Cartilage & Bone

Undifferentiated Mesenchymal Cells

Differnetiate into chondroblasts, which differentiate into chondrocytes

Perichondrium

Outer fibrous layer (dense irregular connective tissue and inner cellular layer). Loose connective tissue with blood vessels to supply cartilage with vascularity.

Cartilage Matrix

High ability to resist compression with proteoglycans and collagen. Highly basophilic due to (-) charged proteins (chondroitin sulfate)

Chondroblasts

Continuously secrete cartilage matrix and become surrounded by their secretion. Found in the periphery of the cartilage matrix, performing appositional growth. Near the perichondrium

Chondrocytes

Mature cells that maintain cartilage matrix, found inside cartilage, living in lacunae, are involved in interstitial growth.

Interstitial Growth

Growth from within, coming from chondrocytes increasing length

Appositional Growth

Growth from without, coming from chondroblasts, increasing the width of cartilage.

Hyaline Cartialge

Articular cartilage and nasal septum. Most abundant cartilage for strength and flexibility

Elastic Cartilage

External ear, epiglottis. More flexible and used for strength too.

Fibrocartilage

Temporal mandibular joint articular surface(TMJ), intervertebral dics. No perichondrium and is found in a parallel linear arrangement. Strongest cartilage capable of withstanding high pressure.

Intramembranous Ossification Bones

Flat bones: maxilla, and mandible

Neural Crest Cells

Progenitor cells for intramembranous ossification aggregate as osteoblasts ossifying cranium

Endochondral Ossification Bones

Long bones, mandibular condyle.

Intramembranous Ossification

Mesenchymal stem cells condense and become osteoprogenitor cells, determining the shape and thickness of forming bone. These cells produce osteoblasts, which secrete osteoid, eventually maturing into osteocytes. Bone remodeling occurs with osteoclasts, promoting vascularization and innervation of developing bone.

Endochondral Ossification

Bones’ initial shape is produced by a cartilage model. Diaphysis becomes completely converted to bone except for the epiphyseal growth plate on either side. Chondrocyte interstitial growth drives long shaft elongation, not the action of osteoblasts.

Epiphyseal Plate

Chondrocytes’ interstitial growth creates a template, where cartilage calcifies, and then osteoblasts come in and produce osteoid, eventually becoming bone.

Compact (Cortical) Bone

Dense, strong, forming outer layer of bones

Cancellous (trabecular bone)

Spongy, center of bone

Osteoid

Hardened bone matrix resulting from vesicles release by osteoblasts filled with hydroxyapatite. Organic ECM for bone with type I collagen and glycoproteins.

Hydroxyapatite

Inorganic mineral phase

Osteoblasts

Form osteoid and build bone

Osteocyte

Mature cells incolved in maintainance of ECM of bone

Osteoclasts

Born from monocytes and breakdown and reabsorption of bone

Osteoclast Function

Degrade bone matrix and collagen fibers releasing calcium and phosphate, making them soluble to be entered into the blood. Send signals to promote angiogenesis (promote vascularization and innervation of bone)

Dynamism of Bone

Undergoes continuous change and remodeling accommodating growth and changes in force and metabolic function. An increase in force applied results in an increase in bone strength.

Wolff’s Law

Bones remodel and adapt their internal structure and mass in response to the mechanical stresses and loads placed upon them.

Bone Remodeling

Bone formation and breakdown regulated (coupled). Long and short range signaling, neutral stimulation, force stimulation.

Bone Remodeling in Teeth

Dental occlusion provides important signal for alveolar bone maintenance. Loss of dental tissue leads to bone reabsorption

Bone Tissue Organization

Types of cells constituting different types of bone are the same but are organized differently

Central Canal

Main area with vessels and innervation

Proliferating Canal

Side channels with vessels and innervation