Chapter 6 Skeletal system (copy)
Introduction to the Skeletal System
Overview of skeletal system: provides structure and framework for the body.
Major components: bone tissue, cartilage, and collagen.
Importance of hyaline cartilage as a precursor for new bone formation.
Types of Cartilage
Types of Cartilage
Hyaline Cartilage: Contains collagen fibers providing support and flexibility. Examples: articular cartilage (ends of long bones), costal cartilage (ribs to sternum), and tracheal rings.
Elastic Cartilage: Contains elastic fibers for high flexibility and resilience (e.g., external ear, epiglottis).
Fibrocartilage: Contains thicker collagen bundles, providing tensile strength (e.g., intervertebral discs, pubic symphysis, and knee menisci).
Structure of the Skeletal System
Axial vs. Appendicular Skeleton
Axial Skeleton: Core structure (skull, vertebral column, ribcage).
Appendicular Skeleton: Appendages (pectoral girdle, upper and lower limbs, pelvic girdle).
Growth of Cartilage
Mechanisms of Cartilage Growth
Appositional Growth: Growth at the outer layer, from the outside in, by chondroblasts in the perichondrium.
Interstitial Growth: Expansion from within, through division of chondrocytes in lacunae, moving from the inside out.
Cartilage Calcification and Ossification
In typical ossification processes, chondrocytes undergo apoptosis, leading to calcification which serves as a template for new bone matrix formation.
Classification of Bones
Types of Bone Structure
Compact Bone (Lamellar): Dense and strong outer area of bones.
Spongy Bone (Trabecular): Lighter, porous structure providing some strength and a framework where bone marrow resides.
Shapes of bones: long, short, irregular, and flat bones (often feature a sandwich model).
Anatomy of Long Bones
Structure of Long Bones
Diaphysis: Shaft of the long bone.
Epiphyses: Ends of the long bone, filled with spongy bone and articular cartilage.
Medullary Cavity: Central cavity within the diaphysis housing yellow bone marrow.
Periosteum: Double-layered membrane on the outer surface.
Epiphyseal Plate (Growth Plate): Region allowing lengthening during youth.
Bone Cells and Their Functions
Osteoprogenitor Cells: Stem cells that can differentiate into osteoblasts.
Osteoblasts: Bone-building cells that secrete matrix and help in mineralization.
Osteocytes: Mature bone cells that maintain bone matrix.
Osteoclasts: Cells responsible for bone resorption and remodeling.
Bone Development Processes
Prenatal Development
Endochondral Ossification: Most of the skeletal system formed from hyaline cartilage; occurs after the second month of embryonic development.
Intramembranous Ossification: Bone development occurs in fibrous membranes, primarily for flat bones of the skull and clavicles.
Postnatal Development
Interstitial Growth: Lengthening of bones occurs at the epiphyseal plate until closure.
Appositional Growth: Widening of bones, involving both osteoblast and osteoclast activity.
Bone Remodeling and Repair
Remodeling Process
Continuous process throughout life involving resorption (osteoclasts) and formation (osteoblasts) of bone.
Typical rates: spongy bone every 3-4 years; compact bone every 10 years.
Bone Repair Process
Hematoma Formation: Initial blood clot forms at the fracture site.
Fibrocartilaginous Callus Formation: Clean-up of debris and bridging of fragmented ends using fibroblasts and cartilage.
Bony Callus Formation: Cartilage is replaced by spongy bone via osteoblast activity.
Remodeling: Final conversion of spongy bone to compact bone, restoring normal structure.
Homeostatic Imbalances
Common Conditions
Osteomalacia: Inadequate mineralization leading to weak bones (e.g., rickets in children).
Osteoporosis: Increased osteoclast activity leads to porous, weak bones.
Conclusion
Understanding the anatomy, processes, and imbalances of the skeletal system is crucial for recognizing how bones function and respond to stress throughout life.