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

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

Stages in the Healing of a Bone Fracture Figure 5.5, step 2 Hematoma External callus New blood vessels Internal callus (fibrous tissue and cartilage) Spongy bone trabecula Hematoma formation Fibrocartilage callus 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 External callus Bony callus of spongy bone New blood vessels Internal callus (fibrous tissue and cartilage) Spongy bone trabecula Hematoma formation Fibrocartilage callus formation Bony callus formation Step 3: Fibrocartilage callus is replaced by a bony callus

Stages in the Healing of a Bone Fracture Figure 5.5, step 4 Hematoma External callus Bony callus of spongy bone Healed fracture New blood vessels Internal callus (fibrous tissue and cartilage) Spongy bone trabecula Hematoma formation Fibrocartilage callus formation Bony callus formation 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 starting to replace cartilage Epiphyseal plate cartilage Articular cartilage Spongy bone In a childIn a fetusIn an embryo New bone forming Growth in bone width Growth in bone length Epiphyseal plate cartilage New bone forming Blood vessels Hyaline cartilage New center of bone growth Medullary cavity Bone collar Hyaline cartilage model (a)

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