Bone and Cartilage Tissues

• Bone and cartilage are specialized connective tissues in the skeletal system.
• Both provide support and structure to the body.
• Bone is a rigid tissue providing support, protection, and locomotion.
• Cartilage is more flexible, providing cushioning and support in specific areas.

Bone Tissue

• Bone consists of cells, fibers, and ground substance.
• The extracellular matrix is mineralized, making bone hard and rigid.
• Bone matrix consists of both organic and inorganic components.
• Organic components mainly consist of collagen fibers, providing flexibility and tensile strength.
• Inorganic components primarily consist of calcium phosphate in the form of hydroxyapatite crystals, providing rigidity.
• Osteocytes are mature bone cells.
• Osteoblasts synthesize bone matrix.
• Osteoclasts resorb bone.
• The periosteum is a connective tissue covering on the outer surface of bones.
• Endosteum is a single layer of cells lining the inner cavities of bone.

Types of Bone

• Compact bone is dense.
• Spongy bone is also known as cancellous bone.
• Compact bone forms the outer layer of bones.
• Spongy bone is found in the interior of bones.
• Compact bone provides strength and resistance to bending.
• Spongy bone contains trabeculae, which are bony spicules that create space for bone marrow.
• Bone marrow is responsible for hematopoiesis.
• Long bones have a diaphysis (shaft) and epiphyses (ends).
• The metaphysis is the region between the diaphysis and epiphysis during bone development, containing the epiphyseal plate (growth plate).

Bone Development

• Ossification is bone formation.
• Intramembranous ossification occurs when bones form directly from mesenchymal tissue.
• Endochondral ossification occurs when bones form from a cartilage template.
• Flat bones of the skull develop through intramembranous ossification.
• Most bones develop through endochondral ossification.
• Primary ossification center is in the diaphysis during endochondral ossification.
• Secondary ossification centers appear in the epiphyses.
• The epiphyseal plate allows long bones to grow in length.
• Appositional growth increases bone thickness.
• Bone remodeling involves bone resorption by osteoclasts and bone deposition by osteoblasts.
• Remodeling occurs throughout life, allowing bone to adapt to stress.

Microscopic Structure of Compact Bone

• Osteons (Haversian systems) are the basic structural units.
• Osteons consist of concentric lamellae, which encircle a central Haversian canal.
• Haversian canals contain blood vessels and nerves.
• Osteocytes reside in lacunae between lamellae.
• Canaliculi are small channels that connect lacunae, allowing for nutrient and waste exchange.
• Volkmann's canals connect Haversian canals to each other and to the periosteum.
• Interstitial lamellae are remnants of old osteons.

Microscopic Structure of Spongy Bone

• Trabeculae are composed of lamellae.
• Trabeculae are oriented along lines of stress to provide strength.
• Osteocytes are located within lacunae in the trabeculae.
• Nutrients reach osteocytes by diffusion through canaliculi that open onto the surface of trabeculae.
• Spongy bone contains bone marrow between trabeculae.
• Spongy bone is lighter than compact bone, reducing overall weight.

Cartilage Tissue

• Cartilage consists of cells (chondrocytes), fibers, and ground substance.
• Cartilage matrix is firm but flexible.
• Cartilage lacks blood vessels and nerves (avascular).
• Nutrients reach chondrocytes by diffusion through the matrix.
• Chondrocytes reside in lacunae within the matrix.
• Perichondrium is a layer of dense connective tissue that surrounds cartilage, providing nutrients and support.

Types of Cartilage

• Hyaline cartilage is the most common type.
• Elastic cartilage is more flexible.
• Fibrocartilage is the strongest.
• Hyaline cartilage is found in articular surfaces, the nose, and the trachea.
• Elastic cartilage is found in the ear and epiglottis.
• Fibrocartilage is found in intervertebral discs and menisci.

Hyaline Cartilage

• Hyaline cartilage has a glassy appearance.
• Contains moderate amount of collagen fibers.
• Provides smooth surfaces for joint movement.
• Important in bone development and growth.

Elastic Cartilage

• Elastic cartilage contains numerous elastic fibers.
• More flexible than hyaline cartilage.
• Provides support and maintains shape.

Fibrocartilage

• Fibrocartilage contains a large amount of collagen fibers.
• Very tough and resistant to compression and tension.
• Provides support and cushioning in joints.
• Intervertebral discs contain fibrocartilage, acting as shock absorbers.

Cartilage Growth

• Appositional growth involves new cartilage matrix being added to the surface of existing cartilage.
• Interstitial growth involves chondrocytes dividing and secreting new matrix within existing cartilage.
• Cartilage has limited capacity for repair.
• Damaged cartilage is often replaced by fibrocartilage scar tissue.