Lecture 2 Flashcards
Bone Composition
Calcium Phosphate Crystals (hydroxyapatite)
Water
Organic Protein (Collagen Fibers arranged in sheets, 85-90% of protein in bone, flexibility)
Main types of bone tissue
Cortical (Compact) Bone
Trabecular (Spongy or Cancellous) Bone
Cortical (Compact) Bone
80% of skeletal mass
Dense outer bone surface
Thickest in the bone shaft
Porosity 5-10%
Trabecular (Spongy or Cancellous) Bone
3D internal structure of bony rods/plates
Concentrated in the bone ends inside the joints
Porosity 75-95%
Bone Lining Cells
Line all bone surfaces and control movement of materials in and out of the bone
Periosteum
Endosteum
Osteoblast: Bone Forming Cell
Derived from bone lining cells
Secrete bone matrix, collagen, and other organic bone matrix components
Move inorganic minerals into the matrix
Osteocyte: Mature Bone Cell
Osteoblasts that have become embedded in lacunae
Maintain bone tissue, sense mechanical strain
Communicate with each other through canaliculi
Osteoclasts: Bone-resorbing cell
Related to white blood cells
Break down bone tissue
Release minerals stored in bone (Calcium, potassium)
Bone Modeling
- Change in bone size and shape through addition and/or removal of bone at the periosteal or endosteal surfaces
- Highest rate during growth, much less after maturity
- Involves independent actions of osteoclasts and osteoblasts
Bone Remodeling
- Replacement of old bone by new bone to repair damage and prevent fatigue
- No net change in bone amount, size or shape
- Occurs throughout life, but is substantially reduced after growth stops
- Involves combined actions of osteoclasts and osteoblasts (basic multicellular unit)
Woven Bone
Laid down very quickly: fetus, fracture repair
Almost random collagen orientation and mineral arrangement
Quite porous and mechanically weak
Lamellar Bone
Laid down slowly
Collagen fibers and mineral arranged in sheets called lamellae
Lamellae house osteocytes in their lacunae
Lamellar Bone Organization: Primary Bone, Circumferential Lamellae
Laid down after initial rapid fetal growth
Secreted by bone lining cells of the periosteum
Wrap around the outside of the bone, parallel to the outer edge.
Lamellar Bone Organization: Primary Bone, Primary Osteons
Start forming in childhood
Form from mineralized cartilage
Ring like structures of concentric lamellae around a central blood vessel canal
No clearly defined perimeter
Secondary Osteons: Haversian Systems
Accumulate throughout life
Concentric lamellae around a central haversian canal
Result of remodeling through existing bone
Surrounded by a distinct cement line
Collagen fibers roughly parallel in each lamellae
Haversian canals are connected by
Volkmann’s peripheral canals
Carry blood vessels and nerves
