Lungs are the site of gas exchange in all species of mammal.
Lungs function in pairs and are formed from an elasticated tissue that is surrounded by blood vessels. The blood vessels carry deoxygenated blood to the alveoli where the gas transfer takes place. The structure of the lungs is known as a bronchial tree which starts with the trachea. The trachea then splits into the two primary bronchi. The Bronchus splits further until it reachers the alveolar ducts, to alveolar sacs and finally the alveoli. This is where the lungs and blood vessels meet and the gas exchange takes place.