cartilage and bone

• clear,
• most common type, matrix contains collagen II

• conatins
• collagen II, high concentration of elastic fibers

• fibrocartilage,
• tendone with chondrocytes replacing fibroblasts, contains high concentration of

TYPE I collagen

• will
• give rise to cartilage

• immature
• proliferating, grow cartilage

can still be proliferative

• adhesive
• glycoprotein holds matrix in place

• Begins with
• mesenchymal connective tissue (embryonic)

• Change shape
• and start to round up, proliferate, mitotsis, beigin to secrete matrix (rich in
• chondronectin)

• As the begin
• to secrete matrix, they are called chondroblasts

• expansion
• of matrix from within, chrondrosblasts aggregate, forms centers of
• chondrification, secrete matrix around cells and separate

• adds
• new cartilage to periphery, surface, fusiform chondrogenic cells (chondroblast
• precursors) reside in perichondrium (fibrous coating outside cartilage); secrete matrix at periphery

• protective
• envelope- 2 layers:

• Fibrous-
• outer layer, more fibrillar less cellular

• Cellular-
• inner layer, less fibrillar, more cellular, less conspicuous after cessation of
• growth

• stimulates cartilage growth, acts thru insulin-like
• growth Factor-1 (IGF-1, somatomedin-C)

• stimulates cartilage growth, acts directly, and thru
• IGF-1

• inhibit cartilage growth, down-regulate type I
• collagen, up-regulate collagenase II

stimulates growth

inhibits cartilage growth

slows cartilage growth & calcification

inhibits collagen synthesis (scurvy)

inhibits calcification (rickets, osteomalacia)

• support, protect,
• site of attachment for muscles/tendons/ligaments, readily mobilize stroes of
• Ca2+

• inert
• (mineralized portion is nonreactive); as tissue- NOT inert, dynamic, living
• tissue, Strength/rigidity of cast iron- but only weights 1/3 as much, relatively
• brittle

• Richly
• vascularized

• cortical,
• more stress placed on boneà
• more bone will develop in that area

• spongy,
• adapts to stress lines placed on bone

• bone adapts
• to loads placed on it, change in mechanical stress dictates structure of living
• bone

• Bony
• elements: place/displace themselves in direction of functional pressure

• Increase or
• decrease mass to reflect functional pressure

• *a bony
• protuberance is there bc a bone has reorganized its elements to support
• function

• 90% of
• organic material is collagen

Collagen fibers are radially arranged

• Collagen fibers of one lamella
• are perpendicular to those in next lamella

• 5% is polysaccharide: rich in aggrecans
• (chondroitin-4 sulfate, chondroitin-6 sulfate, heperan sulfate), rich in
• glycoproteins )osteocalcin, osteopontin, bone sialoprotein)

• 62% inorganic, forms plate which
• align with collagen, mostly hydroxyapatite salt (see slide 16)

• calcified interstitial substance deposited in
• layers (lamellae)

• lacunae - small cavities within
• each lamella, “uniformly” spaced, lenticular-shaped

• canelliculi- canals,
• communication btw osteocyte and haversian systems

• *spongy
• bone has trabelcullae and spicules, NO haversian canals

Bony cells reside in lacunae- tiny tubular passages radiate from lacunae

life lines of osteocytes, cells receive nutrients thru canaliculli

• AKA haversian systems, majority of boen
• arranged in osteons, contain haversian canal

• Haversian
• canal- central point of haversian system

• Central
• canal containing blood vessels

• Runs
• parallel with longitudinal axis of bone

• Surrounded
• by concentrical lamellae

fibrous connective tissue associated with outer surface of bone, envelop and tightly adhere to bone

Sharpy’s fibers: anchor periosteum to underlying bone, collagen from outer layer embed into bone........ Very important!

Fibrous periosteum: Dense, fibrous, relatively acellular, only FIBROBLASTS are present

• Cellular periosteum: inner layer, loose, less fibrous, more cellular, undifferentiated,
• osteogenic cells (bone precursor cells)à may transform into osteoblasts

thin singlular, cellular layer lining bony walls of adjoining marrow cavity, osteogenic cells

Line all bone cavities (including Haversian canals and marrow spaces)

Have osteogenic potential

form osseous tissue, lay down bony matrix

Arise from mesenchymal cells (embryo)

• Osteoprogenitor cells (in adults)- sit on bony surface, basophilic sytoplasm, nucleus away from
• bony surface Of periosteum

Endosteal cells lining bone

• they are full of ER, ribosomes made of RNA, ACIDIC,
• highly active, producing bone matrix (lots of collagen protein)

reside WITHIN lacunae, small lenticular cell, sparse RER and Golgi, long cytoplasmic processes

Maintain health of boen

Participate in Ca and PO4 transport

Cytoplasmic processes connect adjacent osteocytes by way of CANALICULI

specialized macrophages that fuce (multiple nuclei), job is to eat bone

Located in concave areas- HOWESHIP’S lacunae

Can release calcium into bloodstream

Ruffled cell edge to increase SA to internalize whatever it eats up

Clear zone has many polyribosomes to break down calcium salts

• within
• cartilage model of bone, starts in connective tissue matrix

• mesenchymal-
• happens within connective tissue membrane

• presence of pre-existing connective tissue in 1 of 2 forms:
• in a loose primitive mesenchymal form
• as a cartilagenous model

rearrangement of underlying CT

increased vascularity (ingrowth of capillaries)

osteogenic stem cells

• thin layer of uncalcified preosseous tissue,
• surrounds osteocyte adjacent to active osteoblast (osteoblasts secrete osteoid)

• - first deposition of bone, spike like shard
• of new bone

• bony spicules radiating from ossification
• center, spicules have merged

occurs in flat bones of skull (e.g. frontal, occipital and temporal)

pre-existing tissue scaffold, including:

mesenchymal cells-à osteoblastic

primitive fibrous CT

fibers (collagen type I)

cells differentiate and bcome osteoblasts, secrete organic matrix, matrix calcifies

traps cells in lacunae, becoming osteocytes

• occurs in long bones (extremities and vertebral column), pre-existing cartilage anlage
• model

Osseous cuffs form: calcification of midregion cartilage

death and resorption of central chondrocytes

• blood
• vessels penetrate diaphysis (cuff)

• osteogenic
• cells migrate into cavity

transformation of chondrocytes

develop primary ossification site

marrow cavity enlarges

• remaining cartilage anlage forms “plate”
• epiphyseal cartilage plate

secondary center of ossification: blood vessels penetrate epiphysis

growing bone, pool of chonsrocytews

of cartilage cells, not much space

• actively secreting matrix, start laying matrix
• down (blue tint)

• begin to lay Ca2+ salts, calcified
• connective tissue

• large number of osteoclasts to chew away
• calcified cartilage and blasts move in to lay down true bony matrix, pink stain
• is the norm for calcified bone

• at fracture, new hyaline cartilage gets laid into wound, callus (new tissue develops in and
• around fracture site), general same schema as osteogenesis, new bony tissue
• laid down

*repaired bone is often stronger than regular bony areas

callus- area of inflammation around injury