The Skeletal System

1. The Skeletal System Bone Growth and Repair

2. Skeleton • Axial and Appendicular Skeletons • Sex Differences: Generally, the male skeleton is larger and heavier. The epiphysis of long bones are thicker and the points of muscle attachment may be larger as well. Specifically, the female ilium is more flared, the area between the ischial spines and tuberosities is wider, the pelvic cavity is more shallow but wider, the pubic arch is wider.

3. Bone Cells • Osteoprogenitor cells: unspecialized cells present in the inner portion of the periosteum and central canal- can help repair fractures. • Osteoblasts: bone-forming cells – secrete the matrix. • Osteocytes: mature bone cells • Osteoclasts: type of white blood cell found in red marrow – they break down bone

4. Intramembranous Ossification: bone develops between sheets of fibrous connective tissue like the periosteum. This is how the bones of the skull are formed. Endochondral Ossification: hyaline cartilage is replaced by bone as growth is completed. Cartilage begins to breakdown. Osteoblast invade the region and begin to lay down spongy bone. Other osteoblasts begin to lay down compact bone under the periosteum. Epiphyseal plate. Bone Growth and Development

5. Bone Remodeling • In the adult, bone is constantly being broken down and built up again. • Osteoclasts remove worn cells, and assist in depositing calcium in the blood. • After about 3 weeks osteoclasts disappear and osteoblasts form new bone by taking calcium from the blood. Some of these cells get trapped in the matrix and become osteocytes. • Adults require more calcium because of this work. If they don’t have enough then osteoporosis results.

6. Bone Repair • Hematoma (bone bruise): blood escapes from ruptured blood vessels and forms a mass of clotted blood in the space between broken bones (6-8 hours after fracture). • Fibrocartilaginous callus: repair begins and fibrocartilage fills the spaces between the ends of the broken bone (3 weeks).

7. Bone Repair (continued) • Bony callus: Osteoblasts produce trabeculae of spongy bone to convert the fibrocartilage (3-4 months). • Remodeling: Osteoblasts build new compact bone along the peripheral surfaces and osteoclasts reabsorb the spongy bone forming a new medullary (bone marrow) cavity.

8. Types of Fractures • Complete – breaks bone into two parts • Incomplete – partial break • Simple – does not pierce skin • Compound – pierces skin • Impacted – broken ends wedged into each other • Spiral – break is ragged due to twisting of the bone