L4.3.1: Gross Anatomy

• REGIONS:

  ● Diaphysis (shaft) - makes up most of its length

  ● Epiphysis (ends) - composed of spongy bone because it is responsible for growth (has proximal and distal ends)
• Diaphysis – SHAFT

  ○ Makes up most of the bone’s length.

  ■ Hollow tubular area that runs from the proximal up to the distal end.

  ○ Composed of compact bones because it needs strength.
• Epiphysis (Proximal and Distal) – ENDS

  ○ Composed mostly of spongy bone enclosed by a thin layer of compact bone.

  ○ May be involved in hematopoiesis due to the trabeculae.
• Coverings

  • periosteum
  • articular cartilage
  • epiphyseal plate
  • epiphyseal line
  • endosteum
  • medullary cavity
• Periosteum

  ● Covers the diaphysis

  ● Made up of fibrous connective tissue Sharpey’s fiber (Perforating) - an adhesive that makes the periosteum intact inside the diaphysis.

  2 layers:

  ● Fibrous layer (dense irregular)

  ● Cellular layer (cells involved in the growth repair and remodeling of the bone)
• Articular cartilage

  ● Covers the epiphysis

  ● Made of hyaline cartilage

  ● Decreases friction to prevent pain during movement
• Epiphyseal plate

  ● Flat plate of hyaline cartilage seen in young, growing bone

  ● Causes lengthwise growth of long bone

  ● If this plate is still open, it indicates that growth can still happen

  ● Once it closes, growth ends and it will become an epiphyseal line

  ● Undergoes fibrosis
• Epiphyseal line

  ● Remnant of the epiphyseal plate

  ● Seen in adult bones

  ● Cartilage is actually gone, just remnants
• Endosteum

  ● Covers the medullary cavity

  ● It lines the inner surface of the shaft

  ● Still has the presence of cell and fibrous connective tissue like periosteum
• Medullary cavity

  ● The cavity inside the shaft

  ● Contains yellow marrow (mostly fat) in adults

  ● Contains red marrow for blood cell formation in infants until age 6-7

  ○ After this, blood cell formation happens in the liver