Learning Objectives (Slides 1-3)

1. Generalized Functions of the Skeletal System

   • Support: Provides a rigid framework that maintains body shape.

   • Protection: Bones encase and protect vital organs. For example, the skull encases the brain, and the ribcage surrounds the heart and lungs.

   • Movement: Serves as levers for muscles. Movement occurs when muscles contract and pull on bones, allowing joints to function as pivots.

   • Mineral Storage: Primarily stores calcium and phosphorus. Calcium is crucial for muscle contractions, nerve function, and blood clotting.

   • Hematopoiesis: Blood cell formation occurs in the red bone marrow. Red blood cells, white blood cells, and platelets are all produced within bones, specifically the flat bones like the pelvis, sternum, and the ends of long bones.

2. Bone Types and Structures

   • Types:

     • Long Bones: Found in limbs (e.g., femur, humerus). Functions include leverage and movement.

     • Short Bones: Provide stability with little movement (e.g., carpals in the wrist).

     • Flat Bones: Protect organs and serve as points of attachment for muscles (e.g., skull, ribs, sternum).

     • Irregular Bones: Complex shapes for specific functions (e.g., vertebrae).

     • Sesamoid Bones: Embedded within tendons (e.g., patella).

   • Structure:

     • Diaphysis: The shaft of long bones; composed of compact bone that provides strength.

     • Medullary Cavity: Contains yellow marrow, primarily made up of fat cells.

     • Epiphyses: Ends of long bones; contain spongy bone with red bone marrow that supports hematopoiesis.

     • Periosteum: A dense fibrous membrane that covers the surface of bones (except at joints); essential for growth and repair.

     • Endosteum: Thin membrane that lines the medullary cavity.

3. Microscopic Structure of Bone and Cartilage

   • Bone Cells:

     • Osteocytes: Mature bone cells that maintain bone tissue.

     • Osteoblasts: Bone-building cells that secrete the bone matrix.

     • Osteoclasts: Bone-resorbing cells that break down bone tissue.

   • Bone Structure:

     • Compact Bone: Dense and forms the outer layer of bones; contains cylindrical units called osteons or Haversian systems, with central canals for blood vessels and nerves.

     • Spongy Bone: Found in the epiphyses; composed of trabeculae that form an open framework to reduce bone weight while maintaining strength.

   • Cartilage: Provides flexibility and cushioning at joints; lacks blood vessels, meaning it takes longer to heal than bone.

4. Formation, Growth, and Remodeling

   • Bone Formation (Ossification):

     • Endochondral Ossification: Most bones form from cartilage models that are gradually replaced by bone tissue.

     • Intramembranous Ossification: Some flat bones (e.g., skull bones) form directly from connective tissue.

   • Bone Growth:

     • Epiphyseal Plate: A layer of cartilage that allows for longitudinal bone growth during development.

     • Bone Remodeling: Continuous process of bone resorption by osteoclasts and formation by osteoblasts, which allows the bone to adapt to stress and injury.

Functions of the Skeletal System (Slide 4)

• Framework Support: Supports the body by providing a rigid structure that supports soft tissues and muscles.

• Protection: Bones such as the skull and ribcage protect critical organs. The vertebral column protects the spinal cord.

• Movement: Muscles are anchored to bones, and bones act as levers. The movement is facilitated by different joint types.

• Calcium Storage: Bones store calcium that can be released to maintain blood calcium levels, which is critical for physiological processes like nerve signaling and muscle contraction.

• Hematopoiesis: Red bone marrow produces blood cells, crucial for carrying oxygen, immune response, and clotting.

Types of Bones (Slide 5)

• Long Bones: Cylindrical and longer than they are wide, primarily located in the arms and legs.

  • Example: Humerus, femur.

• Short Bones: Equal length, width, and thickness, providing stability.

  • Example: Carpals (wrist bones).

• Flat Bones: Thin, often curved bones that provide a broad surface for muscle attachment and protect internal organs.

  • Example: Skull bones, sternum.

• Irregular Bones: Complex shapes that cannot be classified into other categories.

  • Example: Vertebrae, some facial bones.

• Sesamoid Bones: Small, round bones embedded in tendons to reduce friction.

  • Example: Patella (kneecap).

Structure of Long Bones (Slide 6)

• Diaphysis: A hollow shaft made of compact bone that provides strength without excessive weight.

• Medullary Cavity: Houses yellow bone marrow, which consists largely of adipocytes for energy storage.

• Epiphysis: Located at both ends of the bone; contains spongy bone with spaces filled with red marrow for blood cell production.

• Articular Cartilage: A smooth, slippery cartilage that covers the epiphyses at joint surfaces to reduce friction and absorb shock.

• Periosteum: Outer covering containing blood vessels and nerves that nourish bone.

• Endosteum: Lines the medullary cavity and plays a role in bone growth and repair.

Structure of Flat Bones (Slides 7-9)

• Thin Compact Bone Layer: Encloses spongy bone in the middle.

• Cancellous (Spongy) Bone: Found between compact bone layers, containing bone marrow.

• Diploe: The spongy bone layer within flat bones, provides some shock absorption.

• Trabeculae: The bony framework that makes up the cancellous bone, providing strength without excess weight.

Microscopic Structure of Bones (Slides 10-12)

• Connective Tissues:

  • Bone: Stronger tissue with calcified matrix.

  • Cartilage: Softer, flexible tissue without calcification.

• Bone Types:

  • Spongy Bone: Found primarily in the epiphyses, with trabeculae that create a mesh-like structure filled with red marrow.

  • Compact Bone: Composed of osteons (Haversian systems), providing a dense outer shell for strength and protection.

• Bone Cells:

  • Osteocytes: Mature cells in lacunae, which help maintain bone tissue.

  • Osteoblasts: Produce new bone by laying down the bone matrix.

  • Osteoclasts: Resorb bone tissue, allowing for growth and remodeling.

Osteon (Haversian System) (Slides 13-14)

• Components:

  • Concentric Lamellae: Rings of calcified matrix surrounding a central canal.

  • Lacunae: Small spaces that house osteocytes.

  • Canaliculi: Small channels connecting lacunae, allowing nutrients to reach osteocytes.

  • Central Canal (Haversian Canal): Contains blood vessels and nerves essential for bone health.

  • Trabeculae in Spongy Bone: Provide lightweight support with space for marrow.

Cartilage Tissue Structure (Slide 15)

• Chondrocytes: Cartilage cells located in lacunae.

• Matrix: Flexible, gel-like substance with collagen fibers providing support.

• Avascular Nature: Lack of blood vessels means slower healing compared to bone.

Bone Development (Slides 16-19)

• Bone Formation: Involves the activity of osteoblasts and osteoclasts, resulting in continual renewal and adaptation of bone.

• Osteoblasts: Secrete the organic components of bone matrix and promote mineral deposition.

• Osteoclasts: Break down bone tissue, allowing for resorption and remodeling.

• Endochondral Ossification: Most bones form from hyaline cartilage models that gradually ossify.

• Epiphyseal Plate: Growth region in long bones, which eventually ossifies after puberty to form an epiphyseal line.

Early Bone Development (Slides 20-23)

• Prenatal Development: Initial bone formation primarily consists of cartilage and fibrous structures.

• Endochondral Ossification: The process by which cartilage is replaced by bone, beginning at primary ossification centers in diaphysis and secondary centers in epiphyses.

• Newborn Skeleton: Not fully ossified, allowing for growth and flexibility during early development.

Divisions of the Skeleton (Slides 24-33)

• Axial Skeleton (80 bones): Comprises the skull, vertebral column, and thoracic cage.

  • Skull: Protects the brain and provides structure to the face.

  • Vertebral Column: Consists of 33 vertebrae, divided into cervical, thoracic, lumbar, sacral, and coccygeal regions.

  • Thoracic Cage: Made of ribs and sternum, protects heart and lungs.

• Appendicular Skeleton (126 bones): Includes the upper and lower limbs and their girdles.

  • Pectoral Girdle: Scapula and clavicle, connect the upper limbs to the axial skeleton.

  • Pelvic Girdle: Composed of coxal bones, connects the lower limbs to the axial skeleton.

Differences Between Male and Female Skeletons (Slides 34-35)

• Male Skeleton:

  • Size: Generally larger and denser.

  • Pelvis Shape: Narrow and deep, adapted for supporting more muscle mass.

• Female Skeleton:

  • Pelvis: Wider, shallower, with a larger pelvic inlet and broader pubic angle to facilitate childbirth.

Age Differences and Environmental Factors (Slide 36)

• Bone Maturation: Bones mature and reach their maximum density around age 25.

• Bone Density Decreases: Gradual loss begins after age 50, influenced by hormonal changes, reduced physical activity, and nutrition.

• Environmental Factors: Diet, physical activity, and exposure to stress all influence bone health and structure.

Joints (Slides 37-43)

• Types of Joints:

  • Synarthroses: Immovable joints, such as sutures between skull bones.

  • Amphiarthroses: Slightly movable joints, connected by cartilage (e.g., pubic symphysis).

  • Diarthroses (Synovial Joints): Freely movable joints, categorized by movement type.

    • Ball-and-Socket: Shoulder, hip; allow for multi-directional movement.

    • Hinge: Elbow, knee; movement in one plane.

    • Pivot: Neck; rotational movement.

  • Joint Capsule: Encases the joint, lined with synovial membrane.

  • Synovial Fluid: Lubricates the joint to reduce friction.

Skeletal Conditions (Slides 44-56)

• Bone Tumors:

  • Osteosarcoma: Most common and aggressive bone cancer, often found in the distal femur or proximal tibia.

  • Chondrosarcoma: Cancer of cartilage, usually affects pelvic bones and the proximal femur.

• Metabolic Bone Diseases:

  • Osteoporosis: Characterized by reduced bone density, making bones fragile and susceptible to fractures.

  • Rickets and Osteomalacia: Vitamin D deficiency causes softening of bones; rickets affects children, while osteomalacia affects adults.

  • Paget Disease: Excessive and abnormal bone remodeling, resulting in enlarged but weakened bones.

  • Osteogenesis Imperfecta: Genetic disorder causing brittle bones due to defective collagen.

• Bone Infections:

  • Osteomyelitis: Infection of bone tissue, often caused by Staphylococcus bacteria.

Bone Fractures (Slides 57-58)

• Types of Fractures:

  • Open (Compound): The bone pierces the skin, often requiring surgical intervention.

  • Closed (Simple): Bone is broken but does not break the skin.

  • Complete: Bone is broken into two or more parts.

  • Incomplete: Bone cracks but does not break all the way through.

  • Transverse, Linear, Oblique: Types of fractures based on the direction and location of the break.

Joint Conditions (Slides 59-65)

• Noninflammatory Joint Conditions:

  • Osteoarthritis (Degenerative Joint Disease): Cartilage in joints deteriorates, causing pain and limited movement. Common in weight-bearing joints like the hips and knees.

  • Dislocations and Sprains: Joint injuries due to trauma.

    • Dislocation: Bones are forced out of alignment.

    • Sprain: Injury to the ligaments around a joint.

• Inflammatory Joint Conditions:

  • Rheumatoid Arthritis: Autoimmune condition causing inflammation of the synovial membrane and joint damage.

  • Gouty Arthritis: Uric acid crystals accumulate in joints, leading to painful inflammation.

  • Infectious Arthritis: Caused by bacterial, viral, or fungal infection, often following an injury or systemic infection.