Biology Chapter 6: Bones

Functions of the Skeletal System

• Provides structural support to the body
• Protects vital organs, such as the heart and brain
• Facilitates movement by serving as attachment points for muscles
• Stores minerals, particularly calcium and phosphorus
• Houses bone marrow for blood cell production

Types of Connective Tissue in the Skeletal System

• Hyaline cartilage: smooth and flexible, reduces friction at joints
• Fibrocartilage: tough and durable, found in intervertebral discs and pubic symphysis
• Dense regular collagenous connective tissue: forms tendons and ligaments for stability
• Dense irregular connective tissue: provides protection and structure in periosteum

Spongy vs Compact Bone

• Spongy Bone: Composed of trabecular meshwork; found in interior of bones, lightweight, and allows for flexibility.
• Compact Bone: Dense and strong, forms the outer layer of bones, organized into osteons for structural integrity.

Classification of Bones by Shape

• Long bones (e.g., femur): elongated structure, major weight-bearing bones
• Short bones (e.g., carpals): cube-shaped, provide stability and support, allowing for limited motion
• Flat bones (e.g., sternum): thin, flattened, and provide protection, surface area for muscle attachment
• Irregular bones (e.g., vertebrae): complex shapes that do not fit into other categories

Definitions and Functions of Bone Structures

• Diaphysis: the long central shaft of a bone, supports weight
• Epiphysis: the expanded end of a bone, covered with articular cartilage for joint movement
• Medullary cavity: hollow space within diaphysis that contains bone marrow
• Red bone marrow: site of blood cell production
• Yellow bone marrow: stores fat and serves as an energy reserve
• Periosteum: fibrous membrane covering bones, contains blood vessels and nerves
• Endosteum: membrane lining the medullary cavity, involved in bone growth and repair
• Perforating (Sharpey’s) fibers: collagen fibers that anchor periosteum to bone
• Nutrient foramen: small openings that allow blood vessels and nerves to enter the bone

Bone Extracellular Matrix Components

• Organic components (approx. 33%): osteoid providing flexibility and tensile strength, composed of collagen and ground substance.
• Inorganic components (approx. 67%): hydroxyapatite crystals (calcium and phosphorus), providing compressional strength.

Bone Cell Types

• Osteoblasts: responsible for bone formation and matrix secretion.
• Osteocytes: mature bone cells that maintain bone tissue and communicate with other cells.
• Osteoclasts: involved in bone resorption and remodeling.

Compact Bone Structure

• Osteons (Haversian systems): structural units containing concentric lamellae and a central canal for blood vessels.
• Lamellae: layers of mineralized matrix, oriented to resist twisting forces.
• Lacunae: small cavities housing osteocytes.
• Canaliculi: connect lacunae, facilitating nutrient and waste exchange.

Spongy Bone Structure

• Lacks osteons; contains trabeculae with interspersed osteocytes.
• Provides lightweight support and houses red bone marrow.

Osteogenesis & Ossification Processes

• Intramembranous ossification: develops from mesenchyme (embryonic connective tissue); forms many flat bones.
• Endochondral ossification: develops from hyaline cartilage models; most bones formed this way.

Growth in Length

• Epiphyseal plate: contains zones (reserve, proliferation, hypertrophy, calcification, ossification) crucial for lengthening bones.

Implications of Epiphyseal Plate Injuries

• Damage can result in stunted bone growth or premature closure, affecting adult height.

Appositional Growth

• Involves osteoblasts adding new bone on the outer surface, increasing thickness without changing overall length.

Bone Remodeling Processes

• Consists of deposition (bone formation) and resorption (bone loss), maintaining calcium levels and adapting to physical stress.

Blood Calcium Homeostasis Feedback Loop

• Low calcium triggers parathyroid hormone release, promoting resorption; high calcium increases calcitonin, promoting deposition.

Osteoporosis

• Condition characterized by decreased bone density, increasing fracture risk due to inadequate inorganic matrix; factors include age, sex, and activity level.

Steps in Bone Repair After Fracture

• Formation of a hematoma, followed by soft callus formation, bony callus creation, and eventual remodeling into secondary bone.

Explore the key functions of the skeletal system in this quiz. Understand the types of connective tissues involved and compare spongy versus compact bone. Additionally, learn to classify bones by shape and identify examples within each category.