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58 Cards in this Set
- Front
- Back
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What is cartilage?
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Specialized CT with firm extracellular matrix, allows tissue to bear mechanical stresses w/o distortion
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What is the main fxn of cartilage?
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Support soft tissue
Essential for development of growth of long bones before and after birth Provides shock absorbing and sliding area for joints |
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What are chondrocytes?
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Cells of cartilage located in matrix cavities called lacunae
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What does the extracellular matrix primarily consist of?
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Collagen
Hyaluronic acid Proteoglycans Glycoproteins |
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Elastic cartilage contains significant amounts of what?
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Elastin
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How is cartilage nourished?
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It is avascular and nourished by diffusion
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Describe the CT sheath of cartilage
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Called perichondrium
Dense Contains vascular supply for cartilage |
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What is unique to articular cartilage?
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Has no perichondrium and is sustained by synovial fluid
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What are the 3 types of cartilage?
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1) Hyaline
2) Elastic 3) Fibrocartilage |
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What are the general characteristics of hyaline cartilage?
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Most common
Temporary skeleton Epiphyseal plate component Located in articular surfaces, respiratory passages, and others |
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Describe the matrix of hyaline cartilage
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Type II collagen interacting with proteoglycans
Highly hydrated Matrix immediately surrounding each chondrocyte stains deeply basophilic and is called territorial matrix Next layer of matrix is interterritorial matrix |
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Describe the perichondrium of hyaline cartilage
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Cells of inner perichondrium are chondroblasts which are swollen and actively secreting collagen and ECM components
They differentiate into chondrocytes Outer fibrous layer |
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Describe the chondrocytes of hyaline cartilage
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Usually appear in groups called isogenous groups, result of mitotic division
Surrounded completely by matrix Maintenance fxn |
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What is the histogenesis of hyaline cartilage?
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Chondroblasts differentiate from mesenchymal cells, except in some areas of head
As matrix is synthesized, cells separate Cells become more central in location, developing into chondrocytes Superficial mesenchyme develops into chondroblasts and fibroblasts of perichondrium |
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What are the 2 types of growth of cartilage?
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1) Interstitial growth
2) Appositional growth |
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Describe interstitial growth of cartilage
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From mitotic division of chondrocytes
Occurs only during early phases of cartilage formation and also in epiphyseal plate and articular cartilage |
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Describe appositional growth of cartilage
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Differentiation of perichondrial cells
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What regulates growth of epiphyseal plate chondrocytes?
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Insulin-like growth factor I (IGF-I)- primarily produced in liver in response to GH
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What are some locations of elastic cartilage?
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Auricle of ear, walls of external auditory canal, auditory tube, epiglottis, and cuneiform cartilage
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Describe the matrix of elastic cartilage
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Similar to hyaline, but contains an abundant network of elastic fibers, produced by chondrocytes
Matrix does not calcify |
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Where are some locations of fibrocartilage?
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Intervertebral discs, ligaments, pubic symphysis, some articular discs, tendon insertions, always associated with dense CT
Annulus fibrosus |
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Describe the matrix of fibrocartilage
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Contains type I collagen, so acidophilic
Amorphous matrix is less abundant Arranges in irregular bundles or aligned in parallel along chondrocytes |
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What is unique about the chondrocytes of fibrocartilage?
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Often arranged in long columns
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What are the 4 cell types of bone?
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1) Osteoprogenitor cells
2) Osteocytes 3) Osteoblasts 4) Osteoclasts |
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What purpose does canaliculi of bone serve?
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Metabolites cannot diffuse through calcified matrix so exchange b/w cells and vessels is dependent on these channels
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What are the 2 layers of CT of bone?
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1) Periosteum- outside
2) Endosteum- inside |
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What are some roles of bone?
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1) Support fleshy structures
2) Provide system of levers 3) Protects vital organs 4) Contains bone marrow 5) Site of blood cell formation 6) Source of calcium, phosphate, and other ions |
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Describe osteoprogenitor cells
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Capacity for mitosis and further differentiation and specialization into mature bone cells
Found within innermost layer of periosteum, endosteal lining, and lining of Haversian and Volkman's canals Flat cells with elongated nuclei and inconspicuous cytoplasm Found on surfaces of bone during remodling Stimulation leads to formation of osteoblasts and possibly osteoclasts Derived from mesenchymal cells |
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Describe osteoblasts
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Synthesize the organic components of bone matrix (type I collagen, proteoglycans, glycoproteins) and play important role in calcification
Arrangement resembles epithelium When synthesizing matrix, cells are cuboidal to columnar in shape, basophilic cytoplasm, and high alkaline phosphatase activity Extensive ER, prominent Golgi, and polarization toward bone in active cells Cells flatten and remain bone lining cells when activity decreases Alkaline phosphatase and pyrophosphatase are found in matrix vesicles and liberate phosphate ions from organic phosphate compounds by enzymatic hydrolysis, significant in calcification Osteocalcin binds Ca in matrix, provides for precipitation of calcium ions and cystallization of CaPO4 Have processes which become more evident when surrounded by matrix Lacunae and canaliculi appear b/c matrix is formed around processes Not yet calcified matrix near osteoblast is osteoid- organic component, rich in glycosaminoglycans |
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Describe osteocytes
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Osteoblasts surrounded by bone matrix, lying b/w matrix lamellae
Cell processes make contact forming gap jxns, provides for flow of ions and small molecules, and mechanism for nutrients and metabolites to be passed b/w blood vessels and distant osteocytes Reduced organelles Help maintain matrix and have some resorptive and bone formative fxn |
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Describe osteoclasts
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Large, multinucleated cells that lie in depressions in matrix called resorption pits or Howship's lacunae
Derived from fusion of monocytes Ruffled border, increases resorptive area and allows small particles to be subjected to enzymatic activity Numerous polysomes, some rER, abundant mitochondria, well developed Golgi, and many lysosomes Resorb bone by secreting acid phosphatase, collagenase, and other proteolytic enzymes Calcitonin inhibits resorption by inducing cytoplasmic quiescence and the disappearance of ruffled border |
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What are some roles of PTH in bone formation?
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Stimulates resorption by acting indirectly on osteoclasts
Decreases production of alkaline phosphatase in osteblasts Can stimulate bone formation and has been used in pt treatment |
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What are the two main components of mineralized bone?
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Inorganic salts and organic matrix which makes up 75% of the dry weight of bone
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What are the most abundant substance in bone matrix?
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Calcium and phosphorous form hydroxyapatite crystals and amorphous calcium phosphate
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What forms the majority of the bone matrix?
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The organic matter is 95% type I collagen and ground substance which contain glycosaminoglycans associated with proteins
Glycoproteins are present which bind calcium avidly and may promote calcification of bone matrix |
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What gives bone its hardness?
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Association of hydroxyapatite with collagen fibers
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Describe the periosteum
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Covers external surface of bone
Consists of an outer, fibrous layer of collagen fibers that penetrate the bone matrix and inner cellular layer (osteogenic layer) composed of spindle-shaped osteoprogenitor cells Fibrocytes found in outer layer |
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Describe the endosteum
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Single layer of osteoprogenitor cells lining the marrow and internal cavities
Covering of internal surface of bone |
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What are the two types of bone tissue?
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1) Compact (corticol) bone- dense, without cavities
2) Cancellous (spongy) bone- has interconnecting cavities |
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Describe the anatomy of a long bone
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End is the epiphysis, composed mostly of spongy bone
Cylindrical part is diaphysis, composed mostly of compact bone Contain red marrow- cells are forming- and yellow marrow- fat cells |
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What are the two areas of flat bones?
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1) Two layers of compact bone called plates
2) Separated by layer of spongy bone, diploe |
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What are the two histiological classifications of bone?
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1) Immature, primary, woven or nonlamellar bone (collagen bundles are random)
2) Mature, seconday, or lamellar bone (collagen organized into bone lamellae) |
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Describe primary bone tissue
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First bone tissue to appear during formation
Replaced by secondary bone tissue Irregular array of collagen, reduced mineral content, and more osteocytes than secondary bone |
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Describe secondary bone tissue
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Usually found in adults
Collagen fibers are concentrically arranged in lamellae around a vascular canal Concentric lamellae around a canal is Haversian system or osteon Osteon is main bone structural unit Osteocytes are found b/w and w/in lamellae Lamellae exhibit an organization consisting of haversian systems, outer circumferential lamellae, inner circumferential lamellae, and interstitial lamellae Haversian systems communicates by Volkmann's canals which pass through lamellae |
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What is the cement line?
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Deposit of amorphous material that consists of mineralized matrix w/ few collagen fibers and surround each Haversian system
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What are the two types of histogenesis of bone?
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1) Intramembranous ossification
2) Endochondral (intracartilagenous) ossification |
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Describe intramembranous ossification
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Source of most flat bones
Contributes to growth of short bones and thickening of long bones Takes place w/in mesenchymal tissue Starting point is primary ossification center Group of cells differentriate into osteoblasts which become encapsulated forming osteocytes Islands of bone are spicules which eventually fuse giving bone spongy structure Continuous deposition of bone creates compact bone |
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Describe endochondral ossification
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Takes place within hyaline cartilage
Responsible for formation of short and long bones Consists of two stages |
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Describe the first stage of endochondral ossification
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Associate with hypertrophy of chondrocytes and deposition of calcium salts in matrix b/w lacunae
Formation of calcified cartilage |
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Describe the second stage of endochondral ossification
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Capillaries grow into perichondrium that surrounds middle part of model
Osteoprogenitor cells become osteoblasts that start to lay down a collar of bone Site where periosteal vessels and osteoprogenitor cells grow is periosteal bud or osteogenic bud which eventually replaces most of the cartilage |
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When does an ossification center develop in long bones?
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Toward the end of the second month of gestation
Appears in diaphysis or midsection of bone Two ends are still composed entirely of cartilage |
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At stage of ossification center formation, what 2 things compose developing bone?
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1) Subperiosteal bone collar
2) Decreasing amount of cancellous bone that borders enlarging medullary cavity |
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Describe the development of the secondary ossification center
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Majority formed postnatally
Develops in each cartilagenous epiphysis Secondary growth is radial No bone collar formed here Restricted to two places: articular cartilage and epiphyseal cartilage or epiphyseal plate |
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What are the 5 zones of epiphyseal cartilage?
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Starting at epiphyseal side:
1) Zone of reserve cartilage- moderate-sized chondrocytes and serves to anchor the plate to the bone of the epiphysis 2) Proliferative zone- young chondrocytes dividing rapidly and forming column of stacked cells; produces cells to replace those that die 3) Zone of hypertrophy- large chondrocytes swollen by glycogen, help expand epiphyseal plate and secrete alkaline phosphatase which leads to formation of next zone 4) Zone of calcified cartilage- hyaline matrix becomes increasingly calcified 5) Zone of provisional ossification |
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Describe the zone of provisional ossification
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Primary trabeculae appear, which is primary spongiosa, beginning of metaphysis
Osteoprogenitor cells form osteoblasts which form layers over septa of calcified cartilage matrix Over septa, osteoblasts deposit matrix Bone matrix calcifies, and some osteoblasts become osteocytes Bone spicules formed Most of primary spongiosa converted to secondary spongiosa by simultaneous removal of woven bone and calcified cartilage cores and addition of secondary (lamellar) bone Epiphyseal plate is displaced away from middle of diaphysis, resulting in growth in length of bone |
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What are the two fxns of the zone of provisional ossification?
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1) Drives process of bone elongation
2) Provides scaffolding for construction of cancellous bone w/in metaphysis |
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Describe the mechanisms of calcification
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Contents of matrix vesicles secreted by osteoblasts initiate matrix mineralization
Vesicles can accumulate calcium and contain alkaline phosphatase and pyrophosphatase which cleaves phyrophosphates yielding inorganic phosphate Matrix vesicles accumulate calcium phosphate and after membrane rupture, contents act as nucleation sites for addition of calcium phosphate and other ions, forming hydroxyapatite crystals |
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Describe the synovial membrane
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Diathroses are joints of long bones and have great mobility
Synovial membrane arranged in folds Arrangement is 2-3 cells and are epitheloid Two cell types- secretory and phagocytic Basal lamina not present Secretory cell produces mucin or synovial fluid for lubrication |
