Anatomy of Bones

Anatomy of Bones

Long Bones

  • Long bones are typically found in limbs and are longer than they are wide.
  • Epiphyses: The two ends of a long bone. Contain a lot of spongy bone.
  • Diaphysis: The shaft of a long bone.
  • Medullary Cavity: A cavity lining the shaft.
  • Endosteum: A layer lining the medullary cavity ('within the bone').
  • Articular Cartilage: Cartilage on the surface of the epiphyses to protect the bone at joints.
  • Periosteum: Covers the remainder of the surface of a long bone and serves as a site for stem cells for growth or repair.
  • Epiphyseal Plate/Line: The area where an epiphysis meets a diaphysis.
    • In a child, it's called the epiphyseal plate and is made of cartilage.
    • In an adult, it's called the epiphyseal line and is ossified tissue.

Major Parts of a Long Bone

  • Epiphyses: Widened ends of the long bone (proximal and distal).
  • Diaphysis: The shaft of the long bone.

Tissues

  • Spongy Bone: Primarily found in the epiphyses; some along the diaphysis. Contains red marrow.
    • Red Marrow: Used for making blood, a process known as hemopoiesis or hematopoiesis.
  • Compact Bone: Primarily along the diaphysis for rigidity and storage of minerals.
    • Extracellular Matrix (ECM): Packed with minerals such as calcium phosphate, calcium carbonate, magnesium, etc.

Linings and Coverings

  • Endosteum: The lining of the cavity in the center of the diaphysis. Contains bone stem cells.
  • Periosteum: The outer surface of the bone, present everywhere except where cartilage is found. Contains bone stem cells (osteogenic cells).
  • Medullary Cavity: The cavity in the center of the diaphysis. Contains yellow bone marrow.
    • Yellow Bone Marrow: Storage of fat for long-term energy storage.

Cartilages

  • Articular Cartilage: Found on the surface of both epiphyses, where bones touch each other for protection.
  • Epiphyseal Line: Was formerly the epiphyseal plate (cartilage) in childhood, which ossifies in adulthood once growth plates are no longer active.

Flat Bones

  • Unlike long bones, flat bones do not have a medullary cavity and therefore do not store yellow marrow.
  • Flat bones are plate-like, mainly referring to the bones of the skull and the ribs.
  • Structure:
    • Periosteum on the outer surfaces.
    • Compact bone deep to the periosteum.
    • Internal layer of spongy bone between the two layers of compact bone.
  • No medullary cavity or yellow marrow cavity.