Real-Life Communication
It's the first day of your kinesiology program at university.
You're excited because you studied biology in high school and were fascinated
by muscle movement. On the board, you read that you'll be learning about
the composition of bones in this lecture. You're a bit disappointed,
but if it's just one class, you can handle it.
The professor clears
her throat. "Today we will be looking at the composition of bones, and in
the following lectures we'll be studying bone types and how they function.
Then in a week or so, we'll carry on to skeletal structure."
This
is too much. You raise your hand. "What about muscle movement?" you ask. "I
mean bones are just bones, all that matters in movement is the muscles."
The
professor peers over her glasses to have a closer look at you. "I'm glad
you came to class today," she says. You smile approvingly. "Because you have
an awful lot to learn." Your smile fades. She launches into her lecture.
Lecture
Notes
The skeletal structure is a dynamic, living, developing
and growing construction with a metabolism that both influences function and
is influenced by function. Up to 25 to 30 percent of bone is actually water.
The rest of the bone structure is called two-phase material.
Sixty
to 70 percent of this material is composed of calcium phosphate and calcium
carbonate -- they give bone its ability to resist compression. The balance
is made up of collagen, a protein that provides a bone's ability to resist
tension. Generally speaking, a bone can withstand about six times the stress
that we subject it to in ordinary activity.
After maturity, the proportion
of fluid and of organic material decreases with age. For these and other reasons,
the bones of aged people are brittle, and healing is often more difficult
in these cases.
The organic portion of bone can be divided into cells.
Cells only make up a minute fraction of the total weight of bone matter. Fibrous
malix is formed largely of fibrils of collagen, which can be extracted as
glue or gelatin. The third substance in organic bone material is a protein-sugar
compound called ground substance.
The relationship of ground substance
to the tissue fluid in bone isn't well understood, but along with the
tissue fluid, it's interspersed among the collagenous fibers. All this
organic matter is impregnated with the inorganic bone salts.
After
listening to the start of her lecture, you're convinced that bones are
important material. And they're fascinating! You jot down what notes
you can, and also write questions in the margin that you can look up in your
textbook when you get home.
Questions
- What materials give bone its ability to resist compression?
- What material gives bone its ability to resist tension?
- Why do older people's bones break more easily?
- How much stress can a bone take?
- How much of a bone's total mass is taken up by cell material?
What answers do you find once you get home and read over your notes?