Bones AP1 CH6 PDF

Bones

  • Chapter 6

Overview of the Skeleton

  • Skeleton: Greek for "dried up body"

  • Characteristics: Very strong, Very light

  • Functions:

    • Locomotion

    • Protection

    • Coordinates other functions

  • Formed approximately 3 million years ago when humans began to stand upright.

Problems with the Skeletal Design

  • "S" shaped structure leading to sway back design

  • Particular attention to knees

  • Percentage of Body Mass:

    • Skeleton composition: 20% of body mass

    • Example: A 180 lb person has a skeleton weighing 36 lbs.

Composition of the Skeleton

  • Composed of:

    1. Bones: Represent most of the skeleton; total of 206 bones in adults.

    2. Cartilage: Found only in specific areas.

    3. Joints: Points where two or more bones meet.

    4. Ligaments: Connect bones and reinforce joints.

Types of Cartilage

  • Key locations:

    • Cartilage in external ear

    • Intervertebral discs

    • Cartilage in nose

    • Articular cartilage in joints

    • Costal cartilage in rib attachments

    • Cartilage in epiglottis, larynx, and trachea

    • Meniscus: Pad-like cartilage in the knee joint

  • Classification includes:

    • Axial skeleton

    • Appendicular skeleton

    • Hyaline cartilages

    • Elastic cartilages

    • Fibrocartilages

Classification of Bones by Shape

  • 1) Long Bones:

    • Description: Longer than they are wide (e.g., humerus).

  • 2) Short Bones:

    • Description: Cube-shaped bones (e.g., wrist and ankle); includes bones forming within tendons (e.g., patella).

  • 3) Flat Bones:

    • Description: Thin, flattened, and slightly curved (e.g., sternum, most skull bones).

  • 4) Irregular Bones:

    • Description: Bones with complicated shapes (e.g., vertebrae, hip bones).

Bone Markings

  • Function: Sites of muscle attachment, joint surfaces, routes for blood vessels, and nerves.

Projections for Muscle and Ligament Attachment

  • Tuberosity: Rounded projection

  • Crest: Narrow, prominent ridge of bone

  • Trochanter: Large, blunt irregular surface

  • Line: Narrow ridge of bone

  • Tubercle: Small rounded projection

  • Epicondyle: Raised area above a condyle

  • Spine: Sharp, slender projection

  • Process: Any bony prominence

Projections That Help Form Joints

  • Head: Bony expansion on a narrow neck

  • Facet: Smooth, nearly flat articular surface

  • Condyle: Rounded articular projection

  • Ramus: Armlike bar of bone

Depressions and Openings

  • Meatus: Canal-like passageway

  • Sinus: Cavity within a bone

  • Fossa: Shallow basin-like depression

  • Groove: Furrow

  • Fissure: Narrow, slit-like opening

  • Foramen: Round/oval openings through a bone

Table 6.1: Bone Markings

  • Projection types and their functions provided for quick reference.

Gross Anatomy of Bones

  • Bone Textures:

    • Compact Bone: Dense outer layer

    • Spongy Bone: Honeycomb of trabeculae filled with yellow bone marrow

Structure of Long Bone

  • Components include:

    1. Diaphysis: Tubular shaft forming the axis of long bones

    2. Epiphysis: End components of long bones

  • Interior of epiphysis contains spongy bone, exterior is compact bone.

Bone Membranes

  • Periosteum: Double-layered protective membrane rich in nerves, blood vessels

  • Endosteum: Delicate membrane covering internal surfaces of bones

Microscopic Structure of Bone

  • Haversian System/Osteon: Structural unit of compact bone with components:

    • Osteocytes: Mature bone cells

    • Lacunae: Small cavities containing osteocytes

    • Canaliculi: Hair-like canals connecting lacunae

    • Lamella: Matrix tubes composed mainly of collagen

    • Haversian Canal: Central channel with blood vessels and nerves

Chemical Composition of Bone

  • Inorganic: Hydroxyapatites, mineral salts (65% of bone by mass) primarily calcium phosphates, contributing to hardness and compression resistance.

Response to Mechanical Stress

  • Wolff’s Law: Bone adapts and remodels in response to forces applied on it.

Bone Fractures

  • Classified by:

    1. Position of bone ends after fracture

    2. Completeness of the break

    3. Orientation relative to the long axis

    4. Whether the bone ends penetrate the skin

Types of Bone Fractures

  • Nondisplaced: Ends retain normal position

  • Displaced: Ends misaligned

  • Complete: Broken all the way through

  • Incomplete: Not completely broken

  • Linear: Parallel to long axis

  • Transverse: Perpendicular to long axis

  • Compound (open): Ends penetrate skin

  • Simple (closed): Ends do not penetrate skin

Common Types of Fractures

  • Comminuted: Bone shatters into 3+ pieces; common in elderly.

  • Spiral: Ragged break from twisting forces; typical sports injury.

  • Depressed: Fracture pressed inward; common in skull.

  • Greenstick: Incomplete fracture in children; one side bends, the other breaks.

  • Compression: Crushed bone, occurs in porous bones.

  • Epiphyseal: Separation at epiphyseal line

Table 6.2: Common Types of Fractures

  • Overview of various fracture types and their descriptions for reference.

Homeostatic Imbalances

  • Osteomalacia: Inadequately mineralized bones due to lack of calcium or vitamin D, causing weakness and pain under weight.

  • Rickets: Similar to osteomalacia but in children, leading to deformities.

  • Osteoporosis: Group of diseases with bone resorption outpacing deposition, leading to frail bones, prevalent in postmenopausal women.

Osteoporosis Treatment

  • Suggested:

    • Calcium and vitamin D supplements

    • Increased weight-bearing exercise

    • Hormone replacement therapy (HRT)

    • Natural progesterone cream for new bone growth

    • Statins to increase bone mineral density.