Ch 6 cartilage & bone

•Chondroblasts: produce matrix

•Chondrocytes: surrounded by matrix

•Occupy small spaces called lacunae

•Interstitial growth

within the cartilage

•Appositional growth

Along the cartilage periphery

•Mitosis of chondrocytes in lacunae

•Forms two chondroblasts per lacuna

•Each secretes new matrix; separates the cells now chondrocytes

•Cartilage continues to grow as new matrix is produced from within

Results: Larger piece of cartilage

•Mitosis of stem cells deep to perichondrium

•Stem cells become chondroblasts at periphery

•Chondroblasts produce matrix, become chondrocytes in lacunae

Results: Newest cartilage on outside edges

Diaphysis

• shaft

-•Medullary cavity contains yellow bone marrow

Epiphysis (Proximal and distal)

•Knobby end

• tendons and ligaments

-Articular cartilage •Thin hyaline cartilage reduce friction

Metaphysis

•Region between

•Contains epiphyseal plate

internal surfaces of bones

osteoprogenitor cells, osteoblasts, and osteoclasts

external surfaces bones

•Dense irregular connective tissue

•Attached by perforating fibers embedded in the bone matrix

•Acts as anchor for blood vessels and nerves

~osteoprogenitor cells and osteoblasts

remodeling, growth, fracture repair

mesenchymal stem cells in endosteum and periosteum;

-produce more osteoblasts (stem cell)

form bone matrix (secrete as organic osteoid)

-in lacunae;

maintain matrix

Between lamella

-detect mechanical stress on a bone

dissolve bone matrix (bone resorption), releasing calcium 

•Have ruffled border

•Often located in a resorption lacuna

•Secrete hydrochloric acid and enzymes that dissolve matrix

•Release of stored calcium and phosphate from bone osteolysis

•Primarily hydroxyapatite

•Calcium phosphate and calcium hydroxide

•Open lattice of narrow plates trabeculae

•flat bones, spongy bone is diploe

•vessels and nerves in center of osteon

•Rings of bone around central canal

•interconnecting channels between lacunae

•osteocytes communicate

-perpendicular

- help connect multiple central canals

•Rings of bone immediately internal to the periosteum (external circumferential lamellae) or

internal to the endosteum (internal circumferential lamellae)

•Leftover parts of osteons that have been partially resorbed

formation of bone connective tissue

Intramembranous ossification

•from mesenchyme

•Produces flat bones of the skull, some facial bones, mandible, and central portion of clavicle

Endochondral ossification

•Begins with hyaline cartilage model

• upper and lower limb bones

1.Ossification centers form within thickened regions of mesenchyme

2. Osteoid undergoes calcification

3. Woven bone and surrounding periosteum form

4. Lamellar bone replaces woven bone, as compact bone and spongy bone form

1.The fetal hyaline cartilage model develops

2.Cartilage calcifies, periosteal bone collar forms

3.primary ossification center forms in the diaphysis

4.Secondary ossification centers form in epiphyses

5.Bone replaces cartilage, except the articular cartilage and epiphyseal plates

6.Epiphyseal plates -> epiphyseal lines

layer of hyaline cartilage at the boundary of the epiphysis and diaphysis

Zone of resting cartilage: nearest epiphysis; small chondrocytes in hyaline cartilage

Zone of proliferating cartilage: larger chondrocytes undergoing rapid mitotic cell division

Zone of hypertrophic cartilage: chondrocytes cease dividing and become enlarged

Zone of calcified cartilage: deposited minerals kill the chondrocytes

Zone of ossification: walls between lacunae break down, forming channels that become invaded with capillaries and osteoprogenitor cells

A long bone’s growth in length

-in epiphyseal plate

Growth in a bone’s diameter

-in the periosteum

Continual production resorption of bone

-maintain calcium and phosphate levels

•Nutrient artery/vein: supply the diaphysis of a long bone;

•Metaphyseal arteries/veins: supply the diaphyseal side of the epiphyseal plate

•Epiphyseal arteries/veins: supply the epiphyses

•Periosteal arteries/veins: supply blood to the external circumferential lamellae and superficial osteons

stimulate cartilage growth at epiphyseal plate

osteoblasts,

-bone growth

•calcium deposit from blood to bone

-inhibits osteoclast

•stimulates osteoclasts -resorb bone and increase levels of calcium in the blood

•Vitamin A activates osteoblasts

•Vitamin C required for collagen synthesis

•Vitamin D stimulates calcium absorption from GI tract into blood so that calcium is available for bone formation

increase in bone density by increased osteoblast activity

Bones lose mass with age, weight-bearing exercise help

•Stress fracture: thin break -increased activity

•Traumatic fracture -excess stress to bone

•Pathologic fracture: -bone weakened by disease

•Simple fracture: -does not penetrate the skin

•Compound fracture: -penetrates the skin

1.A fracture hematoma forms

2. A fibrocartilaginous (soft) callus forms

3. A bony (hard) callus forms

4. The bone is remodeled

•Loses ability to produce organic matrix (mainly collagen)

•Loses calcium and other minerals

- Osteopenia: insufficient ossification

decrease in bone mass called osteoporosis