Chapter 6 Cartilage and Bone

Functions of cartilage Support soft tissue keep trachea open cushions vertebrae Provide soft, gliding surface at articulations (joints) Provides model for formation of new bone Comes in 3 types hyaline cartilage fibrocartilage elastic cartilage

Supporting connective tissue Cartilage and bone are considered connective tissue protect and support soft body tissues Cartilage has firm, gel-like extracellular matrix protein fibers and ground substance chondrocytes are mature cartilage cells sit in spaces called lacunae (sing. lacuna) collagen fibers give strength; stronger than other connective tissue elastic fibers give resilience avascular (nutrients absorbed by diffusion)

Hyaline cartilage Table 4.11a-1 Chondrocytes (cartilage cells) sit in lacunae (sing. lacuna) Think of the lacuna as a pocket. The chondrocyte sits in the pocket. Dividing chondrocytes often seen sharing lacuna Extracellular matrix surrounds cells Collagen fibers are very fine; can’t be seen in microscope Lacuna Chondrocyte Extracellular matrix LM 250x

Growth of cartilage Interstitial growth happens within cartilage chondrocyte in lacuna undergoes mitosis now two cells in one lacuna cells called chondroblasts chondroblasts secrete cartilage matrix, get pushed apart lacuna forms around each cell, now called a chondrocyte Happens widely during embryonic development, less as cartilage matures

© The McGraw-Hill Companies, Inc./Photos by Dr. Alvin Telser Fig. 6.2a Interstitial Growth Chondrocyte in lacuna Hyaline cartilage LM 320x 1. Chondrocyte starts to undergo mitosis Lacuna Chondrocyte Cartilage matrix 2. Two chondroblasts occupy one lacuna. Chondroblast Chondroblast Lacuna © The McGraw-Hill Companies, Inc./Photos by Dr. Alvin Telser 6

© The McGraw-Hill Companies, Inc./Photos by Dr. Alvin Telser Fig. 6.2a 3. Chondroblasts produce new matrix, begin to separate. Separate cells called chondrocytes Interstitial Growth Hyaline cartilage New matrix Lacuna Lacuna 1. Chondrocyte starts to undergo mitosis Chondrocyte Chondrocyte Lacuna 4. Cartilage continues to grow internally; chondrocytes produce matrix. Chondrocyte Cartilage matrix New matrix Chondrocyte 2. Two chondroblasts occupy one lacuna. Chondroblast Chondroblast Lacuna © The McGraw-Hill Companies, Inc./Photos by Dr. Alvin Telser 7

Growth of cartilage Appositional growth happens at edges of cartilage stem cells in perichondrium divide, create chondroblasts new chondroblasts start to secrete cartilage matrix new cells push apart, each forms own lacuna

Appositional Growth Perichondrium Matrix Hyaline cartilage Chondrocyte Fig. 6.2b Appositional Growth Matrix Hyaline cartilage Chondrocyte in lacuna LM 320x 1 Stem cells within perichondrium do mitosis Mesenchymal cells Dividing undifferentiated stem cell Perichondrium New cartilage matrix Older cartilage 9

Perichondrium Fig. 6.2b Matrix Hyaline cartilage Appositional Growth Chondrocyte in lacuna LM 320x New undifferentiated stem cells and committed cells that differentiate into chondroblasts are formed. New matrix formed at periphery 2 Undifferentiated stem cells Committed cells differentiating into chondroblasts New cartilage matrix Chondroblast secreting new matrix Older cartilage matrix 10

Perichondrium Fig. 6.2b Matrix Chondrocyte in lacuna Hyaline cartilage Appositional Growth 3 Chondroblasts push apart and become chondrocytes, produce more matrix at periphery Perichondrium Undifferentiated stem cells Chondrocyte secreting new matrix New cartilage matrix Mature chondrocyte Older cartilage matrix 11

Endosteum Osteoprogenitor cell is stem cell Fig. 6.5 (b) Endosteum Osteoprogenitor cell Osteoprogenitor cell is stem cell mitosis creates another stem cell and “committed cell” Osteoblasts secrete osteoid bone matrix later calcium deposits harden osteoid osteoblasts become trapped in bone matrix, become osteocytes Periosteum Osteoblasts Endosteum Compact bone Endosteum Osteoclast Nuclei Bone matrix Canaliculi Osteocyte in lacuna Osteoid Copyright © McGraw-Hill Education. Permission required for reproduction or display. 12

Endosteum Osteoclasts reabsorb bone matrix Fig. 6.5 (b) Endosteum Osteoprogenitor cell Osteoclasts reabsorb bone matrix derived from marrow cells usually located in pit or depression called resorption lacuna free calcium and potassium for use elsewhere in the body (osteolysis) clean up damaged bone Osteoclasts remove bone, osteoblasts replace it Periosteum Osteoblasts Endosteum Compact bone Endosteum Osteoclast Nuclei Bone matrix Canaliculi Osteocyte in lacuna Osteoid Copyright © McGraw-Hill Education. Permission required for reproduction or display. 13

Page 154 Paget’s disease of bone Copyright © McGraw-Hill Education. Permission required for reproduction or display. Paget’s disease of bone Excessive osteoclast activity osteoclasts are too large and too active, remove too much bone Osteoblasts replace lost bone New bone structurally unstable more susceptible to deformation and fractures X-ray of a skull with osteitis deformans. White arrows indicate areas of excessive bone deposition. © Science Source 14

Osteocytes Osteocytes in lacunae in matrix maintain bone matrix send information about stress on bone communicate with each other through canaliculi in spongy bone, osteocytes not in osteons

Parts of long bones outside of bone lined with periosteum Fig. 6.4 Parts of long bones Proximal epiphysis Metaphysis outside of bone lined with periosteum dense irregular connective tissue same tissue found where else? outer layer is fibrous inner layer is cellular perforating fibers anchor periosteum to bone Periosteum Perforating fibers Diaphysis Metaphysis Distal epiphysis 16

Periosteum Protects bone (a) Periosteum Periosteum Fig. 6.5 Circumferential lamellae Perforating fibers Periosteum Fibrous layer Protects bone provides stem cells for bone width growth and fracture repair Cellular layer Canaliculi Osteocyte in lacuna Periosteum Compact bone Endosteum Copyright © McGraw-Hill Education. Permission required for reproduction or display. 17

Case Study: Achondroplasia Matt is a toddler who does not appear to be developing normally Mentally he is normal, but he is very small. His head size is normal, but his arms and legs are very short and don’t appear to be growing normally

Ossification AKA osteogenesis formation and development of bone Intramembranous ossification produces flat bones of skull, some facial bones, part of clavicle osteoid from osteoblasts becomes calcified bone slowly becomes more organized, osteoblasts captured in matrix

Fig. 6.10 Intramembrous Ossification Flat bone of skull 1. Ossification centers form within thickened regions of mesenchyme. Collagen fiber Ossification center Osteoblast Osteoid Mesenchymal cell 20

Fig. 6.10 Intramembrane Ossification Osteoid Osteocyte Osteoblast Newly calcified bone matrix 2. Osteoid undergoes calcification. 21

Fig. 6.10 Intramembrous Ossification Mesenchyme condensing to form the periosteum Blood vessel Trabecula of woven bone 3. Woven bone and surrounding periosteum form. 22

Fig. 6.10 Intramembrous Ossification 4. Lamellar bone replaces woven bone, as compact and spongy bone form. Periosteum Compact bone Lamellar bone Spongy bone 23

Spongy bone Periosteum Flat bone of skull Compact bone Fig. 6.7 24

Ossification Endochondral ossification produces most bones of skeleton chondroblasts secrete cartilage matrix chondrocytes trapped within matrix die, leaves holes in matrix cartilage matrix is calcified osteoblasts lay down calcium phosphate matrix, get trapped in matrix, etc. process continues until growth is complete (teenage years)

Endochondral Ossification Epiphyseal blood vessel capillaries Deteriorating cartilage matrix Developing periosteum Perichondrium Epiphyseal plate Articular cartilage Spongy bone Epiphyseal line (remnant of epiphyseal plate) Compact Medullary cavity Periosteum compact Secondary ossification centers plate Calcified cartilage Blood vessel of periosteal bud Primary center Hyaline Periosteal bone collar Spongy bone Articular cartilage Fig. 6.11 26

proliferating cartilage Fig. 6.12 Epiphyseal plates (b) X-ray of a hand Zone 1: Zone of resting cartilage Zone 2: Zone of proliferating cartilage Zone 3: Zone of hypertrophic cartilage Zone 4: Zone of calcified cartilage Zone 5: Zone of ossification (a) Epiphyseal plate Epiphyses Diaphysis Diaphyses LM 70x 27

Page 160 Epiphyseal plates When a person is growing, epiphysis and diaphysis are separate pieces When bones stop growing longer, cartilage section calcifies, unites epiphysis and diaphysis (Left) the epiphyses are partially fused; likely age 15 to 23 (Right) No fusion; likely younger than 15 years of age. Copyright © McGraw-Hill Education. Permission required for reproduction or display. © David Hunt/Smithsonian Institution 28

Long bone development Fig. 6.13 Bone deposited by osteoblasts Bone resorbed by osteoclasts Adult Young adult Child Infant Growth in length is interstitial growth Growth in width is appositional growth does not require cartilage matrix osteoblasts created by cells in periosteum 29

Case Study: Achondroplasia What if the body doesn’t produce cartilage correctly? Flat bones of head develop normally osteoprogenitor cells continue to produce osteoblasts, which make osteoid Long bones don’t develop normally endochondral ossification can’t happen osteoblasts get made, but don’t have cartilage matrix to lay calcium phosphate onto bones don’t grow

Roloff family (Little People, Big World) Parents Matt and Amy and one son are achondroplasic dwarfs Other 3 children are average height

Bone remodeling Happens throughout life maintains levels of calcium and phosphate in blood heals fractures responds to stresses (including running, weight training) increases size of bone attachment sites on bone Osteoclasts remove bone, osteoblasts replace it usually results in loss of bone density

Medullary cavity (contains yellow bone marrow) Articular cartilage Fig. 6.14 Epiphyseal artery Metaphyseal artery Epiphyseal line Periosteal arteries Periosteum Cellular layer Periosteum Fibrous layer Nutrient artery (in nutrient foramen) Branch of nutrient artery Medullary cavity (contains yellow bone marrow) Compact bone 33

Fractures Oblique Fig. 6.15 Greenstick Pott Transverse Comminuted Spiral Colles Compound (open) 34

Fig. 6.16 Medullary cavity Hematoma Periosteum Compact bone 1 A fracture hematoma forms. 35

Fig. 6.16 Fibrocartilaginous (soft) callus Regenerating blood vessels Medullary cavity Hematoma Periosteum Regenerating blood vessels Compact bone 1 A fracture hematoma forms. 2 A fibrocartilaginous (soft) callus forms. 36

Fig. 6.16 Hard callus Primary bone 3 A hard (bony) callus forms. Medullary cavity Hematoma Hard callus Periosteum Compact bone Fibrocartilaginous (soft) callus Regenerating blood vessels Primary bone 1 A fracture hematoma forms. 2 A fibrocartilaginous (soft) callus forms. 3 A hard (bony) callus forms. 37

Fig. 6.16 Compact bone at break site 4 The bone is remodeled. Medullary cavity Hematoma Hard callus Periosteum Compact bone Fibrocartilaginous (soft) callus Regenerating blood vessels Primary bone 4 1 A fracture hematoma forms. 2 A fibrocartilaginous (soft) callus forms. 3 A hard (bony) callus forms. The bone is remodeled. 38