Chapter 6: Bone Tissue and the Skeletal System

6.1 The Functions of the Skeletal System

• Support: Framework for body; supports soft tissues and maintains posture.

• Movement: Acts as levers for muscles to enable movement.

• Protection: Shields vital organs (e.g., skull protects the brain; ribcage protects heart and lungs).

• Mineral and Fat Storage: Stores minerals like calcium and phosphorus; contains yellow bone marrow for fat storage.

• Hematopoiesis: Red bone marrow produces blood cells.

• Hormonal Role: Produces osteocalcin, regulating insulin secretion and glucose homeostasis.

6.2 Bone Classification

• Long Bones: Longer than wide (e.g., femur, humerus). Leverage for movement.

• Short Bones: Cube-like (e.g., carpals, tarsals). Stability and support.

• Flat Bones: Thin and curved (e.g., skull bones, sternum). Protection and muscle attachment.

• Irregular Bones: Complex shapes (e.g., vertebrae, pelvis). Protection and support.

• Sesamoid Bones: Small, round bones embedded in tendons (e.g., patella). Reduce friction and modify pressure.

6.3 Bone Structure

Macroscopic Structure:

• Diaphysis: Shaft of a long bone.

• Epiphysis: Expanded ends containing spongy bone and red marrow.

• Metaphysis: Contains epiphyseal (growth) plate in growing bones.

• Medullary Cavity: Hollow space in diaphysis, containing yellow marrow.

• Endosteum: Thin membrane lining the medullary cavity; involved in remodeling.

• Periosteum: Fibrous outer covering; provides blood supply and attachment for tendons.

Microscopic Structure:

• Compact Bone: Dense and strong; contains osteons (Haversian systems) housing blood vessels and nerves.

• Spongy Bone: Lighter and porous; contains trabeculae supporting red bone marrow.

Bone Cells:

• Osteogenic Cells: Stem cells that differentiate into osteoblasts.

• Osteoblasts: Bone-forming cells producing bone matrix.

• Osteocytes: Mature bone cells maintaining bone tissue.

• Osteoclasts: Bone-resorbing cells breaking down bone matrix.

6.4 Bone Formation and Development (Ossification)

Two Main Processes:

1. Intramembranous Ossification: Bone forms directly from mesenchymal tissue (e.g., skull, clavicle).

2. Endochondral Ossification: Bone replaces hyaline cartilage (e.g., most bones).

Bone Growth:

• Longitudinal Growth occurs at the epiphyseal plate, consisting of four zones:

  • Resting zone: Inactive cartilage cells.

  • Proliferation zone: Rapidly dividing chondrocytes.

  • Hypertrophic zone: Enlarging chondrocytes.

  • Calcification zone: Calcification of cartilage matrix; allows osteoblasts to form new bone.

• Appositional Growth increases bone diameter.

6.5 Fractures and Bone Repair

Types of Fractures:

• Closed (Simple): Bone breaks but does not puncture skin.

• Open (Compound): Bone breaks and pierces skin.

• Transverse: Straight-across break.

• Spiral: Twisting break.

• Comminuted: Bone shatters into fragments.

• Impacted: One end drives into the other.

• Greenstick: Incomplete fracture common in children.

Stages of Bone Repair:

1. Hematoma Formation: Blood clot at fracture site.

2. Fibrocartilaginous Callus Formation: Stabilizes the break with cartilage and fibrous tissue.

3. Bony Callus Formation: Osteoblasts create new bone.

4. Bone Remodeling: Reshapes bone to restore original structure.

6.6 Exercise, Nutrition, and Hormones Affecting Bone Health

• Exercise: Weight-bearing activities stimulate remodeling and increase bone density.

• Nutritional Requirements:

  • Calcium: Necessary for matrix formation and repair.

  • Vitamin D: Essential for calcium absorption.

  • Vitamin K: Supports mineralization.

  • Magnesium and Fluoride: Contribute to bone strength.

  • Omega-3 Fatty Acids: Reduce inflammation.

• Hormonal Regulation:

  • Growth Hormone: Stimulates growth.

  • Thyroxine: Regulates metabolism.

  • Sex Hormones (Estrogen & Testosterone): Promote formation and inhibit osteoclasts.

  • Parathyroid Hormone: Increases blood calcium by stimulating osteoclasts.

  • Calcitonin: Decreases blood calcium by inhibiting osteoclasts.

6.7 Aging and Bone Tissue

• Aging effects:

  • Reduction in bone mass (more resorption than deposition).

  • Increased fracture risk (osteoporosis common, especially in postmenopausal women).

  • Decreased collagen production, making bones brittle.

• Osteoporosis Prevention:

  • Adequate calcium and vitamin D intake.

  • Regular weight-bearing exercises.

  • Hormonal therapy in severe cases.

Summary of Key Concepts

• Skeletal system provides support, movement, protection, storage, and blood cell production.

• Bone tissue consists of osteocytes, osteoblasts, and osteoclasts involved in remodeling.

• Most bones formed by endochondral ossification; intramembranous forms flat bones.

• Bone fractures heal via hematoma, callus formation, and remodeling.

• Exercise, diet, and hormones significantly influence bone health.

• Aging leads to bone loss, increasing osteoporosis risk.

Chapter 7: The Axial Skeleton

The axial skeleton consists of 80 bones: skull, vertebral column, and thoracic cage, providing protection, support, and integrity.

7.1 Divisions of the Skeletal System

1. Axial Skeleton (80 bones): Skull, vertebral column, thoracic cage.

2. Appendicular Skeleton (126 bones): Limbs and girdles.

7.2 The Skull

Components of the Skull (22 bones):

• Cranial Bones (8 bones): Protect brain and form the cranium.

  • Unique features of cranial bones include:

    • Frontal Bone: Forms forehead; contains supraorbital foramen.

    • Parietal Bones (2): Superior and lateral aspects; articulate via sutures.

    • Temporal Bones (2): Contain structures for hearing; house external auditory meatus.

    • Occipital Bone: Foramen magnum for spinal cord passage.

    • Sphenoid Bone: Keystone of skull; holds the pituitary gland.

    • Ethmoid Bone: Contributes to nasal structure and contains olfactory features.

• Facial Bones (14 bones): Form the face and include:

  • Maxillae (2): Upper jaw; house infraorbital foramen.

  • Mandible (1): Only movable bone of the skull; holds mental foramen.

  • Additional bones feature (e.g., zygomatic, nasal, and lacrimal bones).

Other Unique Skull Features:

• Sutures: Joints between bones in the skull.

• Paranasal Sinuses: Spaces in certain bones, aiding in voice and weight reduction.

• Hyoid Bone: Supports the tongue and crucial for speech.

7.3 The Vertebral Column

• Composed of 26 vertebrae, provides structure and protects the spinal cord.

• Regions:

  • Cervical (7): Smallest vertebrae; includes atlas (C1) and axis (C2).

  • Thoracic (12): Articulates with ribs.

  • Lumbar (5): Largest vertebrae for weight support.

  • Sacrum (5 fused): Forms posterior pelvis; articulates with hip.

  • Coccyx (4 fused): Vestigial structure.

Intervertebral Discs:

• Function in shock absorption; composed of nucleus pulposus and annulus fibrosus.

7.4 The Thoracic Cage

• Protects vital organs; includes the sternum and ribs.

Sternum parts:

• Manubrium: Upper section articulates with clavicles.

• Body: Articulates with ribs.

• Xiphoid Process: Cartilaginous tip at the lower end.

Ribs Types:

• True Ribs (1-7): Directly attach to sternum.

• False Ribs (8-12): Indirect attachment.

• Floating Ribs (11-12): No anterior attachment; protect kidneys.

7.5 Embryonic Development of the Axial Skeleton

• Develops from mesoderm.

  • Stages include notochord formation, somite differentiation, and ossification processes.

• Congenital Abnormalities: Examples include cleft palate and spina bifida.

Key Takeaways

• The axial skeleton consists of crucial bones for vital organ protection.

• Vertebral column and thoracic cage play significant roles in structure and function.

• The development stems from mesodermal tissue and is essential for proper formation.

Chapter 8: The Appendicular Skeleton

• Comprises 126 bones, including limbs and girdles supporting movement.

8.1 The Pectoral Girdle

• Clavicles (2): Only horizontal long bones; commonly fractured due to position.

• Scapulae (2): Triangular bones allowing arm attachment.

8.2 The Upper Limb

• Contains 30 bones: humerus, radius, ulna, carpals, metacarpals, phalanges.

8.3 The Pelvic Girdle

• Comprises two hip bones (os coxae); articulates with the sacrum.

• Differences in Male vs. Female Pelvis:

  • Details regarding pelvic inlet, outlet, and other anatomical differences.

8.4 The Lower Limb

• Contains 30 bones including femur, tibia, fibula, and others important for mobility and support.

8.5 Embryonic Development of the Appendicular Skeleton

• Forms from limb buds and undergoes similar ossification processes as other skeletal developments.

• Congenital Abnormalities: Examples include clubfoot and polydactyly.

Key Takeaways

• Appendicular skeleton crucial for mobility with unique features enhancing function.

• Sex differences in the pelvis reflect adaptations for childbirth.

Chapter 9: Joints

9.1 Introduction to Joints

• Joints are where bones meet, enabling movement and providing stability.

Functional Classification of Joints:

1. Synarthrosis: Immovable (e.g., sutures).

2. Amphiarthrosis: Slightly movable (e.g., pubic symphysis).

3. Diarthrosis: Freely movable (e.g., shoulder joint).

Structural Classification of Joints:

1. Fibrous Joints: Connected by dense connective tissue.

2. Cartilaginous Joints: Connected by cartilage.

3. Synovial Joints: Fluid-filled, allowing movement.

9.2 Fibrous Joints

• Types include sutures, syndesmoses, and gomphoses with their unique characteristics.

9.3 Cartilaginous Joints

• Types include synchondroses and symphyses.

9.4 Synovial Joints

• Structural features allow various degrees of movement.

9.5 Types of Synovial Joints

• Includes six types: plane, hinge, pivot, condyloid, saddle, ball-and-socket.

9.6 Joint Stability & Movement

• Stability factors include joint shape, ligament number, and muscle tone.

9.7 Joint Movements

• Types of movements like flexion, extension, abduction, adduction, and others.

9.8 Common Joint Disorders

• Disorders: Sprains, dislocations, bursitis, osteoarthritis, rheumatoid arthritis, gout, etc.

Key Takeaways

• Joints are fundamental for mobility while maintaining structural integrity of the skeletal system.