Bone Biology and Composition

Bone Structure and Composition

• Bone is a dynamic, mineralized connective tissue that undergoes continuous remodeling cycles of resorption and deposition of new bone tissue.
• Type I collagen is the major protein in bone, with type V collagen and non-collagenous proteins also present.
• Bone-specific proteins include chondroitin sulfate proteoglycan, osteocalcin, and bone sialoprotein.
• Crystalline hydroxyapatite (Ca10(PO4)6(OH)2) confers strength and resilience to bone, along with other inorganic compounds like Na+, Mg2+, CO3²-, and F-.

Non-Collagenous Proteins of Bone

• These proteins account for 10-15% of bone protein mass, but are as common as collagen on a molar basis.
• Most non-collagenous proteins are synthesized by osteoblasts, but some arrive in bone via the circulation.
• Examples include versican, decorin, biglycan, and osteonectin, which may influence cellular proliferation and differentiation.

Osteoblasts and Osteoclasts

• Osteoblasts are specialized cells responsible for synthesizing and secreting organic compounds of bone, such as collagen and proteins.
• Osteoclasts are multinucleated giant cells that resorb bone tissue, regulated by the RANK-RANKL-OPG system.

Bone Remodeling and Calcium Homeostasis

• Bone remodeling involves resorption and deposition of new bone tissue, with 4% of compact bone and 20% of trabecular bone renewed annually in healthy adults.
• Calcitropic hormones, such as PTH, calcitriol, and calcitonin, regulate calcium homeostasis and bone remodeling.

Alkaline Phosphatase and Osteonectin

• Alkaline phosphatase (ALP) is an enzyme that hydrolyzes phosphate esters to generate inorganic phosphate ions needed for hydroxyapatite crystals.
• Osteonectin is a phosphorylated glycoprotein that regulates both cellular activity and matrix mineralization.

Osteocytes and Bone Remodeling

• Osteocytes play a key role in regulating bone remodeling, particularly at sites of skeletal microdamage.
• Osteocytes produce sclerostin, an inhibitor of osteoblast differentiation and function, and fibroblast growth factor 23 (FGF23), which regulates phosphate metabolism.

Osteoclasts and Bone Resorption

• Osteoclasts are multinucleated cells that resorb bone tissue, regulated by the RANK-RANKL-OPG system.
• Osteoclasts are inhibited by calcitonin and activated by PTH, 1,25(OH)2D, PGE2, and IL-11.

Cartilage Structure and Function

• Cartilage is a specialized connective tissue composed of chondrocytes, collagen, and proteoglycans.
• The major proteoglycan in cartilage is aggrecan, which contributes to development, tensile strength, and resilience.

Cartilage Turnover and Disease

• Cartilage exhibits slow but continuous turnover, regulated by anabolic and catabolic factors such as TGF-β, IGF-I, and proteases.
• Inflammatory responses and autoimmune attacks can disrupt cartilage homeostasis, leading to diseases such as achondroplasia.

Bone Structure and Composition

• Bone is a dynamic, mineralized connective tissue that undergoes continuous remodeling cycles of resorption and deposition of new bone tissue.
• Type I collagen is the major protein in bone, with type V collagen and non-collagenous proteins also present.
• Bone-specific proteins include chondroitin sulfate proteoglycan, osteocalcin, and bone sialoprotein.
• Crystalline hydroxyapatite (Ca10(PO4)6(OH)2) confers strength and resilience to bone, along with other inorganic compounds like Na+, Mg2+, CO3²-, and F-.

Non-Collagenous Proteins of Bone

• These proteins account for 10-15% of bone protein mass, but are as common as collagen on a molar basis.
• Most non-collagenous proteins are synthesized by osteoblasts, but some arrive in bone via the circulation.
• Examples include versican, decorin, biglycan, and osteonectin, which may influence cellular proliferation and differentiation.

Osteoblasts and Osteoclasts

• Osteoblasts are specialized cells responsible for synthesizing and secreting organic compounds of bone, such as collagen and proteins.
• Osteoclasts are multinucleated giant cells that resorb bone tissue, regulated by the RANK-RANKL-OPG system.

Bone Remodeling and Calcium Homeostasis

• Bone remodeling involves resorption and deposition of new bone tissue, with 4% of compact bone and 20% of trabecular bone renewed annually in healthy adults.
• Calcitropic hormones, such as PTH, calcitriol, and calcitonin, regulate calcium homeostasis and bone remodeling.

Alkaline Phosphatase and Osteonectin

• Alkaline phosphatase (ALP) is an enzyme that hydrolyzes phosphate esters to generate inorganic phosphate ions needed for hydroxyapatite crystals.
• Osteonectin is a phosphorylated glycoprotein that regulates both cellular activity and matrix mineralization.

Osteocytes and Bone Remodeling

• Osteocytes play a key role in regulating bone remodeling, particularly at sites of skeletal microdamage.
• Osteocytes produce sclerostin, an inhibitor of osteoblast differentiation and function, and fibroblast growth factor 23 (FGF23), which regulates phosphate metabolism.

Osteoclasts and Bone Resorption

• Osteoclasts are multinucleated cells that resorb bone tissue, regulated by the RANK-RANKL-OPG system.
• Osteoclasts are inhibited by calcitonin and activated by PTH, 1,25(OH)2D, PGE2, and IL-11.

Cartilage Structure and Function

• Cartilage is a specialized connective tissue composed of chondrocytes, collagen, and proteoglycans.
• The major proteoglycan in cartilage is aggrecan, which contributes to development, tensile strength, and resilience.

Cartilage Turnover and Disease

• Cartilage exhibits slow but continuous turnover, regulated by anabolic and catabolic factors such as TGF-β, IGF-I, and proteases.
• Inflammatory responses and autoimmune attacks can disrupt cartilage homeostasis, leading to diseases such as achondroplasia.

Bone Structure and Composition

• Bone is a dynamic, mineralized connective tissue that undergoes continuous remodeling cycles of resorption and deposition of new bone tissue.
• Type I collagen is the major protein in bone, with type V collagen and non-collagenous proteins also present.
• Bone-specific proteins include chondroitin sulfate proteoglycan, osteocalcin, and bone sialoprotein.
• Crystalline hydroxyapatite (Ca10(PO4)6(OH)2) confers strength and resilience to bone, along with other inorganic compounds like Na+, Mg2+, CO3²-, and F-.

Non-Collagenous Proteins of Bone

• These proteins account for 10-15% of bone protein mass, but are as common as collagen on a molar basis.
• Most non-collagenous proteins are synthesized by osteoblasts, but some arrive in bone via the circulation.
• Examples include versican, decorin, biglycan, and osteonectin, which may influence cellular proliferation and differentiation.

Osteoblasts and Osteoclasts

• Osteoblasts are specialized cells responsible for synthesizing and secreting organic compounds of bone, such as collagen and proteins.
• Osteoclasts are multinucleated giant cells that resorb bone tissue, regulated by the RANK-RANKL-OPG system.

Bone Remodeling and Calcium Homeostasis

• Bone remodeling involves resorption and deposition of new bone tissue, with 4% of compact bone and 20% of trabecular bone renewed annually in healthy adults.
• Calcitropic hormones, such as PTH, calcitriol, and calcitonin, regulate calcium homeostasis and bone remodeling.

Alkaline Phosphatase and Osteonectin

• Alkaline phosphatase (ALP) is an enzyme that hydrolyzes phosphate esters to generate inorganic phosphate ions needed for hydroxyapatite crystals.
• Osteonectin is a phosphorylated glycoprotein that regulates both cellular activity and matrix mineralization.

Osteocytes and Bone Remodeling

• Osteocytes play a key role in regulating bone remodeling, particularly at sites of skeletal microdamage.
• Osteocytes produce sclerostin, an inhibitor of osteoblast differentiation and function, and fibroblast growth factor 23 (FGF23), which regulates phosphate metabolism.

Osteoclasts and Bone Resorption

• Osteoclasts are multinucleated cells that resorb bone tissue, regulated by the RANK-RANKL-OPG system.
• Osteoclasts are inhibited by calcitonin and activated by PTH, 1,25(OH)2D, PGE2, and IL-11.

Cartilage Structure and Function

• Cartilage is a specialized connective tissue composed of chondrocytes, collagen, and proteoglycans.
• The major proteoglycan in cartilage is aggrecan, which contributes to development, tensile strength, and resilience.

Cartilage Turnover and Disease

• Cartilage exhibits slow but continuous turnover, regulated by anabolic and catabolic factors such as TGF-β, IGF-I, and proteases.
• Inflammatory responses and autoimmune attacks can disrupt cartilage homeostasis, leading to diseases such as achondroplasia.