Human respiratory system:  

Firstly, Nose which has two external nostril opening.  It leads to nasal chamber which further leads to naso-pharynx. Naso-pharynx further leads to trachea through glottis of larynx.

Naso-pharynx: It is a part of pharynx (first part).

Conchae: Wall of each nasal chamber has 3 small bony ridges (just like mountains) called Conchae. It releases heat (like hot water pipes) which worms the air passing through them to body temperature.

Choanal: Also called Internal nares. Nasal chambers opens into naso-pharynx by choanal or internal nares.

Larynx: It is called voice box (Adam’s apple) that produces sound.

Trachea: It is wind pipe (that allows air to pass through it).

Glottis: It is the outer opening of larynx into trachea.

Epiglottis: Leaf like cartilaginous flap that covers the glottis of Larynx during swallowing of food, so that food does not enters into Trachea.

Trachea is a long thin walled tube, it divided into two tubes, Primary bronchi, one goes into left lung and other into right lung. Then, this primary bronchi is divided into 3 secondary bronchi in each lung. Secondary bronchi further divides into tertiary bronchi in each lung. Which further divides into smaller bronchioles, which further divides into smaller alveolar ducts. At last, these alveolar ducts divides into alveolar sacs. Alveolar sacs contain small pouches called alveoli.

Alveoli: It is a very thin, irregular, thin walled and vascularised bag- like structures where main exchange of gases occurs in lungs.

1. Lungs lies in the thoracic cavity on both sides of heart and above the diaphragm.
2. Lungs are enclosed in 2 membranes.

Inner membrane is called Visceral pleuron and outer is called parietal pleuron. A narrow space between these 2 layers is called pleural cavity. It contains a watery fluid called pleural fluid.

Left Lung	Right Lung
It has 2 lobes.	It has 3 lobes.
It has smaller and light weight.	It has slightly large and heavier.

   

Mediastinum: The pleura of 2 sides meet to form a septum called mediastinum. In lower region, 2 pleura separate to form a cavity called Mediastinal cavity for Heart.