bone & skeletal tissue
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Bone & Skeletal Tissue. Chapter 6. Functions of the Skeletal system. Support Protection Movement Mineral storage Hematopoiesis (blood cell formation). Skeletal Cartilages. Cartilages of the respiratory tract. Classification of Bones. Bone are identified by: shape internal tissues - PowerPoint PPT PresentationTRANSCRIPT
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!