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HDTD/Bone- lecture II
Lecturer Dr. Zahraa Qasim Ali
Dear students:
By the end of the second “Bone” lecture, I hope each one of you will be able to:
1. List few notes on bone remodeling.
2. Describe some bone disorders.
3. Define joint structure and describe few joint disorders.
Bone remodeling and calcium balance:
Bone remodeling occurs via osteoblast and osteoclast activity and is an ongoing
process that is also an essential mechanism for maintaining systemic Ca
2+
balance
and exchange with other tissues.
A. Bone remodeling: bone turnover processes require calcium, phosphorus,
and vitamin D. osteoclasts secret factors such as receptor activator of NFκB
(RANK) to stimulate osteoblasts and osteoblast migration into areas to build
new bone matrix. Hormonal regulation of the remodeling process is via
parathyroid hormone (PTH), with calcitriol and estrogen also influencing the
remodeling. Bone remodeling regulation is important so that serum Ca
2+
and
PO
4
levels are maintained.
B. Calcium balance and vitamin D: Calciterol, the active steroid hormone from
vitamin D, participate in regulating calcium levels by altering bone resorption,
gut Ca
2+
transport, and kidney reabsorption of Ca
2+
. Vitamin D levels are
maintained from dietary absorption and from skin synthesis during exposure
2
to sunlight. Vitamin D is then converted to calciferol by hydroxylation
reaction in the liver and kidney. If serum Ca
2+
is below normal range, PTH
induces increased vitamin D formation, and Ca and PO
4
mobilization from
bone to maintain normal Ca
2+
levels.
Bone Disorders:
1. Fractures of normal bone heal when callus formation occurs, and woven
bone then builds up around the fracture site. Inflammatory, reparative, and
remodeling phases occur in bone during healing so that ossification to mature
lamellar bone occurs with healing of the fracture callus.
2. Vitamin D and PTH abnormalities: A vitamin D deficiency in childhood
may cause rickets, or bowing of the soft bones in children, due to abnormal
bone ossification. Osteomalacia is bone demineralization in adults and can
be caused by vitamin D deficiency or bone resorption due to high PTH levels.
Depending on the cause, calcium and vitamin D supplements and reducing
the high PTH levels may help reverse the bone loss. However, vitamin
supplementation must be monitored since toxic levels of vitamin D can cause
soft tissue and blood vessel deposition of calcium and phosphorus, which
results in problems with blood flow and tissue damage.
3. Osteoporosis: it is a gradual loss of bone mass that may occur with aging or
in postmenopausal women….. [to be continued as assignment in SGL]
4. Osteonecrosis: or called: aseptic avascular necrosis is death of bone tissue
caused by trauma, radiation injury, or emboli that block nutritional blood
supply to the bone.
5. Bacterial infection: bacterial infection of the bone may be introduced directly
through wounds and fractures, or during surgical procedures.
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6. Cancer: Because of the high blood, flow in bone marrow, cancer metastases,
especially from the breast, prostate or lung to the bone can cause serious
osteolytic bone lesions and metastatic tumor growth in the bone itself.
7. Disorders of unknown etiology: Paget’s disease is a chronic condition of
abnormal bone remodeling with resorption of normal bone; lytic lesions,
disorganized, excessive bone formation.
Clinical Correlation
It is good to know about
:
[
Paget’s disease of bone or osteitis deformans:
Abnormal persistence of woven bone is a feature of Paget’s disease. It was first
described by Sir James Paget in 1877. Paget’s disease of bone is an osteolytic and
osteosclerotic bone disease of uncertain etiology involving one (monostotic) or more
bones (polyostotic). The condition affects predominantly males over the age of 50
years. The bones are weak and there may be deformities. This disease may be due
to viral etiology, or it may be the result of hereditary predispositions linked to
chromosome 18q21-22
]
Joint and joint disorders
There are three types of joints:
1. Fibrous (e.g. cranial sutures)
2. Cartilaginous (e.g. intervertebral disk & epiphysial plates)
3. Synovial (e.g. ball and socket joint of hip, hinge joints of the elbow and knee,
joints of fingers and toes, plane and pivot joints of clavicle and neck)
The larger joint are synovial types containing membranous sacs (bursae) with
synovial fluid to better cushion the larger joint as they are subject to friction
with movement of the limbs.
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The articular discs of hyaline cartilage cover the ends of bones and may be
renewed by chondrocyte activity in this area. These discs buffer the impact of
movement in most joints.
Some joint disorders are:
1. Gout: is a joint inflammation condition that results in joint tissue destruction
and joint pain.
2. Rheumatoid arthritis: is an autoimmune disease that causes chronic
destructive inflammation in joints.
3. Osteoarthritis (the most common joint disease): destruction of articular
cartilage in weight- bearing joints and fingers. With age or with trauma in
younger ...[SGL assignment]
4. Systemic Lupus Erythematous (SLE): is a chronic autoimmune
inflammatory disease affecting joint tissues causing synovitis (synovial
membrane inflammation) and polyarthralgia (multiple joints pain).
5. Joint injury: traumatic injury may impact joints and limit movement. Major
problems such as rotator cuff injury may damage and cause instability of the
glenohumeral joint of the shoulder.
6. Bursitis: excessive friction or excess use of joints may causes diffuse deep pain
from mechanical stress and pressure on areas around the bursae of joints, such as
that found in “tennis elbow”. Reducing the inflammation (sometimes by
alternating cold and then warm compresses over the joint, or injections of
corticosteroids into the joints are used) and lowering the stress on the joints may
attenuate the pain.