Key Concepts:
Vocabulary: cartilage, ossification, ligament, tendon, scoliosis, osteoporosis
The Skeletal System
How the Skeletal System Works
Main Idea: The skeletal system consists of bones and connective tissue.
Your skeletal system consists of 206 bones and the attached connective tissues. The bones of the skeleton range in size from the tiniest bone of the inner ear (about 0.25 cm long) to the longest bone ofyour thigh. The connective tissues cushion the bones, attach bone to bone, and attach bones to muscles.
Your skeletal system has many functions, including
providing support for the body.
protecting internal tissues and organs from damage.
acting as a framework for attached muscles.
allowing movement of limbs and digits.
producing new red and white blood cells.
storing fat and minerals, such as calcium and phosphorus
Bones
Bones are made up of living tissues formed into different layers. The outer layer is hard, densely packed, compact bone. Beneath that is spongy bone, a less dense bone with a network of cavities filled with red bone marrow, where blood cells are produced. Some bones also contain yellow bone mar- row, a type of connective tissue that stores fat. Figure 14.1 shows the basic structure of a bone.
Bones are categorized by their shape, as shown in figure 14.2. Shapes include long bones, short bones, fiat bones, and irregular bones.
Connective Tissue
There are three types of connective tissue: cartilage, ligaments, and tendons. Cartilage is a strong, flexible connective tissue that can act as a cushion between two bones to reduce friction. It can also act as a :flexible structure for soft parts of the body, such as the tip ofthe nose or the outer ear. All bones begin in the embryo as cartilage. Early in development, the cartilage hardens. This ossification (ah-sih-fih-KAY-shun) is the process by which bone is formed, renewed, and repaired.
Connective tissue can also hold parts ofthe body together. A ligament is a band of fibrous, slightly elastic connective tissue that attaches one bone to another. Ligaments attach to bones to create joints. For example, a ligament attaches the two bones of the forearm to each other, forming the pivot joint. A tendon is a fibrous cord that attaches muscle to the bone. Muscles contract to move parts of the body.
Joints
Joints, such as those shown in Figure 14.3, are points at which bones meet. Some joints, such as the ones between the bones of the skull, do not move. Flexible joints include ball-and-socket joints, hinge joints, pivot joints, and ellipsoidal joints.
Caring for the Skeletal System
Main Idea: A healthy diet, exercise, protective gear, and regular checkups are ways to care for your skeletal system.
As you can see in Figure 14.4 your skeletal system supports your entire body. Your overall health depends on the health of your skeletal system. Eat a healthy diet, get regular physical activity, and have regular checkups to keep your skeletal system healthy. Foods high in calcium, vitamin D, and phosphorus help prevent skeletal disorders.
During regular checkups, your doctor can screen yo for skeletal disorders such as scoliosis, a lateral or side-to~side curvature of the spine. Weight-bearing exercise such as walking or weight training helps bones stay strong. Wearing protective gear during sports reduces the risk of bone fractures.
Understanding Skeletal Problems
Main Idea: Injuries and disorders harm the skeletal system.
Poor nutrition, infections, sports injuries, and poor posture can lead to problems of the skeletal system. Degenerative disorders such as osteoporosis can also cause problems.
Fractures A fracture is any type of break in a bone. In some fractures, called compound fractures, the broken end of the bone breaks through the skin. In a simple fracture, the broken bone does not break through the skin. Fractures are also classified by the pattern of the break:
Hairline fractures: if parts of the bone do not separate.
Transverse fractures: when the fracture is completely
across the bone.
Comminuted fractures: pictured in Figure 14.5, when the bone shatters into more than two pieces.
Injuries to Joints Injuries to joints can occur from overuse, strain, or disease. The following are typical joint injuries:
Repetitive Motion Injury Prolonged, repeated movements such as sewing or computer work can damage tissues. Carpal-tunnel syndrome occurs when ligaments and tendons in the wrist swell, causing numbness, a tingling sensation in the thumb and forefinger, pain, and weakness in the hand.
Osteoporosis is a condition in which there is a progressive loss o f bone tissue. Bones weaken and become brittle. This disease affects millions of older Americans. Bone tissue loss is a natural part ofaging, but healthful behaviors during your teen years can reduce your risk of developing osteoporosis later in life. A bone scan (in which X- rays measure bone density) can detect signs of osteoporosis.Eating foods containing calcium, vitamin D, and phosphorus will help bones remain strong and healthy. Regular weight-bearing physical activity, such as walking and weight training, stimulates bone cells to increase bone mass.
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