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Anatomy & Physiology: Osseous Tissue and Skeletal System

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  • Primary functions of the skeletal system

    Support, storage of minerals and lipids, blood cell production (hematopoiesis), protection, and leverage for movement.

  • Classification of bones by shape

    Sutural, irregular, short, flat, long, and sesamoid bones.

  • Bone markings: projections vs openings

    Projections are sites for muscle, tendon, and ligament attachment or articulations. Openings and depressions allow passage of blood vessels and nerves.

  • Structure of a typical long bone

    Diaphysis (shaft) with compact bone and medullary cavity; epiphysis (ends) mostly spongy bone; metaphysis where diaphysis and epiphysis meet.

  • Structure of flat bones

    Spongy bone (diploë) sandwiched between two layers of compact bone, e.g., parietal bones of the skull.

  • Four types of bone cells

    Osteogenic cells, osteoblasts, osteocytes, and osteoclasts.

  • Osteogenic cells

    Mesenchymal stem cells that divide to produce osteoblasts; located in periosteum and endosteum; assist in fracture repair.

  • Osteoblasts

    Immature bone cells that produce new bone matrix (osteoid) during ossification; become osteocytes when surrounded by matrix.

  • Osteocytes

    Mature bone cells in lacunae; maintain matrix and help repair damaged bone; communicate via canaliculi.

  • Osteoclasts

    Large multinucleate cells that absorb and remove bone matrix by secreting acids and enzymes; important for bone homeostasis.

  • Osteon structure

    Functional unit of compact bone; concentric lamellae surround central canal containing blood vessels; perforating canals carry vessels deep into bone.

  • Spongy bone structure

    Lacks osteons; matrix forms trabeculae network; spaces filled with red bone marrow for blood cell formation; nutrients reach osteocytes by diffusion.

  • Periosteum functions

    Membrane covering bone surface (except joints); isolates bone, provides blood and nerve routes, and participates in growth and repair.

  • Endosteum characteristics

    Incomplete cellular layer lining medullary cavity and trabeculae; contains osteogenic cells, osteoblasts, and osteoclasts; active in growth and remodeling.

  • Ossification vs calcification

    Ossification is bone formation; calcification is deposition of calcium salts during ossification.

  • Endochondral ossification

    Bone develops by replacing hyaline cartilage; primary method for forming long bones.

  • Intramembranous ossification

    Bone develops directly from mesenchymal tissue in the dermis; forms flat bones like mandible and clavicles.

  • Bone remodeling

    Continuous process of bone matrix recycling involving osteocytes, osteoblasts, and osteoclasts; balances bone deposition and removal.

  • Effects of exercise on bone

    Stimulates osteoblast activity; heavily stressed bones become thicker and stronger through mineral recycling.

  • Nutritional requirements for bone health

    Calcium, phosphorus, magnesium, fluoride, iron, manganese, vitamins C (collagen synthesis), A (osteoblast activity), K, and B-12 (bone protein synthesis).

  • Role of vitamin D in bone

    Calcitriol produced in kidneys promotes calcium and phosphate absorption in the digestive tract; deficiency causes soft bones (rickets, osteomalacia).

  • Hormones affecting bone growth

    Growth hormone and thyroxine stimulate growth; sex hormones (estrogen, testosterone) stimulate osteoblasts; PTH and calcitonin regulate calcium homeostasis.

  • Calcium storage in the skeleton

    Bones store 99% of the body's calcium, vital for physiological processes like muscle contraction and nerve function.

  • Parathyroid hormone (PTH) effects

    Increases blood calcium by stimulating osteoclasts, enhancing intestinal absorption via calcitriol, and reducing kidney excretion.

  • Calcitonin effects

    Decreases blood calcium by inhibiting osteoclasts, increasing calcium excretion, reducing calcitriol secretion, and lowering intestinal absorption.

  • Types of bone fractures

    Open (compound) or closed (simple); includes transverse, displaced, compression, spiral, epiphyseal, comminuted, greenstick, Colles, and Pott's fractures.

  • Four steps of fracture repair

    Hematoma formation, callus formation (internal and external), spongy bone formation by osteoblasts, and compact bone formation for remodeling.

  • Effects of aging on the skeleton

    Bones become thinner and weaker (osteopenia); women lose more bone mass than men; epiphyses, vertebrae, and jaws most affected.

  • Osteoporosis overview

    Severe bone mass loss compromising function; affects 29% of women and 18% of men over 45; accelerated by decreased sex hormones after menopause.