Chapter 44
Disorders of the Skeletal System:
Metabolic and
Rheumatic Disorders
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Normal Bone Remodeling
• Osteoblasts are “bone building” cells
• They control bone remodeling by:
– Laying down new bone
– Secreting a compound (RANK ligand) that
controls the osteoclasts, the “bone breaking”
cells
• Normally, bone formation and breakdown are
balanced to:
– Replace damaged bone
– Maintain the amount and density of bone
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Bone Growth
• Bone cells and bone marrow cells produce OPG
– It blocks the action of RANK ligand
– The osteoclasts are not told to function
– Bone breakdown decreases
– Bones grow
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Question
Tell whether the following statement is true or false.
When osteoblasts work harder than osteoclasts, bones
grow.
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Answer
True
Osteoblasts build bone tissue; when they are more active
than osteoclasts, bone grows. When osteoclasts work
harder than osteoblasts, more bone is broken down.
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Discussion
How is bone remodeling affected by the
following?
• Vitamin D?
• Mechanical stress?
• Calcitonin?
• Vitamin C?
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Osteopenia and Osteoporosis
• Osteopenia
– Decreased bone
• Osteoporosis
– Decreased bone mass
– Decreased cancellous (spongy) bone strength
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Discussion
Why are each of these people prone to
osteoporosis?
• A postmenopausal woman
• A 70-year-old man
• A hyperthyroid alcoholic
• An Olympic figure skater who takes steroids to
reduce joint inflammation
• A man with a lung tumor that secretes PTH
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Discussion (cont.)
• Who would be most helped by the following?
• Exercise
• Increased Ca2+ and vitamin D in the diet
• Estrogen receptor stimulators
• Inhibitors of bone resorption
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Osteomalacia
• Bone is not mineralized properly; it is not
rigid
• It is caused by:
– Insufficient calcium absorption
– Insufficient phosphate
• It results in:
– Bone pain and tenderness
– Fractures
– Deformities
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Rickets
• Vitamin D deficiency
• Inadequate calcium absorption from diet
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Paget Disease
• Regions of excessive bone turnover
• New bone is disorganized
• Deformation and fracture common
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Question
Which bone disorder is characterized by “soft” bones?
a. Osteopenia
b. Osteomyelitis
c. Rickets
d. Paget disease
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Answer
c. Rickets
Calcium need vitamin D in order to be absorbed. In the
case of vitamin D deficiency (rickets), calcium cannot be
absorbed, and bones become soft.
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Rheumatoid Arthritis
• Autoimmune disorder
• Antibodies against IgG fragments
• Cause inflammation in the joint
• Abnormal healing responses lay down granulation
tissue (pannus)
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Treatment of Rheumatoid Arthritis
• NSAIDs
• Corticosteroids
• Leflunomide
• Influximab
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Systemic Lupus Erythematosus (SLE)
• Autoantibodies include:
– Antinuclear antibodies (ANA)
– Antibodies against RBCs
– Antibodies against platelets
– Antibodies against coagulation factors
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SLE Can Damage Any Tissue
• Arthralgia
• Skin lesions (butterfly rash)
• Glomerulonephritis
• Pleuritis
• Pericarditis
• Atherosclerosis
• CNS inflammations
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Question
SLE produces antibodies against all but which of the
following?
a. RBCs
b. WBCs
c. Platelets
d. Coagulation factors
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Answer
b. WBCs
SLE is an autoimmune disease that results in the
production of the following antibodies: antinuclear
antibodies, and antibodies against RBCs, platelets, and
coagulation factors. WBCs are not affected.
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Systemic Sclerosis (Scleroderma)
• Collagen deposits in skin and internal organs
Spondyloarthropathies
• Inflammation at the insertions of tendons
and ligaments
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Reactive Arthropathies
• Sterile joint inflammations caused by previous
infection
• The joints are not infected at the time of
inflammation
• Can follow infection with many agents including:
– Chlamydia
– Pseudomonas
– Streptococcus
– HIV
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Osteoarthritis Syndrome
• Degenerative joint disease
• Inflammation of the joints often secondary to
physical damage
• Damaged joint cartilage tries to heal itself
– Creating osteophytes or spurs
• Cartilage contains more water, less collagen
– Cartilage becomes weak, rough, eroded
– No longer protects the surface of the bone
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Gout Syndrome
• Increased serum uric
acid
• Crystals precipitate in
the joint
• Inflammation results
• Tophi are deposits
containing monosodium
urate crystals
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