Bone Anatomy

Bone Anatomy

Long Bone Areas

A long bone, such as the humerus (upper arm bone), can be divided into different areas:

  • Epiphysis: The ends of the bone, both proximal and distal. Mnemonic: "E for End." The epiphysis articulates (forms a joint) with other bones.
    • Proximal Epiphysis (Humerus Example): Forms part of the shoulder joint by articulating with the scapula, enabling upper limb movement.
    • Distal Epiphysis (Humerus Example): Forms part of the elbow joint.
  • Articular Cartilage: A covering of hyaline cartilage found at both proximal and distal epiphyses within a joint to facilitate smooth movement.
  • Diaphysis: The shaft of the bone.
  • Metaphysis: The area between the diaphysis and the epiphyses; this is where bone growth in length occurs. Contains the epiphyseal plate (growth plate).
    • Epiphyseal Plate (Growth Plate): A line of cartilage where bone growth occurs in growing individuals.
    • Epiphyseal Line: The line that forms when the epiphyseal plate closes and the cartilage is replaced by bone in mature individuals.

Bone Structure

  • The long bone is hollow.
  • Medullary Cavity: The hollow space within the diaphysis. Contains yellow bone marrow (primarily fat).
  • Nutrient Artery: Penetrates through the diaphysis and enters the medullary cavity to supply the bone.

Connective Tissue Layers

  • Periosteum: The dense irregular connective tissue layer that wraps around the outside of the bone (perimeter).
    • Analogy: Similar to the periosteal layer of the dura mater surrounding the cranial cavity.
  • Endosteum: The connective tissue layer that lines the medullary cavity inside the shaft of long bones.

Bone Marrow

  • Yellow Bone Marrow: Found within the medullary cavity in adults; primarily fat.
  • Red Bone Marrow: Found within the spongy bone in the epiphyses; responsible for producing red blood cells, white blood cells, and platelets

Types of Bone

  • Compact Bone: Dense bone found in the diaphysis (shaft) and the outer covering of the epiphysis. Appears very dense.
  • Spongy Bone: Bone with many air pockets, resembling a sponge or honeycomb-like structure. Found in the interior of the epiphysis; contains red bone marrow.

Summary of Key Points

  • Epiphysis: Head/ends of the bone.
  • Diaphysis: Shaft of the long bone.
  • Compact Bone: Found in the diaphysis and outer covering of the epiphysis.
  • Spongy Bone: Found in the interior of the epiphysis; contains red bone marrow for blood cell/platelet production.