Justin, Mara, Anna, Tania, Jacqueline,
Gigi, Lindsay
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Cartilage is a flexible
connective tissue found in
many areas in the bodies
of humans and other
animals.
immediately adjacent to
epiphysis are irregularly
scattered cartilage cells,
called the resting cell zone
this is germinal layer that
supplies the developing
cartilage cells
anchors growth plate to bone
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In this zone, chondrocytes, which are the only
cells found in healthy cartilage, are either dying
or dead, leaving cavities that will later become
invaded by bone-forming cells.
Chondrocytes die when they can no longer
receive nutrients or eliminate waste by
diffusion.
This is because the calcified matrix is much less
hydrated than hyaline cartilage.
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there is no active growth in this
layer (no cellular division) and the
chondrocytes (cells found in
healthy cartilage) begin to
terminally differentiate
layer in which chondrocytes
become enlarge and swollen in the
process of maturation leading to
cell death
they hypertrophy at expense of
extracellular matrix & these
enlarged cartilage cells
synthesis of extracellular matrix
permits newly divided cells to
separate from each other;
columns of cartilage cells extend
toward metaphysic (wider portion
of a long bone adjacent to the
growth plate , being constantly
lengthened by cell division
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cells nearer the metaphysis begin to undergo
changes that ultimately lead to their
destruction
increase in enzyme activity increases the
concentration of phosphate ions, which are
required in the calcification process
an absence of alkaline phosphatase and there is
deficient mineralization of the matrix and
widening of the growth plate
this is weakest portion of the growth plate
1. Zone of
Resting
Cartilage
2. Zone of
Proliferation
3. Zone of
Maturation/
Hypertrophy
4. Zone of
Calcified
Cartilage
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Hormones that
affect bone growth
and development
are secreted by
pituitary, thyroid
gland, parathyroid
glands, and the
ovaries and testes
 Secretes
growth hormone (somatotropin) which
stimulates activity in the epiphyseal plates
 Main Regulator of Height
 Stimulates bone and Muscles growth
 Maintains the normal Rates of Protein Synthesis
 Speeds the release of fats as an energy source for
growth
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When a low blood calcium condition exists the
gland responds by releasing the parathyroid
hormone
Stiumlates osteoclasts to break down bone
tissue
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As a result, calcium salts are released into the blood
If blood calcium level is excessively high, the thyroid
gland responds by releasing calcitonin which
inhibits the osteoclast activity allowing the
osteoblasts to form bone tissue
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A peptide hormone produced by cells within
the thyroid gland
Secretion is stimulated by high blood calcium
concentrations, and it acts as a physiologic
antagonist to PTH
Osteoclasts have receptors for calcitonin, but
the effects are transient. Calcitonin also:
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inhibits osteoclast resorption
delays calcium absorption from the intestine
increases calcium urinary excretion
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1,25 dihydroxyvitamin D is an active hormone
which is produced by the kidney
It is not really a vitamin, but the name was given
many years ago, before anybody knew the
function of this molecule. Vitamin D receptors are
present in bone, kidney, intestines, and other cells.
The chemical name is 1,25-dihydroxycholecalciferol, and it
promotes gastrointestinal absorption of calcium and
phosphorus.
 is necessary for bone mineralization.
 stimulates bone resorption when given in high doses
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Produced by the thyroid gland. Bone cells have
receptors for thyroid. This hormone also:
is necessary for growth and maturation of the
skeleton.
 causes increased osteoclastic bone resorption and
osteoporosis when levels are too high.
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Increase Bone resorption
 Parathyroid hormone
Glucocorticoids
Thyroid Hormone
Vitamin D metabolites in high doses
Decrease Bone Resorption
 Calcitonin
Gonadal steroids
Increase Bone Formation
 Growth hormone
Vitamin D metabolites
Gonadal steroids
Decrease Bone Formation
 Glucocorticoids
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A disease that effects your bones and makes them
thin & brittle with several holes in them like a
sponge.
Leads to broken or fractured bones which can be
disabling
Caused by lack of estrogen or testosterone:
hormones that protect against bone loss
Common in women after menopause & men older than
65
 More common in women than men
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Vitamin D and calcium deficiencies contribute to
bone thinning and increase risk of Osteoporosis
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a disease where there is
cellular death (necrosis)
of bone components
due to interruption of
the blood supply.
Blood is responsible for
providing oxygen and
nutrients to the bone
tissue.
Without blood reaching
bone tissue, the bone
tissue dies and the bone
collapses.
• Common Causes:
• Chemotherapy
• Alcoholism
• Excessive steroid
use
• Fractured bones
• Dislocated joints
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softening of the bones due to a
lack of vitamin D or a problem
with the body's ability to break
down and use this vitamin.
The softer bones in osteomalacia
have a normal amount of
collagen, which gives the bones
its structure. However, they lack
the proper amount of calcium
which makes them so soft.
Syptoms include:
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Bone fractures that happen
without a real injury
Muscle weakness
Widespread bone pain, especially
in the hips
• Commonn Causes
• Lack of vitamin D
• Not enough
exposure to
sunlight
• Inability for
intestines to fully
absorb vitamin D
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Rickets is a disorder caused
by a lack of vitamin D,
calcium, or phosphate. It
leads to softening and
weakening of the bones.
Also caused by lack of
Vitamin D. Vitamin D helps
the body control calcium and
phosphate levels. If the blood
levels of these minerals
become too low, the body
may produce hormones that
cause calcium and phosphate
to be released from the bones.
This leads to weak and soft
bones.
• Symptoms:
• Bone
pain/tenderness
• Dental deformities
• Impaired growth
• Short stature (adults
less that 5 ft. tall)
• Skeletal deformities