Main->Readings->5th Grade Readings->Skeleton and Muscles->Part 1
Vocabulary |
A few years ago, one of my students brought a bone into class. "I found it at the beach. What do you think it is?" he said, showing it to me. It was a long straight bone, as long as his arm.
"It's a femur," I said. The femur is the big bone in the rear leg of animals, and you can tell what it is by the big knob at one end, part of a ball-and-socket joint.
"Do you think it's a deer bone?" he said.
"No, it's too thick. Come over here." I walked over to Mr. Bones, the human skeleton which was hanging in the corner of my room. I held the femur up next to Mr. Bones' femur. The two big bones were exactly the same length, thickness, and shape. It was a human leg bone my student had found.
I told my student he should tell the shore police about his bone. He said he would, but I saw him a few years later and he said the femur was still in his garage. I suppose the mystery will never be solved.
I don't know how that human femur ended up at the beach. Most probably, an old cemetery got washed away by the tides, though maybe, just maybe, there was more to the story.
Bones can tell stories because they stick around long after the rest of the body decays and disappears. That is because they are partly made of minerals, and so they are very hard - but even though they are hard, they are living parts of the body. Each bone is an organ, just like your heart or your brain, and it helps your body in many ways.
The skeleton is organized just like other body systems:
The skeleton is made up of organs too, so it is an organ system: the skeletal system. The organs are the bones, the tissues are bone tissues, and the cells are bone cells.
The jobs of the skeletal system are to support the body, give the body shape, protect the organs, allow us to move, and produce blood cells. Some bones have other special jobs, such as the bones of the ear which allow us to hear. There are over 200 bones in your body.
There are several different main types of bone, and one type is the "long bones." The long bones are the ones found in the arms, legs, fingers, and toes. Most of the time, when we think of bones, the long bones are the ones we think of first.
There are different tissues in each bone. The outer part of a long bone is what we see first. It is made of a tissue called compact bone, which is very dense and hard. The inside of the long bone has a hollow space down the middle which contains soft red and yellow marrow tissue. Inside the ends of the long bone are spongy bone tissue, which is very light and foamy-looking. The bone also has a thin outer covering called the periosteum, which brings blood into the bone and makes new hard bone cells.
The ends of the bone are covered and protected with tissue called cartilage, a flexible rubbery tissue. Cartilage also forms your outer ear and the tip of your nose. It is very soft and bendable. Before babies are born, their skeletons are mostly made of cartilage, but by the time humans grow up, their bones become harder and stronger with the mineral calcium.
1. spongy bone 2. compact bone 3. periosteum 4. yellow marrow
5. cartilage
People and animals get calcium to grow bones from their food. Milk and other dairy products and dark-green leafy vegetables have calcium. Some kinds of exercise help the body build up calcium, but smoking, drinking alcohol, drinking too much soda, and being underweight make it difficult for the bones to get enough calcium.
Go on to Part 2: Bones and Joints
This page last modified on July 20, 2000