The Skeletal System

Bone Growth and Repair

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.

Bone Cells Osteoprogenitor cells: unspecialized cells

present in the inner portion of the periosteum and central canal.

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

Bone Growth and Development 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 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.

Bone Repair

1. 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).

2. Fibrocartilaginous callus: repair begins and fibrocartilage fills the spaces between the ends of the broken bone (3 weeks).

Bone Repair (continued)

3. Bony callus: Osteoblasts produce trabeculae of spongy bone to convert the fibrocartilage (3-4 months).

4. Remodeling: Osteoblasts build new compact bone along the peripheral surfaces and osteoclasts reabsorb the spongy bone forming a new medullary cavity.

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