I. cartilage A. perichondrium 1. outer fibrous layer contains fibroblasts that secrete collagen 2. inner chondrogenic layer contains cells that can proliferate and turn into chondroblasts B. cartilage growth 1. appositional growth chondroblasts add new layers of matrix on the outside of an existing piece of cartilage 2. interstitial growth (young cartilage only) chondrocytes inside a piece of cartilage divide, and then secrete new matrix, spreading themselves apart II. bone A. types of bone tissue 1. compact / lamellar bone tissue forms the outer surfaces of all bones very dense, has few spaces 2. cancellous / woven / spongy bone tissue is found inside all bones not very dense, has many spaces Strong/Fall 2008 page 1
B. membranes associated with bones 1. periosteum - layer of tissue that covers the outside surface of all bones except where there is articular cartilage provides a connecting point for tendons, ligaments and joint capsules is connected to underlying bone by perforating fibers a. outer layer - dense irregular c.t. b. inner layer - contains osteoblasts and osteoclasts 2. endosteum = thin layer that lines all inner spaces inside bones, similar to inner layer of periosteum covers trabeculae in cancellous bone lines central and perforating canals in dense bone lines medullary cavity C. gross structure 1. long bones a. diaphysis = shaft b. epiphysis/epiphyses = ends epiphyseal line = where diaphysis and epiphyses fuse (visible inside bone) c. medullary cavity = space inside diaphysis containing bone marrow 2. flat bones diploe D. distribution of compact and spongy bone compression stress = force that pushes on bone along its axis tension stress = force that pushes perpendicular to axis of bone stress is greatest at the outer edge of the bone and decreases towards the middle Strong/Fall 2008 page 2
E. microscopic structure of bone tissue 1. both types of bone tissue have: osteocytes mature bone cells surrounded by matrix, located between lamellae lacuna/lacunae space in which an osteocyte is found canaliculi tiny canals connecting lacunae and osteocytes to each other; they go through the lamellae lamella/lamellae layer of bone matrix 2. compact bone o osteon = structural unit, runs parallel to axis of bone or stress lines o central (Haversian) canals = in center of osteon, contain blood vessels and nerves in osteons, lamellae form concentric circles around the central canal o circumferential lamellae = layers of bone matrix that occur outside the osteons; found on extreme outer and inner surfaces of bones o perforating (Volkmann's) canals = perpendicular to central canals, contain blood vessels that branch into smaller vessels in the central canals Strong/Fall 2008 page 3
3. cancellous / spongy / trabecular bone trabeculae = small irregular and connected pieces of bone tissue in trabeculae, lamellae are arranged in irregular layers the spaces between trabecular contain bone marrow F. chemical composition 1. organic matrix (osteoid) = cells and collagen 35% of tissue mass tensile strength 2. inorganic matrix = hydroxyapatite (calcium phosphate and other mineral salts) 65% of tissue mass deposited as tiny crystals around collagen fibers compression strength G. bone formation (osteogenesis or ossification) 1. intramembranous ossification - skull (except temporal, occipital, ethmoid, sphenoid) and clavicle a. mesencyme cells form c.t. membranes where bones are to be formed b. some mesencyme cells differentiate into osteoblasts and begin to secrete bone matrix c. calcium salts deposit around the osteoid and trap the osteoblasts d. trabeculae enlarge and fuse with each other to form cancellous bone e. the inner and outer surfaces are remodeled into compact bone f. mesencyme forms a periosteum on the outer surfaces and endosteum on the inside Strong/Fall 2008 page 4
2. endochondral all other bones a. hyaline cartilage model in fetus b. bone collar around middle of cartilage cuts off diffusion, cartilage disintegrates c. periosteal bud brings blood vessel and bone cells into cartilage model (primary ossification center) d. cartilage model grows and is gradually replaced by bone tissue e. secondary ossification centers form in epiphyses f. epiphyseal plates are disks of hyaline cartilage between the primary and secondary ossification centers H. bone growth 1. long bones a. length - at first, epiphyseal plates expand faster than they are replaced by bone (this is caused mainly by growth hormone) Strong/Fall 2008 page 5
b. diameter - appositional growth adds new layers to the outside at the same time, osteoclasts removed tissue from the inner surface 2. flat bones - new tissue is added around the edges 3. why long bones grow and then stop growing gonadal steroid hormone secretion begins at puberty these hormones cause increased growth in both bone and cartilage, but faster growth in bone closure of the epiphyseal plates causes bones to stop growing longer I. remodeling - bone removal and replacement 1. process osteoclasts secrete acid to dissolve the calcium salts and then use enzymes to remove the collagen osteoblasts deposit new bone tissue 2. causes a. change in blood calcium levels b. change in stress on bones change in weight change in muscle tone change in activity level J. fracture repair 1. fracture hematoma 2. fibrocartilage callus 3. bony callus - cartilage is replaced by spongy bone 4. remodeling Strong/Fall 2008 page 6