1. Forms cartilage through the secretion of molecules by apposing layers of cells that serve to embed the cells within a matrix

2. Differentiation of cells from inner layer of perichondrium

3. Perichondrium is required

4. Chondroblasts differentiate into chondrocytes

5. Cartilage added around perimeter of cartilage plate

1. Due to matrix pliability, cells of cartilage retain the ability to divide and grow from within the matrix

2. Growth from within

3. Gel-like matrix required

4. Isogenous groups formed

5. Cell number and matrix increase within the cartilage plate

Growth of bones from a template of cartilage (long bones)

Bones formed by adding apposing layers of cells that embed themselves in matrix (flat bones)

1. Found in both cartilage and bone

2. Cavities in which mature cells, surrounded by matrix comprised of collagens and ground substance, reside

1. Chondroblasts

2. Chondrocytes

3. Matrix

4. Perichondrium

1. Spindle-shaped cells derived from mesenchymal cells

2.  Sparse cytoplasm, little RER and golgi, abundant ribosomes

3. Potential to differentiate into chondroblasts

1. Immature cells derived from mesenchymal stem cells in the center of chondrification or chondrogenic cells in inner layer of perichondrium

2. Plump, polarized cells actively synthesizing matrix components

3. Secretion of matrix occurs on side of cell facing cartilage plate

1. Chondroblasts that are surrounded by matrix

2. Located in lacunae

3. Appear as isogenous groups

4. Synthesize chondronectin, collagen, and glycosaminoglycans

1. Type II collagen is predominant

2. Ground substance

1. Mostly water (70%), chondronectin, and proteoglycans

2. Chondronectin serves as critical adhesive glycoprotein (type II collagen, GAGs, integrins, etc.)

3. Abundant negative charges (attracts cations, which attracts water)

4. GAGs form electrostatic bonds with collagen and form a cross-linked network to further increase the ability to resist tensile forces

More intense basophilic staining immediately around the lacunae (rich in GAGs)

Appears bluish-gray, characteristic of hyaline cartilage

1. A dense connective tissue sheat surrounding cartilage

2. Consists of immature cells, chondroblasts, fibroblasts, and Type I collagen

3. Inner chondrogenic layer differentiates into chondroblasts and secretes matrix

4. Vascularized, and supplies nutrients to cartilage cells

1. Hyaline cartilage

2. Elastic cartilage

3. Fibrocartilage

1. Located in walls of large airways (nose, larynx, trachea) ventral ends of ribs, and articular surfaces of bones within joints

2. Provides stiff but somewhat flexible support and reduces friction between bony surfaces

3. Has perichondrium

4. Type II collagen

1. Located in auricle of  ear, epiglottis, and larynx

2. Provides support, but tolerates distortion without damage and returns to original shape

3. Has perichondrium

4. Type II collagen and elastic fibers

1. Possesses a matrix with aligned bundles of dense collagen fibers interspersed with linear rows of chondrocytes in lacunae

2. Located in areas subject to much stress or weight bearing (intervertebral discs, attachments of some ligaments to bones, menisci of knees, symphysis of pubis)

3. NO PERICHONDRIUM, SO NO APPOSITIONAL GROWTH

4. Type I collagen (stains acidophilic), scant matrix

5. Chondrocytes in fibrocartilage derived from fibroblasts

1. Cells: osteoprogenitor cells, osteoblasts, osteocytes, osteoclasts

2. Fibers: primarily Type I collagen

Extracellular matrix with hydroxyapatite crystals, proteoglycans and proteins

1. Serve as precursors for bone cells

2. Derived from mesenchymal (retain ability to undertake mitosis)

3. Differentiate into osteoblasts; high oxygen tension

4. Scant cytoplasm with abundant free ribosomes

1. Responsible for the synthesis of organic components of bone matrix (called "osteoid" prior to mineralization)

2. Synthesize collagens, proteoglycans, glycoproteins

3. Receptors for parathyroid hormone

4. Located in sheet of cuboidal cells apposed to growing edge of bone in periostem and endosteum

5. Highly synthetic with abundant RER (basophilic), polarized

6. Extend processes apposing osteoblasts and form desmosomal junctions

7. Differentiate into osteocytes

1. Responsible for maintaining bone matrix via synthesis of matrix components

2. Located in compact bone and cancellous bone

3. Occupy lacunae and extended processes form canaliculi

4. Nutrients and metabolites from capillaries exchanged through canalculi and lacunae

5. Death results in resorption of matrix

1. Organic matter

a. Type I collagen

b. Proteoglycans

c. Glycoproteins (osteocalcin, osteospondin, sialoproteins)

2. Inorganic matter

a. Calcium and phosphorus, also bicarbonate, citrate, magnesium, sodium, and potassium

b. Hydroxyapatite crystals, calcium phosphate

c. Minerals give bone its characteristic hardness

1. Results from calcium or vitamin D deficiency in children

2. Vitamin D is necessary for the intestinal absorption of calcium

3. Rickets is characterized by improper calcification of bone matrix and formation of distorted bone spicules, leading to slow bone growth and deformed shape

1. The adult form of Rickets

2. Softening of bones is characterized by deficient calcification of newly formed bone and partial decalcification of already calcified matrix

3. Bones become soft, flexible and brittle, cauisng deformities different from Rickets

4. May be aggravated during pregnancy due to increased demands for calcium from (maternal and fetal)

1. Type I collagen

2. Fibers arranged helically with respect to long axis of Haversian canal

1. Periosteum

2. Endosteum

1. On bone surface, except articulating surfaces

2. Outer dense fibrous CT layer with fibroblasts

3. Inner layer with osteoprogenitor cells and osteoblasts

1. Central (marrow) cavity of bone

2. Usually a single layer of osteoblasts

3. Osteoclasts in Howship's lacunae

1. Long bones

2. Flat bones

3. Irregular bones

4. Short bones

5. Sesamoid bones

6. Sutural bones

1. Bulbous end (epiphysis), which is spongy bone with a thin shell of compact bone (cartilage on articulating surface)

2. Diaphysis= cylindrical part between the two epiphyses made up of compact bone surrounding spongy bone lining marrow cavity

3. Ex. humerus of arm

1. Primarily matrix deposited in concentric lamellae

2. Lacunae, each filled with 1 osteocyte

3. Cytoplasmic extensions radiating out from each lacunae (canalculi)

4. Lamellae organized into Haversian systems (osteon), which contain blood vessels, lymphatics, and loose CT

5. Interstitial lamellae (old lamellae in disrepair), inner and outer circumferential lamellae (just inside periosteum and just under the endosteum, respectively)

6. Volkmann's canal-like Haversian canal, but perpendicular to osteon

7. Periosteum and endosteum

1. Displays a meshwork of trabeculae separating cavities filled with marrow

2. Essentially identical to compact bone, but with fewer Haversian systems, only an endosteum, and osteoclasts in Howship's lacunae

1. Inner and outer layer (plates) of compact bone enclosing a middle layer of spongy bone

2. Ex. parietal bone

1. Spongy bone enclosed by thin layer of compact bone

2. Ex. vertebra

1. Like flat bones, with an inner and outer layer of compact bone surrounding spongy bone

2. Ex. carpal and metacarpal bones

1. Found in locations where tendon passes over a joint

2. Ex. patella

1. Ex. sutures in the skull

Outside compact bone, except area of joint articulation

1. First type synthesized during development and repair

2. Irregularly arranged collagen bundles, less minerals, more osteocytes than secondary bone

1. Usually in adults

2. Classified as spongy or cpmpact based largely on arrangement of collagen fibers (arranged in parallel lamellae in spongy bone and concentric lamellae surrounding a canal in compact bone)

1. Bone always develops by replacement of preexisting connective tissue

2. Growth is appositional (intramembranous ossification and endochondrial ossification)

3. Primary bone laid down as network of trabeculae, then converted to secondary bone (usually compact) by filling in the spaces between the trabeculae

4. Areas of primary bone, resorption, and secondary bone appear side by side

1. Leads to formation of flat bones

2. Participates in growth of short bones

3. Contributes to the thickening of long bones

4. Occurs in consecutive steps that overlap

1. Primary ossification center- layer of mesenchymal tissue forms and cells contact each other

2. Mesenchymal cells differentiate into osteoblasts and regions of mesenchymal cells with continuous mitotic activity form periosteum and endosteum

3. Osteoblasts secrete osteoid (noncalcified matrix) away from osteoprogenitor cells

4. Osteoblasts with matrix become osteocytes; collagen fibers randomly oriented and primary bone is formed

5. Calcium phosphate deposits in bone matrix, calcifying matrix

6. Spicules form (islands of developing bone)

7. Osteoblasts incorporated into bone

8. Secondary bone is formed and collagen fibers become more regularly arranged in areas to be compact bone

9. Central vascular CT surrounding spicules of bone is transformed into hematopoietic tissue in areas to become spongy bone

1. Involves the replacement of hyaline cartilage template by bone

2. Involved in the formation of short and long bones (lengthen)

3. Begins with a cartilage model of bone already developed

4. Model is formed by both interstitial and appositional growth methods

1. Hyaline cartilage model

2. Periosteal bone collar forms

3. Hyaline cartilage begins to calcify

4. Metaphyseal trabeculae no longer needed and calcified cartilage remains

5. Formation of epiphyseal trabeculae and secondary ossification center

6. Lower epiphyseal plate disappears adn epiphyseal and metaphyseal trabeculae fuse

7. Upper epiphyseal plate disappears and metaphyseal trabeculae fuse

1. Penetrates hole in bone collar made by osteoclasts

2. Consists of blood vessels carrying osteoprogenitor cells and hematopoietic cells

1. Forms in the epiphysis at each end of the forming bone (no bone collar formed)

2. Ossification spreads in all directions except for articular cartilage at bulbous ends of long bones and the epiphyseal plate

1. A portion of cartilage that connects the epiphysis to the diaphysis

2. Retains same thickness during maturation, and is responsible for all subsequent growth in long bones

3. Eventually replaced by bone (end of potential for longitudinal growth)

1. Resting zone

2. Proliferative zone

3. Maturation or hypertrophic zone

4. Calcification zone

5. Ossification zone

1. Normal hyaline cartilage

2. Random chondrocytes with a few isogenous groups

1. Rapidly dividing chondrocytes form columns parallel to long axis of bone via process of interstitial growth (no perichondrium on articulating surfaces)

2. Looks like stack of dimes

1. Nondividing chondrocytes continue to enlarge and become vacuolated

2. With the cell enlargements, lacunae enlarge, matrix diminishes, adn the "cytes" are separated by thin septa of matrix

1. Thin septa of cartilage (basophilic) become calcified by deposition of calcium phosphate salts

2. With mineralization, the diffusion is inhibited and chondrocytes die

1. As chondrocytes degenerate, blood vessels invade the area and bring osteoprogenitor cells

2. Differentiate into osteoblasts and mature into osteocytes that deposit bone matrix that is calcified

3. Bone spicules form

4. Presence of calcified cartilage that stains blue, encased in bone matrix that is stained red

1. Occurs by intramembranous ossification in the diaphysis

2. Shaft  build by sub-periosteal and sub-endosteal intramembranous bone formation

Results in the formationof new Haversian systems and the resorption and deposition of bone

1. Associated with periosteum and endosteum for intramembranous ossification

2. Entrance of blood vessels increases osteoblastic activity and the formation of new Haversian systems

1. Associated with osteoclasts in marrow cavity

2. Parathyroid hormone binds to osteoblasts, make RANKL, binds to RANK receptor on osteoclast precursors, stimulation to increase osteoclasts

1. Localized hemorrhaging fills zone of injury

2. Haversian system become necrotic

3. Blood clot solidifies and cells (fibroblasts) and small blood vessels form granulation tissue

4. Internal callus forms-clot invaded by osteoprogenitor cells from endosteum and multipotential cells from bone marrow

5. Osteoprogenitor cells differentiate and make bone

6. External callus forms and grows

7. Primary bone forms and becomes secondary bone

8. Resorption of callus

1. Bone resorption is more prominent than bone formation

2. Enhanced bone resorption, decreased bone formation or both

3. Bone becomes more porous

4. Paget's disease-uncontrolled osteoclastic activity

1. Condition of vitamin C deficiency

2. Inhibits matrix formation, distorts chondrocytes, and interferes with repair of fractures by altering collagen deposition

3. Bleeding gums and loosening of teeth

1. Due to excess production of parathyroid hormone

2. Marked resorption of bone with decalcification, elevated blood calcium, and abnormal deposits of calcium in several orgagns (metastatic calcification)

1. Herniation of an intervertebral disc

2. Rupture of annulus fibrosis and expulsion of nucleus pulposes, causing disc to flatten

3. Disc can slip from its position between vertebrae and compress spinal cord

4. Most common in posterior region, which contains fewer collagen fibers

5. Lower back pain

1. A degeneration of articular cartilage due to excessive wear and tear

2. Eventual bone to bone trauma leads to a painful swollen joint