6.7 Bone Formation (Anatomy)

Interstitial Growth

(Endogenous Growth) - When the cartilage model grows in length by continual cell division of chondrocytes, accompanied by further secretion of the cartilage EM.

Appositional Growth

(Exogenous Growth) - Growth of the cartilage in thickness due to the deposition of EM material on the cartilage surface of the model by new Chondroblasts that develop from the Perichondrium.

Periosteum

Once the Osteoprogenitor cells in the Perichondrium differentiate into Osteoblasts & the Perichondrium begins to form bone the outer layer is referred to as a Periosteum.

Epiphyseal Line

The cartilage present at the junction of the diaphysis and epiphyses; a remnant of the epiphyseal plate.q

Bone Remodeling

The ongoing replacement of old bone tissue by new bone tissue.

Steps of Intramembranous Ossification

1. Develop Ossification Center 2. Calcification 3. Formation of Trabeculae 4. Development of Periosteum

Steps of Endochondral Ossification

1. Development of The Cartilage Model 2. Growth of The Cartilage Model 3. Development of The Primary Ossification Center 4. Development of The Medullary (Marrow) Cavity 5. Development of The Secondary Ossification Center 6. Formation of Articular Cartilage and The Epiphyseal (Growth Plate)

Factors that can trigger bone remodeling

1. Exercise 2. Lifestyle modifications 3. Changes in diet

Bones Extracellular Matrix is about...

15% Water, 30% Collagen Fibers, and 55% Crystalized Mineral Salts. Dry bones are 60% inorganic materials and 40% organic materials. The most abundant mineral salt in bone is Calcium Phosphate.

Ossification

Bone formation. This occurs in four situations: 1. Initial formation of bones in embryo and fetus 2. Growth of bones during infancy, childhood, and adolescence until their adult sizes are reached. 3. Remodeling of bone (replacement of old bone by new bone tissue throughout life). 4. Repair of fractures throughout life.

Secondary Ossification Center

Develop after the Epiphyseal artery enters the epiphyses. The secondary ossification center varies from the primary ossification center in that spongy bone is created and kept in the epiphyses. Ossification proceeds outward from the center of the epiphysis toward the outer surface of the bone.

Bone Growth In Length

Involves two parts 1. Interstitial growth of cartilage on the epiphyseal side of the epiphyseal plate 2. Replacement of cartilage with bone by Endochondral ossification on the diaphyseal side of the epiphyseal plate

Primary Ossification

Proceeds inward from the external surface of the bone. Region of formation of long bone begins in center of hyaline cartilage shaft. As the bone ossifies it leaves a cavity in the Diaphysis. After the Primary Ossification site is set up towards the middle of the diaphysis ossification spreads to the proximal and distal ends of the bone.

Bone Deposition

The addition of minerals and collagen fibers to bone by osteoblasts

Bone Resorption

The removal of minerals and collagen fibers from bone by osteoclasts.

Epiphyseal Growth Plate

This is the site that allows a bone to grow in length. A layer of Hyaline cartilage in the metaphysis of a growing bone made of 4 parts: 1. Zone of Resting Cartilage 2. Zone of Proliferating Cartilage 3. Zone of Hypertrophic Cartilage 4. Zone of Calcified Cartilage [R.P.H.C.=Real Pizza Has Cheese]

Perichondrium

A Mesenchymal covering that encases the Cartilage Model

Ossification Center

A cluster of mesenchymal cells that differentiate into osteoprogenitor cells then into osteoblasts. Osteoblasts then secrete the organic EM of bone until they are surrounded by it.

Mesenchyme

A connective tissue found mostly in an embryo and is the tissue from which most other connective tissue develop.

Hydroxyapatite

A crystal which is made by Calcium Phosphate and Calcium Hydroxide combined.

Calcification

When Hydroxyapatite, Calcium Carbonate, and ions such as Magnesium, Fluoride, Potassium, and sulfate combine, crystalize and harden.

Cartilage Model

When Mesenchyme are directed to crowd together in the general shape of future bone and then develop into Chondroblasts. The Chondroblasts then secrete cartilage EM thus making a Hyaline cartilage model resembling the future bone.

Intramembranous Ossification

When bone forms directly within condensed Mesenchyme, which is arranged in sheet like layers that resemble membranes.

Endochondral Ossification

When bone forms within Hyline Cartilage that develops from Mesenchyme.

Zone of Resting Cartilage

[1] - This layer is nearest the epiphysis and consists of small, scattered chondrocytes. The term "resting" is used because the cells do not function in bone growth. Rather, they anchor the epiphyseal plate to the epipyhysis of the bone

Zone of Proliferating Cartilage

[2] - Slightly larger chondrocytes arranged like a stack of coins undergo interstitial growth as they dived and secrete EM. The chondrocytes in this zone divide to replace those that die at the diaphyseal side of the epiphyseal plate.

Zone of Hypertrophic Cartilage

[3] - This layer is made of large, maturing chondrocytes arranged in columns.

Zone of Calcified Cartilage

[4] - Region is only a few cells thick and is made of dead chondrocytes surrounded by calcified EM. Osteoclasts dissolve the calcified cartilage and Osteoblasts and capillaries invade the region rapidly and lay down bone EM. This results in the zone of calcified cartilage becoming "new diaphysis" that is firmly cemented to the rest of the diaphysis of the bone.