For particles with an aerodynamic diameter less than 1 µm, Brownian diffusion is a major way for deposition in airways where the bulk flow is very low or absent.

Alveoli are tiny ends of the alveolar ducts. These tiny air sacs function to exchange oxygen and carbon dioxide in the blood. Certain respiratory diseases cause a thickening of the alveoli walls, which restricts movement, causing breathing difficulties.

The lowest portion is called the laryngopharynx, which extends downward and becomes continuous with the esophagus and larynx. Both the oropharynx and laryngopharynx are digestive and respiratory pathways.

Inhaled substances that are not deposited in other parts of the respiratory tract get deposited in gas-exchange sacs. The conducting airways terminate in gas-exchange sacs, which are made up of respiratory bronchioles and alveolar ducts.

The respiratory tract (or system) is a complex arrangement of organs and tissues. Its main functions are taking in oxygen and getting rid of carbon dioxide. The respiratory tract can be separated into two parts: (a) the proximal-conducting, non-respiratory airways that include the nose, pharynx, larynx, trachea, bronchi, and non-alveolar bronchioles, and (b) the distal respiratory region (i.e., respiratory bronchioles, alveolar ducts, and alveoli).

Nose is the first potential target for inhaled substances, except when one breathes through the mouth. Nose is important in odour detection. Interior parts of the nose warm, moisten, and filter air. This helps to protect the lungs from harm. Some inhaled material is trapped in the nasal cavity. The trapped material can, however, be transported from there to the throat, where it is swallowed. Nose blowing can also remove deposited material from the nose.

Respiration in the echinodermata (starfish and sea urchins) is carried out using a very primitive version of gills called papulae. These thin protuberances on the surface of the body contain diverticula of the water vascular system.

Elephant is the only animal known to have no pleural space. Rather, its parietal and visceral pleura are both composed of dense connective tissue and joined to each other via loose connective tissue. This lack of a pleural space, along with an unusually thick diaphragm, is thought to be an evolutionary adaptation allowing the elephant to remain underwater for long periods of time while breathing through its trunk which emerges as a snorkel.

Elastic cartilage or yellow cartilage is a type of cartilage present in the outer ear, larynx, and epiglottis. It contains elastic fiber networks and collagen fibers. The principal protein is elastin.

Both the lungs and the skin serve as respiratory organs in amphibians. The skin of these animals is highly vascularized and moist, with moisture maintained via secretion of mucous from specialized cells. While the lungs are of primary importance to breathing control, the skin's unique properties aid rapid gas exchange when amphibians are submerged in oxygen-rich water.

All of the above given options are non-respiratory functions of respiratory system.

The nasal chamber opens into nasopharynx, which is a portion of pharynx, the common passage for food and air. Nasopharynx opens through glottis of the larynx region into the trachea. Larynx is a cartilaginous box which helps in sound production and, hence, called the sound box.

Lungs are cone-shaped and extend from the collar bone to the surface of the diaphragm. The mid-line of each lung contains a region known as the hilus, the area through which blood and lymphatic vessels, nerves and primary bronchi enter and leave. Each lung is divided into lobes, three in the right lung and two in the left, within which there are smaller divisions known as lobules.

The trachea, or windpipe, divides into two principal bronchi (plural for bronchus) as it enters the lungs. The principal bronchi are further divided into smaller bronchi. Further divisions of the bronchi eventually lead to tiny tubes, called bronchioles, which lead to tiny air sacs known as alveoli.

The sinuses are hollow areas or cavities in the bones of the skull that are lined with mucous membranes and that open into the nasal cavity. The sinuses provide resonance for the voice. When the sinuses are inflammed and filled with mucus the voice has a different quality, often referred to as nasal in character.

Moving further down the respiratory tract, we reach the larynx, or voice box, which contains the vocal cords. The voice is produced by controlled vibrations of the vocal cords as air is pushed out of the lungs and through the larynx.

Influenza, commonly called the flu, is an acute, contagious, respiratory tract infection, which is caused by one of the influenza viruses. The severity of influenza symptoms depends on the type of influenza virus, and the age and health of the patient. Influenza may produce no symptoms, mild-to severe symptoms, or fatal illness.

Asthma is a condition in which the airways of the lungs become either narrowed or completely blocked, obstructing normal breathing. This obstruction of the lungs, however, is reversible, either spontaneously or with medication. That is why asthma is technically called Reversible Obstructive Airway Disease (ROAD).

Bronchiolitis is the inflammation of the bronchioles, the small airways.

Pneumonia is an infection of the lung tissue. It is usually associated with cough, sputum, fever and shortness of breath. There are various kinds of pneumonia. In adults, most pneumonia are due to bacterial infections (the most common infectious cause of pneumonia is the bacteria, Streptococcus Pneumoniae).

Breathing begins with a dome-shaped muscle located at the bottom of the lungs which is known as diaphragm. When we breathe in, the diaphragm contracts and flattens out and pulls downward. Due to this movement the space in the lungs increases and pulls air into the lungs. When we breathe out, the diaphragm expands and reduces the amount of space for the lungs and forces air out.

Air breathed in through the nose is warmed, moistened and filtered as it passes through the conchae, three bony projections which are lined with mucous membrane composed of cells which can trap particles of dust and germs.

Pleurisy is inflammation of the lining of the lungs and chest (the pleura) that leads to chest pain (usually sharp) when you take a breath or cough. Pleurisy may develop when you have lung inflammation due to infections such as pneumonia or tuberculosis. It is often a sign of a viral infection of the lungs. 

A collapsed lung or pneumothorax is the collection of air in the space around the lungs. This buildup of air puts pressure on the lung, so, it cannot expand as much as it normally does when one takes a breath.

Sarcoidosis is a rare disease that results from inflammation. Basically sarcoidosis is a lung's disease but it can occur in almost any organ. It is a multisystem (involves the entire body) granulomatous (small growths or lumps) disease that produces inflammation or swelling of the tissues in any part of the body.