Anatomy & Physiology - Chapter 06: Bones and Skeletal Tissues

Anatomy and Physiology - Chapter 06: Bones and Skeletal Tissues

Basic Structure, Types, and Locations of Skeletal Cartilage

  • Skeletal Cartilage:

    • Composed of highly resilient, molded cartilage tissue predominantly made of water.
    • Lacks blood vessels and nerves, making it avascular.

  • Chondrocytes:

    • These are the cells encased in small cavities called lacunae.
    • Found within a jelly-like extracellular matrix.
Types of Cartilage

  • Three Types of Cartilage:

    1. Hyaline Cartilage:
    • Provides support, flexibility, and resilience.
    • Most abundant type, contains only collagen fibers.
    • Locations:
      • Articular cartilage in joints
      • Costal cartilage in ribs.
    1. Elastic Cartilage:
    • Similar to hyaline cartilage but contains elastic fibers.
    • Location: External ear.
    1. Fibrocartilage:
    • Contains thick collagen fibers, offering great tensile strength.
    • Locations:
      • Menisci of the knee
      • Vertebral discs.
Functions of Bones
  • Bones have several critical functions:
    • Support:
    • Provides a framework for the body and soft organs.
    • Protection:
    • Protects vital structures such as the brain, spinal cord, and other organs.
    • Anchorage:
    • Acts as levers for muscle action.
    • Mineral and Growth Factor Storage:
    • Primarily stores calcium.
    • Blood Cell Formation:
    • Hematopoiesis occurs within the red marrow cavities of bones.
    • Triglyceride Storage:
    • Fat is stored in bone cavities as an energy reserve.
Classification of Bones

  • Total Number of Bones: 206 named bones exist within the human skeleton.

  • Two Primary Groups:

    1. Axial Skeleton:
    • Comprises the trunk of the body.
    • Includes:
      • Skull
      • Vertebral column
      • Rib cage.
    1. Appendicular Skeleton:
    • Comprises bones of the upper and lower limbs, including girdles attaching limbs to the axial skeleton.

  • Shapes of Bones:

    • Long Bones:
    • Longer than they are wide; examples include limb bones.
    • Short Bones:
    • Cube-shaped bones found in the wrist and ankle; includes sesamoid bones like the patella.
    • Flat Bones:
    • Thin, flat, slightly curved bones such as the sternum, scapulae, ribs, and most skull bones.
    • Irregular Bones:
    • Bones with complicated shapes including vertebrae and hip bones.
Gross Anatomy of Bone

  • Compact and Spongy Bone:

    • Compact Bone:
    • Dense outer layer found on every bone, appearing smooth and solid.
    • Spongy Bone:
    • Composed of a honeycomb structure made of small, needle-like or flat pieces called trabeculae.
    • The open spaces between trabeculae are filled with red or yellow marrow.

  • Structure of a Typical Long Bone:

    • All long bones consist of a shaft (diaphysis) and bone ends (epiphyses):
    • Diaphysis:
      • Tubular shaft forming the long bone.
      • Surrounded by compact bone encasing a central medullary cavity, which in adults is filled with yellow marrow.
    • Epiphyses:
      • Ends of long bones featuring compact bone externally and spongy bone internally.
      • Covered by articular cartilage at joint surfaces.
      • Contains an epiphyseal line, a remnant of the epiphyseal plate indicating where bone growth occurs during childhood.

  • Membranes:

    • Periosteum:
    • Covers the external surfaces of bones except at joints.
    • Serves as anchoring points for tendons and ligaments.
    • Endosteum:
    • Delicate connective tissue membrane covering the internal surfaces of bones.
    • Lines canals passing through compact bone.
Vascularization and Innervation of Bone
  • Blood Vessels and Nerves:
    • Bones are well vascularized.
    • Nutrient arteries and veins serve the diaphysis, supplying bone marrow and spongy bone, and branching outward to supply compact bone.
Bone Markings

  • Definition:

    • Bone markings are sites of muscle, ligament, and tendon attachment on external surfaces; they also relate to joint formation and conduits for blood vessels and nerves.

  • Types of Bone Markings:

    1. Projections That Are Sites of Muscle and Ligament Attachment:
    • Tuberosity: Large rounded projection; may be roughened.
    • Crest: Narrow ridge of bone, usually prominent.
    • Trochanter: Very large, blunt, irregularly shaped process (notable in femur).
    • Line: Narrow ridge, less prominent than crest.
    • Tubercle: Small rounded projection.
    • Epicondyle: Raised area on or above a condyle.
    • Spine: Sharp, slender, pointed process.
    1. Surfaces That Help to Form Joints:
    • Head: Bony expansion carried on a narrow neck.
    • Facet: Smooth, nearly flat articular surface.
    • Condyle: Rounded articular projection, often with corresponding fossa.
    1. Depressions and Openings for Passage of Blood Vessels and Nerves:
    • Groove/Furrow: Narrow indentation.
    • Fissure: Slit-like opening.
    • Foramen: Round or oval opening through a bone.
    • Meatus: Canal-like passageway.
    • Sinus: Cavity within a bone, often filled with air and lined with mucous membrane.
    • Fossa: Shallow basin-like depression, sometimes serving as an articular surface.
Microscopic Anatomy of Bone

  • Major Cell Types in Bone Tissue:

    • Osteoprogenitor Cells:
    • Mitotically active stem cells that can differentiate into osteoblasts when stimulated.
    • Osteoblasts:
    • Bone-forming cells responsible for synthesizing bone matrix.
    • Osteocytes:
    • Mature bone cells residing in lacunae, responsible for maintaining bone matrix and communicating with osteoblasts and osteoclasts for remodeling.
    • Osteoclasts:
    • Multinucleate cells involved in bone resorption, breaking down bone material.

  • Microscopic Anatomy of Compact Bone:

    • Composed of:
    • Osteon (Haversian System): The structural unit of compact bone, elongated cylinder running parallel to the long axis, acts as a weight-bearing pillar.
    • Lamellae: Rings of bone matrix surrounding the central canal, with collagen fibers arranged in varied directions to provide strength.
    • Central (Haversian) Canal: Runs through the core of an osteon, containing blood vessels and nerve fibers.
    • Lacunae: Small cavities housing the osteocytes; lamellae may also exist outside the osteons.

  • Microscopic Anatomy of Spongy Bone:

    • Appears disorganized but is structured along lines of stress to resist forces.
    • Trabeculae: Provide strength, likened to cables on a suspension bridge.
    • While osteons are absent, trabeculae do contain irregularly arranged lamellae and osteocytes, with capillaries in the endosteum supplying essential nutrients.