Bone and Cartilage: Anatomy and Composition

Describe the function of osteocytes in bone

• Matrix maintenance

• Remodelling

Describe the function of osteoclasts in bone

• Responsible for bone resorption

• Secrete proteases, which destroy the organic matrix

• Release protons, creating an acidic environment, causing demineralisation

Describe the function of osteoblasts in bone

• Synthesise and secrete osteoid

• Active in mineralisation process

Describe the function of the matrix in bone

• Mechanical support

• Structural integrity and rigidity

• Lubrication

• Nutrition

Describe the function of minerals in bone

• Structural integrity and rigidity

• Compressive strength

• Hardness

Describe the function of collagen in bone

• Provide toughness and flexibility

• Provide framework for mineralisation

Describe the function of cells in cartilage

• Maintain tissue

• Synthesise and organise extracellular matrix

Describe the function of the matrix in cartilage

• Mechanical support

• Structural integrity and rigidity

• Lubrication

• Nutrition

Describe the function of collagen in cartilage

• Providing tensile strength

• Stability

• Elasticity

Describe the formation of osteocytes

• When mature osteoblasts become trapped within the matrix they secrete during bone remodeling or formation

Describe the formation of osteoclasts

• Hematopoietic stem cells from the myeloid/monocyte lineage fuse to form giant, multinucleated bone-resorbing cells

Describe the formation of osteoblasts

• From mesenchymal stem cells (MSCs) through a process called osteogenic differentiation, which occurs in the bone marrow and periosteum

Describe the formation of the matrix

• Osteoblasts secrete organic materials, primarily type I collagen, to form a soft framework called osteoid, which is subsequently hardened through mineral deposition

Describe the formation of collagen

• By osteoblasts, in a multi-step process involving intracellular synthesis and extracellular assembly

Describe how bone undergoes a constant remodelling cycle

• Bone undergoes continuous renewal, where old or damaged tissue is resorbed by osteoclasts and replaced by new, mineralized matrix deposited by osteoblasts

• Continuous remodeling ensures that the skeleton can adapt, repair, and maintain structural integrity

Describe how bone is involved in mineral and endocrine homeostasis

• Bone acts as a vital reservoir for calcium and phosphate, releasing them into the bloodstream as needed

• Also functions as an endocrine organ, releasing molecules like osteocalcin to regulate energy and glucose metabolism

Draw out the different layers of a cross-section of the bone, including:

• Cement layer

• Lacuna

• Lamellae

• Haversian canal

• Canaliculi

List the minerals that are stored in bone tissue

• Calcium

• Phosphorous 

• Magnesium 

• Sodium

• Potassium

• Citrate

Describe the role of calcitriol in calcium regulation

• Stimulating intestinal calcium absorption

• Promoting renal reabsorption of calcium

• Assisting in bone mineralization or resorption

Describe the role of parathyroid hormone in calcium regulation

• Raising low blood calcium levels by stimulating bone resorption

• Increasing renal calcium reabsorption

• Increasing intestinal calcium absorption by vitamin D activation

Draw out the cycle of calcium regulation