bio 20300 anatomy and physiology unit 8 study guides

Key Concepts

• Bones provide structural support, protect vital organs, enable movement, store minerals, and produce blood cells
• Bone tissue consists of cells (osteoblasts, osteocytes, osteoclasts) and an extracellular matrix composed of organic and inorganic components
• Bones are classified based on their shape (long, short, flat, irregular, sesamoid) and location in the body
• Bone formation occurs through intramembranous and endochondral ossification processes
  • Intramembranous ossification directly forms bone from mesenchymal cells (skull bones)
  • Endochondral ossification replaces a cartilage model with bone tissue (long bones)
• The skeletal system works in conjunction with the muscular system to facilitate movement and maintain posture
• Bones continuously remodel throughout life in response to mechanical stress and hormonal signals

Bone Composition and Structure

• Bone is a highly specialized connective tissue composed of cells and an extracellular matrix
• The extracellular matrix consists of organic components (collagen fibers, proteoglycans) and inorganic components (hydroxyapatite crystals)
• Bones have a dense outer layer called cortical (compact) bone and a spongy inner layer called trabecular (cancellous) bone
  • Cortical bone provides strength and rigidity
  • Trabecular bone has a honeycomb-like structure that reduces weight and allows for blood cell production
• Osteoblasts are bone-forming cells that secrete the organic matrix and regulate mineralization
• Osteocytes are mature bone cells embedded within the matrix that maintain bone tissue
• Osteoclasts are large, multinucleated cells responsible for bone resorption and remodeling

Types of Bones

• Long bones are found in the limbs (femur, humerus) and consist of a shaft (diaphysis) and two ends (epiphyses)
  • The diaphysis contains the medullary cavity, which houses bone marrow
  • Epiphyses are covered by articular cartilage and facilitate joint movement
• Short bones are roughly cube-shaped and provide stability (carpals, tarsals)
• Flat bones have a thin, flat shape and often serve a protective function (skull bones, ribs, sternum)
• Irregular bones have complex shapes and fit into specific locations (vertebrae, sacrum, coccyx)
• Sesamoid bones are small, round bones embedded within tendons that reduce friction (patella)

Bone Formation and Growth

• Osteogenesis (bone formation) begins during embryonic development and continues throughout life
• Intramembranous ossification directly converts mesenchymal cells into osteoblasts, which form bone tissue
  • This process occurs in the flat bones of the skull and the clavicles
• Endochondral ossification involves the replacement of a cartilage model with bone tissue
  • Long bones, vertebrae, and the pelvis develop through this process
• During endochondral ossification, chondrocytes in the cartilage model undergo hypertrophy and apoptosis, allowing for vascularization and osteoblast invasion
• Bone growth occurs at the epiphyseal plate (growth plate) located between the diaphysis and epiphysis of long bones
  • Chondrocytes in the epiphyseal plate proliferate, hypertrophy, and are replaced by bone tissue, leading to longitudinal growth
• Bone remodeling is a continuous process of bone resorption by osteoclasts and bone formation by osteoblasts, maintaining bone strength and mineral homeostasis

Skeletal System Functions

• Provides structural support and framework for the body, allowing for upright posture and movement
• Protects vital organs such as the brain (skull), heart and lungs (rib cage), and spinal cord (vertebral column)
• Serves as attachment points for muscles, tendons, and ligaments, enabling movement and locomotion
• Acts as a reservoir for minerals, particularly calcium and phosphorus, which can be released into the bloodstream when needed
• Houses bone marrow, which produces red blood cells, white blood cells, and platelets (hematopoiesis)
• Stores energy reserves in the form of fat (yellow bone marrow) in the medullary cavities of long bones
• Contributes to the regulation of acid-base balance by releasing or absorbing alkaline salts

Major Bones and Their Locations

• Skull: Cranial bones (frontal, parietal, occipital, temporal) and facial bones (maxilla, mandible, zygomatic)
• Vertebral column: Cervical (7), thoracic (12), lumbar (5), sacral (5 fused), and coccygeal (3-5 fused) vertebrae
• Thoracic cage: Ribs (12 pairs) and sternum (manubrium, body, xiphoid process)
• Pectoral girdle: Clavicle and scapula
• Upper limb: Humerus, radius, ulna, carpals, metacarpals, and phalanges
• Pelvic girdle: Ilium, ischium, and pubis (fused to form the hip bone)
• Lower limb: Femur, patella, tibia, fibula, tarsals, metatarsals, and phalanges

Joints and Articulations

• Joints are points of contact between bones that allow for varying degrees of movement
• Fibrous joints are connected by dense connective tissue and allow little to no movement (sutures in the skull)
• Cartilaginous joints are connected by cartilage and allow limited movement (pubic symphysis, intervertebral discs)
• Synovial joints are the most common and movable joints, featuring a joint cavity filled with synovial fluid (knee, hip, shoulder)
  • Synovial fluid lubricates the joint and reduces friction between the articulating surfaces
  • The joint capsule, ligaments, and muscles surrounding the joint provide stability and support
• Joint movement is described by the degree of freedom and the type of motion (flexion, extension, abduction, adduction, rotation)
• Arthritis is a common disorder affecting joints, causing inflammation, pain, and reduced mobility

Clinical Applications and Disorders

• Osteoporosis is a condition characterized by decreased bone mass and increased fracture risk, often associated with aging and hormonal changes
  • Treatments include weight-bearing exercise, calcium and vitamin D supplementation, and medications (bisphosphonates)
• Fractures are breaks in the continuity of bone tissue, classified as simple (closed) or compound (open)
  • Healing involves hematoma formation, callus formation, and remodeling
• Rickets (children) and osteomalacia (adults) are caused by vitamin D deficiency, leading to impaired mineralization and soft, weak bones
• Osteosarcoma is a malignant bone tumor that typically affects the long bones of the limbs
• Paget's disease is a chronic disorder characterized by excessive bone remodeling, resulting in enlarged, deformed bones
• Herniated discs occur when the soft inner material of an intervertebral disc protrudes through the outer layer, compressing spinal nerves
• Arthritis, including osteoarthritis (degenerative) and rheumatoid arthritis (autoimmune), causes joint inflammation, pain, and stiffness