Post on 12-Jan-2016
transcript
Chapter 6:
Osseous Tissue and Bone Structure
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The Skeletal System
• Skeletal system includes:– bones of the skeleton– cartilages, ligaments, and other
connective tissues that stabilize the bones
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Skeletal System
Functions:1. Support: framework & structure of body2. Storage of minerals and lipids
Minerals: calcium and phosphate - for osmotic regulation, enzyme
function, nerve impulses
Yellow marrow: triglycerides3. Blood cell production: all formed elements - red marrow: stem cells hematopiesis4. Protection: surround soft tissues
5. Leverage for movement:- levers upon which skeletal muscles act3
Classification of Bones
• Bone are identified by:– shape– internal tissues– bone markings
SHAPE:1. Long bones2. Flat bones3. Sutural bones4. Irregular bones5. Short bones6. Sesamoid bones
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Shape of Bones
1. Long Bones:- Longer than wide, consist of
shaft and 2 ends - e.g. bones of appendages
2. Short Bones:- Approx. equal in all dimensions- e.g. carpals, tarsals
3. Flat Bones:- Thin, 2 parallel surfaces - e.g. skull, sternum, ribs,
scapula
Figure 6–1a5
Shape of Bones
4. Irregular Bones:- Complex shapes- E.g. vertebrae, os coxa
5. Sesamoid Bones:- Seed shaped, form in tendon- E.g. patella, total number can
vary
6. Sutural Bones:- Extra bones in sutures of skull
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Bone Structure
• A bone is an organ consisting of many tissue types:
– Osseous, nervous, cartilage, fibrous CT, blood, etc.
All bones consist of 2 types of bone tissue1. Compact bone:
- solid, dense bone, makes up surfaces and shafts
2. Spongy Bone/Cancellous bone:- meshy, makes up interior of bones, houses
red marrow in spaces7
Bone Markings• Bones are not flat on the surface:
– Have projections, depressions, and holes for muscle attachment, blood & nerve supply
• Depressions or grooves:– along bone surface
• Projections:– where tendons and ligaments attach– at articulations with other bones
• Tunnels:– where blood and nerves enter bone 8
Bone Markings
Table 6–1 (2 of 2)9
Long Bones Structure
1. Diaphysis:- Hollow shaft of compact bone
2. Medullary (marrow) cavity:- Center of diaphysis, contains
yellow marrow- Triglycerides for energy reserve
3. Epiphysis:- Expanded end of bone, surface
of compact bone- Center filled with spongy bone
with red marrow in spaces- Produces blood cells
Figure 6–2a10
Long Bones Structure
4. Epiphyseal line or plate:- Cartilage that marks connection of
diaphysis with epiphysis- Line: adults, narrow (aka metaphysis)- Plate: thick, allows growth during
childhood
5. Periosteum:- 2 layer covering around outside of bone:
- Outer Fibrous Layer- Inner Cellular Layer
6. Endosteum:- Cellular layers, covers all inside surfaces
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7. Articular Cartilage:- Hyaline cartilage on end where bone contacts
another, no periosteum or perichondrium
Joint/Articulation:- connection between two bones, surrounded by CT capsule, lined with synovial membrane
Joint cavity filled with synovial fluid to reduce friction on articular cartilage
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Flat Bone Structure
• Thin layer of spongy bone with red marrow between two layers of compact bone
• Covered by periosteum and endosteum• Site of most hematopoiesis
– Production of blood cells and cell fragments that are suspended in plasma (RBC, WBC, and platelets
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Characteristics of Bone Tissue
• Periosteum: – covers outer surfaces of bones – consist of outer fibrous and inner
cellular layers
• Endosteum:– Inner, cellular layer of periosteum
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Bone Histology
• Bone = osseous tissue, supporting CT• Consists of specialized cells in a
matrix of fibers and ground substance• Characteristics of bone:
1. Dense matrix packed with calcium salts2. Osteocytes in lacunae3. Canaliculi for exchange of nutrients and
waste4. Two layer periosteum, covers bone except
at articular surfaces 16
Bone Histology
• Matrix = 98% of bone tissue– 1/3 = osteoid; organic part:
• Collagen fibers + ground substance• Tough and flexible
– 2/3 = densely packed crystals of hydroxyapatite (calcium salts, mostly calcium phosphate)• Hard but brittle
• Cells = only 2% of bone1. Osteocytes2. Osteoblasts3. Osteoprogenitor cells4. Osteoclasts
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Cells located in Bones1. Osteocytes = mature bone cells
-no cell division-located in lacunae between layers of matrix called
lamellae-canaliculi link lacunae to each other and blood supply-osteocytes linked to each other via gap junctions on
cell projections in canaliculi:- allow exchange of nutrients and
wastes-Function
1. To maintain protein and mineral content of matrix2. Can also participate in bone repair:
-become stem cell like when broken free of lacuna
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LM X 362
Canaliculi
Osteocytesin lacunae
Matrix
Bloodvessels
Central canal
PERIOSTEUM
Fibrouslayer
Cellularlayer
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Cells located in Bones
2. Osteoblasts - Immature bone cells- Perform osteogenesis:
- Formation of new bone matrix
- Produce osteoid - Organic components of matrix that is not
yet calcified to form bone
- Promote deposit of calcium salts which spontaneously form hydroxyapatite
- Once enclosed in lacuna by matrix, osteoblast differentiates into osteocyte and no longer produces new matrix 20
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Cells located in Bones
3. Osteoprogenitor Cells – mesenchymal cells- bone stem cell that produces daughters
- daughters become osteoblasts for repair and growth
- located in endosteum and inner periosteum
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Cells located in Bones
4. Osteoclasts- large, multinuclear- derived from monocytes (macrophages)- perform osteolysis =
- digest and dissolve bone matrix- release minerals:
1. For use in blood or 2. Recycling during bone
remodeling24
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Cells located in Bones
Osteocyte: Mature bonecell that maintains thebone matrix
Osteoblast: Immature bone cell that secretes organic components of matrix
Osteoclast: Multinucleate cell that secretes acids and enzymes to dissolve bone matrix
Osteoprogenitor cell: Stem cell whose divisions produce osteoblasts
Osteoid Osteoblast Matrix MatrixMatrix
Marrow cavity
Osteoprogenitorcell OsteoclastCanaliculiOsteocyte
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Homeostasis
• Bone building (by osteocytes) and bone recycling (by osteoclasts) must balance:– more breakdown than building, bones
become weak– exercise causes osteocytes to build
bone
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How would the strength of a bone be affected if the ratio of
collagen to hydroxyapatite increased?
1. Strength increases, flexibility increases.
2. Strength increases, flexibility decreases.
3. Strength decreases, flexibility. decreases.
4. Strength decreases, flexibility increases. 28
If the activity of osteoclasts exceeds the activity of osteoblasts in a bone,
how will the mass of the bone be affected?
1. stable mass, but re-positioned matrix
2. mass will not be affected3. more mass4. less mass
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The difference between compact bone
and spongy bone.
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Structure of Compact Bone
• Consists of osteons:– Parallel to surface
• Each osteon is around a central canal:– Contains blood vessels and nerves
• Perforating canals perpendicular to osteons act to connect the osteons
• Osteon is built of layers of matrix secreted by osteoblasts– Each layer = concentric lamella
• Osteocytes are located in lacunae between lamellae
• Ostocytes are connected to neighboring cells and central canal via canaliculi
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Structure of Compact Bone
• Interstitial lamellae fill spaces between osteons
• Circumferiential lamellae run perimeter inside and out in contact with:– endosteum and periosteum
• Compact bone is designed to receive stress from one direction– Very strong parallel to osteons– Weak perpendicular to osteons 32
Compact Bone
Figure 6–533
Structure of Spongy Bone
• Lamellae = meshwork called trabeculae (no osteons)
• Red marrow fills spaces around trabeculae• Osteocytes in lacunae are linked by canaliculi• No direct blood supply (no central canals)• Nutrients diffuse into canaliculi in trabeculae
from red marrow• Spongy bone make up:
– low stress bones– Areas of bone where stress comes from multiple
directions
• Provide light weigh strength 34
Bone Marrow
• Red Marrow:– Located in space between trabeculae– Has blood vessels– Forms red blood cells– Supplies nutrients to osteocytes
• Yellow Marrow:– In some bones, spongy bone holds
yellow bone marrow:• is yellow because it stores fat
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Structure of Spongy Bone
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Periosteum and Endosteum
• Compact bone is covered with membrane:– periosteum on the outside – endosteum on the inside
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Periosteum
1. Fibrous outer layer:- Dense irregular CT
2. Cellular Inner layer:- Osteoprogenitor cells
Functions:1. Isolate bone from surrounding tissues2. Site for attachment for tendons and
ligaments3. Route for nerves and blood vessels to enter
bone4. Participates in bone growth and repair 38
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Endosteum• Thin cellular layer• Lines medullary cavity, central canals,
and covers trabeculae• Consists of:
– osteoblasts, osteoprogenitor cells, and osteoclasts
• Cells become active during bone growth and repair
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Endosteum
Figure 6–8b41
Bone Growth• Begins 6-8 weeks post fertilization• Continues through puberty (18-25 y)• Osteogenesis = ossification = formation
of bone• Not calcification
– Hardening of matrix or cytoplasm with calcium
– Can happen to many tissues• Two types of Ossification:
1. Intramembranous: forms flat bones2. Endochondrial: forms long bones 42
Bone Development
• Human bones grow until about age 25• Osteogenesis:
– bone formation
• Ossification: Deposition of calcium salts– the process of replacing other tissues
with bone
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The difference between intramembranous ossification and
endochondral ossification.
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Intramembranous Ossification
• Bone develops from mesenchyme or fibrous CT in deep layers of dermis
• Also called dermal ossification:– because it occurs in the dermis– produces dermal bones such as mandible
and clavicle– Produces skull bones
• There are 4 main steps in intramembranous ossification
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Intramembranous Ossification: Step 1
• Ossification center appears in the fibrous CT membrane– Mesenchymal cells aggregate– Differentiate into osteoblasts– Begin ossification at the ossification center
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Intramembranous Ossification: Step 2
• Bone matrix (osteoid) is secreted within the fibrous membrane– Osteoblasts begin to secrete osteoid, which is
mineralized within a few days– Trapped osteoblasts become osteocytes
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Intramembranous Ossification: Step 3
• Woven bone and periosteum form– Accumulating osteoid is laid down between embryonic
blood vessels, which form a random network– Vascularized mesenchyme condenses on the external
face of the woven bone and becomes periosteum around spongy bone
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Intramembranous Ossification: Step 4
• Bone collar of compact bone forms and red marrow appears– Trabeculae just deep to the periosteum thickens,
forming a woven bone collar that is later replaced with mature lamellar bone
– Spongy bone, consisting of distinct trabeculae, persists internally and its vascular tissue becomes red marrow
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Endochondral Ossification
• Ossifies bones that originate as hyaline cartilage
• Most bones originate as hyaline cartilage– Cartilage grows by interstitial and
appositional growth – Cartilage is slowly replaced from the
inside out
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Endochondral Ossification
• Growth and ossification of long bones occurs in 6 steps
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Endochondral Ossification: Step 1
• Primary ossification center begins to form:– Chondrocytes in the center of
hyaline cartilage:• Enlarge in diaphysis• Surrounding matrix calcifies
killing the enclosed chondrocytes
• die, leaving cavities in cartilage
Figure 6–9 (Step 1)52
Endochondral Ossification: Step 2
• Blood vessels grow around the edges of the cartilage – Cells in the perichondrium change
to osteoblasts: •Secrete osteoid
– Osteiod is mineralized and produces a layer of superficial bone around the shaft which will continue to grow around the diaphysis and become compact bone (appositional growth)
Figure 6–9 (Step 2)53
Endochondral Ossification: Step 3
• Capillaries and fibroblast migrate into the primary ossification center:– Blood vessels enter the
cartilage– Bringing fibroblasts that
become osteoblasts and secrete osteoid• Mineralized into rebeculae
– Spongy bone develops at the primary ossification center and continues to growth toward the epiphysis
Figure 6–9 (Step 3)54
Endochondral Ossification: Step 4
Figure 6–9 (Step 4)
• Remodeling creates a marrow cavity:– Osteoclasts degrade trabeculae in
the center to create the marrow cavity
– Bone increases in length by interstital growth of the epiphyseal plate followed by replacement of plate cartilage by spongy bone•Cartilage continues to grow on
epiphyseal side and is replaced by bone on diaphysis side
– Bone increases in diameter by appositional growth from cellular layers of peristeum
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Endochondral Ossification: Step 5
• Secondary ossification centers form in epiphyses:– Capillaries and osteoblasts
enter the epiphyses:•creating secondary
ossification centers
Figure 6–9 (Step 5)56
Endochondral Ossification: Step 6• Epiphyses become
ossified with spongy bone– Hyaline cartilage remains
on articular surfaces (not calcified or ossified)
– Ossification continues at both 1°and 2° ossification centers until all epiphyseal cartilage has been replaced with bone epiphyseal closure
– Adult bone retains the epiphyseal line
Figure 6–9 (Step 6)57
• Appositional growth:– compact bone thickens
and strengthens long bone with layers of circumferential lamellae
Figure 6–9 (Step 2)
Endochondral Ossification
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During intramembranous ossification, which type(s) of
tissue is/are replaced by bone?
1. hyaline cartilage2. fibrous connective tissue3. mesenchymal connective
tissue4. osteoid tissue
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In endochondral ossification, what is the original source of osteoblasts?
1. de novo synthesis2. cells brought with via the
nutrient artery3. cells of the inner layer of
the perichondrium4. chondrocytes from the
original model60
The characteristics of adult bones.
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Epiphyseal Lines
Figure 6–1062
Epiphyseal Lines
• When long bone stops growing, after puberty:– epiphyseal cartilage disappears – is visible on X-rays as an epiphyseal
line
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A child who enters puberty several years later than the average age
is generally taller than average as an adult. Why?
1. Epiphyseal plates fuse during puberty.
2. Bone growth continues throughout childhood.
3. Growth spurts usually occur at the onset of puberty.
4. All of the above.64
The skeletal system remodels and maintains
homeostasis.
The effects of nutrition, hormones, exercise, and
aging on bone.65
Bone Remodeling
• Bones are not static: constantly recycled and renewed
• 5-7% of skeleton is recycled/week• Osteoclasts secrete:
1. Lysosomal enzymes: digest osteoid2. Hydrochloric acid: solubilize calcium salts
• Osteoblasts secrete:1. Osteoid (organic matrix)2. Alkaline phosphatase: induces
mineralization of osteoid- Complete mineralization takes ~1 week 66
Bone Remodeling
• Bones Adapt:– Stressed bones grow thicker– Bumps and ridges for muscle attachment
enlarge when muscles are used heavily– Bones weaken with inactivity: up to 1/3 or
mass is lost with few weeks of inactivity– Heavy metals can get incorporated
• Condition of bones depends on interplay between osteoclast and osteoblast activity 67
Skeleton as a Calcium Reserve
• Calcium is important for normal function of neurons and muscle
• Blood calcium: 9-11 mg/100ml• If blood levels are too high:
– Nerve and muscle cells are non responsive
• If blood levels are too low:– Nerve and muscle cells are hyper-
excitable convulsions, death68
The Skeleton as Calcium Reserve
• Bones store calcium and other minerals
• Calcium is the most abundant mineral in the body
• Calcium ions are vital to:– membranes– neurons– muscle cells, especially heart cells
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Skeleton as a Calcium Reserve
• Calcium homeostasis depends on:1. Storage in the Bones2. Absorption in the GI3. Excretion at the Kidneys
** These factors are controlled by hormones to regulate blood calcium levels
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If blood calcium levels Low:
• Parathyroid hormone (from parathyroid gland) triggers:
1. Increase osteoclast activity - decrease storage
2. Enhanced calcitriol action - increase absorption
3. Decreased calcium excretion at the kidneys 71
If Blood Calcium levels High
• Calcitonin (from thyroid gland) triggers:
1. Inhibition of osteoclast activity
2. Increased calcium excretion at the kidneys
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Nutritional and Hormone Effects on Bone
• Many nutrients and hormones are required for normal bone growth and maintenance:
1. Calcium and phosphate salts2. Calcitriol3. Vitamin C4. Vitamin A5. Vitamin K and B126. Growth Hormones7. Thyroxin8. Estrogens and Androgens9. Calcitonin10. Parathyroid Hormone 73
Nutritional and Hormone Effects on Bone
1. Calcium and phosphate salts- From food, for mineralization of matrix
2. Calcitriol- From kidneys, for absorption of calcium and
phosphate
3. Vitamin C- From food, for collagen synthesis and osteoblast
differentiation
4. Vitamin A- From carotene in food, for normal bone growth in
children
5. Vitamin K and B12- From food, for synthesis of osteoid proteins
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Nutritional and Hormone Effects on Bone
6. Growth Hormones- From pituitary gland, for protein synthesis and cell
growth7. Thyroxin
- From thyroid gland, for cell metabolism and osteoblast activity
8. Estrogens and Androgens- From gonads, for epiphyseal closure
9. Calcitonin- From thyroid gland AND
10. Parathyroid Hormone- From parathyroid gland, to regulate calcium and
phosphate levels in body fluids- Affects bone composition 75
Hormones for Bone Growth and Maintenance
Table 6–276
Abnormalities
• Genetic/Physiological Abnormalities1. Giantism: – too much Growth hormone prior to
epiphyseal closure, bones grow excessively large
2. Acromegaly: - too much GH after closure, bones don’t
grow but all cartilage does - ribs, nose, ears, articular cartilage
3. Pituitary Dwarfism: - not enough GH, bones fail to elongate
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Abnormalities• Diet Related Abnormalities:
1. Scurvy: - lack of Vit. C- causes low collagen content,
reduced bone mass, bones brittle
2. Osteomalacia: - lack calcitriol, osteoid produced but
not mineralized, bones flexible-Called Rickets in children and leads to
permanent deformity78
A seven-year-old child has a pituitary tumor involving the cells that secrete growth
hormone (GH), resulting in increased levels of GH. How will this condition affect the
child’s growth?
1. The individual will be taller.2. The individual will be
shorter.3. Growth of the individual will
be erratic and slow.4. Excessive growth will be
limited to axial skeleton.79
Why does a child who has rickets have difficulty walking?
1. Joints become fused, preventing movement.
2. Bones are brittle and break under body weight.
3. Bones are flexible and bend under body weight.
4. Motor skills are impaired.80
What effect would increased PTH secretion have on blood calcium
levels?
1. higher level of calcium2. lower level of calcium3. uncontrolled level of
calcium4. no effect on blood calcium,
PTH effects calcium in the bones
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How does calcitonin help lower the calcium ion concentration of
blood?
1. by inhibiting osteoclast activity
2. by increasing the rate of calcium excretion at the kidneys
3. by increasing the rate of calcium uptake by intestinal cells
4. 1 and 2
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Types of fractures and how do they heal.
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Fractures
• Fractures:– cracks or breaks in bones– caused by physical stress
• Bones break in response to excessive stress
• Bones are designed to heal• Fractures are repaired in 4 steps
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Fracture Repair: Step 1
• Bleeding:– produces a clot (fracture
hematoma)– Seals off dead
osteocytes and broken blood vessels
Figure 6–15 (Step 1)85
Fracture Repair: Step 2• Cells of the endosteum and
periosteum:– Divide and migrate into fracture
zone– Cells of Periosteum:
• create external callus of fibrocartilage
– Cells of Endosteum: • create internal callus of spongy
bone
• Calluses stabilize the break: – external callus of cartilage and
bone surrounds break– internal callus develops in
marrow cavity Figure 6–15 (Step 2)86
Fracture Repair: Step 3
• Osteoblasts:– replace cartilage with
spongy bone
• Fracture gap is now filled with all spongy bone
Figure 6–15 (Step 3)87
Fracture Repair: Step 4
• A bulge from the callus marks the fracture point
• Osteoblasts and osteocytes remodel the fracture for up to a year:– Spongy bone is replaced with
compact bone and excess callus material is removed
Figure 6–15 (Step 4)88
The effects of aging on the skeletal system.
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Effects of Aging
• Bones become thinner and weaker with age
1. Osteopenia = reduction in bone mass– All adults suffer in some degree– Osteoclasts out-work osteoblast
• sex hormones in youth inhibit osteoclasts
– Women: 8%/decade after 40– Men: 3%/decade after 40
90
Effects of Aging
2. Osteoporosis = reduction in bone mass that compromises function
• More common in women: – Over age 45, occurs in:
• 29% of women• 18% of men
– Thinner bones to start– Greater rate of osteopenia
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(a) Normal spongy bone SEM X 25
(b) Spongy bone in osteoporosis SEM X 21
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Effects of Bone Loss
• The epiphyses, vertebrae, and jaws are most affected:– resulting in fragile limbs– reduction in height– tooth loss
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Hormones and Bone Loss
• Estrogens and androgens help maintain bone mass
• Bone loss in women accelerates after menopause
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Why is osteoporosis more common in older women than in
older men?
1. Testosterone levels decline in post-menopausal women.
2. Older women tend to be more sedentary than older men.
3. Declining estrogen levels lead to decreased calcium deposition.
4. In males, androgens increase with age.
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SUMMARY (1 of 2)
• Bone shapes, markings, and structure• The matrix of osseous tissue• Types of bone cells• The structures of compact bone• The structures of spongy bone• The periosteum and endosteum• Ossification and calcification• Intramembranous ossification• Endochondrial ossification
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SUMMARY (2 of 2)
• Blood and nerve supplies • Bone minerals, recycling, and
remodeling• The effects of exercise• Hormones and nutrition• Calcium storage• Fracture repair• The effects of aging
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