Skeletal System: Cartilage, Bone Structure, and Bone Development

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Chapter 6: Skeletal System Overview

Hyaline, Elastic, and Fibrocartilage Help Form the Skeleton

The human skeleton is supported by three main types of cartilage: hyaline cartilage, elastic cartilage, and fibrocartilage. Each type has unique properties and functions in the body.

Hyaline cartilage: Maintains the shape of a structure while allowing great flexibility. It is the most abundant cartilage type and provides support with some pliability.
Elastic cartilage: Provides support with flexibility and resilience. Found in structures such as the external ear and epiglottis.
Fibrocartilage: Resists compression and provides great tensile strength. Located in intervertebral discs and menisci of the knee.

Major Cartilages of the Adult Skeleton

Cartilage is distributed throughout the skeleton, serving various structural and functional roles.

Type of cartilage	Location in the body
Hyaline	Covers the ends of most bones at movable joints; connects ribs to sternum; forms the larynx, trachea, and nose
Elastic	External ear, epiglottis
Fibrocartilage	Intervertebral discs, menisci of knee, pubic symphysis

Cartilage Growth

Appositional growth: Cartilage-forming cells in the perichondrium secrete new matrix against the external face of existing cartilage tissue.
Interstitial growth: Chondrocytes within the cartilage divide and secrete new matrix, expanding the cartilage from within.

Note: The hard extracellular matrix of cartilage tissue does not allow for mitosis. (False statement correction.)

Bones Perform Several Important Functions

Functions of the Skeleton and Bone Tissue

Support: Provides a framework that supports the body and cradles soft organs.
Protection: Protects vital organs (e.g., skull protects the brain, rib cage protects the heart and lungs).
Anchorage: Skeletal muscles attach to bones by tendons and use bones as levers to move the body.
Mineral storage: Reservoir for minerals, especially calcium and phosphate, which can be released into the bloodstream as needed.
Blood cell formation: Hematopoiesis occurs in red marrow cavities of certain bones.
Triglyceride (fat) storage: Fat is stored in bone cavities as a source of energy.
Hormone production: Bones produce osteocalcin, a hormone that helps regulate bone formation and protects against obesity and glucose intolerance.

Major Regions of the Skeleton

Axial and Appendicular Skeleton

Axial skeleton: Consists of the skull, vertebral column, and rib cage. Functions mainly in protection, support, and carrying other body parts.
Appendicular skeleton: Consists of the bones of the upper and lower limbs and the girdles (shoulder and hip bones) that attach the limbs to the axial skeleton. Functions primarily in movement and manipulation of the environment.

Bone Classification by Shape

Long bones: Longer than they are wide (e.g., femur, humerus).
Short bones: Cube-shaped (e.g., carpals, tarsals).
Flat bones: Thin, flattened, and usually curved (e.g., sternum, ribs, skull bones).
Irregular bones: Complicated shapes (e.g., vertebrae, hip bones).

Bone Structure: Compact and Spongy Bone

Gross Anatomy of Bones

Compact bone: Dense outer layer that looks smooth and solid.
Spongy bone: Internal to compact bone; consists of a honeycomb of small needle-like or flat pieces called trabeculae.
Diaphysis: Shaft of a long bone; contains the medullary cavity with yellow marrow in adults.
Epiphyses: Ends of long bones; contain red marrow in certain locations.
Periosteum: Double-layered membrane covering the external surface of bones except at joints.
Endosteum: Delicate membrane covering internal bone surfaces.
Articular cartilage: Covers joint surfaces of epiphyses, reducing friction and absorbing shock.

Red and Yellow Bone Marrow

Red marrow: Site of hematopoiesis (blood cell formation); found in trabecular cavities of spongy bone in flat bones and the heads of femur and humerus in adults.
Yellow marrow: Stores fat; found in the medullary cavity of long bones in adults.

Bone Markings

Bone markings are features on bones that serve as sites of muscle, ligament, and tendon attachment, as well as passages for nerves and blood vessels.

Bone Marking	Projections that are sites of muscle and ligament attachment	Surfaces that help to form joints	Depressions and openings for passage of blood vessels and nerves
Meatus			X
Condyle		X
Tubercle	X
Foramen			X
Spine	X
Trochanter	X
Facet		X
Fossa			X
Epicondyle	X
Tuberosity	X
Head		X

Histology of Compact and Spongy Bone

Osteons (Haversian systems): Structural units of compact bone; consist of concentric lamellae surrounding a central canal.
Trabeculae: Irregularly arranged lamellae and osteocytes in spongy bone.
Osteocytes: Mature bone cells that monitor and maintain bone matrix.
Canaliculi: Tiny canals that connect lacunae to each other and to the central canal.

Bone Cells

Osteoblasts: Bone-forming cells that secrete bone matrix.
Osteoclasts: Large cells that resorb or break down bone matrix.

Chemical Composition of Bone

Organic components: Include osteoid (collagen fibers and ground substance), which provide tensile strength and flexibility.
Inorganic components: Mainly hydroxyapatite (mineral salts, primarily calcium phosphate), which provide hardness and resistance to compression.

Analogy: The organic components are like the rebar in concrete, providing flexibility and tensile strength, while the inorganic components are like the concrete, providing hardness and compressive strength.

Bone Development: Intramembranous vs. Endochondral Ossification

Intramembranous Ossification

Bone develops from a fibrous membrane.
Forms flat bones, such as the cranial bones and clavicles.

Endochondral Ossification

Bone forms by replacing hyaline cartilage.
Forms most of the skeleton, including long bones.
Sequence: cartilage model forms → bone collar forms → cartilage in center calcifies → periosteal bud invades → secondary ossification centers form in epiphyses → epiphyses ossify.

Epiphyseal Plates and Bone Growth

Longitudinal growth: Occurs at the epiphyseal plate (growth plate) by proliferation of cartilage cells, followed by ossification.
Appositional growth: Bone increases in thickness by addition of new bone tissue at the surface.

The epiphyseal plate consists of several zones:

Resting (quiescent) zone
Proliferation zone: cartilage cells undergo mitosis
Hypertrophic zone: older cartilage cells enlarge
Calcification zone: matrix becomes calcified; cartilage cells die
Ossification zone: new bone forms

Summary Table: Zones of Epiphyseal Plate

Zone	Main Activity
Resting	Inactive cartilage
Proliferation	Cartilage cells divide rapidly
Hypertrophic	Older cartilage cells enlarge
Calcification	Matrix calcifies, cells die
Ossification	New bone forms

Key Equation:

Bone growth in length:

Additional info: These notes are based on standard content for introductory Anatomy & Physiology courses, with logical inferences made where the original material was incomplete or in question format.