BONE GROWTH & REMODELING Ch 5 Skeletal System

Formation of the Human Skeleton In embryos, the skeleton is primarily hyaline cartilage During development, much of this cartilage is replaced by bone Cartilage remains in isolated areas Bridge of the nose Parts of ribs Joints

Bone Growth (Ossification) Epiphyseal plates allow for lengthwise growth of long bones during childhood New cartilage is continuously formed Older cartilage becomes ossified Cartilage is broken down Enclosed cartilage is digested away, opening up a medullary cavity Bone replaces cartilage through the action of osteoblasts

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)

Figure 5.5 In a fetus In an embryo Bone collar Hyaline cartilage model Bone starting to replace cartilage In a child Medullary cavity New center of bone growth Hyaline cartilage Epiphyseal plate cartilage Growth in bone length New bone forming Invading blood vessels Epiphyseal plate cartilage Articular cartilage Spongy bone New bone forming Growth in bone width

Figure 5.5, step 1 In an embryo Bone collar Hyaline cartilage model Bone starting to replace cartilage

Figure 5.5, step 2 In a fetus Medullary cavity New center of bone growth Hyaline cartilage Growth in bone length Invading blood vessels

Figure 5.5, step 3 In a child Epiphyseal plate cartilage New bone forming Invading blood vessels Epiphyseal plate cartilage Articular cartilage Spongy bone New bone forming Growth in bone width

Figure 5.6 Bone growth Bone grows in length because: Bone remodeling Growing shaft is remodeled as: Cartilage grows here. Cartilage is replaced by bone here. Cartilage grows here. Cartilage is replaced by bone here Bone is resorbed here. Epiphyseal plate Articular cartilage Bone is resorbed here. Bone is added by appositional growth here.

How bones grow…

Types of Bone Cells Osteocytes—mature bone cells Osteoblasts—bone-forming cells Osteoclasts—giant bone-destroying cells Break down bone matrix for remodeling and release of calcium in response to parathyroid hormone Bone remodeling is performed by both osteoblasts and osteoclasts

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 Comminuted—bone breaks into many fragments Compression—bone is crushed Depressed—broken bone portion is pressed inward Impacted—broken bone ends are forced into each other Spiral—ragged break occurs when excessive twisting forces are applied to a bone Greenstick—bone breaks incompletely

Repair of Bone Fractures 1. Hematoma (blood-filled swelling) is formed 2. Break is splinted by fibrocartilage to form a callus 3. Fibrocartilage callus is replaced by a bony callus 4. Bony callus is remodeled to form a permanent patch

Figure 5.7, step 1 Hematoma forms. Hematoma 1

Figure 5.7, step 2 Internal callus (fibrous tissue and cartilage) Hematoma forms. Fibrocartilage callus forms. Hematoma Spongy bone trabecula New blood vessels External callus 1 2

Figure 5.7, step 3 Internal callus (fibrous tissue and cartilage) Hematoma forms. Fibrocartilage callus forms. Bony callus forms. Hematoma Bony callus of spongy bone Spongy bone trabecula New blood vessels External callus 1 2 3

Figure 5.7, step 4 Internal callus (fibrous tissue and cartilage) Hematoma forms. Fibrocartilage callus forms. Bony callus forms. Bone remodeling occurs. Hematoma Bony callus of spongy bone Spongy bone trabecula New blood vessels External callus Healed fracture