Skeletal Cartilages

Introduction to Skeletal Cartilages

The human skeleton initially consists primarily of cartilage, which is gradually replaced by bone during development. Cartilage remains in areas where flexibility is required throughout life.

• Cartilage is a resilient, molded tissue composed mainly of water.

• It contains no blood vessels or nerves.

• The perichondrium is a layer of dense connective tissue surrounding cartilage, acting as a girdle to resist outward expansion and containing blood vessels for nutrient delivery.

• Cartilage is made up of chondrocytes, which are cells encased in small cavities called lacunae within the extracellular matrix.

Types and Locations of Cartilage

There are three main types of cartilage in the human body, each with distinct properties and locations.

• Hyaline cartilage

  • Provides support, flexibility, and resilience.

  • Most abundant type; contains only collagen fibers.

  • Locations: articular (joints), costal (ribs), respiratory (larynx), nasal cartilage (nose).

• Elastic cartilage

  • Similar to hyaline cartilage but contains elastic fibers.

  • Locations: external ear, epiglottis.

• Fibrocartilage

  • Contains thick collagen fibers, providing great tensile strength.

  • Locations: menisci of knee, intervertebral discs.

Growth of Cartilage

Cartilage grows by two mechanisms, allowing for expansion and maintenance throughout life.

• Appositional growth (from the outside out):

  • Cartilage-forming cells in the perichondrium secrete matrix against the external face of existing cartilage.

  • New matrix is laid down on the surface of cartilage.

• Interstitial growth (from the inside out):

  • Chondrocytes within lacunae divide and secrete new matrix, expanding cartilage from within.

  • New matrix is made within cartilage.

Calcification of cartilage occurs during normal bone growth in youth and sometimes in old age, but hardened cartilage is not the same as bone.

Functions of Bones

Overview of Bone Functions

Bones perform several vital functions necessary for the structure and physiology of the human body.

• Support: Provides structural support for the body and soft organs.

• Protection: Protects the brain, spinal cord, and vital organs.

• Movement: Acts as levers for muscle action.

• Mineral and growth factor storage: Reservoir for calcium, phosphorus, and growth factors.

• Blood cell formation: Hematopoiesis occurs in red marrow cavities of certain bones.

• Triglyceride (fat) storage: Fat, used as an energy source, is stored in bone cavities.

• Hormone production: Osteocalcin secreted by bones helps regulate insulin secretion, glucose levels, and metabolism.

Classification of Bones

Axial and Appendicular Skeleton

The human skeleton is divided into two main groups based on location:

• Axial skeleton:

  • Forms the long axis of the body.

  • Includes the skull, vertebral column, and rib cage.

• Appendicular skeleton:

  • Comprises bones of the upper and lower limbs.

  • Includes girdles attaching limbs to the axial skeleton.

Bone Shapes

Bones are also classified according to one of four shapes:

• Long bones: Longer than they are wide; found in limbs.

• Short bones: Cube-shaped; found in wrist and ankle. Sesamoid bones (e.g., patella) form within tendons.

• Flat bones: Thin, flat, and slightly curved; includes sternum, scapulae, ribs, and most skull bones.

• Irregular bones: Complicated shapes; includes vertebrae and hip bones.

Summary Table: Types of Cartilage and Their Locations

Summary Table: Bone Classification by Location

Summary Table: Bone Classification by Shape

Additional info: These notes are based on textbook slides and provide foundational knowledge for understanding the skeletal system in human anatomy and physiology. The tables summarize key comparisons and classifications for efficient exam review.