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Chapter 6

BIOL 2404 Chapter Notes - Chapter 6: Intramembranous Ossification, Endochondral Ossification, Hyaline Cartilage

Course Code
BIOL 2404

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Chapter 6: Histology and Physiology of Bones
Functions of the Skeletal System
Skeletal system has four components
Bones are organs composed of
Vascular tissue
Function of Bones
Support: form the framework that supports the body and cradles soft organs
Protection: provide a protective case for the brain, spinal cord, and vital
Movement: provide levers for muscles
Storage: reservoir for minerals, especially calcium and phosphorus
Blood cell production: hematopoiesis occurs within the marrow cavities of
Chondroblasts produce cartilage and become chondrocytes
Chondrocytes are located in lacunae surrounded by matrix
The matrix of cartilage contains collagen fibers (for strength) and
proteoglycans (trap water)
The perichondrium surrounds cartilage
The outer layer contains fibroblasts
The inner layer contains chondroblasts
Cartilage grows by appositional and interstitial growth
Bone Histology
Bone Matrix
Approximately 35% organic and 65% inorganic material
Collagen provides flexible strength
Hydroxyapatite (calcium phosphate crystal) provides
weight-bearing strength
Bone Cells
Osteoblasts produce bone matrix and become osteocytes
Osteoblasts connect to one another through cell processes and
surround themselves with bone matrix to become osteocytes
Osteocytes are located in lacunae and are connected to one
another through canaliculi
Osteoclasts break down bone
Osteoblasts originate from osteochondral progenitor cells
Osteoclasts originate from stem cells in red bone marrow
Ossification (Osteogenesis)
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Osteoblasts on a preexisting surface, such as cartilage or bone. The
cell processes of different osteoblasts join together
Osteoblasts have produced bone matrix. The osteoblasts are now
Bone tissue is classified as either woven or lamellar bone, according to the
organization of collagen fibers
Woven bone
Has collagen fibers oriented in many different directions
It is remodeled to form lamellar bone
Lamellar bone
Mature bone
Arranged in thin layers called lamellae
Has collagen fibers oriented parallel to one another
Bone can be classified according to the amount of bone matrix relative to the
amount of space present within the bone
Cancellous bone has many spaces
Internal layer which is a honeycomb of trabeculae filled with
red or yellow bone marrow
Compact bone is dense with few spaces
External layer
Lamellae combine to form trabeculae
Beams of bone that interconnect to form a lattice-like structure
with spaces filled with bone marrow and blood vessels
Trabeculae are oriented along lines of stress and provide structural
Compact Bone
Consists of organized lamellae
Circumferential lamellae form the outer surface of compact
Concentric lamellae surround central canals, forming osteons
Interstitial lamellae are remnants of lamellae left after bone
Canals within compact bone provide a means for the exchange of
gases, nutrients, and waste products
From the periosteum (endosteum) perforating canals carry
blood vessels to central canals
Canaliculi connect central canals to osteocytes
Bone Anatomy
Individual bones are classified according to their shape
Long bones
Longer than they are wide
Most bones of the upper and lower limbs
Short bones
About as wide as they are long
Bones of the wrist (carpals) and ankle (tarsals)
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