section 2, chapter 7 skeletal system
DESCRIPTION
skeletal system lecture for anatomy & physiologyTRANSCRIPT
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Chapter 7, Section2
Bone Homeostasis
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Homeostasis of Bone Tissue
Calcium is constantly exchanged between blood and bone.
Bone resorption = Osteoclasts breakdown bone.
• Releases Calcium into the blood
• Stimulated by Parathyroid Hormone (PTH)
Bone deposition = osteoblasts deposit new bone
• Absorbs Calcium from the blood
• Stimulated by Calcitonin
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Factors Affecting Bone Development, Growth and
Repair
1. Nutrients
a. Vitamin D – promotes Ca2+ absorption in small intestine
• Vitamin D deficiency = softened and deformed bones
• Osteomalacia in adults
• Rickets in children• Rickets in children
b. Vitamin A – Balances bone resorption and deposition
• Vitamin A deficiency = retards bone development
c. Vitamin C – Required for collagen synthesis
• Vitamin C deficiency = results in fragile bones
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Factors Affecting Bone
Development, Growth and Repair
2. Hormones
a. Calcitonin
• Secreted from thyroid gland
• Promotes bone deposition
b. Parathyroid Hormone
• Secreted from parathyroid glands
• Promotes bone resorption
Figure 7.13 Hormonal regulation of blood
calcium and resorption
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2. Hormones
c. Growth Hormone (GH)
• Secreted from pituitary gland
• Promotes bone growth at
epiphyseal plates
Factors Affecting Bone Development, Growth and
Repair
Pituitary Gigantism
over secretion of GH during childhood
Pituitary Dwarfism
insufficient GH during childhood
Acromegaly
• Over secretion of GH as an adult
• Occurs after epiphyseal plates have sealed
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2. Hormones
d. Sex Hormones (testosterone & estrogen)
• Promotes long bone growth at puberty
• Also stimulates ossification at epiphyseal plates
Factors Affecting Bone Development, Growth and
Repair
3. Exercise3. Exercise
• Contracting muscles pull
on bones and promotes
bone thickening
Figure 7.12 The thickened bone on the
left is better able to withstand forces
from muscle contractions.
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Incomplete Fractures
Greenstick
fracture Fissuredfracture Fissured
fracture
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Spiral
fracture
Comminuted
fractureOblique
fracture
Transverse
fracture
Complete Fractures
fracturefracturefracturefracture
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When a bone breaks blood vessels
rupture and the periosteum tears.
Step 1.
Blood soon forms a
hematoma (blood clot).
Hematoma in foot
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Step 2.
Osteoblasts invade from periosteum
and deposit temporary spongy bone.
Step 3.
Fibroblasts deposit a mass of
fibrocartilage “cartilaginous callus”
&
Phagocytes remove hematoma
Osteoclasts remove bony debris
and deposit temporary spongy bone.
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Step 5.
Osteoclasts remove excess
bone, remodeling the bone
the bone close to its original
shape.
Step 4.
Osteoblasts replace the
cartilaginous callus with
bone, forming a bony callus
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Osteopenia “low bone mass”
Over time, osteoclasts outnumber osteoblasts, and
more bone is resorbed than can be deposited. Bone
mass decreases as a result.
Bone loss is rapid in menopausal Osteopenia “low bone mass”
• Progresses towards osteoporosis
Osteoporosis “porous bone”
• Bones develop spaces and canals
• Bones are fragile and easily broken
• Common in menopausal women
(from the low estrogen levels)
Bone loss is rapid in menopausal
women due to reduced estrogen
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Ways to delay or prevent osteoporosis:
1. Exercise daily.
2. Consume enough calcium and
vitamin D every day.
3. Do not smoke.
End of Chapter 7,
Section 2