Bone and Bone Tissue REAL

Bone tissue matrix

Composed of collagen fibers and hydroxyapatite

Osteocytes

Mature bone cells that maintain bone tissue

Osteoblasts

Bone building cells that secrete matrix

Osteoclasts

Cells that break down bone

Woven bone

Bone with randomly oriented collagen fibers formed during embryonic development and initial repair

Woven bone function

Temporary bone that is later remodeled for strength

Lamellar bone

Organized bone with collagen fibers arranged in layers called lamellae

Lamellae

Sheets or layers of organized bone tissue

Lamellar bone location

Found in all bones after remodeling

Spongy bone

Porous bone with less matrix and more space

Spongy bone other names

Also called cancellous bone or trabecular bone

Spongy bone location

Found inside irregular bones such as vertebrae and inside flat bones such as sternum

Spongy bone percentage

About 20 percent of total skeleton mass

Spongy bone function

Provides strength and protection without adding excess weight

Compact bone

Dense bone with minimal space

Compact bone other name

Also called cortical bone

Compact bone location

Forms outer layer of all bones and most of long bone shafts

Compact bone percentage

About 80 percent of total skeleton mass

Compact bone function

Supports body weight and muscle forces

Trabeculae

Rod or plate like structures forming framework of spongy bone

Trabeculae contents

Contain bone marrow and blood vessels

Trabeculae orientation

Aligned along lines of stress for strength

Osteocytes in spongy bone

Located in lacunae and connected by canaliculi

Canaliculi

Small channels connecting osteocytes

Spongy bone surfaces

Contain osteoclasts and osteochondral progenitor cells

Osteon

Structural unit of compact bone

Central canal

Canal in osteon containing blood vessels

Concentric lamellae

Rings of bone surrounding central canal

Circumferential lamellae

Lamellae that surround entire bone

Interstitial lamellae

Lamellae that fill spaces between osteons

Perforating canals

Canals that allow blood vessels to enter compact bone

Central canals direction

Run parallel through bone

Perforating canals direction

Run perpendicular connecting canals and outer surface

Periosteum

Outer covering of bone with fibrous layer and osteogenic layer

Periosteum outer layer

Dense fibrous connective tissue

Periosteum inner layer

Osteogenic layer that forms bone

Endosteum

Inner lining of bone similar to osteogenic layer

Epiphysis

Proximal and distal ends of long bones

Diaphysis

Shaft of a long bone

Metaphysis

Region connecting epiphysis and diaphysis

Articular cartilage

Cartilage covering epiphysis for joint movement

Spongy bone in epiphysis

Contains red or yellow marrow

Compact bone in diaphysis

Surrounds spongy bone

Medullary cavity

Hollow cavity in diaphysis containing marrow

Endosteum location

Lines the medullary cavity

Epiphyseal line

Ossified remnant of growth plate indicating growth completion

Diaphysis structure

Mostly compact bone with a thin inner layer of spongy bone

Epiphysis structure

Primarily spongy bone

Metaphysis structure

Transition region between epiphysis and diaphysis

Epiphyseal plate

Hyaline cartilage growth plate between epiphysis and diaphysis

Epiphyseal plate function

Responsible for bone length growth

Epiphyseal plate outcome

Becomes epiphyseal line after ossification

Medullary cavity in children

Contains red marrow

Medullary cavity in adults

Contains yellow marrow in long bones and skull

Red marrow in adults

Found in proximal epiphysis and pelvic bones where blood cell production occurs

Ossification

Process of bone tissue formation

Ossification start

Begins around 8 weeks in embryos

Intramembranous ossification

Bone formation from connective tissue membranes

Intramembranous ossification bones

Skull mandible and clavicle

Intramembranous process

Mesenchyme forms membrane and osteoblasts ossify it

Endochondral ossification

Bone formation from a cartilage model

Endochondral process step 1

Mesenchyme becomes osteochondral progenitor cells

Endochondral process step 2

Formation of hyaline cartilage model

Endochondral process step 3

Blood vessels invade cartilage

Endochondral process step 4

Chondroblasts become osteoblasts

Endochondral process step 5

Osteoblasts replace cartilage with lamellar bone

Endochondral ossification location

Occurs at epiphyseal plate

Bone length growth

Occurs at epiphyseal plate using interstitial growth

Bone thickness growth

Occurs by appositional growth

Zone of resting cartilage

Chondrocytes divide slowly

Zone of proliferating cartilage

Chondrocytes divide rapidly

Zone of hypertrophy

Chondrocytes enlarge and mature

Zone of calcified cartilage

Matrix calcifies and blood vessels invade

Ossification zone

Osteoblasts replace cartilage with lamellar bone

Appositional growth

Bone growth in thickness by addition of matrix to surface

Appositional growth cells

Osteoblasts in periosteum

Appositional growth result

Leads to formation of osteons

Circumferential lamellae formation

Produced by periosteal osteoblasts

Bone remodeling

Continuous process of bone breakdown and formation

Bone remodeling cells

Osteoclasts break down bone and osteoblasts build bone

Bone remodeling effect

Medullary cavity enlarges while thickness remains relatively constant

Bone remodeling example

Dominant arm of an athlete becomes denser due to repeated stress

Bone remodeling response

Exercise stimulates osteoblasts to build stronger bone