by dbui89


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Properties and functions of Cartilage
Consistency of ECM allows it to bear mechanical stress without permanent distortion. Provides firmness, elasticity, and tensile strength, shock absorbing functions, forms smooth surfaces of synovial joints. Key tissue in fetal skeletal development and most growing bones
Avascular, nutrition is by diffusion, because of this cartilage regenerates very slowly.
Appositional growth
Growth of cartilage from the surface
Intersitial growth
Growth of cartilage from the inside of the cartilage
Perichondrium
Connective tissue capsule covering the perichondrium, composed of dense connective tissue, allows passage for blood/lymph vessels/nerves.
Chondroblast
One of the two main types of cells in the cartilage, found on surface, derived from mesenchymal cells of the perichondrium. Actively secretes cartilage matrix, abundant RER and Golgi. Responsible for appositional growth.
Chondrocytes
One of two main types of cells found in cartilage, are chondroblasts that were embedded in cartilage matrix within lacunae. Specialized cells that maintain the ECM of cartilage. Large, rounded cells, capable of mitosis and responsible for interstitial growth.
Isogenous groups
Cluster of cells caused by chondrocytes undergoing mitosis.
Properties of cartilage ECM
Composed of collagen, GAG's, Proteoglycans, and multiadhesive proteins. 40% of dry weight is collagen type II. Doesn't bundle, forms thin fibrils.
Under microscope, matrix is not uniform. Matrix surrounding lacunae (chondrocytes) have fewer collagen fibrils, richer in GAG's. Called territorial matrix. Stains more intensely because of GAG's. Space in between is called interterritorial matrix. Stains less intensely.
Hyaline cartilage
Principal type of cartilage found in the body. Well-developed perichondrium composed of dense irregular connective tissue. Matrix does not have collagen fibers visible in a light microscope. Chondrocytes often arranged in isogenous groups.
Forms the embryonic skeleton and serves as a template for bony skeleton. Forms articular surfaces of most movable joints, epiphyseal plates, costal cartilages
Elastic cartilage
A type of cartilage, has well-developed perichondrium, matrix has elastic fibers that are visible under light microscope. Does not ossify (cannot be used as a template for bone). Chrondrocytes in large distended lacunae.
Found in ear auricle, external auditory cnal walls. Eustachian tube, and epiglottis.
Fibrocartilage
A type of cartilage, "hybrid" between hyaline cartilage and dense irregular connective tissue. Does not have perichondrium. Matrix has type I and II collagen, visible under light microscope.
Found in intervertebral discs, pubic cartilage, sternoclavicular and temporomandibular join.
Chondrosarcoma
Malignant proliferation of cartilage, can develop in any cartilage, but most common in pelvis, proximal femur, and proximal humerus. Very slow growing.
Characteristics of bone
Type of connective tissue, mineralized ECM, vascular, designed to withstand compression, deformation, and stress, very limited diffusion through tissue.
Compact bone
Forms the outer rigid shell of the bone
Spongy bone
Forms the series of spicules and trabeculae on inner side of compact bone that extends into the marrow cavity.
Marrow cavity
Cavity within the bone filled with reticular (hemopoietic) connective tissue or fat. As we grow older, more of the hemopoietic cells are replaced with fat, causing the regular red marrow to become a discolored yellow marrow.
Periosteum
Dense irregular connective tissue. Has two layers.
External fibrous layer, consists of collagen fibers mostly
Internal osteogenic layer contains osteoprogenitor cells.
Endosteum
Thin layer of connective tissue with osteoprogenitor cells.
Organic matrix of bone
Similar to dense connective tissue, large number of collage type I bundles, little ground substance
Inorganic matrix of bone
Composed mostly of calcium phosphate in hydroxyapatite crystals. Calcium carbonate is also present in small amounts.
Osteoprogenitor cells
Found in periosteum and endosteum, derived from mesenchymal cells. Differentiates into osteoblasts.
Osteoblasts
Nearly identical to osteoprogenitor cells, principle bone-forming cell. Secretes matrix onto surface of the bone (appositional growth). Active osteoblasts are cuboidal cells with basophilic cytoplasm, well defined RER and Golgi. Inactive are squamous.
Found only at boundary between bone and adjacent tissue.
Osteocytes
Osteoblasts that have become trapped in matrix, housed in lacunae. Forms narrow tunnels (canaliculi) in all directions, connecting to adjacent osteocytes, creates a network to provide nutrition. Involved in maintenance of bone and deposition/mobilization of clacium from the matrix.
Osteoclasts
Very large, multinucleated (up to 50) cells. Derived from monocytes in the bone marrow, responsible for resorption of bone.
How does an osteoclast resorb bone?
THe osteoclast attaches to the clear zone of the bone, an actin-rich area. The part of the cell in direct contact is called the ruffled border and contains multiple membrane infoldings. The osteoclast secretes H+, collagenase, and other lysosomal enzymes into the pockets formed by the ruffled border, promoting local digestion of collagen and dissolving the calcium phosphate crystals. The depression in the matrix forms Howship's lacuna.
Osteosarcoma
20% of bone cancers, malignant cells produce osteoid, occur most commonly in teenagers at rites of rapid bone growth (distal femur, proximal tibia, and proximal humerous)
Osteoid osteoma
Small benign tumor in appendicular skeleton or spine, acute night pains
Paget's disease
Enlarged and deformed bones. High osteoclast activity followed by deposition of irregular patches of primary bone.
Primary (woven) bone
Immature type of bone initially laid down, irregular and interwoven collagen fibers.
Secondary (lamellar) bone
Layered collagen fibers, much stronger than primary bone.
Osteon
Primary structural unit of secondary bone, concentric cylindrical structure around a central canal, runs parallel to long axis of bone.
Haversian canal
Canal inside osteon, contains neurovascular bundle surrounded by connective tissue, lined with osteoblasts
Volkmann's canals
Transverse channels, blood vessels and nerves use these canals to travel between Haversian canal.
Intersititial lamellae
Old Haversian canal remnants, destroyed by newly formed osteons.
Outer circumferential lamellae
Outer lamellae of bone surrounding entire bone structure, laid down by osteoblasts from periosteum.
Inner circumferential lamellae
Inner surface of bone, laid down by osteoblasts from endosteum.
Intramembranous ossification
Form of bone development, bone formed directly from connective tissue. Mesenchymal cells differentiate into osteoblasts that initially secrete the bone matrix and network of the primary ossification center. Forms mostly flat bones.
Endochondral ossification
Form of bone development, bone replaces cartilaginous template. Forms mostly long and short bones.
Cartilage model formed, serves as a scaffold, bone forms in the middle of cartilage, blood vessels invade and turn area into periosteum, bony collar formed y intramembranous ossification, chondrocytes die from lack of nutrition, blood vessel and osteoprogenitor cells migrate to degenerating cartilage, differentiate into osteoblasts, begins secreting bone matrix, remodelling replaces calcified cartilage with bone.
Secondary ossification ceters
Located in epiphyses of long bones, forms articular cartilage and epiphyseal growth plate (responsible for bone growth)
Primary ossification centers
Located in diaphysis if a long bone
Zones of the epiphyseal growth plate
Zone of reserve cartilage, contains typical hyaline cartilage and chondrocytes
Zone of proliferation, rapid tissue growth of chondrocytes, large isogenous groups form columns of stacked cells
Zone of hypertrophy, swollen chondrocytes, enlarged lacunae, compressed matrix
Zone of calcification, apoptotic chondrocytes, cartilage matrix calcifies.
Zone of ossification, bone tissue present, synthesized by osteoblasts over calcified cartilage.
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