Skeletal System

bone marrow 1. the part of a bone that produces blood cells

bone marrow In the centers of long bones are large openings called cavities. These cavities and the spaces in spongy bone are filled with a substance called marrow. Some marrow is yellow and is composed of fat cells. Red marrow produces red blood cells at an incredible rate of 2 million to 3 million cells per second.

cartilage 2. a soft, flexible tissue that makes up most of the skeleton of an infant and is found in the nose, ears, and the at the end of long bones of adults

cartilage The ends of bones are covered with a smooth, slippery, thick layer of tissue called cartilage. Cartilage does not contain blood vessels or minerals. Cartilage is flexible and important in joints because it acts as a shock absorber.

cartilage It also makes movement easier by reducing friction that would be caused by bones rubbing together. Months before your birth, your skeleton was made of cartilage. Gradually the cartilage broke down and was replaced by bone.

cartilage At birth, your skeleton was made up of more than 300 bones. As you developed, some bones fused, or grew together, so that now you have only 206 bones.

Anyplace where two or more bones come together is a joint. The bones making up healthy joints are kept far enough apart by a thin layer of cartilage. The bones are held in place at these joints by a tough band of tissue called a ligament. Muscles move bones by moving joints.

joint 3. a place where two bones come together

ligament 4. a strong connective tissue that hold bones together at movable joints

Without the protection of the cartilage at the end of your bones, they also would wear away at the joints. Cartilage helps make joint movement easier. It reduces friction and allows bones to slide more easily over each other.

osteoarthritis 5. a condition where bones become weak and break easily due to the loss of minerals such as calcium

Arthritis is the most common joint problem. About one out of every seven people in the United States suffers from arthritis with the same symptoms: pain, stiffness, and swelling of the joints. Osteoarthritis results when cartilage breaks down because of years of use. Rheumatoid arthritis is an ongoing condition in which the body’s immune system tries to destroy its own tissues.

A ball-and-socket joint consists of a bone with a rounded end that fits into a cuplike cavity on another bone. A ball-and-socket joint provides a wide range of motion.

A hinge joint has a back-and-forth movement like hinges on a door. Elbows, knees, and fingers have hinge joints.

Hinge joints have a smaller range of motion and are not dislocated as easily, or pulled apart, as a ball-and- socket joint can be.

JointLocationType of Movement Ball-and- socket shoulders hips A wide range of movement Hingeknees elbows fingers back-and-forth movement like hinges on a door smaller range of motion than ball and socket and are not dislocated as easily, or pulled apart, as a ball-and-socket joint can be)

In a pivot joint, one bone rotates in a ring of another bone that does not move. Turning your head is an example of a pivot movement.

A fourth type of joint is a gliding joint in which one part of a bone slides over another bone. Gliding joints are used the most in your body.

Gliding joints also move in a back- and-forth motion and are found in your wrists and ankles and between vertebrae.

Joints are broadly classified as immovable or movable. An immovable joint allows little or no movement. The joints of the bones in your skull and pelvis are classified as immovable joints.

JointLocationType of Movement PivotArm Turning your head one bone rotates in a ring of another bone that does not move GlidingWrists Ankles Between vertebrae (bones of the spine) one part of a bone slides over another bone (most used type in your body) Im- movable Skull Pelvis Don’t move

Question 1 Which is NOT a function of your skeletal system? A. gives shape and support to body B. protects internal organs C. produces blood cells D. produces calcium and phosphorous

The answer is D Calcium and phosphorous are stored in bones but they are not produced in bones

Question 2 What type of joint is shown in this diagram? A. ball-and-socket B. gliding C. hinge D. immovable

The answer is C. A hinge joint has back and forth movement like the hinges on a door. Elbows, knees, and fingers have hinge joints.

Question 3 Which is a place where two or more bones come together? A. cartilage B. ligament C. muscle D. joint

The answer is D. Cartilage keeps the bones in joints far enough apart that they don’t rub together.