Bone Histology Part 2: Mechanical Properties

Study Notes

Mechanical Properties of Bone

Bone exhibits tensile strength primarily due to collagen and compressive strength due to minerals.
Compressive properties of bone are twice that of tensile properties.
Tensile fractures are more prevalent than compression fractures.

Homogenous Cellularity

Bone contains mesenchymal cells, osteoprogenitor cells, osteoblasts (which secrete osteoid), and osteocytes (located in lacunae).
Active osteoblasts are columnar in shape; inactive osteoblasts are flat and do not secrete matrix.
Osteocytes are embedded in lacunae and communicate via gap junctions to maintain calcium balance.
Osteoclasts, derived from fused macrophages, dissolve and phagocytize bone, creating Howship’s lacunae with a scalloped edge.

Types of Bone

Woven Bone
- Immature, fibrous structure easily sectioned due to low mineralization.
- Lacunae are distributed randomly and the matrix is eosinophilic.
- Commonly found in developing bones, fracture sites, and in osteosarcoma.
Lamellar Bone
- Represents mature bone with highly organized layers that contain lacunae.
- Arranged around Haversian (osteonal) canals housing blood vessels.
- Requires special preparation techniques such as demineralization or ground sectioning.

Configurations of Bone

Cancellous Bone (Spongy or Trabecular)
- Characterized by scattered bone spicules, prevalent in developing bones.
- Predominantly located in the medullary cavity and epiphysis.
Dense Bone (Compact or Cortical)
- Consists of closely packed osteons or layers of bone, concentrated in the diaphysis of long bones.

Organization of Lamellar Bone

Haversian Systems (Osteons)
- Osteocytes are organized in concentric rings around a central canal.
Non-Haversian Systems
- Interstitial bone, representing osteons that do not surround a central canal.
Circumferential Bone
- Formed through appositional growth, resulting in additional layers at the periosteum and endosteum.
- Outer circumferential bone is formed by the periosteum; inner circumferential bone by the endosteum.

Bone Remodeling & Regulation of Serum Calcium

A decrease in calcium levels triggers osteolysis, with osteocytes extracting calcium from the bone matrix without structural alterations.
Long-term calcium demand leads to hypocalcemia, necessitating osteoclast action to remove entire osteons, which can result in osteoporosis if not filled properly.
Rickets, a result of vitamin D deficiency, causes softening and weakening of bones, impairing calcium absorption.

Description

Explore the mechanical properties of bone in this quiz on bone histology. Learn about tensile and compressive strength, and the roles of various cell types such as osteoblasts and osteocytes. Understand how these properties impact bone fractures.