Spicule osseous tissue resting zone proliferation

spicule
Osseous tissue
Resting zone
Proliferation zone
Cartilage cells undergo mitosis.
Hypertrophic zone
Older cartilage cells enlarge.
Ossification zone
New bone formation is occurring.
Calcification zone
Matrix becomes calcified;
cartilage cells die; matrix
begins deteriorating.
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Epiphyseal plate
• Resting zone: cells nearest the epiphysis that are
relatively small and inactive
• Columns of stacked cartilage cells are inside the resting
zone (in direction of diaphysis)
• Proliferation zone is made up of chondroblasts at the top
of the stack which divide quickly which pushes the
epiphysis away from the diaphysis causing the bone to
elongate
• Hypertrophic zone: older chondrocytes have enlarged
(hypertrophied) and are positioned deep in the stack
• Calcification zone: The older hypertrophied chondrocytes
signal the surrounding cartilage matrix to calcify and
produce a calcification zone
• Ossification zone: new bone formation
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Postnatal Childhood and Adolescent
Growth of Endochondrial Bones
• Bones lengthen entirely by growth from
the epiphyseal plates
• Cartilage is replaced with bone tissue in
diaphysis side as quickly as it grows
• Whole bone lengthens
• Epiphyseal plate maintains constant
thickness during growth of diaphysis
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Postnatal Growth of
Endochondrial Bones
• Growing bones widen as they lengthen
– Osteoblasts —add bone tissue to the
external surface along the diaphysis
– Osteoclasts —remove bone from the
internal surface along the diaphysis as
remodeling takes place with increase in
diameter
• Appositional growth —growth of a bone by
addition of bone tissue to its surface
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5/12/17
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Hormone Regulation of Bone Growth
• Growth hormone —produced by the
pituitary gland
– Stimulates epiphyseal plates
• Thyroid hormone —ensures that the
skeleton retains proper proportions
• Steroid hormones (estrogen and
testosterone)
– Promote bone growth
– Later induce closure of epiphyseal plates
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At end of adolescence,
long bone growth ends
• Chondroblasts divide less often and then
stop dividing
• Epiphyseal plates become thinner
• Cartilage stops growing and is replaced by
bone tissue
• Long bones stop lengthening when the bone
of the diaphysis and epiphysis fuse and
epiphyseal plates close
• People can no longer grow in height once
their epiphyseal plates have closed
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Bone Remodeling:
bone is a dynamic tissue
• 500 mg of calcium may enter or leave the
adult skeleton each day
• Cancellous (spongy) bone of the skeleton
is replaced every 3–4 years in most bones
• Compact bone is replaced every 10 years
in most bones
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Bone deposition and resorption
• Occurs at periosteal (periosteum) and
endosteal (endosteum) surfaces
• In adults, this occurs primarily at the
endosteal surface
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Bone Remodeling
• Bone deposition/formation —
accomplished by osteoblasts
• Bone resorption —accomplished by
osteoclasts
• Maintains normal levels of Ca
+
and PO
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3-
in
body fluids
•