The human respiratory system consists of the nose, nasal cavity, trachea, bronchi bronchioles, lungs and alveoli. The nose and nasal cavity are airways the air enters the nose through the nostrils. the trachea is also called the windpipe. The air from the nasal cavity enters into the trachea. The lungs are inside the chest cavity and are protected by the rib cage. The diaphagram is a flat and muscular sheet like structure present below the lungs that helps in inhaling and exhaling. humans respire aerobically .