Introduction to Bone and Skeletal System

• Durability of Bones: Bones and teeth are the most durable remains of a living organism, serving as vivid reminders of life.

• Dynamic Nature of Skeleton: The skeleton is composed of dynamic tissues, consisting of cells permeated with nerves and blood vessels.

• Osteology: The study of bone.

Components of the Skeletal System

• Skeletal System Composition: Made of bones, cartilages, and ligaments.

  • Cartilage: Serves as a precursor to most bones and covers many joint surfaces of mature bone.

  • Ligaments: Hold bones together at joints.

  • Tendons: Connect muscle to bone.

Functions of the Skeleton

• Support: Provides structural support to the body, holding up muscles.

• Protection: Safeguards vital organs such as the brain, spinal cord, heart, and lungs.

• Movement: Facilitates movements through limb actions and muscle-bone interaction.

• Electrolyte Balance: Regulates calcium and phosphate ion levels.

• Acid-base Balance: Buffers blood against pH changes.

• Blood Formation: Red bone marrow produces blood cells.

Bone Tissue Overview

• Definition: Osseous tissue is a type of connective tissue hardened by calcium phosphate and minerals (calcification).

• Composition: Bones consist of bone tissue, marrow, cartilage, adipose tissue, nervous tissue, and fibrous connective tissue.

• Remodeling: Continual physiological interaction and remodeling occurs with other organ systems.

General Bone Features

• Types of Bones:

  • Flat Bones: Protect soft organs; curved but wide and thin.

  • Long Bones: Longer than wide and act as rigid levers.

  • Short Bones: Equal in length and width; allow gliding movement.

  • Irregular Bones: Elaborate shapes that do not fit other categories.

• Compact vs. Spongy Bone:

  • Compact Bone: Dense outer shell of long bones.

  • Spongy Bone: Lighter, found at the ends of long bones and in the middle of others, contains red bone marrow.

• Key Structures:

  • Diaphysis: Shaft of long bone, primarily compact bone.

  • Epiphyses: Enlarged ends of long bone for joint strength.

  • Articular Cartilage: Covers joint surfaces for smooth movement.

  • Nutrient Foramina: Tiny holes allowing blood vessels to penetrate bone.

  • Periosteum: External sheath covering bone, important for growth and fracture healing.

  • Endosteum: Thin layer lining the marrow cavity, involved in bone remodeling.

  • Epiphyseal Plate: Hyaline cartilage site for bone length increase; turns into an epiphyseal line in adults.

Bone Cells

• Types of Bone Cells:

  • Osteogenic Cells: Stem cells in endosteum and periosteum that produce osteoblasts.

  • Osteoblasts: Bone-forming cells that synthesize the organic component of bone matrix.

  • Osteocytes: Former osteoblasts trapped in matrix; regulate bone density and calcium levels.

  • Osteoclasts: Large cells that dissolve bone, playing a critical role in bone remodeling.

• Bone Remodeling: Combination of actions from both osteoblasts and osteoclasts is key to bone reshaping.

The Bone Matrix

• Composition: About one-third organic (collagen, glycoproteins) and two-thirds inorganic (hydroxyapatite, calcium carbonate).

• Bone Characteristics: Bone is a composite of ceramic and polymer, providing strength and flexibility.

• Conditions Related to Matrix:

  • Rickets: Soft bones due to calcium deficiency.

  • Osteogenesis Imperfecta: Brittle bones from lack of collagen.

Spongy Bone

• Structure: Made of slivers (spicules) and thin plates (trabeculae) with spaces for marrow.

• Functionality: Provides strength with reduced weight, adapting to mechanical stress.

Bone Marrow

• Types:

  • Red Bone Marrow: Produces blood cells, present in children and certain adult bones.

  • Yellow Bone Marrow: Fatty tissue, present in adults as red marrow turns to yellow.

Bone Growth and Remodeling

• Types of Growth:

  • Length Growth: Via epiphyseal plates.

  • Width Growth: Appositional growth through new bone deposition from periosteum.

• Bone Remodeling: Occurs continually to repair microfractures and adapt to stress, guided by Wolff's law.

Calcium Homeostasis

• Role of Calcium: Essential for bodily functions like muscle contraction and blood clotting; predominantly stored in bones.

• Hormonal Regulation:

  • Calcitriol: Active form of Vitamin D; increases calcium absorption and stimulates osteoclasts.

  • Calcitonin: Lowers blood calcium by inhibiting osteoclasts and stimulating osteoblasts.

  • Parathyroid Hormone (PTH): Raises blood calcium, promotes osteoclast activity, and enhances renal absorption of calcium.

• Disorders:

  • Hypocalcemia: Causes include Vitamin D deficiency, thyroid tumors.

  • Osteoporosis: Severe loss of bone density, especially post-menopause in women.

Treatment of Bone Disorders

• Fractures: Treatment varies from closed reduction, open reduction, to the use of casts or traction.

• Osteoporosis Management: Medications, lifestyle changes, and possibly hormone replacement are key treatment strategies.

Conclusion

• Bone Health: Maintaining a balanced diet rich in calcium and engaging in physical activity are essential for healthy bone growth and maintenance throughout life.