Bone Structure

Macroscopic Bone Structure:

• diaphysis- bone shaft, body.
• epiphyses- distal and proximal ends of the bone.
• metaphyses- regions where the diaphysis joins the epiphyses.
• articular cartilage- a thin layer of hyaline cartilage covering the part of the epiphysis where the bone forms an articulation (joint) with another bone. It reduces friction and absorbs shock. Damage repair of this cartilage is limited.
• periosteum- a tough sheath of dense irregular connective tissue that surrounds the bone surface wherever it's not covered by articular cartilage. It contains cells that allow the bone to grow in diameter, nourishes bone tissue, assists in fracture repair, and serves as a point of attachment for ligaments and tendons.
• medullary cavity- space within the diaphysis that contains yellow bone marrow.
• endosteum- thin membrane that lines the medullary cavity; contains a single layer of bone-forming cells.

Microscopic Bone Structure:

• matrix - 25% water, 25% collagen fibers, and 50% crystallized mineral salts.
• calcification- crystallization of mineral salts that have been deposited in the collagen fibers of the matrix.

3 major cell types:

1. osteoblasts - bone-building cells. These cells synthesize and secrete matrix components.
2. osteocytes- osteoblasts that have become trapped in the bone matrix. They are mature bone cells that help maintain the bone tissue.
3. osteoclasts- huge cells derived from fusion of monocytes, concentrated in the endosteum. They break down bone matrix for reabsorption.