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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


• Blood vessels grow into the area:– to supply the osteoblasts

• Spicules connect: – trapping blood vessels inside bone

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


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



• Bleeding:– produces a clot (fracture hematoma)– establishes a fibrous network

• Bone cells in the area die


• 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


• Osteoblasts:– replace central cartilage of external calluswith spongy bone


• 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


• Spiral fractures



• Displaced fractures


• Colles’ fracture


• Greenstick fracture

• Epiphyseal fractures


• 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!