Skeletal System: Bone Structure and Function

7.1 Introduction to the Skeletal System

  • Components of the skeletal system:

    • Bones of the skeleton

    • Cartilage

    • Ligaments

    • Other connective tissue structures

  • Bones:

    • Primary organs of the skeletal system

    • Rigid framework of the body

    • Additional functions: protection, support, leverage for movement, hematopoiesis (blood cell production), mineral storage

7.1 Introduction to the Skeletal System (Continued)

  • Types of Bones:

    • Compact Bone:

    • Dense or cortical bone

    • Makes up 80% of total bone mass

    • Spongy Bone:

    • Cancellous or trabecular bone

    • Located internally to compact bone and appears porous

    • Makes up 20% of total bone mass

7.1 Introduction to the Skeletal System (Continued)

  • Cartilage:

    • Semirigid connective tissue, more flexible than bone

    • Types of Cartilage:

    • Hyaline Cartilage:

      • Attaches ribs to sternum, covers ends of some bones, found within growth plates

    • Fibrocartilage:

      • Forms intervertebral discs, pubic symphysis, menisci of the knee

  • Adaptations of Connective Tissue:

    • Ligaments: Connect bone to bone

    • Tendons: Connect muscle to bone

7.2a General Functions of Bones

  • Basic Functions:

    • Support and protection

    • Levers for movement

    • Hematopoiesis (blood cell production) occurs in red bone marrow

    • Storage of mineral (calcium and phosphate) and energy reserves

7.2b Classification of Bones

  • Bone Types by Shape:

    • Long Bones: Greater in length than width (e.g., femur, humerus)

    • Short Bones: Nearly equal length and width (e.g., carpals and tarsals)

    • Flat Bones: Flat, thin, slightly curved surfaces (e.g., cranial bones)

    • Irregular Bones: Elaborate and complex shapes (e.g., vertebrae)

7.2c Gross Anatomy of Bones

  • Regions of a Long Bone:

    • Diaphysis: Elongated shaft, primarily compact bone with spongy bone extending inward, containing a medullary (marrow) cavity

    • Epiphysis: Knobby ends of long bones

    • Proximal epiphysis: Closest to the trunk

    • Distal epiphysis: Farthest from the trunk

    • Composed of an outer layer of compact bone and an inner region of spongy bone

    • Articular Cartilage: Present on joint surfaces to reduce friction and absorb shock

    • Metaphysis: Area where diaphysis meets epiphysis; contains epiphyseal plate for growth in length

    • Periosteum: Tough sheath covering outer surfaces of bone, has fibrous and cellular layers with collagen fibers

    • Endosteum: Lines internal surfaces of medullary cavity, contains osteoprogenitor cells and osteoblasts

7.2d Bone Marrow

  • Types of Bone Marrow:

    • Red Bone Marrow (Myeloid Tissue): Hematopoietic, located in spongy bone and medullary cavity; produces blood cells

    • Yellow Bone Marrow: Fatty tissue resulting from degeneration of red marrow; can revert to red marrow during severe anemia

7.2e Microscopic Anatomy: Bone Connective Tissue

  • Bone Composition:

    • Cell Types:

    • Osteoprogenitor cells: Stem cells that differentiate into osteoblasts

    • Osteoblasts: Create osteoid (organic part of bone matrix)

    • Osteocytes: Mature cells maintaining bone matrix

    • Osteoclasts: Large cells responsible for bone resorption

  • Extracellular Matrix:

    • Organic Components: Osteoid (collagen and proteoglycans) provides tensile strength and flexibility

    • Inorganic Components: Hydroxyapatite formed from calcium phosphate and hydroxide contributes rigidity

7.2e Microscopic Anatomy: Bone Formation

  • Bone Formation (Ossification) begins with secretion of osteoid and finishes with calcification (hydroxyapatite deposition)

  • Requirements for Calcification:

    • Vitamin D, Vitamin C, calcium, and phosphate

7.2e Microscopic Anatomy: Bone Remodeling

  • Bone Resorption: Breakdown of bone matrix by osteoclasts, releasing calcium and phosphate into the bloodstream

  • Clinical View: Osteitis deformans results in excessive resorption and deposition of poorly formed bone

7.7 Effects of Aging

  • Consequences of Aging on Bones:

    • Decrease in bone tensile strength and mineral density leading to brittle bones (osteopenia)

  • Osteoporosis: Severe bone loss affecting normal function, increased fractures, influenced by aging and hormone levels

7.8 Bone Fracture and Repair

  • Types of Fractures:

    • Stress fractures

    • Pathologic fractures

    • Simple fractures

    • Compound fractures

    • Each type requires specific healing processes, including formation of hematoma, callus, and tissue remodeling