Guided Notes for the Skeletal System

Part One

1. The skeleton is subdivided into 2 divisions: the axial skeleton, the bones that form the longitudinal axis of the body, and the appendicular skeleton, the bones of the limbs and girdles.

2. In addition to bones, the skeletal system includes joints, cartilages, and ligaments, which are fibrous cords that bind the bones together at joints.

5 Major Functions of the Skeletal System

A. Support: bones form the internal framework that supports and anchors all soft organs

B. Protection: bones protect soft body organs.C. Movement: skeletal muscles use bones as levers to

move the body and its parts.D. Storage: fat is stored in the internal cavities of

bones. Bone itself is a storehouse for minerals, such as calcium and phosphorus.

E. Blood Cell Formation: hematopoiesis occurs within the narrow cavities of certain bones

4. The adult skeleton is composed of 206 bones.

5. There are 2 basic types of bone, or osseous tissue. Compact bone is dense and looks smooth and homogeneous. Spongy bone is composed of small needle-like pieces of bone and lots of open space.

4 Groups of Bones

A. Long Bones: typically longer than they are wide. They are mostly compact bone. All the bones of the limbs are long bones.

B. Short Bones: generally are cube-shaped. They contain mostly spongy bone. The bones of the wrist and ankle are short bones. Sesamoid bones, such as the patella, is a specialized type of short bone

4 Groups of Bones

C. Flat Bones: are thin, flattened and usually curved. They have 2 thin layers of compact bone sandwiching a layer of spongy bone. Most bones of the skull, ribs, and the sternum are flat bones.

D. Irregular Bones: bones that don’t fit into a category above. Examples are the vertebrae and the hip bones.

Structure of Long Bones

A. Diaphysis: shaft of the bone; makes up most of its length. It is composed of compact bone

B. Periosteum: a fibrous connective tissue membrane that covers and protects the diaphysis

C. Epiphysis: the ends of a long bone, consisting of a thin layer of compact bone enclosing an area of spongy bone

D. Articular Cartilage: the cartilage that covers the epiphysis

8. In adults, the cavity of the shaft is primarily a storage area for adipose (fat) tissue. It is called the yellow marrow.

9. In infants, this area forms blood cells, and red marrow is found there. In adult bones, red marrow is confined to the cavities of spongy bone of flat bones and the epiphyses of long bones.

10. Bone is one of the hardest materials in the body, and although relatively light in weight, it has a remarkable ability to resist tension and other forces acting on it. The calcium salts deposited in the matrix give bone its hardness, whereas the collagen fibers provide for bone’s flexibility and great tensile strength.

11. Bones are remodeled continually in response to changes in 2 factors:

A. Calcium levels in the blood

B. The pull of gravity and muscles on the skeleton

12. When blood calcium levels drop below homeostatic levels, parathyroid hormone (PTH) is released into the blood. PTH activates osteoclasts, which are giant bone-destroying cells that break down bone matrix and release calcium ions into the blood. On the other hand, when blood calcium levels are too high, calcium is deposited in bone matrix as hard calcium salts.

13. Rickets is a disease of children in which the bones fail to calcify. Rickets is usually due to a lack of calcium in the diet or a lack of vitamin D, which is needed to absorb calcium in the bloodstream.

Simple and Compound Fractures

Simple fractures are clean breaks which do not break the skin

Compound fractures are when a broken bone end penetrates through the skin

15. A fracture is usually treated by reduction, which is the realignment of broken bone ends. In closed reduction, the bone ends are coaxed back into their normal position by the physician’s hands. In open reduction, surgery is performed and the bone ends are secured together with pins or wires.

Repair of bone fracturesA. Blood vessels are ruptured when the bone breaks.

As a result, a blood-filled swelling called a hematoma forms.

B. The break is splinted by a fibrocartilage callus.C. As more osteoclasts and osteoblasts migrate into the

area and multiply, fibrocartilage is gradually replaced by a callus of spongy bone called the bony callus.

D. Over the next few months, the bony callus is remodeled in response to the mechanical stresses placed on it.