Chap07 Bone Tissue

Support: Provides structural support for the body; limb bones and vertebrae support body weight, jaw bones support teeth, and some bones support viscera.
Protection: Safeguards vital organs including the brain, spinal cord, heart, and lungs.
Movement: Facilitates movement through limb motions, breathing, and other actions reliant on the skeletal structure.
Electrolyte Balance: Maintains calcium and phosphate levels in the body.
Acid-Base Balance: Buffers the blood against large pH fluctuations by adjusting phosphate and carbonate salt levels.
Blood Formation: Red bone marrow acts as the primary site for producing blood cells.
Hormone Secretion: Bone cells secrete hormones influencing insulin action and moderating stress responses.

Definition: Bone (osseous tissue) is a type of connective tissue where the matrix is hardened through mineral content (calcium phosphate and others).
Mineralization/Calcification: Refers to the hardening of bone.
Composition of a Bone: Each bone (an organ) consists of osseous tissue, bone marrow, cartilage, adipose tissue, nervous tissue, and fibrous connective tissue.
Terminology: The term "bone" can refer either to the physical organ or to the osseous tissue itself.

Variety of Shapes:
- Flat Bones: Thin, curved plates that protect organs (e.g., parietal bones of the skull).
- Long Bones: Longer than wide, serve as rigid levers (e.g., humerus, femur).
- Short Bones: Similar in length and width (e.g., wrist and ankle bones).
- Irregular Bones: Complex shapes (e.g., vertebrae).
General Anatomy of Long Bone:
- Compact Bone: Dense outer layer enclosing the marrow cavity.
- Spongy Bone: Loosely organized tissue found at the ends and center, adding strength while minimizing weight.
- Diaphysis: Shaft providing leverage.
- Epiphysis: Enlarged end of a long bone, strengthening joints and anchoring ligaments.
- Epiphyseal Line: Marks the area of past growth (epiphyseal plate).
- Articular Cartilage: Covers joint surfaces enabling smooth movement.
- Nutrient Foramina: Small openings for blood vessels.
- Periosteum: Sheath covering outer bone, consisting of outer fibrous and inner osteogenic layers.
- Endosteum: Lining of marrow cavity and internal surfaces.
- Flat Bones Structure: Consists of two layers of compact bone surrounding a middle layer of spongy bone (diploe).

Types of Bone Cells:
- Osteogenic Cells: Stem cells in the inner layers of periosteum and endosteum that develop into osteoblasts.
- Osteoblasts: Bone-forming cells responsible for synthesizing the organic matrix and promoting its mineralization.
- Osteocytes: Mature osteoblasts trapped in the matrix; they aid in regulating bone remodeling and maintaining bone tissue.
- Osteoclasts: Large cells that dissolve bone, playing a key role in resorption and remodeling.

Composition:
- Organic Matter: Includes collagen and proteins, about one-third of the matrix.
- Inorganic Matter: Predominately hydroxyapatite (calcium phosphate), accounting for about two-thirds.
Importance: The combination of organic and inorganic materials gives bone its strength and flexibility.
Diseases: Rickets (deficiency in minerals) leads to weakened bones, whereas osteogenesis imperfecta (defect in collagen) leads to brittle bones.

Microarchitecture: Characterized by concentric lamellae surrounding central (Haversian) canals, forming osteons, with collagen fibers arranged in a helical pattern for strength.

Anatomy: Features a lattice structure with trabeculae, providing strength without excessive weight. All osteocytes are located close to bone marrow, in contrast to few osteons present.

Overview: This process forms flat bones like those of the skull.
Stages:
1. Osteoid Tissue Deposition: Osteoblasts lay down osteoid in mesenchyme.
2. Calcification: Mineralization of osteoid results in trapping osteocytes.
3. Honeycomb Formation: Formation of spongy bone with periosteum developing.
4. Compact Bone Formation: Surface filling creates compact bone around a spongy core.

Overview: Involves development from a cartilage model; most bones in the body develop this way.
Stages:
1. Formation of early cartilage model from mesenchyme.
2. Primary ossification center formation.
3. Vascular invasion creating marrow cavities and secondary ossification centers.
4. Develops to adult bone structure with a single marrow cavity.

Mineral Deposition: Process of crystallization in which minerals are deposited into bone via osteoblasts.
Mineral Resorption: Dissolution of bone by osteoclasts, releasing minerals back into the bloodstream.

Importance: Calcium is vital for numerous body functions; around 18% is exchanged yearly with blood.
Regulation: Calcium levels are regulated through hormones including calcitriol (activates osteoclasts), calcitonin (inhibits resorption), and parathyroid hormone (promotes calcium retention).

Overview: Phosphate supports DNA and energy production, with regulation via dietary intake and kidneys.

Types of Fractures: Include stress fractures from trauma and pathological fractures from disease. Healing involves stages from hematoma formation, soft callus, hard callus, to remodeling.

Osteoporosis: Age-related loss of bone density, assessed through bone densitometry. Treatment includes medication and prevention strategies like exercise.