Bone tissue histology Flashcards
Which are the mode of formation of bone tissue?
Connective (intramembranous ossification) & Cartilage model (endochondral ossification).
Both forms result in spongy bone & compact bone.
What’s the connective model ? Which bones develop like this ?
Intramembranous ossification that occurs in area os mesenchyme. Osteoblats differentiate directly.
Bones that develop this way are:
- flat bone (crâne)
- part of the mandible and clavicles
What’s endochondral ossification? Whichs bones are concerned by it?
Occurs in pre-existing cartilage models. Mesenchymal cells differenciates into chondrocytes.
It concerns:
- most long bones,
- vertebral column,
- ribs
- pelvis
Describe Intramembranous ossification (connective model)
1) Formation of primary bone: Mesenchymal cells aggregate in a richly vascularised connective tissue and differentiate in :
- Osteoprogenitors
- Osteoblasts : secrete osteoide, calcified in a few days. Form a network of trabecular bone (woven bone). Vascular mesenchyme becomes periosteum.
2) Secondary bone formaton: Lamellar bone replaces woven bone
- Ostéoclasts migrates to the trabecular surface and resorb primary bone matrix
- Deposition of concentric lamellae autour des vaisseaux par les ostéoblastes forme des ostéons dans l’os haversien.
- The space between trabeculaeau contains primary bone marrow
- Trabeculae thicken and form external and internal bone plates (compact bone).
- Diploe is made of spongy bone. Its vascular tissue becomes red bone marrow.
Which are the 4 steps happenning in the primary ossification centers for endochondral ossification ? Where does it take place?
Happens in the diaphysis.
1) Begins with Hyaline cartilage templates
- developed from mesenchyme by condensation
- with differentiated chondoroblasts and chondrocytes
2) Primary ossification center in the diaphysis.
- Perinchondrium becomes periosteum
3) under periosteum, chondrocytes a) hyperhtrophy b) die.
a) secrete collagen type X, angiogenic factors (VEGF) and enzyme alkaline phosphatase. and Secrete MMP which degrade surrounding matrix. Cartilage is errodes. A primitive marrow cavity appears.
4) Blood vessels invade the diaphysis, bringing mesenchymal and osteoprogenitor cells. Osteoblasts lay down woven (primary) bone. Calcified cartilage template resorbed by osteoclasts. Osteoblasts lay down primary woven bone.
Diaphysis is remodelled to form a medullar cavity.
In endochondral ossification, where are the secondary ossification centers located ?
Happens in the epiphysis, periphery of the bone possessing hyaline articular cartilage.
Where is the epiphtyseal growth plate located?
What is its structure?
What is its role?
At the junction between epiphysis and diaphysis, so between the primary and secondary ossification centres.
Cartilagae tissue containing chondrocytes, arranged in columns.
Responsible for bone elongation, provedes a temporary scaffolding on which new bone is laid down.
What replaces growth plate in the adult?
Spongy lamellar bone
How many zones can we distinguish in growth plates? Which ones?
5 zones:
- Reserve
- Proliferative
- Maturation and hypertrophy
- Provisional calcification
What is the reserve zone of the growth plate (aka resting cartilage)?
Small clusters of flattened / rounded quiescent chondrocytes. Randomly arranged.
What is the proliferative zone?
Belongs to growth plate.
- Chondrocytes undergo rapid mitosis (infuence of growth hormone).
- Daugther cells are stacked in columns.
What is the maturation and hypertrophy zone?
Mitosis ceases Lacunae enlarged Cellular accumuulation of : -lipid -glycogen -alklaline phosphatase
What is the zone of provisional calcification?
This partitions or spicules of basophilic calcified cartilage.
Dead chondrocites are resorbed
Lacunae eroded
Richly ascularized primary marrow extends into the newly opened spaces
Osteoblasts differentiate from mesenchymal cells
What is the ossification zone?
At the metaphysis.
Osteoblasts gather on exposed plates of calcified cartilage and secrete osteoid.
Which are the main steps of bone repair? which tissues are involved?
Made from a viable periosteum.
3 phases:
- Inflammatory phase
- Reparative phase (callus ossification)
- Remodelling phase
What are the steps in the inflammatory phase of bone repair?
- Inflammation and edema
- Bleeding from the marrow cavity and surrounding tissue
- formation of a blood clot (hematoma) in the injured site
- Death of osteocytes and necrose of bone fragments
- Infiltration of fibroblasts and new capillaries
- Migration of different cells to form granulation tissue:
- -leukocytes
- monocytes
- macrophages
Which are the steps of callus ossification?
- Migration of mesnechymal cells from both the periosteum and endosteum
- Osteoclasts resorb dead bone
- Chondrocytes form a cartilaginous callus around and between fragments to unite them
- Osteoblasts form trabuceale of new woven bone that replaces the calus
- New bone meet
What is happening during the remmodelling phase?
- Woven bone remodels into lamellar bone overtime
- New osteons of compact bone are constructed
- Medullar cavity is re-established
Which cells make tendons?
Tenocytes or Tendinocytes
What are the constitutives elements of tendons?
ECM
Callegen type I
Cells (Tenocytes / Tendinocytes)
What is epitenon? What is it made of ?
Loose conjonctive tissue surrounding collagen fiber bundles. It is itself surrounded by the paratenon. The final bundle makes up the tendon. Epitenon contains :
- Vascular & Limphatic structures
- Nervs
What’s an enthesis? Which type of enthesis exist?
Transition zones between tissues and sites of mechanical stress concentration. Attach to bones:
- ligaments
- tendons
- capsule
Fibrous (or direct) enthesis and Fibrocartilaginous enthesis.
What is fibrous (direct) enthesis for?
Connecting dense conjonctive tissue that directly attaches to the bone. Stress is dissipated among a wider area.
Attachement sites of ligaments, tendons, and capsules to metaphyseal or diaphyseal bone.
Present in the appendicular skeleton.
Limited pathologies.
How do we call entheseal diseases?
Enthesopathies
What is fibrocartilaginous entheses?
4 zones during the transition from tendon / ligament to bone.
On the epiphyses or apophyses of long or small bones. Fibrocartilage is only present on part of the attachement site.
Narrow attachement site, main source of pathologies.
What are the 4 zones of fibrocartilaginous entheses?
1) End of the tendon
2) Uncalcified fibrocartilage
3) Calcified fibrocartilage
4) Bone
What is the end of the tendon made of in fibrocartilageneous enthesis?
- Longtudinally oriented tenocytes
- // collagen & elastic fibers
- conective tissues merges with peritenon
- balance the different moduli of elasticity
What is the uncalcified fibrocartilage made of in the fc enthesis?
- Chondrocytes in pair and rounded
- aggrecans (that attract water)
- stress is dissipated from the tidemark and into the tendo itself
What is calcified fibrocartilage made of?
Abrupte passage from uncalcified to calcified at the calcification front or tidemart .
Basophilic blue line
Mechanical boundary between soft and hard tissue
Irregular passage from calcified zone to subchondral bone.
Collagen Sharpey fibers penetratrantes the trabecular bone.
No periosteum at the attachement site.
What’s the use for calcified fibrocartilage (CF)?
- Gradual transmission of forces
- Barrier against diffusion
- Reduce risk of infection
What is the subchondral bone plate made of?
Trabecular bone mostly. This contributes to stress dissipation.
