BIOL_121_-_Chapter_6_-_Bone_Tissue_and_the_Skeletal_System__1___2__copy

Skeletal System OverviewAn organ system composed of bones, cartilage, and joints supporting movement, protection, and support.

Bone Composition

• Bones (Osseous Tissue): Hard, dense connective tissue forming the skeletal framework. Approximately 206 bones in adult humans.

• Cartilage: Semi-rigid connective tissue allowing flexibility and smooth surfaces for movement.

• Joints: Where two or more bones meet, allowing movement.

Compact Bone vs. Spongy Bone

• Compact Bone:

  • Dense and forms the outer layer of bones, providing strength to withstand compression forces.

  • Composed of tightly packed osteons (Haversian systems) which are cylindrical structures containing a central canal that houses nerves and blood vessels.

  • Contains fewer spaces compared to spongy bone, leading to its strength and ability to support weight.

  • Found primarily in the diaphysis (shaft) of long bones.

• Spongy Bone (Cancellous Bone):

  • Found mainly at the end of long bones (epiphyses) and inside flat bones like the pelvis and skull.

  • Has a porous, honeycomb-like structure with trabecular (thin rod-like elements) that provide lightweight support.

  • Contains red bone marrow where blood cell production occurs, making it vital for hematopoiesis.

  • The structure allows for the absorption of shock and provides flexibility.

Bone Cells and Matrix

• Bone Cells: Include osteocytes, osteoblasts, osteogenic cells, and osteoclasts.

• Matrix Components: Primarily calcium salts and collagen.

Types of Cartilage

• Hyaline Cartilage: Found in joints, growth plates, and provides cushioning.

• Fibrocartilage: Forms intervertebral discs, menisci, and provides tensile strength.

Functions of the Skeletal System

• Supports the body: Provides structure and shape.

• Facilitates movement: Works in conjunction with muscles.

• Protects internal organs: Shields vital organs, e.g., rib cage protects heart/lungs.

• Produces blood cells: Hematopoiesis occurs in red bone marrow.

• Stores and releases minerals and fat: Reservoir for calcium and phosphorus.

Mineral and Fat Storage

• Bone Matrix: Acts as a reservoir; can release minerals into the bloodstream.

• Fat Storage: Yellow bone marrow contains fat (adipose tissue) used for energy.

• Hematopoiesis: Red bone marrow produces red and white blood cells and platelets.

Bone Classification

• Long Bones: Cylindrical (e.g., femur, humerus), function as levers.

• Short Bones: Cube-like (e.g., carpals), provide stability and support.

• Flat Bones: Thin/curved (e.g., ribs, skull), protect organs and allow muscle attachment.

• Irregular Bones: Various shapes (e.g., vertebrae), perform multiple functions.

• Sesamoid Bones: Small, round bones (e.g., patella), embedded in tendons, protect from pressure.

Structure of Long Bones

• Diaphysis: Tubular structure; medullary cavity holds yellow bone marrow.

• Epiphysis: Ends of the bone; spongy bone filled with red marrow; covered with articular cartilage.

• Metaphysis: Connects diaphysis and epiphysis; contains growth plate in youth.

• Periosteum: Fibrous tissue covering outer bone, contains blood vessels/nerves.

Bone Markings and Features

• Articulations: Connections between bones (e.g., knee joint).

• Projections and Depressions: Various shapes providing attachment points for muscles and ligaments.

Bone Cells

• Osteoblasts: Responsible for bone formation.

• Osteocytes: Mature bone cells maintaining bone matrix; housed in lacunae.

• Osteogenic Cells: Undifferentiated cells that can divide and form new osteoblasts.

• Osteoclasts: Cells that resorb (break down) bone, essential for bone remodeling.

Bone Formation Processes

• Ossification: Formation of bone (begins in 6th/7th week of development).

• Intramembranous Ossification: Occurs in flat bones; forms bone directly from mesenchymal tissue.

• Endochondral Ossification: Involves replacing cartilage with bone; occurs in long bones.

How Bones Grow

• Length: Growth occurs at epiphyseal plates through zones of chondrocyte activity.

• Diameter: Appositional growth remodels bone through resorption and deposition by osteoblasts and osteoclasts.

Bone Remodeling

Continuous cycle of bone resorption by osteoclasts and formation by osteoblasts. Influenced by physical activity, nutrition, and hormones.

Hormonal Regulation of Bones

• Growth Hormone: Stimulates growth and bone density.

• Thyroid Hormone: Supports bone growth.

• Sex Hormones: Promote bone formation during adolescence and close growth plates.

• Parathyroid Hormone: Increases osteoclast activity, releasing calcium into the blood.

• Calcitonin: Opposes parathyroid hormone effects, promotes calcium deposition in bones.

Disorders of the Skeletal System

• Osteoporosis: Decrease in bone mass leading to fractures.

• Paget’s Disease: Disorganized bone remodeling.

• Rickets: Vitamin D deficiency in children.

• Osteomalacia: Softening of bones due to vitamin D deficiency in adults.

• Osteosarcoma: Bone cancer common in young adults.

• Osteomyelitis: Bone infection usually from bacteria.

• Achondroplasia: Genetic disorder affecting bone growth, resulting in dwarfism.

Nutritional Needs for Bone Health

• Calcium: Vital for bone strength, sourced from dairy, seafood, and green leafy vegetables.

• Vitamin D: Essential for calcium absorption, can be synthesized by sunlight exposure.

• Other nutrients: Include Vitamin K, Magnesium, Fluoride, and Omega-3 fatty acids for overall bone health.