Cells
Directions: Read the
passage. Then answer questions about the passage below.
Your body is
made of trillions of tiny living things. They are called cells.
There are 210 different kinds of cells in your body. Each kind
of cell has a different shape. Each kind of cell is a different
size. Each kind of cell has a different job.
The same types of cells usually work together in
groups. The groups are called tissues. More cells can be made
when the cells split. They form more cells that are just like
the parents.
Some of your cells are nerve cells. They are also called neurons.
They carry signals through your body. The signals are messages
that tell your body to move. Your brain has about 100 billion
neurons!
The connections between neurons are called
synapses. Each neuron has between 1,000 and 10,000 synapses.
There are about one quadrillion synapses in your brain. That's
1,000,000,000,000,000 synapses in your brain!
There are about 1 billion neurons in your spinal
cord, the bundle of nerves that goes from your brain all the way
down your back. Some of your cells are red blood cells. They
carry oxygen (O) through your body. They pick up carbon dioxide
(CO2) and help your body get rid of it.
Your body wants to eliminate CO2 because it is a
waste product. Blood also helps your body stay warm. Conversely,
blood cools off your brain, because it gets very hot. Some of
your cells are white blood cells. The white blood cells help
your body fight sickness.
Some of the white blood cells, called T–cells,
fight viruses and other cells that do not belong in your body.
T–cells work with B–cells to fight off the disease cells. They
tell your brain to give you a fever so the disease cells will
not be able to grow. Many diseases cannot grow when your body is
hot. And some white cells eat disease cells! Go white blood
cells!
Some of your cells are bone cells. They are also called osteocytes.
Osteocytes make bone. The bone grows to form all around them.
The osteocytes get food through tiny strings that go to nearby
blood vessels. Blood vessels are the tubes that carry blood in
your body. Some of your cells are skin cells. They are also
called epithelial cells. They grow your skin.
Your skin keeps dirt off
your tissues. Your skin forms the outside of some organs, like
your stomach and lungs. An adult has about 9 pounds of skin on
his or her body. Some of your cells are liver cells. They are
also called hepatocytes. These cells check your blood. They make
sure your blood has the right amount of sugars in it.
They also help clean poisons from your body. They help make
substances that help your blood to clot, or stick together. They
clean alcohol from your body if you drink alcohol or take
medicine with alcohol in it. Some of your cells are fat cells.
Their job is to store fat.
The fat is a place where your body keeps or stores energy. The
fat pads the organs in your body. The layers of fat also help
keep your body warm.
Your body weight depends on how fast your body stores fat compared
to how fast your body uses up energy. Some of your cells are
muscle cells. Your muscles are made of these cells.
They are also called
myocytes. Your neurons send the messages to move muscles that
are connected to your bones and your skeletal muscles.
However, your nerve cells
do not tell your heart muscles when to beat. Your heart muscles
and smooth muscles have inner signals that tell them to move.
Smooth muscles are muscles that you do not have to think about,
like the muscles that work in the digestion of food. Your cells
are busy all the time.
Even while you are sleeping, your cells
are working hard to keep your body alive and healthy.
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