Cartilage and Bone PDF

Cartilage and bone Jean-Pierre Louboutin 10/9/2024 + Cartilage - Definition - Cartilage cells - Cartilage matrix - Perichondrium - 3 types of cartilages:. hyaline. elastic. fibrous + Bone - Definition - 2 types of bones :. compact. cancellous (spongy) - Bone cells - Bone matrix - Proces...

Cartilage and bone Jean-Pierre Louboutin 10/9/2024 + Cartilage - Definition - Cartilage cells - Cartilage matrix - Perichondrium - 3 types of cartilages:. hyaline. elastic. fibrous + Bone - Definition - 2 types of bones :. compact. cancellous (spongy) - Bone cells - Bone matrix - Process of bone formation: ossification + Endochondral ossification. primary center of ossification. secondary (epiphyseal) center of ossification + Intramembranous ossification Cartilage + Cartilage - Definition - Cartilage cells - Cartilage matrix - Perichondrium - 3 types of cartilages:. hyaline. elastic. fibrous cartilage + Bone - Definition - 2 types of bones :. compact. cancellous (spongy) - Bone cells - Bone matrix - Process of bone formation: ossification + Endochondral ossification. primary center of ossification. secondary (epiphyseal) center of ossification + Intramembranous ossification  Definitions - Special form of connective tissue - Develops from mesenchyme and consists of cells, extracellular matrix composed of connective tissue and ground substance - Avascular, gets nutrients via diffusion through ground substance - Exhibits tensile strength, resilient to compression and provides firm structural support for soft tissues - Cells: chondrocytes and chondroblasts - Three types of cartilage classified upon the amount and type of fibers present in the extracellular matrix: + hyaline + elastic + fibrocartilage Different types of cartilages  Cartilage cells - Primitive mesenchyme cells differentiate into chondroblasts that synthesize the matrix - Mature cartilage cells (chondrocytes) become enclosed and trapped in lacunae - Inner layer of surrounding connective tissue (perichondrium) is chondrogenic  Chondrogenesis A: Mesenchyme: precursor of all types of cartilages B: Mitosis and early differentiation give chondroblasts C: Chondroblasts produce extracellular matrix and are separated from each other D: Multiplication of chondroblasts give rise to isogenous cell aggregates  Cartilage matrix - Produced and maintained by chondroblasts and chondrocytes - Extracellular ground substance contains hyaluronic acid and sulfated glycosaminoglycans (GAGs) and proteoglycans - Highly hydrated - Varying proportions of collagen (I or II) and elastic fibers characterize cartilage as hyaline (II), elastic (II) or fibrocartilage (I) - Collagen and elastic fibers give cartilage matrix its firmness - Semirigid tissue that can act as shock absorber  Perichondrium - Most of hyaline and elastic cartilage is surrounded by a peripheral layer of vascularized, dense irregular connective tissue, called perichondrium - Perichondrium has two layers: + Outer (external) fibrous layer contains type I collagen fibers and fibroblasts + Inner (internal) layer is cellular and chondrogenic - Chondrogenic cells form the chondroblasts that secrete the cartilage matrix - Fibrocartilage and hyaline cartilage on the articulating surfaces of bones are not lined by perichondrium Developing fetal hyaline cartilage + Cartilage - Definition - Cartilage cells - Cartilage matrix - Perichondrium - 3 types of cartilages:. hyaline. elastic. fibrous cartilage + Bone - Definition - 2 types of bones :. compact. cancellous (spongy) - Bone cells - Bone matrix - Process of bone formation: ossification + Endochondral ossification. primary center of ossification. secondary (epiphyseal) center of ossification + Intramembranous ossification  Types of cartilage Hyaline cartilage - Most common type - In embryos, hyaline cartilage: skeletal (or cartilage) model for bone - During growth, cartilage bone model progressively replaced with bone by a process called endochondral ossification - In adults, most of hyaline cartilage has been replaced with bone - Exceptions: articular surfaces of bones, end of ribs, larynx, nose, trachea, bronchi, where it persists throughout life without calcification - Matrix of hyaline cartilage: type II collagen fibers embedded in a firm amorphous hydrated extracellular matrix rich in proteoglycans and glycoproteins - In addition, chondronectin is an adhesive glycoprotein that binds to glycosaminoglycans and collagen fibers, providing adherence of chondroblasts and chondrocytes to collagen - Perichondrium with fibroblasts surround the cartilage - Inner chondrogenic layer produces chondroblasts differentiating into chondrocytes - Chondrocytes (whose function is to maintain cartilage) are trapped in compartments called lacunae - Some lacunae can contain isolated chondrocytes or more than one (isogenous groups)- Two types of matrix between lacunae: territorial and interterritorial - Interterritorial (intercellular) matrix (1) stains lighter than the territorial matrix (around the lacunae) (2) Chondrocytes Interterritorial Interterritorial - Isolated matrix Chondrocytes matrix - Isogenous groups Trachea 1 2 2 1 Lacunae Perichondrium Inner Lacunae Perichondrium with fibroblasts chondrogenic layer with fibroblasts Trachea Hyaline cartilage (high magnification) Hyaline cartilage (trachea) Cells and matrix of mature hyaline cartilage Hyaline cartilage Hyaline cartilage P: perichondrium; C: chondrocytes; P: perichondrium; C: chondrocytes; M: matrix M: matrix Hyaline cartilage (trachea)  Elastic cartilage - Elastic cartilage is similar to hyaline cartilage except for the presence of numerous elastic fibers within the matrix. Collagen type II - Elastic cartilage is very flexible - Examples: epiglottis, external ear, walls of the auditory tube - Larger chondrocytes in lacunae are more prevalent in the interior of the plate - Smaller and flatter chondrocytes are located peripherally in the inner chondrogenic layer of perichondrium A: Chondrocytes contained in lacunae (C) C: Lacunae B: Matrix rich in elastic fibers C A B Elastic cartilage: epiglottis (Silver staining) Elastic cartilage: epiglottis (Silver staining) Elastic cartilage: pinna (Verhoeff staining for elastin)  Fibrous cartilage - Matrix filled with irregular and dense bundles of type I collagen fibers - Small chondrocytes in lacunae usually distributed in rows rather than in isogenous groups - Chondrocytes can be rare - No perichondrium - Alternating layers of cartilage matrix and dense layers of type I collagen fibers - Collagen fibers orient themselves in the direction of functional stress - Examples: intervertebral disks, symphysis pubis, certain joints  Lacunae Collagen fibers Chondrocytes Distribution of the chondrocytes in rows Fibrous cartilage: intervertebral disk Bone  Dance of Death, Lubeck, 14th century Ankou, Kapala cup, Brittany, Tibet, ? 18th century Catacombs, Paris, 18th century Crystal skull, Mayan tzompantli, Chichen Itza, British museum, Mexico, 10th century 19th century + Cartilage - Definition - Cartilage cells - Cartilage matrix - Perichondrium - 3 types of cartilages:. hyaline. elastic. fibrous cartilage + Bone - Definition - 2 types of bones :. compact. cancellous (spongy) - Bone cells - Bone matrix - Process of bone formation: ossification + Endochondral ossification. primary center of ossification. secondary (epiphyseal) center of ossification + Intramembranous ossification  Definition - Bone is a special form of connective tissue - Composed of cells, fibers and extracellular matrix - Bones become calcified because of mineral deposition in the matrix - They become hard and can bear more weight than cartilage - They are the rigid skeleton of the body - Provide attachment sites for muscles and organs - Protect the brain in the skull, heart and lung in the thorax, urinary and reproductive organs between the pelvic bones - Role in hematopoiesis (i.e., hematopoietic stem cells) - Reservoir of calcium, phosphate and other minerals  Bone types Trabeculae - Two types of bone: + compact bone + cancellous (spongy or trabecular) bone - In long bones, outer cylindrical part is the dense compact bone 1 - Inner surface of compact bone adjacent to the marrow cavity is the cancellous 2 (spongy or trabecular) bone - Cancellous bone is not dense and contains numerous interconnecting areas - Periosteum: membrane that lines the outer surface of all bones (1). Endosteum lines Compact Cancellous the inner surface of all bones (2) bone bone - In newborns, marrow cavities of long bones are red and produce blood cells. In adults, these cavities are yellow and filled with fat cells  Compact bone - In compact bone, collagen fibers arranged in thin layers of bone: lamellae parallel to each other in the periphery of the bone, or concentrically arranged around a canal - Concentric lamellae surrounding the canals containing blood vessels, nerves and loose connective tissue are called the osteons (Haversian systems) - Space in the osteon containing the blood vessels and nerves is the central (Haversian) canal - Most of the compact bone consists of osteons - Lacunae contain osteocytes Section of osteon - In a long bone, the outer (external) circumferential lamellae close to the periosteum. Inner circumferential lamellae surround the bone marrow cavity Blood vessels in Haversian canal Lacunae with osteocyte inside Concentric lamellae Marrow cavity Cancellous bone Compact bone  - Each osteon consist of layers of concentric lamellae arranged around a central (Haversian) canal containing vessels and nerves - Lamellae contain osteocytes in spaces called lacunae - External circumferential lamellae form the external wall of a compact bone (beneath the periosteum) - Interstitial lamellae are located between osteons Low magnification High magnification - Lamellae contain osteocytes in spaces called lacunae - Radiating from each lacuna are tiny canals: canaliculi - Canaliculi penetrate the lamellae, anastomose with the canaliculi from other lacunae and form a network of communicating channels with other osteocytes. Some canaliculi open direcly into central canal - Anastomoses between central canals are called perforating (Volkmann’s) canals Lacunae Central canal Osteon Dry, compact bone (transverse section) Dry, compact bone (longitudinal section)  Dry, compact bone: an osteon (transverse section) CC: central canal; L: concentric lamellae; O: osteocytes; C: canaliculi Osteon (transverse section) P: Volkmann’s canals  Cancellous (spongy or trabecular) bone - Consists primarily of slender bone trabeculae (1) that enclose irregular marrow cavities with blood vessels - Bone trabeculae can merge with compact bone containing primitive osteon or mature osteon - Osteocytes (2) visible in lacunae in trabeculae 1 - Between bone trabeculae: marrow cavities with blood vessels and 3 hematopoietic tissue giving rise to new 2 blood cells (3) 4 - Lining the bone trabeculae in the 3 marrow cavities: thin layer of cells called endosteum. Cells in periosteum and endosteum give rise to bone- forming osteoblasts Cancellous bone with trabeculae and bone marrow cavities: sternum (transverse section) Cancellous bone: sternum (transverse section)  Bone cells + Osteoprogenitor cells are pluripotential, undifferentiated, stem cells derived from the connective tissue mesenchyme - Located in the inner layer of the periosteum and internal endosteum that lines the marrow cavities - During bone development, osteoprogenitor cells proliferate and differentiate into osteoblasts - Differentiation depends on gene called Wnt: if Wnt signaling high in mesenchyme: osteoblasts are formed, if Wnt low: chondrocytes are formed + Osteoblasts are present on the surfaces of bone - They synthesize, secrete and deposit osteoid, the organic component of the new bone matrix - Osteoid is uncalcified and does not contain any minerals. Shortly after its deposition, it is mineralized and becomes bone + Osteocytes: mature form of osteoblasts - Smaller than osteoblasts. Trapped in lacunae. Maintain homeostasis of bone and blood concentrations of calcium and phosphate - Mineralized bone matrix is much harder than cartilage, so nutrients and metabolites cannot freely diffuse through it to the osteocytes. There is a unique system of channels called canaliculi which open in the osteons. The canaliculi keep the osteocytes alive by bringing nutrients to the osteocytes and allow gaseous exchanges  Osteocytes in lacunae a. Transmission electron microscopy showing osteocyte in lacuna with canaliculi (C) b and c. Picture showing communications between lacunae through canaliculi (C) + Osteoclasts : multinucleated cells found along bone surfaces where resorption (removal), remodeling and repair of bone take place - Osteoclasts belong to the macrophage-mononuclear monocyte cell line. They begin to digest the bone matrix and form a depression, called a Howship’s lacunae Osteoclast (Ocl) digesting bone matrix (B). Osteocyte (Oc) seen in lacuna  Osteoblasts, osteocytes and osteoclasts Ob: osteoblasts; Oc: osteocytes; Ocl: osteoclasts; B: bone matrix; M: mesenchyme; O: osteoid  Bone matrix - Consists of collagen fibers (90% of the organic substance) and ground substance - Collagen type I: dominant form of collagen form in the bone - Inorganic component of bone matrix: calcium and phosphate in the form of hydroxyapatite crystals - Hardness of the matrix due to its content of inorganic salts (hydroxyapatite) that become deposited between collagen fibers - Calcification begins few days after the deposition of organic bone substance (or osteoid) by the osteoblasts - Osteoblasts are capable of producing high local concentration of calcium phosphate in the extracellular space, which precipitates on the collagen molecules - 75% of the hydroxyapatite is deposited in the first few days of the process, but complete calcification may take several months + Cartilage - Definition - Cartilage cells - Cartilage matrix - Perichondrium - 3 types of cartilages:. hyaline. elastic. fibrous cartilage + Bone - Definition - 2 types of bones :. compact. cancellous (spongy) - Bone cells - Bone matrix - Process of bone formation: ossification - Endochondral ossification. primary center of ossification. secondary (epiphyseal) center of ossification - Intramembranous ossification  Process of bone formation: ossification - Bone development begins in the embryo by 2 different processes: + Endochondral ossification. Primary ossification center. Secondary ossification center + Intramembranous ossification - Bones exhibit the same structure whatever the process of ossification - Ossification starts in clavicle at 6.5 weeks post conception, then mandible and maxilla - 8 weeks: ossification of humerus, radius, then femur, tibia, ulna - 9 weeks: ossification of vertebral bodies, then frontal, zygomatic, squamous temporal bones - Birth: most of long bones show ossification at center of body, but most ends are still cartilaginous  Endochondral ossification Primary ossification center - Used to form short and long bones - Temporary hyaline cartilage model precedes bone formation, followed by proliferation of chondrocytes - Chondrocytes divide, hypertrophy and mature and the hyaline cartilage model begins to calcify: zone of hypertrophy and calcification - As calcification of the cartilage model continues, diffusion of nutrients and gases through the calcified matrix decreases - As a consequence, chondrocytes die and the calcified matrix serves as a structural framework/scaffold for the deposition of bony material - External surrounding connective tissue is called the periosteum - Mesenchymal cells cells from the inner layer of periosteum differentiate into osteoprogenitor cells, and blood vessels from the periosteum invade the calcified degenerating cartilage model. Red bone marrow cavity is formed - Whole new area: Zone of ossification Endochondral ossification: development of a long bone (panoramic view, longitudinal section)  Zone of ossification Zone of chondro- Zone of prolifera- Zone of reserve cyte hypertrophy ting chondrocytes cartilage and calcification of cartilage cavity matrix Plates of in lacunae Periosteum (surrounding Chondrocytes Perichondrium Red bone marrow connective tissue) calcified cartilage Endochondral ossification: zone of ossification  - Cartilage matrix becomes calcified in Zone of reserve zone of calcified cartilage and cartilage chondrocytes die - Only remaining tissue is calcified cartilage matrix - Blood sinusoids invade calcifying cyte hypertrophy ting chondrocytes cartilage that becomes eroded; Zone of chondro- Zone of prolifera- red bone marrow cavity is formed - Osteoprogenitor cells from inner periosteum differentiate into osteoblasts - Osteoblasts then invade the area (with and calcification blood vessels) and begin to lay bone on of cartilage the calcified cartilage matrix (purple matrix at the bottom) which is beginning to be invaded by osteoblasts. This forms the first bone spicules Bone spicule - Osteoprogenitor cells proliferate and differentiate into osteoblasts that secrete the osteoid matrix - Osteoblasts deposit osteoid and bone around the remaining plates of calcified cartilage and form the periosteal bone collar - Formation of new periosteal bone keeps pace with the formation of new endochondral bone - Osteoblasts then surrounded by bone in the lacunae and are now called osteocytes (one osteocyte per lacuna) - Red bone marrow fills the cavity of newly formed bone with hematopoietic cells - Numerous cells (erythrocytes, megakaryocytes, granulocytes) as well as bony spicules and blood vessels are found in the bone marrow Endochondral ossification: zone of ossification - Remnants of calcified cartilage matrix (dark purple) appear covered by light- stained bone tissue - Newly formed bone surrounded by osteoblasts - Osteoblasts synthesize osteoid matrix - Some osteoblasts trapped by the osseous matrix become osteocytes - Osteocytes maintain homeostasis of bone and blood concentrations of calcium and phosphate Osteoblasts Osteocyte - As the spicules form, they also become remodeled, a process which continues as long as bone is living - Remodeling starts with osteoclasts, which are multinucleated cells that have a highly eosinophilic cytoplasm - Osteoclasts belong to the macrophage- mononuclear monocyte cell line Bony spicules - They are responsible for resorption (removal) of bone and repair - They begin to digest the bone matrix and as they do, they form a depression, called a Howship's lacuna - The osteoblasts then take over and lay down new bone in the direction of the remodeling - Thus, bone can be remodeled to withstand stresses, exercise, etc. - Hormones regulate calcium release and its deposition in bones - When calcium level falls below normal, parathyroid hormone (PTH) released from the parathyroid glands stimulates osteoclasts to resorb bone matrix, releasing more calcium in the blood - When calcium level is above normal, calcitonin, released by the parafollicular cells of the thyroid gland inhibits osteoclast activity and decreases bone resorption Calcium stained by Alizarin Red S (orange) in finger of newborn Calcium deposit (black) during endochondral ossification. Staining of calcium by Von Kossa staining Calcium deposit (black) during endochondral ossification. Staining of calcium by Von Kossa staining  Formation of osteons - Vascular tufts of connective tissue from periosteum invade bone, forming primitive osteons - Bone reconstruction and remodeling will continue as initial osteons , then later ones are broken down and replaced by new ones - Primitive osteons present a large central canal surrounded by a few concentric lamellae - Central canals contain primitive osteogenic connective tissue and blood vessels - Bone formation continues in some of the osteons: osteoblasts are present around central canals Formation of osteons Bone formation: primitive bone marrow and development of osteons  Secondary ossification center - Mesenchyme tissue, osteoblasts and blood vessels form a primary ossification center in the developing bone that first appears in the diaphysis (shaft of the long bone) followed by a secondary ossification center in the epiphysis (articular surface of the expanded end) - In all developing long bones, cartilage in the diaphysis and epiphysis is replaced by bone, except in the epiphyseal plate region, located between the diaphysis and epiphysis - Growth in this region continues and is responsible for lenghtening the bone until bone growth stops - Expansion of the 2 ossification centers eventually replaces all cartilage with bone, including the epiphyseal plate - Only exceptions: articulating ends of long bones where a layer of permanent cartilage covers the bone: articular cartilage  - Epiphyseal plate is seen between primary and secondary ossification centers - Proliferating chondrocytes (1) and zone of chondrocytes hypertrophy and calcification of cartilage (2) seen in the epiphyseal plate - Spicules of calcified cartilage (3) and primitive bone marrow cavities are seen in the shaft of the bone (4) and secondary center of ossification (5) Spicules of calcified cartilage Epiphyseal Secondary center Epiphysis of ossification 5 Epiphyseal plate Diaphysis plate 1 2 3 4 Formation of secondary (epiphyseal) centers of ossification Endochondral ossification: formation of secondary (epiphyseal) centers of ossification and epiphyseal plate in long bone (longitudinal section) Endochondral ossification illustrating the progressive stages of bone formation from a cartilage model to bone  Intramembranous ossification - In intramembranous ossification, bone development is not preceded by a cartilage model - Bone develops from the connective tissue mesenchyme - Some mesenchymal cells differentiate directly into osteoblasts that produce the surrounding osteoid matrix which quickly calcifies - Numerous ossification centers are formed. They anastomose and produce a network of spongy bone that consists of plates, thin rods, and spines called trabeculae - Osteoblasts then become surrounded by bone lacunae and become osteocytes. They establish a complex cell-to-cell connection through the canaliculi - Examples: clavicles, maxilla, mandible, and most of the flat bones of the skull - In developing skull, centers of bone development grow radially, replace the connective tissue and then fuse. In newborns, the fontanelles in the skull represent the soft membranous regions where intramembranous ossifications of skull bones is in the process of ossification  Intramembranous ossification Blood vessels Developing Continuity of periosteum osteoblasts from with marrow cavity periosteum Connective tissue Trabeculae Osteoblasts of bone Osteocytes Vessel Marrow cavity Intramembranous ossification Intramembranous ossification: developing mandible Intramembranous ossification: developing skull bone Intramembranous ossification: developing skull bone  Disorders of the skeleton + Disorders of bone development - Rickets in children and osteomalacia in adults - Bone poorly calcified and growth plates fail to calcify - Bone weakness due to dietary vitamin D deficiency, lack of exposure of the skin to ultraviolet light, , or both + Osteoporosis - Low bone-mineral density - Common in elderly of both genders- More frequent in women - Related to decline in estrogen level, which inhbits bone resorption by osteoclasts + Rheumatoid arthritis - Chronic inflammation of joints - Involves synovial membrane - May be due to autoimmune reaction Ex-vivo gene transfer in bone marrow stem cells Ex-vivo gene transfer in bone marrow stem cells Carl June, UPenn Potential approach for delivering therapeutic gene in hereditary blood disorders (e.g., Fanconi anemia, sickle cell disease) or HIV-positive patients or improving bone marrow transplantation or delivering stem cells to injured organs Targeting of bone marrow (BM) stem cells in vivo by direct injection into the femoral cavity - Using a viral vector carrying a transgene - Following the distribution of BM stem cells in the body by studying transgene expression Virus BM stem cells Transgene Study of the distribution of the transgene in the body Migration of BM stem cells ?  IN VIVO SV(RNAIR5-REVM10.AU1) GENE TRANSFER TO HEMATOPOIETIC STEM CELLS (HSCS) LEADS TO DOWN- REGULATION OF CCR5 IN PBMC OF RABBITS MOCK SV(RNAiR5-RevM10.AU1) OVERLAY TD CCR5+ MOCK CCR5+ 26 weeks expression of CCR5 in PBMC of rabbits 30 M TD2 TD3 TD4 25 CCR5 % of CCR5 expression 20 56 15 mock TD weeks 10 GAPDH 5 0 RT-PCR 0 5 10 15 20 25 30 35 40 45 50 55 60 weeks after injection  Oxidative stress Platelets activation CD55, CD59 - Complement cascade Fibrinolytic cascade Coagulation cascade HO-1 Innate immunity-Defensins + Osteoblasts, Endothelial - cells - SP1, CP1 ADM3100 SDF-1-CXCR4 - HSCs + Cytokines Peripheral - Growth G-CSF factors blood + α4β1 integrin-VCAM-1 Stress - Organ injury Inflammation Complement cascade Exercise Fibrinolytic cascade Drugs Coagulation cascade Innate immunity-Defensins Factors influencing migration of hematopoietic stem cells (HSCs) from bone marrow to peripheral blood  Objectives + Cartilage - To Know definitions, cell types and extracellular matrix - To know different types of cartilages + Bone - To know definitions - To know differences between compact and cancellous bone - To know different bone cells and bone matrix - To know different types of ossifications and cells involved