section 6-1: introduction to the skeletal system

Skeletal system includes:• Bones of the skeleton• Cartilages, ligaments and other

connective tissues that stabilize and connect

Functions of skeletal system• Support• Storage of minerals and lipids• Blood cell production• Protection• Leverage

SECTION 6-1: Introduction to the skeletal system

Bone shapes

SECTION 6-2: Classification of Bones

• Irregular• Sesamoid• Sutural

• Long• Flat• Short

Bone Structure• Compact bone (dense)• Spongy bone (cancellous)

Figure 6.1 Classification of Bones by Shape

• Diaphysis• Epiphyses• Metaphysis• Articular cartilage• Marrow cavity

• Filled with red or yellow marrow

A typical long bone includes

• Articular cartlilage

Figure 6.2 Bone Structure

Osseous tissue

1. solid matrix- Crystals of hydroxyapatiteCa3(PO4)2+ Ca(OH)2

2. Collagen-

3. Vascular-

SECTION 6-3: Bone Histology

4. Wrappeda. Endosteumb. Periosteum

i. fibrous layer

ii. Cellular layer(osteogenic)-

iii. Sharpey’s Fibers

SECTION 6-3: Bone Histology

1. Osteocytes = mature bone cells-Maintain, repair bone

2. Osteoblasts= synthesize new matrix- become osteocyte

3. Osteoclasts=dissolve bone matrix-multicuncleated, differentiate from WBC

4.Osteoprogenitor =cells differentiate into osteoblasts, repair fractures

Cells in bone:

Figure 6.3 The Histology of Compact Bone

• Basic unit of compact bone is an osteon• Osteocytes arranged around a central

canal• Perforating canals extend between

adjacent osteons• Spongy bone contains trabeculae

Compact bone and spongy bone

Figure 6.4 The Structure of Osseus Tissue

Figure 6.5 The Distribution of Forces on a Long Bone

Bones and stress• Compact bone

located where stresses are limited in direction

• Spongy bone located where stresses are weaker or multi-directional

• Ossification = converting other tissue to bone1. Intramembranous 2. Endochondral

• Calcification = depositing calcium salts within tissues

SECTION 6-4: Bone development and growth

Calcification

deposition of Ca++ salts w/in a tissue

1. Intramembraneous Ossification

• Bones form w/in a thin CT membrane• Used to form flat bones (cranium,

mandible, clavicle)

• Begins with osteoblast differentiation

• Dermal bones produced

• Begins at ossification center

Intramembranous ossification

forming bone: red

cartilage: blue

Steps of Intramembraneous Ossification in cranium1. Mesenchymal cells form a thin CT

membrane covering brain2. Some mesenchymal cells differentiate into

osteoblasts in the center of each membrane.(Occurs 6 weeks after fertilization)

3. Osteoblasts secrete bone @ these locations(called primary centers of ossification)

4. Ossification spreads in all directions

Steps of Intramembraneous Ossification in cranium

5. @ birth ossification is not complete, membrane remains as sutures and fontanels(soft spots)

Fetal skulls at 13-34 weeks gestation; fontanels typically close at 6 months

Fontanelles

• indentations of fibrous membrane between bones of fetal skull

• Intramembranous ossification is not complete until 20-22 months

• anterior• posterior• sphenoid• mastoid

Figure 6.7 Intramembranous Ossification

• Cartilage model gradually replaced by bone at metaphysis• Increasing bone length

• Timing of epiphyseal closure differs• Appositional growth increases bone

diameter

Endochondral ossification

Bone Growth1. Appositional- increases diameter, while medullary

cavity hollowed out

Figure 6.10 Appositional Bone Growth

Bone Growth

2. Interstitial- occurs at epiphyseal platesa. Chondroblasts produce new cells that are pushed toward epiphysisb. At the diaphysis end of plate older cartilage is converted into bone

http://www.personal.psu.edu/staff/m/b/mbt102/bisci4online/bone/bone_growth4.swf

Figure 6.9 Bone Growth at an Epiphyseal Cartilage

continually changing• Remodeling• Exercise• Hormone levels

• Growth hormone and thyroxine increase bone mass

• Calcitonin and PTH control blood calcium levels

SECTION 6-5: Dynamic Nature of Bone

Figure 6.12 A Chemical Analysis of Bone

• 99% body’s calcium in the skeleton• Calcium ion concentration maintained by

bones GI tract and kidneys• Calcitonin and PTH regulate blood calcium

levels• Calcitonin decreases blood calcium

levels• PTH increases blood calcium levels

The skeleton is a calcium reserve

Effects on bone growth1.Growth hormone- produced by pituitary

gland; targets growth plate activitya. Excess causes giagantism

b. Low levels cause pituitary dwarfism• normally proportioned• treatment with growth hormone

Effects on bone growth2. Testosterone- produced by the testes

and adrenal glands in males and by the adrenal glands in females-Responsible for the growth “spurt’ at puberty-Overproduction in males causes closure of the epiphyseal line(Caution for anabolic steroid users)

Effects on bone growth

3. Estrogen- produced by the ovaries in females; -stimulates osteoblasts

-promotes closing of the epiphyseal line -MENOPAUSE causes bone loss!!!

Effects of aging include1. Osteopenia (inadequate ossification)

begins between ages 30 and 40, • osteoblast activity declines, while

osteoclast activity remains level, • Women lose 8% of bone mass per

decade, while men lost only 3% in the same time period

2. Osteoporosis

SECTION 6-7: Aging and the Skeletal System

Osteoporosis

• When the loss of bone mass compromises normal function a person is diagnosed with osteoporosis.

When the loss of bone mass compromises normal function a person is diagnosed with osteoporosis

Figure 6.16 The Effects of Osteoporosis

Effects on bone growth4. Parathyroid hormone- produced by the

parathyroid glands in the neck-Stimulates the osteoclasts to Ca++ to be released from the bone to enter the blood-Ca++ necessary for muscles and nerves to function properly

Figure 6.13 Factors that Alter the Concentration of Calcium Ions in Body Fluids

Effects on bone growth5. Calcitonin- produced by the thyroid

gland- Inhibits osteoclasts so Ca++ remains in the bone , promotes ostepoblasts

Figure 6.13 Factors that Alter the Concentration of Calcium Ions in Body Fluids

Effects on bone growth6. Vitamin D- some is produced in the skin ;

Most is ingested in food-Necessary for the absorption of Ca++ from the intestine into the blood

• -Osteomalacia (Rickets in children)• causing softened, weakened bones• Main symptom is pain when weight is put on

the affected bone

Bone Fractures (Breaks)

• Bone fractures are classified by:Simple(closed) vs. compound(open)

Types of Bone Fractures• Linear

• the fracture is parallel to the long axis of the bone

• Transverse • the fracture is perpendicular to the long

axis of the bone

Types of Bone Fractures

• Greenstick • incomplete fracture

where one side of the bone breaks and the other side bends

• common in children

• Comminuted• bone fragments into three or more pieces• common in the elderly

• Spiral• ragged break when bone is

excessively twisted• common sports injury

• Depressed• broken bone portion

pressed inward• typical skull fracture

• Compression• bone is crushed; common in

porous bones

• Epiphyseal• epiphysis separates from

diaphysis along epiphyseal line; occurs where cartilage cells are dying

1. Fracture hematoma2. Internal and External callus3. Cartilage replaced by bone4. Osseous callus removed

Bone graft- a transplant of bone to stimulate repair

Fracture repair

Figure 6.14 Steps in the Repair of a Fracture

Figure 6.14

section 6-1: introduction to the skeletal system

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