Briefly describe the structure and function of the respiratory system

Structure: The respiratory system starts at the mouth and nose with the pharynx, and continues as the trachea - this is covered with the epiglottis that prevents food and other material entering the lower airways. The trachea descends and branches into the two bronchi. These split further into bronchioles and finally air sacs called alveoli - these have very thin walls. Alongside all of these, capillaries run. Function: Gaseous exchange of oxygen and CO2. During inhalation, fresh air is taken into the lungs. This contains oxygen. The air enters the alveoli where is can easily diffuse across the thin walls into the nearby blood capillaries. Red blood cells uptake this oxygen and in return, carbon dioxide is removed from them. The CO2 enters the alveoli. During exhalation, the CO2 is breathed out of the body. The oxygen returns to the heart, carried on red blood cells, where it can be pumped round the body for use in respiration.