Anatomy and Physiology 1: Chapter 6 - Osseous Tissue

Overview of the Skeletal System

• Components: Bones, cartilage, ligaments, and connective tissues.
• Functions:
  • Support
  • Storage of minerals (e.g., calcium) and lipids (fat in yellow bone marrow)
  • Blood cell production in red bone marrow
  • Protection of organs (e.g., rib cage, skull)
  • Leverage for muscles

Bone Classification by Shape

• Sutural (Wormian) Bones: Small, flat, irregular bones found between skull sutures; not present in everyone.
• Irregular Bones: Complex shapes; e.g., vertebrae, pelvic bones.
• Short Bones: Boxy; e.g., carpal bones (wrist) and tarsal bones (ankles).
• Flat Bones: Thin, parallel surfaces; e.g., bones of the skull, sternum, ribs.
• Long Bones: Long and slender; e.g., humerus, femur.
• Sesamoid Bones: Small, round, flat; found in tendons (e.g., patella).

Structure of a Long Bone

• Diaphysis: Shaft of the bone; consists of compact (dense) bone.
• Epiphysis: Ends of the bone; consist mostly of spongy (trabecular) bone.
• Metaphysis: Area where diaphysis and epiphysis meet.
• Marrow (Medullary) Cavity: Contains bone marrow (red and yellow).
• Articular Cartilage: Smooth, thin cartilage covering joint surfaces.

Bone Tissue

• Matrix: Dense due to calcium salts; contains collagen fibers.
• Osteocytes: Mature bone cells in lacunae; maintain bone matrix.
• Canaliculi: Narrow passageways allowing exchange between osteocytes and blood vessels.
• Periosteum: Membrane covering outer surface of bones.

Bone Cells

1. Osteogenic Cells: Stem cells in periosteum and endosteum; produce osteoblasts.
2. Osteoblasts: Immature cells that produce new bone matrix.
3. Osteocytes: Mature bone cells maintaining bone tissue.
4. Osteoclasts: Large, multinucleated cells that dissolve bone matrix (osteolysis).

Bone Matrix

• Composition: Two-thirds calcium phosphate, one-third collagen.
• Hydroxyapatite: Primary calcium salt in matrix.

Compact Bone Structure

• Osteons: Units of dense bone.
• Central Canal: Contains blood vessels.
• Lamellae: Layers of matrix.
• Canaliculi: Connect osteocytes to blood supply and each other.

Spongy Bone Structure

• Trabeculae: Mesh-like structure with open spaces.
• Red Bone Marrow: Between trabeculae; forms blood cells.
• Yellow Bone Marrow: Stores fat.

Periosteum and Endosteum

• Periosteum: Protective outer layer of bone; fibrous and cellular.
• Endosteum: Lines marrow cavity; active during bone growth and repair.

Bone Ossification and Growth

• Endochondral Ossification: Replaces cartilage model with bone; primary method for forming most bones.
• Intramembranous Ossification: Occurs in dermis; forms flat bones like the skull and clavicles.
• Growth Plates: Cartilage allowing bone lengthening; close at end of growth (epiphyseal line).

Bone Remodeling

• Continuous process involving osteocytes, osteoblasts, and osteoclasts.
• Balanced activity maintains bone density.
• Exercise stimulates bone-strengthening.

Nutritional and Hormonal Influence

• Nutrients: Calcium, phosphorus, vitamin D3 (for calcitriol), small amounts of magnesium, fluoride.
• Hormones: Growth hormone, thyroxine, sex hormones, calcitonin, parathyroid hormone (PTH).

Calcium Homeostasis

• Skeleton as Calcium Reserve: 99% of body’s calcium stored in bones.
• Parathyroid Hormone (PTH): Increases blood calcium levels.
• Calcitonin: Decreases blood calcium levels.

Fracture Repair

1. Hematoma Formation: Blood clot stabilizes fracture.
2. Callus Formation: Internal (spongy bone) and external (cartilage) calluses stabilize break.
3. Spongy Bone Formation: Replaces cartilage in callus.
4. Compact Bone Formation: Remodels bone to original shape.

Age-Related Changes

• Osteopenia: Reduced bone mass; common with aging.
• Osteoporosis: Severe loss of bone mass; higher risk in post-menopausal women.
• Hormonal Effects: Affect bone density, especially post-menopause in women.

Visual References

• Images illustrating bone components, ossification steps, x-rays showing growth plates and epiphyseal lines, and more are essential for understanding detailed structures and processes described.