Unit+2.1+Lecture_updated

Chapter 06: Bones and Skeletal Tissues

6.1 Skeletal Cartilages

  • Initially made mostly of cartilage; replaced by bone, except in flexible areas.

Basic Structure, Types, and Locations of Cartilage

Structure

  • Skeletal cartilage: highly resilient, composed mainly of water, lacks blood vessels and nerves.

  • Perichondrium: connective tissue layer surrounding cartilage, aids in nutrient delivery and resists expansion.

  • Chondrocytes: cartilage cells found in lacunae within the extracellular matrix.

Types of Cartilage

  1. Hyaline Cartilage

    • Most abundant, provides support, flexibility, and resilience.

    • Contains only collagen fibers.

    • Found in joints, ribs, larynx, and nose.

  2. Elastic Cartilage

    • Similar to hyaline but contains elastic fibers.

    • Located in the external ear and epiglottis.

  3. Fibrocartilage

    • Contains thick collagen fibers; offers great tensile strength.

    • Found in menisci of knees and intervertebral discs.

Growth of Cartilage

  • Appositional Growth: matrix secreted by cartilage-forming cells in perichondrium.

  • Interstitial Growth: chondrocytes divide and secrete new matrix within cartilage.

  • Calcification: occurs during normal bone growth or can happen during aging; hardened cartilage differs from bone.

6.2 Functions of Bones

  • Support: Provides structure for body and organs.

  • Protection: Safeguards vital organs like the brain and spinal cord.

  • Movement: Bones act as levers for muscle action.

  • Mineral Storage: Stores calcium, phosphorus, and growth factors.

  • Blood Cell Formation: Hematopoiesis occurs in red marrow.

  • Triglyceride Storage: Fat storage for energy.

  • Hormone Production: Bones secrete osteocalcin for regulating insulin.

6.3 Classification of Bones

Groups by Location

  • Axial Skeleton: Skull, vertebral column, rib cage.

    • Functions: protect, support, carry body parts.

  • Appendicular Skeleton: Limb bones and girdles (shoulder and hip bones).

Groups by Shape

  1. Long Bones: Longer than wide, e.g., limb bones.

  2. Short Bones: Cube-shaped, e.g., wrist and ankle bones.

  3. Flat Bones: Thin and curved, e.g., sternum, ribcage.

  4. Irregular Bones: Complicated shapes, e.g., vertebrae.

6.4 Bone Structure

  • Bones are organs with various tissue types: bone tissue, cartilage, nervous and connective tissue.

  • Compact Bone: Dense, outer layer.

  • Spongy Bone: Internal structure, contains marrow.

  • Structure Levels: Gross, microscopic, and chemical.

6.5 Bone Development

  • Ossification: formation of bone tissue, begins in month 2 of fetal development.

  • Types of Ossification:

    • Endochondral Ossification: Replacement of hyaline cartilage by bone, forming most of the skeleton.

    • Intramembranous Ossification: Bones form from a fibrous connective tissue membrane, mainly in flat bones (e.g., skull).

6.6 Bone Remodeling

  • Regular cycling of bone mass: 5-7% recycled weekly.

  • Both resorption (breakdown) and deposit (building) occur.

  • Osteoclasts: break down bone; Osteoblasts: build bone.

  • Mechanical stress and hormonal signals regulate remodeling.

6.7 Bone Repair

  • Fractures: classified by position, completeness, and skin penetration.

  • Treatment involves reduction (realignment) and immobilization.

  • Stages of Repair:

    1. Hematoma formation.

    2. Fibrocartilaginous callus formation.

    3. Bony callus formation.

    4. Bone remodeling.

  • Healing and strength develop through mechanical stressors.