skeletal

Functions of the Skeletal System

  • Support: Keeps body upright.

  • Protection: Safeguards vital organs.

  • Movement: Facilitated by muscles acting on bones.

  • Blood Formation: Occurs in bone marrow.

  • Electrolyte Balance: Bones store and release calcium and potassium ions.

  • Acid-Base Balance: Bones buffer blood to maintain neutral pH by absorbing/releasing phosphate and carbonate salts.

Bone Tissue (Osseous Tissue)

  • Composed of:

    • Cells

    • Osteogenic cells (stem cells)

    • Osteoblasts

    • Osteocytes

    • Osteoclasts

    • Matrix

    • One third organic

    • Two thirds inorganic

Organic Portion of Bone

  • Made primarily of collagen.

  • Functions:

    • Allows flexibility

    • Absorbs pressure

Inorganic Portion of Bone

  • Composed of hydroxyapatite, a crystallized salt formed of calcium and phosphate.

  • Provides strength to the tissue and is a key storage form of calcium.

  • Bone requires both components:

    • Absence of organic component results in brittle, fragile bones.

    • Absence of hydroxyapatite results in rubbery, weak bones.

Types of Bone Cells

  • Osteogenic Cells:

    • Serve as stem cells that give rise to most other bone cell types.

    • Located in the endosteum and inner layer of periosteum.

    • Capable of continuous multiplication.

  • Osteoblasts:

    • Derived from osteogenic cells.

    • Non-mitotic: Do not reproduce themselves; new osteoblasts come only from osteogenic cells.

    • Function: Form bone by producing organic components of the matrix, lowering blood calcium levels by removing it from the bloodstream to build bone matrix.

  • Osteocytes:

    • Mature osteoblasts that become trapped in the matrix they secrete.

    • Function: Maintain bone homeostasis.

  • Osteoclasts:

    • Arise from the fusion of about four stem cells in the bone marrow.

    • Very large, bone-dissolving cells.

    • Release hydrochloric acid to dissolve the matrix, increasing blood calcium levels.

    • Work in coordination with osteoblasts for proper bone tissue balance.

    • Found on bone surfaces with ruffled borders to increase surface area for efficient reabsorption of bone matrix.

Types of Bone Tissue

  • Compact Bone:

    • Strong, designed for weight bearing.

    • Formed by osteons:

    • Structure: One central canal surrounded by concentric rings.

    • Appearance: Tree ring like.

    • Central Canal: Contains blood vessels and nerves.

    • Perforating Canals: Smaller canals running perpendicular to central canals.

    • Lamellae: Rings of matrix surrounding central canal.

    • Lacunae: Tiny cavities containing osteocytes.

    • Canaliculi: Extensions branching from lacunae, allowing communication between osteocytes.

  • Spongy Bone:

    • Lattice-like structure of rods, spines, and projections resembling a sponge.

    • Components:

    • Spicules: Spikes/projections protruding into cavities.

    • Trabeculae: Thin-plate structures formed by projections, contain lamellae but no central canal, filled with marrow.

    • Function: Develops along lines of stress to disperse pressure, allowing strength without added weight.

Comparison of Bone Types

  • Analogy: Compact Bone = Chocolate Cookie; Spongy Bone = Filling in Oreo Cookie.

  • Long bones have spongy bone at the epiphysis and compact bone forming the outer layer.