Chapter 6: Skeletal System: Bones and Bone Structure
Chapter 6: Skeletal System: Bones and Bone Structure
Page 1
Introduction to skeletal system.
Page 2 - Living Bone
Bone is classified as living tissue.
Unlike fossilized bones which undergo mineralization.
A child’s bones are continuously growing and contributing to the overall bodily support and function.
Credit: James Emery
Page 3 - Overview of the Skeletal System
Definition: Bone (osseous tissue) is a hard, dense connective tissue that constitutes most of the adult skeleton.
Functions:
Provides support for the body.
In areas where bones move, cartilage (semi-rigid connective tissue) enhances flexibility and facilitates movement.
Components of the skeletal system include:
Bones of the skeleton
Cartilages
Ligaments
Other connective tissues.
Page 4 - Functions of the Skeletal System
Primary functions include:
Supports the body.
Facilitates movement.
Protects internal organs.
Produces blood cells (hematopoiesis).
Stores and releases minerals and fat.
Page 5 - Support, Movement, and Protection
The skeletal system's bones and cartilage provide a scaffold for supporting the body’s organs, muscles, and skin.
Bones act as levers enabling movement; muscles attach to bones and span joints, which act as fulcrums.
Page 6 - Figures and Diagrams
Figure 6.2: Illustrates how bones function supports movement as levers when muscles contract across joints.
Credit: Benjamin J. DeLong
Page 7 - Organ Protection
Bones serve protective functions by surrounding and covering vital internal organs:
Ribs protect lungs and heart.
Vertebral column protects the spinal cord.
Cranium protects the brain.
Page 8 - Brain Protection
Figure 6.3: Cranium completely encircles the brain to prevent non-traumatic injury.
Page 9 - Mineral Storage and Hematopoiesis
Bone matrix serves as a reservoir for essential minerals like calcium and phosphorus.
Function of Calcium Ions:
Crucial for muscle contractions.
Controls flow of ions for nerve impulse transmissions.
Page 10 - Fat and Blood Cell Storage
Bones are sites for fat storage and blood cell production.
Bone Marrow:
Softer connective tissue present in most bones.
Types of Bone Marrow:
Yellow Marrow: Contains adipose tissue, serves as an energy source.
Red Marrow: Site of hematopoiesis (blood cell production).
Produces red blood cells, white blood cells, and platelets.
Page 11 - Examples of Bone Marrow
Figure 6.5: Shows head of femur containing both yellow and red marrow.
Page 12 - Bone Classification
Bones classified based on:
Shape
Structure
Page 13 - Shapes of Bone
Types of Bone Shapes Include:
Irregular
Short
Flat
Long
Sesamoid
Page 14 - Irregular Bones
Characteristics: Complex shapes.
Examples: Spinal vertebrae, pelvic bones.
Page 15 - Short and Flat Bones
Short Bones:
Shape: Boxy.
Examples: Carpal and tarsal bones.
Flat Bones:
Shape: Thin with parallel surfaces.
Examples: Skull roof, sternum, ribs, scapulae.
Page 16 - Long and Sesamoid Bones
Long Bones:
Shape: Long and slender.
Found in arms, legs, palms, soles, fingers, and toes.
Sesamoid Bones:
Typically small, round, and flat.
Develop within tendons near joints (e.g., knees, hands, feet).
Location and quantity can vary among individuals.
Example: Patellae.
Page 17 - Visual Classification of Bones
Figure 6.6: Illustration of various bone classifications based on shape, including examples.
Page 18 - Anatomy of a Long Bone
Diaphysis (Shaft):
Comprised of compact bone surrounded by periosteum.
Contains a central space known as the medullary cavity (marrow cavity) lined with endosteum.
Epiphysis:
Wide part at each end consists mostly of spongy bone (trabecular bone).
Metaphysis:
Junction where diaphysis and epiphysis meet.
Page 19 - Anatomical Features of Long Bone
Figure 6.7: Depicts the main anatomical characteristics of a typical long bone.
Page 20 - Periosteum and Endosteum
Figure 6.8: Visual representation of periosteum and endosteum:
The periosteum covers the outer surface of bone.
Endosteum lines the medullary cavity.
Page 21 - Anatomy of a Flat Bone
Example: Parietal Bones of the Skull:
Comprised of spongy bone situated between compact bone layers (cortex).
The spongy layer in the cranium is termed the diploë.
Page 22 - Cross-section of Flat Bone
Figure 6.9: Shows cross-section of a flat bone revealing the arrangement of spongy bone lined by compact bone.
Page 23 - Bone Markings
Bone Markings (Surface Features) Include:
Projections:
Areas for attachment of muscles, tendons, and ligaments.
Areas where bones articulate with each other.
Openings and Depressions:
Pathways for blood vessels and nerves.
Page 24 - Features of Bones
Figure 6.10: Illustrates various surface features of bones related to function, location, and attachment sites for ligaments and tendons.
Page 25 - Bone Tissue Characteristics
Bone Tissue Features:
Dense, supportive connective tissue containing specialized cells (osteocytes).
Solid extracellular matrix comprising collagen fibers.
Page 26 - Matrix of Bone
Characteristics of Bone Matrix:
Dense matrix from calcium salt deposits.
Osteocytes reside within lacunae organized around blood vessels.
Canaliculi: Narrow passageways facilitating nutrient and waste exchange.
Periosteum: Covers external surfaces of bones, excluding joints and comprises an outer fibrous layer and an inner cellular layer.
Page 27 - Composition of Bone Matrix
Key Components:
Calcium phosphate (Ca3(PO4)2): Comprises nearly two-thirds of bone mass.
Interacts with calcium hydroxide (Ca(OH)2) to form hydroxyapatite (Ca10(PO4)6(OH)2) crystals.
May also include calcium carbonate (CaCO3) and various ions like magnesium.
Note: A bone without a calcified matrix retains its normal appearance but becomes very flexible.
Page 29 - Bone Matrix Composition
Bone Matrix Proteins:
About one-third of bone mass consists of collagen fibers.
Page 30 - Bone Cells
Types of Bone Cells (2% of Bone Mass):
Osteogenic Cells: Undifferentiated cells that develop into osteoblasts.
Osteoblasts: Cells producing new bone matrix during osteogenesis.
Osteocytes: Mature bone cells that maintain the matrix and help repair any damage.
Osteoclasts: Cells responsible for bone resorption and mineral release.
Page 31 - Overview of Bone Cells
Figure 6.11: Depicts the four types of cells found within bone tissue, including osteogenic cells transitioning into osteoblasts, and osteoblasts maturing into osteocytes.
Page 32 - Osteogenic Cells
Osteogenic Cells Description:
Mesenchymal cells capable of division to yield osteoblasts.
Found in the inner cellular layer of periosteum and endosteum.
Play a role in fracture repair.
Page 33 - Osteoblasts Function
Osteoblasts:
Immature cells that synthesize new bone matrix during osteogenesis (ossification).
Produce osteoid (unmineralized matrix) which becomes calcified over time.
Osteoblasts trapped by the matrix transition into osteocytes.
Page 34 - Osteocytes Function
Osteocytes:
Function as mature bone cells, do not undergo division.
Reside in lacunae within the matrix layers.
Have cytoplasmic extensions via canaliculi for nutrient, waste, and gas exchange.
Key Functions:
Maintain protein and mineral content of the matrix.
Aid in repair of damaged bone.
Page 35 - Osteoclasts Function
Osteoclasts:
Cells designed for bone resorption and matrix removal.
Large and multinucleate.
Secretes acids and protein-digesting enzymes to dissolve bone matrix and release minerals.
This process (osteolysis) is crucial for maintaining homeostasis.
Derived from stem cells that produce monocytes and macrophages.
Page 36 - Compact vs. Spongy Bone
Types of Bone:
Compact Bone:
Comprised of osteons; found in the diaphysis of long bones and forms outer layers of flat bones.
Spongy Bone:
Composed of trabeculae; located in the epiphyses of long bones and in the center of flat bones.
Page 37 - Compact Bone Structure
Osteon: Functional unit of compact bone composed of a central canal containing blood vessels.
Features:
Lamellae: layers of bone matrix around central canal.
Perforating canals: perpendicular channels carrying blood vessels to deep bone.
Concentric, interstitial, and circumferential lamellae make up the organizational structure.
Page 38 - Illustration of Compact Bone
Figure 6.12: Cross-section showing the structure of compact bone and its basic structural unit (osteon).
Page 39 - Components of Osteons
Detailed Components of Osteons Include:
Lacunae, central canal, lamellae arranged in a concentric manner.
Page 40 - Trabecular Arrangement in Bone
Trabecular and Osteon Arrangement:
Illustration showing organization of osteons and lamellae in compact bone with vascular structures.
Page 41 - Orientation of Collagen Fibers
Highlights the orientation of collagen fibers in adjacent lamellae of an osteon.
Page 42 - Spongy Bone Structure
Spongy bone lacks organized osteons; instead, it features an open network of trabeculae.
Nutrient Supply: Red marrow present in spaces between trabeculae; forms blood cells and contains vessels supplying osteocytes.
Yellow marrow found at other locations stores fat.
Page 43 - Composition of Spongy Bone
Figure 6.13: Diagram illustrating structure of spongy bone with trabeculae supporting red marrow.
Page 45 - Function of Trabecular Forces
Weight-bearing Functionality:
Trabecular arrangement in the epiphysis of femur transmits forces from pelvis to the compact bone of femoral shaft, managing stress through tension and compression.
Page 47 - Blood and Nerve Supply
Figure 6.15: Illustrates blood vessels and nerves entering bone via the nutrient foramen.
Page 48 - Bone Coverings: Periosteum
Periosteum Description:
A membrane covering outer bone surfaces, excluding joint cavities.
Comprises outer fibrous and inner cellular layers.
Fibers interwoven with tendon fibers, enhances structural integity.
Perforating (Sharpey’s) Fibers:
Incorporated into bone tissue enhancing attachment strength.
Page 50 - Functions of Periosteum
Primary Functions:
Isolates bone from surrounding tissues.
Provides a passageway for blood vessels and nerves.
Involved in the growth and repair of bone.
Page 51 - Endosteum
Endosteum Description:
Incomplete cellular layer lining the medullary cavity.
Functions during bone growth, repair, and remodeling.
Covers trabeculae of spongy bone and lines central canals of compact bone.
Composed of flattened osteogenic cells.
Page 53 - Bone Development
Bone Development Terms:
Ossification (Osteogenesis): The formation of bone.
Calcification: Giving rise to calcium salt deposits during ossification.
Involves two primary ossification types:
Intramembranous ossification
Endochondral ossification
Bone growth continues until about age 25.
Page 54 - Intramembranous Ossification
Definition: Formation that occurs within a membrane (dermis).
Produces: Dermal bones (cranial bones, facial structures, mandible, and clavicles).
Page 55 - Steps of Intramembranous Ossification
Process Stages:
Mesenchymal cells cluster and form ossification centers.
Osteoid secretions trap osteoblasts which then transition into osteocytes.
Trabecular matrix and periosteum form.
Development of compact bone over trabecular bone and condensing blood vessels into red marrow.
Page 56 - Endochondral Ossification
Definition: Formation that occurs within cartilage.
How Most Bones Form: Primary ossification center forms in hyaline cartilage gradually being replaced by bone.
Page 57 - Stages of Endochondral Ossification
Steps:
Mesenchymal cells become chondrocytes.
Formation of the cartilage model and perichondrium.
Capillaries invade cartilage; perichondrium turns to periosteum and a primary ossification center develops.
Continued cartilage growth at the ends.
Secondary ossification centers develop; cartilage persists at epiphyseal (growth) plate and joint surfaces.
Page 58 - Longitudinal and Interstitial Growth
Process:
Interstitial growth increases height; secondary ossification centers develop.
Epiphyseal Closure: Indicates completion of epiphyseal growth measured through the width of cartilages.
Visible on X-rays as an epiphyseal line after closure occurs.
Page 59 - Mechanism of Long Bone Growth
Bone Growth Stages:
Chondrocytes enlarge in the shaft center, reduced to struts that calcify, leading to cell death and cavity formation.
Blood vessels encircle the cartilage; perichondrium cells convert to osteoblasts, forming a bone coating over cartilage.
Internal blood vessels and cells invade central region, producing spongy bone at primary ossification center, which spreads along the shaft. Remodeling forms a medullary cavity as growth continues.
Osteoblasts move toward epiphysis, while new cartilage continues growth at epiphyseal side, leading to lengthening of the bone.
Page 60 - Progression of Growth Stages
Figure 6.18: Diagram illustrates the zones in the epiphyseal plate responsible for longitudinal growth, detailing changes in chondrocytes and zones of calcification.
Page 61 - Epiphyseal Plate and Line
Figure 6.19: Depicts progression from epiphyseal plate (growing bone) to epiphyseal line (mature bone).
Page 62 - Visual Representation of Growth Changes
X-ray images showing growing epiphyseal cartilage and corresponding epiphyseal lines in adults.
Page 63 - Appositional Growth
Definition: Growth in width which thickens and strengthens long bones.
Process involves adding circumferential lamellae to the outer bone surface while osteoclasts remove bone matrix internally, enlarging the medullary cavity.
Page 64 - Bone Remodeling
Overview: Continuous process crucial for bone maintenance involving recycling of the bone matrix.
Participates osteocytes, osteoblasts, and osteoclasts, where activities are normally balanced:
Removal faster than replacement leads to weakened bones.
Excessive deposition strengthens bones.
Page 65 - Types of Bone Fractures
Definition: Fractures are cracks or breaks in bones from physical stress, classified as either open (compound) or closed (simple).
Major types:
Transverse
Displaced
Compression
Spiral
Epiphyseal
Comminuted
Greenstick
Colles
Pott’s
Page 66 - Comparison of Fracture Types
Figure 6.20: Providing visual examples comparing healthy bone and various fracture types including closed, open, and various fracture categories.
Page 68 - Fracture Healing Process
Fractures are repaired in four stages:
Formation of fracture hematoma (large blood clot).
Callus formation leading from internal and external callus stabilization.
Spongy bone formation replacing internal callus’s cartilage.
Compact bone formation leading to repaired structure potentially thicker and stronger than original.
Page 71 - Stages of Fracture Repair
Figure 6.21: Stages depicted in healing a fracture through hematoma formation to internal and external calli development.
Page 72 - Influence of Exercise
Effects of Exercise on Bone:
Bones undergo mineral recycling to adapt to mechanical stress, becoming thicker and stronger.
Weight-bearing exercises particularly stimulate osteoblast activity.
Bone Degeneration: Rapid loss occurs from inactivity, with up to one-third of mass lost in a few weeks.
Page 73 - Nutritional and Hormonal Effects
Minerals Required: Calcium and phosphorus (along with small amounts of magnesium, fluoride, iron, manganese) are vital for bone health.
Calcitriol: Synthesized from Vitamin D3 in kidneys, essential for calcium and phosphate ion absorption.
Page 74 - Vitamin D Synthesis
Figure 6.22: Synthesis pathway of vitamin D includes:
Sunlight providing precursors.
Absorption via the intestines and liver action producing calcidiol.
Kidneys converting to biologically active calcitriol, aiding calcium metabolism and absorption.
Page 75 - Vitamins and Bone Health
Key Vitamins in Bone Health:
Vitamin C: Essential for collagen synthesis and osteoblast differentiation.
Vitamin A: Stimulates osteoblast activity.
Vitamins K and B12: Necessary for synthesizing bone proteins.
Page 76 - Hormonal Influences on Bone
Hormones Affecting Bone Growth:
Growth hormone and thyroxine stimulate bone growth.
Sex hormones (estrogen and testosterone) influence osteoblast activity.
Parathyroid hormone and calcitonin maintain calcium homeostasis.
Page 77 - Calcium Reserve in Skeleton
Calcium Storage in Bones:
Bones store 99% of the body’s calcium and other minerals.
Calcium is the most abundant mineral, vital for many physiological processes.
Page 78 - Bone Composition
Composition Breakdown:
Bone contains:
99% of body's calcium
33% organic compounds (mostly collagen)
Inorganic Components: Totaling 67%, include potassium, sodium, magnesium, carbonate, phosphate.
Page 79 - Aging Effects on Skeletal System
Bone Aging Changes:
Bones become thinner and weaker as individuals age.
Osteopenia: Inadequate ossification, begins between age 30-40, with variable rates of loss between men and women.
Most affected areas: Epiphyses, vertebrae, jaws leading to fragile limbs, height reduction, and tooth loss.
Page 80 - Bone Mass and Age
Figure 6.23: A graph depicting the relationship between age and bone mass peaked at around 30 years of age; highlighting more rapid loss in women than men.
Page 81 - Osteoporosis Overview
Definition: Osteoporosis is a condition characterized by severe bone mass loss affecting normal function, prevalent in individuals over 45.
Statistics: 29% of women and 18% of men affected.
Significant hormonal influence leading to accelerated loss in women post-menopause.
Page 82 - Spongy Bone Changes in Osteoporosis
Visual Comparison: Differences between normal spongy bone and spongy bone affected by osteoporosis.
Page 83 - Conclusion
Summary of key points from Chapter 6: Skeletal System focusing on bone structure, function, classification, growth, repair, and influences on bone health.