Bone & Skeletal Tissue
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Transcript of Bone & Skeletal Tissue
Bone & Skeletal Tissue
Chapter 6
Functions of the Skeletal system
1. Support2. Protection3. Movement4. Mineral storage5. Hematopoiesis (blood cell formation)
Skeletal Cartilages
Cartilages of the
respiratory tract
Classification of Bones
• Bone are identified by:– shape– internal tissues– bone markings
Bone Shapes
1. Long bones2. Flat bones3. Sutural bones4. Irregular bones5. Short bones6. Sesamoid bones
Long BonesFigure 6–1a
Long Bones
• Are long and thin• Are found in arms, legs, hands, feet,
fingers, and toes
Flat Bones
Figure 6–1b
Flat Bones
• Are thin with parallel surfaces• Are found in the skull, sternum, ribs, and
scapula
Sutural Bones
Figure 6–1c
Sutural Bones
• Are small, irregular bones• Are found between the flat bones of the
skull
Irregular Bones Figure 6–1d
Irregular Bones
• Have complex shapes • Examples:
– spinal vertebrae – pelvic bones
Short Bones
Figure 6–1e
Short Bones
• Are small and thick• Examples:
– ankle – wrist bones
Sesamoid Bones
Figure 6–1f
Sesamoid Bones
• Are small and flat• Develop inside tendons near joints of
knees, hands, and feet
Bone Markings
• Depressions or grooves:– along bone surface
• Projections:– where tendons and ligaments attach– at articulations with other bones
• Tunnels:– where blood and nerves enter bone
Bone Markings
Bone MarkingsTable 6–1 (2 of 2)
Long Bones
• The femur
Figure 6–2a
Structure of a long
bone
The Humerus
Long Bones
• Diaphysis: – the shaft
• Epiphysis: – wide part at each end– articulation with other bones
• Metaphysis: – where diaphysis and epiphysis meet
Flat Bones
• The parietal bone of the skull Figure 6–2b
Compact Bone Structure
Spongy Bone
Figure 6–6
Spongy Bone Structure
Bone Cells
• Make up only 2% of bone mass:– osteocytes– osteoblasts– osteoprogenitor cells– osteoclasts
Bone Cells: Osteoblasts, Osteocytes & Osteoclasts
Periosteum
Figure 6–8a
Endosteum
Figure 6–8b
Bone Development
• Human bones grow until about age 25• Osteogenesis:
– bone formation• Ossification:
– the process of replacing other tissues with bone
Intramembranous Ossification
• Also called dermal ossification:– because it occurs in the dermis– produces dermal bones such as mandible and
clavicle• There are 3 main steps in
intramembranous ossification
Intramembranous
Ossification: Step 1
Figure 6–11 (Step 1)
Intramembranous Ossification: Step 1
• Mesenchymal cells aggregate:– differentiate into osteoblasts– begin ossification at the ossification center – develop projections called spicules
Step 2
Intramembranous Ossification: Step 2
• Blood vessels grow into the area:– to supply the osteoblasts
• Spicules connect: – trapping blood vessels inside bone
Step 3
Figure 6–11 (Step 3)
Intramembranous Ossification: Step 3
• Spongy bone develops and is remodeled into:– osteons of compact bone– periosteum– or marrow cavities
Endochondral Ossification
• Ossifies bones that originate as hyaline cartilage
• Most bones originate as hyaline cartilage
Endochondral
Ossification: Step 1
• Chondrocytes in the center of hyaline cartilage:– enlarge– form struts and calcify– die, leaving cavities in
cartilage
Figure 6–9 (Step 1)
Step 2
Endochondral Ossification: Step 2
• Blood vessels grow around the edges of the cartilage
• Cells in the perichondrium change to osteoblasts: – producing a layer of superficial bone around
the shaft which will continue to grow and become compact bone (appositional growth)
Step 3• Blood vessels enter
the cartilage:– bringing fibroblasts
that become osteoblasts
– spongy bone develops at the primary ossification center
Step 4• Remodeling creates a
marrow cavity:– bone replaces cartilage
at the metaphyses
Step 5
• Capillaries and osteoblasts enter the epiphyses:– creating
secondary ossification centers
Step 6
Endochondral Ossification: Step 6
• Epiphyses fill with spongy bone:– cartilage within the joint cavity is articulation
cartilage– cartilage at the metaphysis is epiphyseal
cartilage
• Appositional growth:– compact bone thickens and
strengthens long bone with layers of circumferential lamellae
Endochondral OssificationPLAYFigure 6–9 (Step 2)
Endochondral Ossification
Appostional Growth
Blood Supply of Mature
Bones• 3 major sets of
blood vessels develop
Figure 6–12
Blood Vessels of Mature Bones
• Nutrient artery and vein: – a single pair of large blood vessels– enter the diaphysis through the nutrient
foramen– femur has more than 1 pair
• Metaphyseal vessels:– supply the epiphyseal cartilage– where bone growth occurs
Blood Vessels of Mature Bones
• Periosteal vessels provide:– blood to superficial osteons– secondary ossification centers
Mature Bones
• As long bone matures:– osteoclasts enlarge marrow cavity– osteons form around blood vessels in
compact bone
Effects of Exercise on Bone
• Mineral recycling allows bones to adapt to stress
• Heavily stressed bones become thicker and stronger
Bone Degeneration
• Bone degenerates quickly • Up to 1/3 of bone mass can be lost in a
few weeks of inactivity
Wolff’s Law
Tension and compression cycles create a small electrical potential that stimulates bone deposition and increased density at points of stress.
Effects of Hormones and Nutrition on Bone
• Normal bone growth and maintenance requires nutritional and hormonal factors
Minerals
• A dietary source of calcium and phosphate salts: – plus small amounts of magnesium, fluoride,
iron, and manganese
Calcitriol
• The hormone calcitriol:– is made in the kidneys– helps absorb calcium and phosphorus from
digestive tract– synthesis requires vitamin D3 (cholecalciferol)
Vitamins
• Vitamin C is required for collagen synthesis, and stimulates osteoblast differentiation
• Vitamin A stimulates osteoblast activity • Vitamins K and B12 help synthesize bone
proteins
Other Hormones
• Growth hormone and thyroxine stimulate bone growth
• Estrogens and androgens stimulate osteoblasts
• Calcitonin and parathyroid hormone regulate calcium and phosphate levels
Hormones for Bone Growth and Maintenance
Chemical Composition of Bone
Figure 6–13
Bone homeostasis
Calcitonin and Parathyroid Hormone Control
• Bones:– where calcium is stored
• Digestive tract:– where calcium is absorbed
• Kidneys:– where calcium is excreted
Parathyroid Hormone (PTH)
• Produced by parathyroid glands in neck• Increases calcium ion levels by:
– stimulating osteoclasts – increasing intestinal absorption of calcium – decreases calcium excretion at kidneys
Parathyroid Hormone (PTH)Figure 6–14a
Calcitonin Figure 6–14b
Calcitonin
• Secreted by C cells (parafollicular cells) in thyroid
• Decreases calcium ion levels by:– inhibiting osteoclast activity– increasing calcium excretion at kidneys
A misleading view of bone homeostasis
Calcitonin does not play a central role in maintaining blood plasma Ca++ levels in adults.It is important to maintaining bone density, though.
Fracture Repair: Step 1
Figure 6–15 (Step 1)
Fracture Repair: Step 1
• Bleeding:– produces a clot (fracture hematoma)– establishes a fibrous network
• Bone cells in the area die
Fracture Repair: Step 2
Figure 6–15 (Step 2)
Fracture Repair: Step 2
• Cells of the endosteum and periosteum:– Divide and migrate into fracture zone
• Calluses stabilize the break: – external callus of cartilage and bone
surrounds break– internal callus develops in marrow cavity
Fracture Repair: Step 3
Figure 6–15 (Step 3)
Fracture Repair: Step 3
• Osteoblasts:– replace central cartilage of external calluswith spongy bone
Fracture Repair: Step 4
Figure 6–15 (Step 4)
Fracture Repair: Step 4
• Osteoblasts and osteocytes remodel the fracture for up to a year:– reducing bone calluses
Common fracture types
Figure 6–16 (1 of 9)
The Major Types of Fractures
• Pott’s fracture
• Comminuted fractures
• Transverse fractures
Figure 6–16 (3 of 9)
• Spiral fractures
Figure 6–16 (4 of 9)
Figure 6–16 (5 of 9)
• Displaced fractures
Figure 6–16 (6 of 9)
• Colles’ fracture
Figure 6–16 (7 of 9)
• Greenstick fracture
• Epiphyseal fractures
Figure 6–16 (9 of 9)
• Compression fractures
Depression fracture of the skull
Age and Bones
• Bones become thinner and weaker with age• Osteopenia begins between ages 30 and 40 • Women lose 8% of bone mass per decade,
men 3%
Effects of Bone Loss
• The epiphyses, vertebrae, and jaws are most affected:– resulting in fragile limbs– reduction in height– tooth loss
Osteoporosis
• Severe bone loss • Affects normal function• Over age 45, occurs in:
– 29% of women– 18% of men
Hormones and Bone Loss
• Estrogens and androgens help maintain bone mass
• Bone loss in women accelerates after menopause
Cancer and Bone Loss
• Cancerous tissues release osteoclast-activating factor:– that stimulates osteoclasts– and produces severe osteoporosis
Some decorative
arrangements
I dare not Jim!