b'ChapterUpper Airway Air enters through the mouth and nose where it is warmed, filtered and moistened before passing through the pharynx (the common pathway for air and food). The air then flows through the voice box (larynx) into the windpipe (trachea). Liquid and food are prevented from entering the trachea by a trapdoor structure called the epiglottis. This is a flap of tissue that covers the opening of the larynx, protecting the lower airways and lungs by slamming shut when we swallow. Windpipe(Trachea)Lower AirwayLungsLeaving the larynx, air flows down the trachea (about 12cm long in an adult). This is formed from semi rigid rings ofAir cartilage, which prevent the tracheaPassagesfrom collapsing when inhaling.(Bronchi)The trachea then divides into two smallertubes (left and right main bronchi) which enter the left and right lung.Air SacsWithin the lungs, the bronchi branch into smaller tubes called bronchioles which(Alveoli)eventually divide into millions of tiny air sacs known as alveoli.The alveoli are clustered together and surrounded by smaller blood vessels known ascapillaries. Oxygen is taken up by the alveoli and attach to haemoglobin, found in the red blood cells. It is then transported to the heart and pumped through blood vessels around the body. Carbon Dioxide is given off by the cells into the blood then transported back to the?heart and lungs to be exhaled.Did you know?Your lungs are jam packed with millions of tiny air sacs. If your lungs and air sacs were stretched out and laid flat, they would cover an entire tennis court.22 How Your Body Works'