Bone Tissue and Structure:
A Brief Outline
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.