1.6. Human Skeletal System http://www.ck12.org
Bone Growth
Early in human development, the skeleton consists of only cartilage and other connective tissues. At this point, the
skeleton is very flexible. As the fetus develops, hard bone begins to replace the cartilage, and the skeleton begins
to harden. Not all of the cartilage, however, is replaced by bone. Cartilage remains in many places in your body,
including your joints, your rib cage, your ears, and the tip of your nose.
A baby is born with zones of cartilage in its bones that allow growth of the bones. These areas, calledgrowth plates,
allow the bones to grow longer as the child grows. By the time the child reaches an age of about 18 to 25 years, all
of the cartilage in the growth plate has been replaced by bone. This stops the bone from growing any longer. Even
though bones stop growing in length in early adulthood, they can continue to increase in thickness throughout life.
This thickening occurs in response to strain from increased muscle activity and from weight-lifting exercises.
Vocabulary
- bone marrow: Soft connective tissue in spongy bone; makes blood cells.
- cartilage: Dense connective tissue that provides a smooth surface for the movement of bones at joints.
- compact bone: Dense outer layer of bone that is very hard and strong.
- growth plate: Area of growing tissue near the ends of the long bones in children and adolescents.
- ligament: Band of fibrous connective tissue that holds bones together.
- periosteum: Tough, fibrous membrane that covers the outer surface of bone.
- skeletal system: All the body’s bones, cartilage, and ligaments.
- spongy bone: Light, porous inner layer of bone that contains bone marrow.
Summary
- Bones, cartilage, and ligaments make up the skeletal system.
- Functions of the skeletal system include providing support, protecting the soft organs of the body, aiding in
movement, and making blood cells.
Practice
Use the resource below to answer the questions that follow.
- What makes up the axial skeleton? What makes up the appendicular skeleton?
- What is the scapula commonly known as? What is it’s function? What other bone helps in this function?
- How many thoracic vertebrae do humans have? Where are they located in the spinal column?
- To which type of vertebrae do ribs attach?
Review
- List four functions of the skeletal system.
- Describe the types of tissue that make up a bone.