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The Skeletal System


                    The adult human skeletal system has 206

                   bones that provide support, protection and

shape to the body. It also allows the body to store minerals,

make blood cells, and grow.

Learning Objectives

By the end of this lesson, students should be able to:

  • Name five functions of the skeletal system.

  • Compare and contrast five types of joints.

  • Identify major bones of the human skeleton.



ball-and-socket—a joint that allows circular movement; an example is the hip joint.

bone—hard, whitish tissue that makes up the skeletons of humans and other vertebrates.

hinge—a joint that allows back and forth movement ; an example is the elbow joint or the knee joint.


joint—where two or more bones come together.


ligament—strong bands of tissue that connect bones to each other at joints.


pivot—a joint in which the round surface on one bone rotates in a ring on another bone.

tendon—a tough band of tissue that connect muscles to bones.


Functions of the Skeletal System

1) Shape, support, and protection

   Look at the diagram of the human skeleton. You can easily see the bones that shape, support, or protect your internal body organs. For example, what is the function of the bones of your head? They protect your brain, eyes, and ears. What is the function of your ribs? The ribs protect your heart and lungs.

   Bones protect your internal organs, but they also provide shape. For example, your skull protects your brain, but it also shapes your head and face.  Bones of the ribs provide shape to your chest.


2) Movement

   Bones and muscles work together to allow the body to move. You couldn’t move with your bones alone and you couldn’t move with just muscles. Muscles attach to bones and pull the bone to allow movement with support.


3) Blood Cell Production

   Blood cells are produced in bone marrow. (Two types of white blood cells, T cells and B cells, are also produced in lymph nodes and the spleen. T cells are also produced in the thymus gland.)

   There are two kinds of marrow: red and yellow. In adults, yellow marrow stores fact and does not produce blood cells. Red marrow is present in spongy bone of the skull, ribs, sternum, clavicles, vertebrae, and pelvis. Red marrow forms red blood cells, white blood cells, and platelets. 


Fast Fact: By the time you are an adult, red bone marrow is found only in a few bones, including the humerus, the pelvis, the ends of the femur and the ends of the tibia.


4) Storage

Bone tissue stores minerals such as calcium, magnesium, sodium, and potassium.


Bones of the Human Skeleton-Anterior View
















Bones of the Human Skeleton—Posterior View
















Types of Joints

   A joint is any place in your body where two or more bones meet. There are different kinds of joints in the human body which allow for different kinds of movement.

1) Ball-and-socket joint—allows you to rotate certain body parts. Examples of ball-and-socket joints are the hip joint and the shoulder joint.







2) Hinge joint—allows you only back and forth movement in one direction only, like a door on a hinge. Hinge joints are found in the elbows, knees, fingers and toes.











3) Gliding joint—allows a sliding movement. Gliding joints are found in your wrists and ankles.









4) Pivot joint—allows bones to twist sideways against each other. Pivot joints are found in the vertebrae.









5) Fixed joint—allows no movement at the joint. These are found in the cranium (skull bones) in an adult. When a child is born, the bones of the skull are movable to allow the brain to grow. As the child gets older, the bones fuse together and fissures (lines between the bones) form.











   You may have broken a bone when you were playing a sport, riding your bike, roller skating, or even by falling. A broken bone is a fracture. Fractures can also occur because of a softening of the bone due to a lack of calcium, called osteoporosis. (Stress fractures occur because of overuse and are commonly seen among athletes.)

   There are several types of fractures. Look at the diagram below to see the different kinds of fractures as you read the short description of each.


Types of Fractures

Closed or simple—the bone is broken, but it does not break the skin.

Open or compound—the bone is broken and it pierces the skin.

Transverse—the fracture is at right angles to the long axis of the bone.

Greenstick—the fracture is only on one side of the bone and does not go all the way through to the other side.

Stress--There is a hairline crack in a bone, sometimes not even visible on an X-ray, that is caused by repeated injury or stress on the bone.

Comminuted—a fracture that results in three or more bone fragments.












X-rays help determine the position of the fractured bones. If necessary, the orthopedist (a doctor who specializes in bones) will correct the position of the bones to allow for proper healing. This correction is called "reduction" of the bones.


Fracture Treatment

   If you break a bone, your doctor may correct the bone’s position and apply a fiberglass cast to immobilize the bone while it heals. In some fractures, the bone’s position must be corrected surgically to repair the break. Sometimes, the bones will not heal correctly without plates, rods or screws holding the bones together.









Image: Fractures of the lower arm bones (radius and ulna) before and after surgery to repair the breaks.  


Check for Understanding:

1. List four functions of the skeletal system.





2. Compare and contrast the kinds of joints: 

a. ball-an-socket

b. hinge

c. pivot

d. gliding

e. fixed


3. Label the diagrams of the skeletons below.

side view of a human skull
anterior view of a human skeleton-labeled
posterior view of a human skeleton-labeledleton-posterior view-labeled.jpg
two diagrams showing the placement of human hip bonesal sys-ball n socket joint.jpg
diagram of a human hinge joint at the elbowkeletal-hinge joint.jpg
x-ray of human gliding joints in two hands
diagram of human pivot joints in the vertebraeletal-pivot joint.jpg
side view of fixed joints in a human skull-labeledeletal-fixed joints.jpg
diagram of types of fractures- transverse, lenear, nondislaced, displaced, spiral, greenstick, comminuted
x-rays and photo of types of fracture treatments
NDH logo.jpg
anterior view of human skeleton-unlabeled
posterior view of human skeleton-unlabeledeton-posterior view-unlabeled.jpg
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