Chapter 7: The Skeletal System – Structure, Components, and Functions

Chapter 7: The Skeletal System

Learning Outcomes

• Identify the tissues and organs that make up the skeletal system and their anatomical relationships.

• Classify bone markings and describe their functions.

• Name and describe the adult skull bones, their articulations, and differences between adult and fetal skulls.

Skeletal System Components

Bones, Cartilages, and Ligaments

The skeletal system is composed of several types of tissues and structures that work together to provide support, protection, and movement for the body.

• Bone: A mineralized connective tissue containing blood, bone marrow, cartilage, adipose, nervous, and fibrous connective tissues. Bones provide structural support, protect organs, and serve as levers for movement.

• Cartilage: A flexible connective tissue that serves as a precursor for bone tissue during development and covers most joints in adults, reducing friction and absorbing shock.

• Ligaments: Strong bands of fibrous connective tissue that hold bones together at joints (articulations), providing stability and guiding movement.

Types of Cartilage in the Skeletal System

• Hyaline Cartilage: Found in articular surfaces of bones, costal cartilages (ribs), respiratory tract, and nasal cartilages. It is the most common type and serves as a model for endochondral ossification (bone formation).

• Elastic Cartilage: Located in the ear and epiglottis, this cartilage is highly elastic and flexible.

• Fibrocartilage: Found in intervertebral discs and knee menisci, it is highly compressible and has great tensile strength, providing resistance to pressure and stretch.

Bones in the Typical Adult Skeleton

Overview and Classification

The adult human skeleton typically consists of 206 bones, which are grouped into two main divisions: the axial and appendicular skeletons.

• Axial Skeleton (80 bones): Forms the central axis of the body.

  • Skull: 22 bones

  • Auditory ossicles: 6 bones

  • Hyoid bone: 1 bone

  • Vertebral column: 33 bones (in early development; some fuse in adulthood)

  • Thoracic cage: 25 bones (ribs and sternum)

• Appendicular Skeleton (126 bones): Includes the limbs and girdles.

  • Pectoral girdles: 4 bones (clavicles and scapulae)

  • Upper limbs: 60 bones

  • Hip bones: 2 bones (each formed by fusion of ilium, ischium, and pubis)

  • Lower limbs: 60 bones

Note: The number of bones in infants is higher (~270) due to unfused bones that later fuse during development.

Special Bone Types

• Sesamoid Bones: Bones that form within tendons in response to strain, such as the patella (kneecap).

• Sutural (Wormian) Bones: Extra bones that can form within the sutures of the skull.

Summary Table: Major Skeletal Components

Component	Location	Main Function
Bone	Throughout skeleton	Support, protection, movement, mineral storage
Hyaline Cartilage	Joints, ribs, nose, respiratory tract	Reduces friction, precursor to bone
Elastic Cartilage	Ear, epiglottis	Flexibility, maintains shape
Fibrocartilage	Intervertebral discs, knee menisci	Shock absorption, tensile strength
Ligament	Joints	Stabilizes joints, guides movement

Key Terms and Definitions

• Articulation: A joint where two or more bones meet.

• Ossification: The process of bone tissue formation.

• Endochondral Ossification: Bone development from a cartilage model, typical of long bones.

• Intramembranous Ossification: Bone development directly from mesenchymal tissue, typical of flat bones like the skull.

Example: Clinical Relevance

• Damage to articular cartilage in joints can lead to osteoarthritis, a common degenerative joint disease.

• Ligament injuries, such as an anterior cruciate ligament (ACL) tear, are common in athletes and can destabilize joints.

Additional info: Later sections of this chapter would cover bone markings, skull anatomy, and differences between adult and fetal skulls, as indicated by the learning outcomes.