasts recruited and remove unwanted bone
Osteoblasts then recruited to form new bone
What happens in appositional bone growth?
Growth by increasing layers (i.e. diameter of bone around diaphysis increases)
What is the mechanism for appositional growth?
Ostoeblasts secrete osteoid against shaft of cartilage model
What are the different names for spongy bone?
Spongy/trabecular/cancellous
Two types of bone in a long bone?
Spongy or compact bone
Where is spongy bone found?
Interior of epiphyses
Describe structure/feature of cancellous bones?
Many interconnecting cavities
Describe arrangement of spongy and compact bone?
Interior of epiphyses is spongy bone, surrounded by compact bone (outer layer of diaphysis)
Describe how spongy and compact bones are arranged/joined?
Trabeculae of cancellous bone attach to overlying compact bone at right angle resist compressive forces
What is the arrangement of spongy and compact bone in flat bones?
Cancellous bone sandwiched between 2 plates of compact bone
What are the alternate names for primary and secondary bone?
Woven bone
Lamellar bone
Describe the structure of woven bone?
Collagen fibres in irregular arrangement
Little mineralisation
Lots of osteocytes
What happens to primary/woven bone in adults?
Replaced by secondary bone
Where is primary bone found?
Tooth socket
Secondary bone can be either?
Compact or spongy
Describe structure of secondary bone?
Cylindrical Osteons connected by canaliculi
Osteon contains Haversian canal along length of diaphysis
Collagen fibres arranged in lamellae/rows. Lamellae arranged around central (Haversian) canal (contains neurovascular bundle)
Where is red bone marrow found?
Red bone marrow is found between the trabeculae in spongy bone
Where are osteocytes found relative to lamellae?
Between concentric layers of lamellae
What makes up lamellae in secondary bone?
Collagen fibres arranged in lamellae/rows
What connects osteons?
Canaliculi
Why is trabecular bone beneficial?
Lighter (can be moved easily by muscle)
What does bone mineralisation prevent?
Diffusion of nutrients & waste products
Describe where vessels are found in bone?
In central canal and joined through perforating/Volkman’s canals horizontally
What are Volkmanns canals?
Horizontal connections between Haversian canals (blood vessels)
What do osteocytes extend, what does this allow?
Cytoplasmic processes into canliculi - allows exchange of nutrients/waste between bone and blood and commuication between osteocytes
How are osteocytes linked to surface osteoblasts and other osteocytes, why is linkage between osteocytes important?
Canaliculi and gap junctions - osteocyes can communicate when force applied (sense lines of stress)
What does red bone marrow do?
Make blood cells
What does yellow bone marrow do?
Store fat
What bone growth occurs at epiphysial plates?
Longitudinal bone growth
What is bone growth from the inside driven by chondrocyte hypertrophy?
Interstitial bone growth
