SKELETAL SYSTEM

Functions of Bones• Support – hard framework that supports and

anchors body – bones of legs act as pillars to • Protection – fused bones of the skull provide

a snug enclosure for the brain – vertebrae surround the spinal cord – rib cage protects vital organs

• Movement – skeletal muscles attach to bones by tendons and act as levers to move the body

• Storage – bone matrix (calcium, phosphorus, potassium, sodium, sulfur, magnesium, & copper) – deposits and withdrawals are constant

• Blood cell formation – hematopoiesis occurs within the marrow cavities of certain bones

Bone Markings

• Projections– Tuberosity – large, rounded projection that

may be roughened– Crest – Narrow ridge of bone– Trochanter – Very large, blunt, irregularly

shaped process (only on the femur)– Spine – sharp, slender, often pointed

projection– Process – any bony prominence

Bone Markings (ctd.)

• Projections That Help Form Joints

– Facet – smooth, nearly flat, articular surface– Condyle – rounded articular projection– Ramus – Arm-like bar of bone

• Depressions and Openings– Meatus – canal-like passageway– Sinus – Cavity within a bone filled with air and

lined with mucous membrane– Fossa – Shallow, basin-like depression in a

bone often serving as an articular surface– Fissure – Narrow, slit-like opening– Foramen – Round or oval opening through a

bone

Bone Markings (ctd.)

Bone Fractures, Development, and Degeneration

http://www.youtube.com/watch?v=Mz2UuhbtrwY

Bone Fractures

• Fracture—break in a bone• Types of bone fractures

– Closed (simple) fracture—break that does not penetrate the skin

– Open (compound) fracture—broken bone penetrates through the skin

• Bone fractures are treated by reduction and immobilization

Common Types of Fractures

Table 5.2

Stages in the Healing of a Bone Fracture

Figure 5.5, step 1

Hematoma

Hematomaformation

Step 1: Hematoma (blood-filled swelling) is formed

Stages in the Healing of a Bone Fracture

Figure 5.5, step 2

Hematoma

Externalcallus

Newbloodvessels

Internalcallus(fibroustissue andcartilage)

Spongybonetrabecula

Hematomaformation

Fibrocartilagecallus formation

Step 2: Break is splinted by fibrocartilage to form a callus

Stages in the Healing of a Bone Fracture

Figure 5.5, step 3

Hematoma

Externalcallus

Bonycallus ofspongybone

Newbloodvessels

Internalcallus(fibroustissue andcartilage)

Spongybonetrabecula

Hematomaformation

Fibrocartilagecallus formation

Bony callusformation

Step 3: Fibrocartilage callus is replaced by a bony callus

Stages in the Healing of a Bone Fracture

Figure 5.5, step 4

Hematoma

Externalcallus

Bonycallus ofspongybone

Healedfracture

Newbloodvessels

Internalcallus(fibroustissue andcartilage)

Spongybonetrabecula

Hematomaformation

Fibrocartilagecallus formation

Bony callusformation

Bone remodeling

Step 4: Bony callus is remodeled to form a permanent patch (spongy bone to compact bone)

Skeletal Changes

Throughout Life

• Ossification Centers in a 12-week-old Fetus

Skeletal Changes Throughout Life

• Fetus– Long bones are formed of hyaline cartilage– Flat bones begin as fibrous membranes– Flat and long bone models are converted to

bone

• Birth– Fontanels remain until around age 2

Bone Growth (Ossification)

• Bones are remodeled and lengthened until growth stops– Bones are remodeled in response to two

factors• Blood calcium levels• Pull of gravity and muscles on the skeleton

– Bones grow in width (called appositional growth)

Long Bone Formation and Growth

Figure 5.4a

Bone startingto replacecartilage

Epiphysealplatecartilage

Articularcartilage

Spongybone

In a childIn a fetusIn an embryo

New boneforming

Growthin bonewidth

Growthin bonelength

Epiphysealplate cartilage

New boneforming

Bloodvessels

Hyalinecartilage

New center ofbone growth

Medullarycavity

Bone collar

Hyalinecartilagemodel

Long Bone Formation and Growth

Figure 5.4b

The Fetal Skull

• The fetal skull is large compared to the infant’s total body length

• Fontanels—fibrous membranes connecting the cranial bones– Allow the brain to grow– Convert to bone within 24 months (2 years)

after birth

The Fetal Skull

Figure 5.13a

The Fetal Skull

Figure 5.13b

Skeletal Changes Throughout Life

• Adolescence– Epiphyseal plates become ossified and long bone

growth ends. These plates become an Epiphyseal line and can be seen on an X-ray.

• Size of cranium in relationship to body– 2 years old—skull is larger in proportion to the

body compared to that of an adult– 8 or 9 years old—skull is near adult size and

proportion– Between ages 6 and 11, the face grows out from

the skull

Skeletal Changes Throughout Life

Figure 5.33a

Skeletal Changes Throughout Life

• Osteoporosis– Bone-thinning disease afflicting

• 50% of women over age 65 • 20% of men over age 70

– Disease makes bones fragile and bones can easily fracture

– Vertebral collapse results in kyphosis (also known as Dowager’s Hump)

– Estrogen aids in health and normal density of a female skeleton