Histology and Physiology
of Bone
Part 2
Bone Growth
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Bone Development
• Bones develop in the fetus by
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• Intramembranous Ossification– Form within sheet-like layers of connective tissue.
– Primitive connective tissue cells enlarge and
differentiate into osteoblasts (bone forming cells)
– Osteoblasts deposit bone matrix on collagen fibers
of tissue forming trabeculae of woven bone.
– Osteoblasts continue to lay down matrix on the
surface forming cancellous (spongy) bone.
– Red bone marrow develops within the spaces and
cells surrounding this developing bone specializes
to form periosteium
– Osteoblasts from periosteium lay down bone
matrix to form an outer surface of compact bone.
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• Centers of ossification– These centers expand to form a bone by gradually
ossifying the membrane.
– So, the centers of ossification have the oldest
bone while the expanding edges the youngest.
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• Endochondral Ossification– Remember…bone starts as a hyaline cartilage
model!
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• Steps of endochondral ossification…
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• Primary ossification centers appear early in
fetal development (~8 or 9 weeks) and
secondary ossification centers appear about 1
month before birth.
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Bone Growth
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• Growth in Bone Length:
– Long bones and bony projections increase in
length because of growth at the epiphyseal plate.
– Growth at the epiphyseal plate involves formation
of new cartilage by interstitial cartilage growth
followed by appositional bone growth on the
surface of the cartilage.
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– The hypertrophied chondrocytes die and are
replaced by osteoblasts from the endosteum.
– Through appositional bone growth…osteoblasts
deposit new bone matrix on the calcified cartilage
matrix.
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• Growth in Bone Width…
– Fast bone growth=
• Osteoblasts from periosteum lay down bone to form
series of ridges with grooves between them.
• Periosteum covers bone ridges and extend to bottom of
grooves and 1 or more BVs from periosteum lie in each
groove.
• Osteoblasts continue to produce bone, ridges grow and
extend toward each other till they meet…forming a
tunnel that contains BVs.
• Osteoblasts in the periosteum lining the tunnel
(endosteum) continue to lay down bone to form
concentric lamella, which eventually forms osteons.
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Factors that affect bone growth:
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• Nutrition…
• Vitamin D
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• Hormones…
– Hormones are important for bone growth.
– Growth hormone:
– Sex Hormones:
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Bone Remodeling
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Bone Repair
Step 1- Hematoma formation
• When a bone is injured/fractured, the BVs in
the bone and surrounding periosteum are
damaged = hematoma formed.
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Step 2- Callus formation
• A callus
• The callus forms as the clot dissolves.
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Step 3- Callus Ossification
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Step 4- Bone remodeling
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