The respiratory system is located in your head and chest. It is made up of the air passages in your nose and throat, your lungs, and the muscles in your chest and diaphragm. The respiratory passageways in the body are known as the “bronchial tree”, because they look like an upside down tree. These passages start in the nose and mouth and enter the lungs. Your lungs are the main organs in the respiratory system. Your body has two lungs and each lung is made up of smaller units called lobes. The lungs are each covered by a thin layer called the pleural membrane. Deep within the lungs are tiny air sacs called alveoli, which look like bunches of grapes. There are about 30,000 alveoli in each lung. The alveoli are elastic so they can expand and contract when air moves in and out of them. The alveoli have a network of blood vessels traveling through them.