Introduction

• The skeletal system includes the bones of the skeleton and cartilages, ligaments and other connective tissues that stabalize and interconnect bones. It's functions include structural support, storage of minerals and lipids, blood cell production, protection and leverage for muscle movements.

Classification of bones

Bone Shapes

• Includes long, short, flat, irregular, sesamoid and sutural bones.

Bone Structure

• Long bones have a diaphysis, epiphysis, articular cartilage and a marrow cavity. Smaller bones and flat bones often lack a marrow cavity.
• The two type of bone tissue is compact and spongy. The marrow canal contains yellow bone marrow (for lipid storage) and the spaces in spongy bone contains red bone marrow (for blood cell production)

Bone Histology

Bone tissue

• a supporting connective tissue made with a solid matrix

The Matrix of Bone

• Largely made of hydroxyapotite crystals (Ca, PO4, and OH molecules) with a collagen foundation

Cells in Bone

• Osteocytes, located within lacunae, are the most abunant cells. Osteoblasts synthesize the bony matrix by osteogenesis. Osteoclasts dissolve the matrix through osteolysis. Osteoprogenitor cells are precursor cells which become osteoblasts.

Compact and Spongy Bone

• The basic functional unit of compact bone is the osteon, containing osteocytes arranged around a central canal (Haversian). Lamellae are layers of calcified matrix. Canaliculi within and between lamellae interconnect lacunae and allow cells to connect through cellular extensions.
• Spongy bone contains trabeculae, typically in an open network of struts and bars. No canal network is found within the matrix.
• Compact bone is located where stresses (forces) come from a limited range of directions, such as along the diaphysis of some bones. Spongy bone is located where stresses are few or come from many directions, such as the epiphysis of some bones.

The Periosteum and Endosteum

• A bone is covered by a fibrous periosteum and lined within by the endosteum.
• Both tissues contain osteoprogenitor cells and osteoblasts, while the endosteum also has osteoclasts.