Bone Histo Flashcards
Compact bone
Hard outer cortex surrounding spongy bone
Lamellar bone
Spongy bone
Cancellous/Trabecular
Lamellar/woven
Spaces for bone marrow
Inner layer
Woven bone
Immature/premature Turns into lamellar bone Loose collagen fibers More cells, less mineral content Forms during fracture repair Forms quickly, not very strong
Lamellar bone
Mature/secondary Does not stain with H&E staining Forms slowly, strong Adult form of bone Regular parallel array of collagen fibers
Bone matrix
90% ECM, 10% water
Organic
Inorganic
Organic bone matrix
35% of bone
90% type I collagen fibers
Has ground substance made of: proteoglycans, glycoproteins, cytokines/growth factors, vitamin K dependent proteins
Osteoid (unmineralized bone)
Inorganic bone matrix
Makes up most of bone
Calcium phosphate and hydroxyapatite
Creates hardness/stiffness
Osteoprogenitor cells
Make osteoblasts
Mesenchymal in origin
Able to differentiate and proliferate
Inner layer of periosteum and endosteum
Osteoblasts
Epithelial-like cells with cuboidal or columnar shape
Alkaline phosphatase that goes away when they turn into osteocytes
Deposit osteoid and control their mineralization
Osteocytes
Osteoblasts within lacunae surrounded by the osteoid matrix they deposited
Has lamellae—>canaliculi to get nutrients
Life of bone matrix depends on these
Osteoclasts
Macrophage/monocytes lineage
Monocytes traveling in blood that became these when they entered bone
Create an acidic environment with H+ATPase to break down bone
Important during bone remodeling/renewing
In Howship’s lacunae
Periosteum
Surrounds bone except for articular surfaces Nutrition of osseous tissue New cellls for growth and repair Inner layer: Osteoprogenitor cells Outer layer: Nerves and blood supply Fibroblasts and collagen Sharpers fibers: anchoring collagen fibers that go through lamellae
Endosteum
Inner layer of bone
Contains osteoprogenitor cells
Surrounds spongy bone
Osteon
Concentric lamellae surrounding longitudinal vessels
Interstitial lamellae
Separates one osteon from another
Has cement line separating osteons
Outer circumferential lamellae
Sits under periosteum
External surface of compact bone
Inner circumferential lamellae
Adjacent to endosteum
Internal surface of bone
Osteocytes
Surrounded by canaliculi that project into the lamellae
Occupy a lacunae
Bone cells that support the matrix
Haversion canal
Longitudinal vessels in the middle of osteons
Volkmann’s canal
Transverse vessels that connect Haversion canals
Intramembranous Ossification
Mesenchymal cells—> bone
Entrapment of first osteocytes; formation of periosteum
Surface bone is filled in by bone deposition, converting spongy bone to compact bone
Spongy bone still exists in middle layer
Endochondral ossification
Mesenchyme develops in hyaline cartilage covered with perichondrium
Perichondrium stops producing chondrocytes and starts producing osteoblasts
Chondrocytes in the middle start to enlarge= primary ossification center
Chondrocytes die in this area
Blood vessels penetrate the primary ossification center
Produces the primary marrow cavity
Spongy bone formed
Osteoclasts follow the dying chondrocytes that are moving toward the end of the bone and eat them, enlarging the marrow cavity
Chondrocytes enlargement and death create a secondary ossification center in the epiphysis
Epiphysis fills with spongy bone
Cartilage is limited to the epiphyseal plate
Zones of endochondral ossification
In direction of growth Zone of resorption Zone of calcified cartilage Zone of hypertrophy Zone of proliferation Zone of reserved cartilage
Bone fracture repair
Formation of fracture hematoma gets rid of necrotic bone pieces by inflammatory mediators
Fibrocartilaginous callus formation via chondroblasts
Bony callus formation via osteoblasts
Bone remodeling via osteoclasts
Achondroplasia
AD mutation if FGFR3 FGFR3 normally inhibits endochondrial growth, but it is prematurely activated and prevents growth earlier in these individuals Dwarfism Shortening of extremities Normal trunk length
Rickets
In children calcium or Vitamin D deficiency during growth—>defect in mineralization of cartilage in growth plate Bowed lower limbs Bowing of distal radius and ulna Delayed closure of fontanelles
Osteomalacia
Adult form of rickets Progressives softening and bending of bone GI disease or Vit D deficiency Bone and joint pain Muscle weakness Fracture
Osteoporosis
Imbalance between osteoclasts resorption of bone and osteoblasts deposition of bone
Elderly and postmenopausal females
Easy fractures
