Classification and Structure of Bones and Cartilages: Anatomy & Physiology Study Notes

Classification and Structure of Bones and Cartilages

Overview

The skeletal system provides the structural framework for the human body, supporting movement, protecting organs, and serving as a reservoir for minerals. Bones and cartilages are the primary tissues that form the skeleton, each with distinct functions and structural characteristics.

Major Functions of the Skeletal System

• Support: Provides a rigid framework that supports the body and cradles soft organs.

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

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

• Mineral Storage: Stores minerals such as calcium and phosphorus, which can be released into the bloodstream as needed.

• Blood Cell Formation: Houses bone marrow, which produces blood cells (hematopoiesis).

• Fat Storage: Yellow bone marrow stores fat as an energy reserve.

Classification of Bones

Main Types of Bones

Bones are classified based on their shape and structure, which relate to their functions.

• Long Bones: Longer than they are wide; primarily found in the limbs (e.g., femur, humerus). Function as levers for movement.

• Short Bones: Approximately equal in length and width; found in the wrist (carpals) and ankle (tarsals). Provide stability and support with limited movement.

• Flat Bones: Thin, flattened, and usually curved; found in the skull, ribs, and sternum. Protect internal organs and provide surfaces for muscle attachment.

• Irregular Bones: Complex shapes that do not fit into other categories; found in the vertebrae and some facial bones.

• Sesamoid Bones: Embedded within tendons; example is the patella (kneecap). Reduce friction and modify pressure.

Bone Structure

• Compact Bone: Dense outer layer that provides strength and protection.

• Spongy (Cancellous) Bone: Porous inner layer that contains red bone marrow.

• Diaphysis: Shaft of a long bone, composed mainly of compact bone.

• Epiphysis: Ends of long bones, composed mainly of spongy bone.

• Periosteum: Tough, fibrous membrane covering the outer surface of bones.

• Endosteum: Thin membrane lining the internal bone surfaces.

Cartilages of the Skeleton

Types of Cartilage

• Hyaline Cartilage: Most abundant; provides support, flexibility, and resilience. Found at the ends of long bones, nose, trachea, and larynx.

• Elastic Cartilage: Contains more elastic fibers; maintains shape while allowing flexibility. Found in the ear and epiglottis.

• Fibrocartilage: Highly compressible and strong; found in intervertebral discs, pubic symphysis, and menisci of the knee.

Axial and Appendicular Skeleton

Axial Skeleton

Composed of bones that form the long axis of the body, including the skull, vertebral column, and rib cage. Functions primarily in protection, support, and carrying other body parts.

Appendicular Skeleton

Includes the bones of the limbs and girdles (shoulder and pelvic) that attach them to the axial skeleton. Functions mainly in movement and manipulation of the environment.

Bone Markings

Purpose and Types

Bones display various markings that serve as sites for muscle, ligament, and tendon attachment, as well as passages for nerves and blood vessels. These markings are classified as projections, depressions, and openings.

Name of Bone Marking	Description	Illustration/Example
Process	Any bony prominence	Spinous process of vertebra
Crest	Narrow ridge of bone; usually prominent	Iliac crest
Trochanter	Large, blunt, irregularly shaped process	Greater trochanter of femur
Head	Bony expansion carried on a narrow neck	Head of femur
Foramen	Round or oval opening through a bone	Foramen magnum of skull
Fossa	Shallow, basin-like depression in a bone	Mandibular fossa
Meatus	Canal-like passageway	External acoustic meatus
Sinus	Cavity within a bone, filled with air and lined with mucous membrane	Frontal sinus

Microscopic Structure of Bone

Osteon (Haversian System)

• Osteon: The structural unit of compact bone, consisting of concentric rings (lamellae) of bone matrix surrounding a central canal.

• Lacunae: Small spaces between lamellae that house osteocytes (bone cells).

• Canaliculi: Tiny channels that connect lacunae, allowing for nutrient and waste exchange.

Summary Table: Bone Types and Examples

Bone Type	Example	Main Function
Long Bone	Femur, Humerus	Movement, support
Short Bone	Carpals, Tarsals	Stability, support
Flat Bone	Skull, Ribs, Sternum	Protection, muscle attachment
Irregular Bone	Vertebrae, Pelvis	Protection, support
Sesamoid Bone	Patella	Reduce friction, modify pressure

Key Terms and Definitions

• Osteocyte: Mature bone cell that maintains bone tissue.

• Osteon: The fundamental unit of compact bone.

• Periosteum: Dense membrane covering the outer surface of bones.

• Epiphysis: The end part of a long bone.

• Diaphysis: The shaft or central part of a long bone.

• Cartilage: Flexible connective tissue found in various forms throughout the body.

Additional info:

• Bone markings are essential for understanding anatomical relationships and for identifying sites of muscle and ligament attachment.

• Microscopic bone structure is crucial for understanding bone growth, repair, and metabolic functions.