Semi-rigid connective tissue, more flexible than bone.
Composed of chondrocytes (cartilage cells) and extracellular matrix.
Avascular (lacks blood vessels):
Nutrients obtained through diffusion.
Types of cartilage:
Hyaline cartilage:
Most common type.
Attaches ribs to sternum.
Covers ends of some bones.
Cartilage within growth plates.
Provides smooth surfaces for movement in joints.
Fibrocartilage:
Contains thick collagen fibers.
Weight-bearing cartilage that withstands compression.
Located in:
Intervertebral discs.
Pubic symphysis.
Cartilage pads of knees (menisci).
Elastic cartilage:
Contains elastic fibers.
Flexible and resilient.
Found in:
External ear (auricle).
Epiglottis.
- Ligaments:
- Connect bone to bone.
- Provide stability to joints.
- Tendons:
- Connect muscle to bone.
- Facilitate movement by transmitting force from muscles to bones.
Types of Cells in Bone Connective Tissue
Bone is composed of cells and extracellular matrix:
Bone cells:
Osteoprogenitor cells: stem cells that differentiate into osteoblasts.
Osteoblasts: bone-forming cells that secrete osteoid.
Osteocytes: mature bone cells that maintain the bone matrix.
Osteoclasts: bone-resorbing cells that break down bone tissue.
Osteoprogenitor cells
Osteoblasts
Osteocytes
Osteoclasts
Microscopic Anatomy: Bone Connective Tissue
Bone matrix has organic and inorganic components.
Organic components:
Osteoid produced by osteoblasts, contains:
Collagen protein: provides flexibility and tensile strength.
Semisolid ground substance of proteoglycans and glycoproteins.
Gives bone tensile strength by resisting stretching.
Contributes to bone flexibility.
Inorganic components:
Salt crystals, calcium phosphate \text{Ca}_3(\text{PO}_4)_2
Crystals deposit around collagen fibers.
Harden matrix and account for rigidity of bones.
Bone remodeling:
Involves the removal of old bone by osteoclasts and deposition of new bone by osteoblasts.
Essential for bone growth, maintenance, and repair.
Influenced by hormones and mechanical stress.
General Functions of Bones
Support:
Bones provide structural support for the body.
Protection:
Bones protect internal organs from injury.
Movement:
Bones serve as attachment sites for skeletal muscles, soft tissues, and some organs.
System of levers: muscle contraction exerts a pull on the skeleton.
Hemopoiesis:
Blood cell production occurs in red bone marrow.
Red bone marrow contains hematopoietic stem cells that differentiate into blood cells.
Storage of mineral and energy reserves:
Bone stores body’s reserve of calcium and phosphate.
Released from bone into blood as needed.
Calcium essential for muscle contraction, blood clotting, nerve impulse transmission.
Phosphate.
Lipids stored in yellow bone marrow of adult bones.
Blood Supply and Innervation of Bone
Blood supply:
Bone highly vascularized, e.g., in regions of spongy bone.
Vessels enter from periosteum.
Nutrient foramen:
Small opening or hole in bone.
Artery entrance and vein exit here.
Nerves:
Bones are innervated with sensory nerves.
Nerves detect injuries and transmit pain signals.
Red bone marrow (Reticular CT):
Hemopoietic (blood cell forming).
In children:
Located in spongy bone and medullary cavity of long bones.
In adults:
Located only in selected areas of axial skeleton:
Skull, vertebrae, ribs, sternum, ossa coxae, proximal epiphyses of humerus and femur.
Bone Fracture and Repair
Breaks in bone:
Fractures.
Result of unusual stress or sudden impact.
Increased incidence with age:
Due to normal thinning and weakening of bone.
Types of fractures:
Stress fracture:
Thin break caused by increased physical activity.
Bone experiences repetitive loads (e.g., runners).
Pathologic fracture:
Occurs in bone weakened by disease.
Simple fracture:
Broken bone not penetrating skin.
Compound fracture:
One or both ends of the bone pierce overlying skin.
Bone repair:
Fracture hematoma formation: blood clot forms at the site of the fracture.
Soft callus formation: fibroblasts and chondrocytes deposit collagen and cartilage.
Hard callus formation: osteoblasts deposit bone tissue to replace the soft callus.
Bone remodeling: osteoclasts remodel the bone to its original shape.
Bone Remodeling
Bone remodeling:
Continuous process of bone breakdown and formation.
Involves osteoclasts (bone resorption) and osteoblasts (bone deposition).
Regulated by hormones (e.g., parathyroid hormone, calcitonin) and mechanical stress.
Important for maintaining bone health and calcium homeostasis.