4-2 The Human Body - Respiratory System

When you breathe in, air passes through your mouth and nose, down your windpipe and into your lungs.  Your lungs fill with air and your chest expands.  This is the respiratory system at work.  Breathing is an involuntary action.  This means the brain takes care of it without any conscious effort on your part.  The respiratory system not only brings air into and out of the body, it also brings oxygen to the blood.

When you breathe in, a thin sheet of muscle just below your lungs, called the diaphragm, moves down.  This action helps air to enter your mouth or nose.  The air is then moistened, warmed, and filtered.  Air then passes down the throat and moves past the voice box.  It travels down the windpipe, and into tubes in the lungs called bronchi.  The bronchi branch into smaller tubes and then into millions of tiny air sacs called alveoli.  The oxygen passes from the air in the alveoli into the capillaries and is carried away by the blood.  Carbon dioxide is passed out of the body when you exhale.

Directions: Answer the questions about the respiratory system.

brings oxygen to the blood
passes carbon dioxide into the body
carries blood back to the heart

is an involuntary action.

mouth and nose
lungs

The thin sheet of muscle just below the lungs is called the .

capillaries

bronchi

alcove

The tubes in the lungs are called .

Tiny air sacs in the lungs are called .

oxygen
carbon dioxide