Unit 3: Skeletal System – Cartilage, Bone, and Development Study Guide

Types and Locations of Cartilage

Overview of Cartilage Types

Cartilage is a specialized connective tissue found in various locations throughout the body, providing support, flexibility, and cushioning.

• Hyaline Cartilage: Found in nose, trachea, larynx, costal cartilage, articular cartilage, and fetal skeleton. Provides smooth surfaces for joint movement and structural support.

• Elastic Cartilage: Found in ear and epiglottis. Contains elastic fibers for flexibility.

• Fibrocartilage: Found in intervertebral discs, pubic symphysis, and menisci. Provides strong support and withstands heavy pressure.

Examples and Applications

• Articular cartilage in joints reduces friction and absorbs shock.

• Menisci in the knee stabilize and cushion the joint.

Red vs. Yellow Bone Marrow

Functions and Locations

Bone marrow is a soft tissue found within bones, responsible for blood cell production and fat storage.

• Red Marrow: Produces blood cells; found in flat bones and proximal epiphyses of long bones.

• Yellow Marrow: Stores fat; found in medullary cavities of long bones.

Bone Cell Types

Major Bone Cells and Their Functions

Bones are dynamic tissues maintained by specialized cells.

• Osteoprogenitor Cells: Stem cells that produce osteoblasts.

• Osteoblasts: Build bone matrix by secreting collagen and other proteins.

• Osteocytes: Mature bone cells that maintain bone tissue.

• Osteoclasts: Break down bone matrix for remodeling and calcium release.

Cartilage Cell Types

Chondrocytes and Their Role

Cartilage is maintained by specialized cells called chondrocytes.

• Chondroblasts: Produce cartilage matrix during growth and repair.

• Chondrocytes: Maintain cartilage within lacunae (small spaces).

Components of Bone

Organic and Inorganic Matrix

Bones are composed of both organic and inorganic materials, contributing to their strength and flexibility.

• Organic (35%): Collagen and ground substance provide flexibility.

• Inorganic (65%): Calcium phosphate and other salts provide strength.

Growth Types

Bone Growth Mechanisms

Bones grow in length and width through two main processes.

• Interstitial Growth: Growth from within, increasing length.

• Appositional Growth: Growth at the surface, increasing width.

Bone Formation & Growth

Ossification Processes

Bones form through two main processes during development.

• Intramembranous Ossification: Bone forms from mesenchyme (flat bones).

• Endochondral Ossification: Bone replaces cartilage (long bones).

Hormones Affecting Bone

Hormonal Regulation of Bone Growth

Several hormones influence bone growth and remodeling.

• Growth Hormone (GH): Stimulates growth.

• Thyroid Hormone: Regulates metabolism.

• Calcitonin: Decreases blood calcium levels.

• Parathyroid Hormone (PTH): Increases blood calcium levels.

• Sex Hormones: Accelerate growth and closure of growth plates.

Bone Repair

Stages of Bone Healing

Bone repair after fracture occurs in four main stages:

1. Hematoma formation

2. Fibrocartilaginous callus formation

3. Bony callus formation

4. Remodeling

Types of Fractures

Classification of Bone Fractures

Fractures are classified based on their pattern and severity.

• Simple

• Compound

• Comminuted

• Spiral

• Greenstick

• Transverse

• Oblique

• Compression

• Depressed

Bone Markings

Types and Functions

Bones have specific markings that serve as sites for muscle attachment, passage of nerves and blood vessels, and articulation with other bones.

• Depressions: Fossa, groove

• Openings: Foramen, canal

• Projections: Tubercle, process, condyle, spine

Sex Differences – Skull

Male vs. Female Skull Characteristics

There are distinct anatomical differences between male and female skulls.

• Male: Slanted frontal bone, pronounced arches

• Female: Vertical frontal bone, delicate margins

Sex Differences – Pelvic Girdle

Male vs. Female Pelvis

The pelvic girdle differs between sexes to accommodate childbirth in females.

• Male: Narrow, tall, heart-shaped inlet

• Female: Broad, oval inlet, wider angle

Fontanelles and Closure

Developmental Timeline

Fontanelles are soft spots on a baby's skull that allow for growth and development.

• Posterior: 2-3 months

• Anterolateral: 6 months

• Posterolateral: 6-18 months

• Anterior: 18-24 months

Spinal Curvature Development

Primary and Secondary Curvatures

The vertebral column develops curvatures for balance and movement.

• Primary (thoracic, sacral): Present at birth

• Secondary (cervical, lumbar): Develop with movement

Bursae & Menisci

Functions in Joints

Bursae and menisci are structures that reduce friction and stabilize joints.

• Bursae: Fluid sacs reducing friction

• Menisci: Fibrocartilage pads for stability

Ligament vs. Tendon

Connective Tissue Comparison

Ligaments and tendons are both connective tissues but serve different functions.

• Ligament: Connects bone to bone

• Tendon: Connects muscle to bone

Levers in the Body

Classes of Levers

The musculoskeletal system uses levers to produce movement.

• 1st class: Fulcrum between effort and load (e.g., neck)

• 2nd class: Load between fulcrum and effort (e.g., calf raise)

• 3rd class: Effort between fulcrum and load (e.g., biceps curl)

Summary Table: Bone Cell Types and Functions

Cell Type	Function
Osteoprogenitor	Stem cells that produce osteoblasts
Osteoblast	Build bone matrix
Osteocyte	Maintain bone tissue
Osteoclast	Break down bone matrix

Summary Table: Cartilage Types and Locations

Type	Location	Function
Hyaline	Nose, trachea, larynx, costal cartilage, articular cartilage, fetal skeleton	Support, smooth movement
Elastic	Ear, epiglottis	Flexibility
Fibrocartilage	Intervertebral discs, pubic symphysis, menisci	Strength, shock absorption

Key Formula: Bone Composition

The proportion of organic and inorganic components in bone can be expressed as:

$\text{Bone} = 0.35 \times \text{Organic} + 0.65 \times \text{Inorganic}$