In order for human beings to survive, we have to breathe, and so we have the respiratory tract, which is the passage that air travels along from the outside to our lungs. The respiratory system consists of the respiratory tract and respiratory organs, and is known as pulmonary respiration. In humans, the respiratory tract is a complex system, made up of six key organs.

The nasal cavaty:- Nasal cavity lies above the mouth cavity. Tye nasal cavity communicate to the outside through external nostrils and internally with the pharynx by internal nostrils. Both cilia and mucus check the entry of dust particles in the respiratory passage.

Pharynx:- From the nasal cavity, the air moves into the pharynx which is common area to both digestive and respiratory tracts.The pharynxopens into larynx or voice box through the glotis.The glotis can be covered by the leaf like cartilage epiglotis during swallowing of food.

The Larynx: This is a cartilagious, box-like structure that is situated at the tracheal opening. The larynx will move up or down when we swallow to allow the passage of air or food, safely. It also is responsible for human speech, as it contains two vocal chords that vibrate to produce sound.

The Trachea: The trachea is the next organ through which air flows. This is a tube that is eleven centimeters in length with a twenty five centimeter diameter. In order to keep the trachea opened, there is an incomplete C-shaped cartiligious ring within the trachea wall.

The Bronchi and Bronchioles. The next stop for air is the two primary bronchi that split off from the trachea. These serve the function of carrying the air into the next organ, the lungs. The right bronchus divides into three bronchi, each extending respectively into the three lobes of the right lung. On the other side, the left bronchi divides into two bronchi that extend into the two lobes of the left lung.

Lungs:- There are two lungs in the thoracic cavity.The thoracic cavaty is bounded by vertebral coloumn arrives sternum and diaphragm.The lungs are highly elastic hollow dark coloured spongi bag like structure. The lungs rest on a sheet of muscle called the diaphragm which forms the floor of the thoracic.

The lungs are probably one of the most complex organs in the respiratory tract, with the right lung divided into three lobes and the left lung divided into two. The lungs are enclosed by the pleural cavity, which is itself surrounded by two membranes that secrete an oily matter called pleural fluid, which permeates the Pleural cavity.