Osseous Tissue and Skeletal System

Functions of the Skeletal System

• Provides support and structure to the body
• Facilitates movement by serving as levers for muscles
• Stores minerals (e.g., calcium) and lipids for energy
• Produces blood cells through hematopoiesis
• Protects vital organs (e.g., brain, heart)
• Offers leverage for mechanical advantage during movement

Classification of Bones

• Long bones: Examples include femur and humerus
• Short bones: Examples include carpals
• Flat bones: Examples include parietal and sternum
• Irregular bones: Examples include vertebrae and pelvis
• Sesamoid bones: Develop within a tendon, e.g., patella
• Sutural bones: Variable bones found in the skull

Bone Structure

• Comprised of compact bone (dense) and spongy bone (cancellous)
• Long bone anatomy includes:
  • Diaphysis: Shaft of the bone
  • Epiphyses: Ends of the bone
  • Metaphysis: Region where diaphysis and epiphyses meet
  • Articular cartilage: Hyaline cartilage at the ends
  • Marrow cavity: Central hollow space for red or yellow marrow
  • Periosteum: Protective outer membrane

Bone Histology

• Solid matrix of osseous tissue with mineral deposits in lamellae
• Cells scattered in a matrix of collagen and calcium salts
• Osteocytes: Mature bone cells located in lacunae
• Osteoblasts: Bone-forming cells responsible for osteogenesis
• Osteoclasts: Cells that dissolve bone matrix
• Osteoprogenitor cells: Stem cells that differentiate into osteoblasts

Types of Bone Development

• Endochondral ossification:
  • Hyaline cartilage model transformed into bone
  • Occurs at primary and secondary ossification centers
  • Involves chondrocyte hypertrophy and blood vessel invasion
• Intramembranous ossification:
  • Bone developed directly from connective tissue, without cartilage
  • Primarily gives rise to flat bones of the skull and clavicles

Bone Remodeling

• Continuous process replacing old bone with new tissue
• 25% of bone replaced annually; notable for distal femur (every 4 months)
• Hormones like growth hormone and thyroxine enhance bone mass
• Calcitonin and parathyroid hormone (PTH) regulate calcium levels:
  • Calcitonin: Decreases blood calcium by stimulating osteoblasts
  • PTH: Increases blood calcium by stimulating osteoclasts

Calcium Homeostasis

• 99% of the body's calcium stored in the skeleton
• Calcium levels in blood maintained by bones, gastrointestinal tract, and kidneys

Fracture Repair Process

• Fracture hematoma: Blood clot forms at the fracture site
• External callus: Hard tissue forms around the outside
• Internal callus: Fibrous tissue forms within the bone

Bone Markings

• Characteristic features unique to each bone and individual
• Include elevations, projections, depressions, and grooves

Aging and Skeletal Disorders

• Osteopenia: Normal age-related bone loss
• Osteoporosis: Severe bone loss leading to dysfunction, influenced by genetics, diet, and exercise
• Kyphosis: Exaggerated thoracic curve
• Lordosis: Exaggerated lumbar curve
• Scoliosis: Abnormal lateral curve of the spine
• Spina bifida: Incomplete fusion of vertebrae
• Herniated disc: Nucleus pulposus protrudes, compressing nerves
• Compression fracture: Loss of height in vertebrae due to pressure