Overview
This lecture covers the structure, types, and functions of cartilage and bone, the process of bone formation and growth, bone remodeling and repair, and common bone diseases.
Types of Cartilage
- There are three types of cartilage: hyaline, elastic, and fibrocartilage.
- Hyaline cartilage is the most abundant, providing support with flexibility; found in joints, ribs, respiratory system, and nose.
- Elastic cartilage contains more elastic fibers, allowing repeated bending; found in the ear and epiglottis.
- Fibrocartilage is the strongest due to thick collagen fibers; located in knee menisci, intervertebral discs, and pubic symphysis.
Structure and Classification of Bones
- Bones are organs composed of various tissues (connective, nervous, blood vessels, cartilage, etc.).
- Two main bone types: compact (dense outer layer) and spongy (internal, honeycomb-like structure).
- Bones classified by location: axial (skull, vertebral column, ribs, sternum) and appendicular (limbs, pelvis, shoulder girdle).
- Classified by shape: long (femur), short (wrist/ankle), flat (sternum, skull), irregular (vertebrae), sesamoid (patella).
Bone Anatomy and Marrow
- Long bones have diaphysis (shaft) and epiphyses (ends); covered by periosteum and endosteum membranes.
- Articular cartilage (hyaline) covers joint surfaces for cushioning.
- Red marrow produces blood cells; yellow marrow stores fat; newborns have mostly red marrow, adults mostly yellow.
Microscopic Bone Structure
- Osteon (Haversian system) is the structural unit in compact bone; composed of concentric lamellae.
- Central (Haversian) canals contain nerves and blood vessels.
- Canaliculi connect bone cells for communication and nutrient transfer.
- Bone cells: osteogenic (stem), osteoblasts (form bone), osteocytes (maintenance), osteoclasts (resorb bone).
Bone Formation and Growth
- Bone develops by intramembranous (flat bones, skull, clavicle) or endochondral (replacement of hyaline cartilage) ossification.
- Interstitial (length) and appositional (width) growth are driven by chondrocytes and osteoblast activity.
- Epiphyseal plate closure (around age 18-21) halts further length growth.
- Bone mass is constantly remodeled (spongy bone replaced every 3-4 years, compact every 10 years).
Bone Repair and Disorders
- Fracture types: non-displaced/displaced, complete/incomplete, closed (simple)/open (compound), comminuted, compression, spiral, epiphyseal, depression, greenstick.
- Fracture repair involves reduction (realignment), formation of hematoma, fibrocartilaginous callus, bony callus, and bone remodeling.
- Osteomalacia (adults) and rickets (children) involve soft bones due to vitamin D or calcium deficiency.
- Osteoporosis is increased bone resorption over formation, leading to brittle bones (common in post-menopausal women).
Key Terms & Definitions
- Cartilage â Flexible connective tissue with three types: hyaline, elastic, fibrocartilage.
- Osteon â Cylindrical structural unit of compact bone.
- Epiphyseal Plate â Growth plate where bone lengthens during childhood/adolescence.
- Ossification â Process of bone formation.
- Osteoblast â Bone-forming cell.
- Osteoclast â Bone-resorbing cell.
- Periosteum â Membrane covering outer bone surface.
- Endosteum â Membrane lining inner bone surfaces.
- Red Marrow â Site of blood cell formation.
- Yellow Marrow â Site of fat storage.
- Osteoporosis â Bone disorder with increased bone fragility.
Action Items / Next Steps
- Review lab specimens to compare different bone types and cartilage locations.
- Study bone diagrams, especially showing microscopic structure and fracture types.
- Ensure adequate calcium, vitamin D intake, and engage in weight-bearing exercise.