The respiratory system allows humans to breathe through inhalation and exhalation, and it also cleans the air that is breathed in. The nose contains tiny hairs that remove particles from the air. This provides a defense against bacteria that would otherwise get into the body.
Air that is breathed in goes through the trachea, which is also called the windpipe. The trachea is divided into tubes called bronchial tubes, which contain even smaller tubes called bronchioles. The air then goes into tiny sacs called alveoli, which are surrounded by blood vessels that remove the oxygen from the air and send it to the blood. The blood goes to the heart and is pumped all over the body, giving cells the oxygen they need.