Bone Tissue Notes

Bone Tissue Background

  • Bone is a type of connective tissue.
  • Connective tissue has a lot of extracellular matrix (ECM), meaning fewer cells and more non-cellular material.
  • Bone is dynamic; it is constantly being remodeled.
  • The entire skeleton is replaced about once every 10 years.

Extracellular Matrix of Bone

  • The ECM of bone is primarily composed of minerals.
  • The most abundant mineral is calcium phosphate, also known as hydroxyapatite.
  • Other forms of calcium, such as calcium carbonate, are also present.
  • Bones also contain collagen, providing flexibility and preventing fractures.

Functions of the Skeletal System

  • Support: Maintains posture and holds the body upright.
  • Protection: Protects soft organs (e.g., ribs protecting the heart and lungs).
  • Movement: Skeletal muscles attach to bones to facilitate movement.
  • Hematopoiesis: Red marrow in bones produces red blood cells, white blood cells, and platelets.
    • Hemoblasts (blood stem cells) in red marrow create millions of new blood cells daily.
  • Storage:
    • Bones store minerals like calcium CaCa and phosphate PO4PO_4 (phosphorus with oxygen).
    • Magnesium MgMg is also stored.
    • Fat is stored in yellow marrow within the hollow cavity of long bones.
    • Yellow marrow serves as a last-resort energy storage during starvation.
  • pH Balance: Bones can balance pH by dissolving bone to release calcium, using an acid in the process.

Classification of Bone Tissue

  • Compact Bone:
    • More minerals and densely packed.
    • Provides support and rigidity.
  • Spongy Bone:
    • Less minerals, meaning less ECM.
    • Contains more cavities.
    • Lightens the bones.
    • Cavities house red marrow for hematopoiesis.

Bone Shapes

  • Bones are classified into four major shape categories:

    • Long Bones:
      • Longer than they are wide.
      • Examples: phalanges, humerus, radius, ulna, femur, tibia, fibula, metacarpals, and metatarsals.
    • Short Bones:
      • Equal in height and width.
      • Examples: patella, carpals, and tarsals.
    • Flat Bones:
      • Plate-shaped with a large, broad surface.
      • Examples: frontal bone, parietal bones, occipital bones, and ribs.
    • Irregular Bones:
      • Do not fit into the other three categories; funky-shaped bones.
      • Examples: hip, vertebrae, sphenoid, and ethmoid.

Examples of Bone Shapes

  • Flat Bones: Frontal bone and ribs.
  • Irregular Bones: Sphenoid, atlas, axis, cervical vertebrae, and coxae (hip bones).