Unit 1 Topic 4 Flashcards
Hyaline Cartilage
-found in articular surfaces, trachea, larynx, bronchi, epiphyseal plate, costal cartilage, and embryonic skeleton
What percentage of hyaline cartilage is chondrocytes?
-5% is chondrocytes living in launae (where mature cells develop
-Nests: isogenous groups of chondrocytes; represent dividing chondrocytes; more active cells have more basophillic cytoplasm
What percentage of extracellular matrix is in hyaline cartilage?
-95% extracellular matrix which is synthesized by chondrocytes and contains 3 classes of molecules
What 3 classes of molecules are found in extracellular matrix?
-Collagen: primarily type III
-Proteoglycans and GAGS: use aggrecan to collect water
-Multi adhesive proteins: cell matrix interactions
What percentafe of ECM is water and why?
- 60-80% of ECM due to the ability of GAGs to attract water which provides rigidity and flexibility
What is extracellular matrix surrounded by?
-vascular/innervated by perichondrium
-composed of dense connective tissue (type I collagen) containing fibroblasts with chondrogenic cells
Description of Elastic Cartilage
-found in pinna of ear and epiglottis
-high elastic fiber content allows deformation and return to original shape and type II collagen
-surrounded by perichondrium
Description of Fibrocartilage
-found in interverbral disks, pubic symphysis, meniscus of knee joint; intermediate between DRCT and hyaline cartilage
What are some features of fibrocartilage?
-similar to a tendon with chondrocytes
-withstands compression and sheering forces
-Matrix contains type I and type II collagen with different proteoglycans
-Cells include chondrocytes in lacunae and fibroblasts not in lacunae
-no perichondrium
What types of collagen are found in hyaline cartilage?
primarily type II collagen
What type of collagen is found in elastic cartilage?
type II collagen
What types of collagen are found in fibrocartilage?
type I and II
What are the matrix components of hyaline cartilage?
-95% ECM which contains
60-80% water, type III collagen, proteoglycans and GAGS (aggrecan), multiadhesive proteins for cell matrix interactions
What are the matrix components of fibrocartilage?
contains type I and II collagen with different proteoglycans, cells incuding chondrocytes in lacunae and fibroblasts not in lacunae
What types of cartilage has perichondrium?
-Hyaline: has perichondrium
-Elastic: has perichondrium
-Fibrocartilage: no perichondrium
Interstital Cartilage Growth
division of cells and addition of ECM materials form within the cartilage (epiphyseal plate, isogenous groups and active chondrocytes
Appositional Growth
surface growth by addition of new cells and ECM at the perichondrial surface (outside)
Inorganic Components of Bone
~70% containing primarily hydroxyapatite crystals that are deposited on/around collagen fibers
Organic Components of Bone
~30% containing collagen (~90% type I), proteoglycans/GAGs, and non-collagenous proteins
What is the process of bone mineralization?
-Osteoid is secreted as organic ECM including osteocalcin (protein hormone that facilitates Ca2+ binding) and matrix vesicles \
-Ca2+ binds to secreted osteocalcin creating high extracellular Ca2+
-High Calcium stimulates osteoblasts to secrete alkaline phosphatase (ALP), which increases extracellular phosphate (PO4), further increasing extracellular Calcium
-Osteoblasts release matrix vesicles which contain ALP and pyrophosphatase, cleaving phosphate groups from nearby molecule in the matrix
-Calcium phosphate crystals to form
-This initiates matrix mineralization by the formation and deposition of hydroxyapatite crystals
Progenitor Cells
-Derived from mesenchymal cells in the presence pf CBFA1/RUNX2 transcription factor
-Found on external (periosteum) and interal (endosteum) of bone surfaces
-Can differentiate into osteoblast
Osteoblasts
-Differentiated cell secreting organic unmineralized matrix (osteoid) and alkaline phosphatase in membrane-bound vesicles to initiate mineralization
Osteocytes
-Osteoblasts completely trapped in/surrounded by matrix it has secreted
-Reside in lacunae
Osteoclasts
-Large, multinucleated cells that derive from mononuclear hematopoietic cells under the influence of RANK-RANKL signaling and dissolve bone matrix
-Found in the endosteum, and periosteum, and on internal surface of bone in indentations called Howship’s lacunae
-Ruffled border with microvilli-type structures that increase Surface Area for exocytosis of hydrolytic enzymes and secretion of protons
-The acidic microenvironment facilitates hydroxyapatite crystal breakdown
-Lysosomal enzymes and metalloproteinases break down organic matrix components
Intramembranous Ossification
-formation of bone from a connective tissue sheath
-Condensation of embryonic and differentiation of mesenchymal cells into osteoprogenitor cell with further differentiation into osteoblasts
-Matrix mineralizes as bony spicules form and unite to form spongy bone trabeulae and eventually compact bone forms on the periphery
Endochondral Ossification
erosion of hyaline cartilage model and replacement with bone
What is the sequence of endochondral ossification?
-Development of hyaline cartilage model
-Growth of cartilage model.Formation of the bone collar on diaphysis by intramembranous ossification. Chondrocyte hypertrophy and calcification of diaphysis
-Developmental of primary ossification center in diaphysis. Vascular invasion in this region. Chondrocytes undergo hypertrophy and calcify their matrix. Bone tissue replaces calcified cartilage
-Development of the medullary cavity: Bone breakdown by osteoclasts forms the medullary cavity
-Development of secondary ossification centers : These occur in the epiphysis of the bone. Same process of bone replacing calcified cartilage
-Formation of articular cartilage and epiphyseal plate: Both structures consist of hyaline cartilage
Zone of Reserve Cartilage
no cell division or active matrix production
Zone of Proliferation
cells divide and organize into distinct columns and actively produce type II and type IX collagen along with other matrix proteins
Zone of Hypertrophy
cells enlarge/accumulate glycogen. VEGF is released (which initiates vascular invasion) and production of type X collagen (serves as a scaffold for hypertrophied cartilage) increases. The matrix is compressed into linear bands between columns of hypertrophied cartilage cells that secrete alkaline phosphatase, initiating calcification
Zone of Calcification
hypertrophied cells undergo apoptosis while matrix calcification increases
Zone of Resorption/Vascular Invasion
small blood vessels invade, carrying osteoprogenitor cells from the perichondrium on their surface. These cells differentiate into osteoblasts and deposit osteoid on the surface of the cartilage spicules. Cartilage matrix is resorbed and more osteoid is deposited. Osteoblasrs become trapped in mineralized bone matrix, converting them to osteocytes. This primary bone is then remodeled by osteoclasrs into compact or spongy bone
What is a mixed spicule?
calcified cartilage matrix and bone
