Respiratory System

What is Respiratory System?

The respiratory system consists of a group of organs and tissues that help us to breathe. The main parts of this system include a pair of lungs, a series of airways for air passages, blood vessels, and the muscles that facilitate breathing.

Respiratory system

Features of the human respiratory system

  • The energy is generated by the breakdown of glucose molecules in all living cells of the human body.
  • Oxygen is inhaled and is transported to various parts and are used in the process of burning food particles (breaking down of glucose molecules) at the cellular level in a series of chemical reactions.
  • The obtained glucose molecules are used for discharging energy in the form of ATP- adenosine triphosphate molecules by the human body to fulfil essential life processes.

Respiratory Tract

The complete respiratory tract consists of the nose, pharynx, larynx, trachea, bronchi, and bronchioles.

The air that we inhale has the following composition:

  • Nitrogen – 78%
  • Oxygen – 21%
  • Carbon dioxide – 0.03 – 0.04%
  • Traces of Hydrogen and Noble gases

From the above list, the air contains more oxygen than carbon dioxide. The air is inhaled with the help of nostrils, and in the nasal cavity, the air is cleansed by the fine hair follicles present within them. The cavity also has a collective group of blood vessels that keep the air warm. This air then passes to the pharynx, then to the larynx and into the trachea.

The trachea and the bronchi are coated with ciliated epithelial cells and goblet cells (secretory cells) which discharges mucus to moisten the air as it passes through the respiratory tract and also traps the fine bits of dust or bacteria that have been escaped from the hairs of the nasal openings. The motile cilia strike in an ascending motion such that the mucus and other foreign particles are carried back to the buccal cavity where it might be either cough out or swallowed.

Once the air reaches bronchus, it moves into the bronchioles, and then into the alveoli. From the alveoli, the formation of respiratory surfaces occurs in humans.

Respiratory System Organs

Excluding the lungs, there are several other associated organized structures that together constitute the respiratory system. This system is connected to the circulatory system as the transference of the gases takes place through the blood.


The nose possesses a couple of exterior nostrils which are divided by a framework of cartilaginous structure termed as the septum. This is the structure that evenly separates the right nostril from the left nostril. Tiny hair follicles that cover the interior lining of nostrils acts as the body’s first line of defence against foreign pathogens. Furthermore, they provide additional humidity for inhaled air.


Two cartilaginous chords lay the framework for the larynx. They are situated at the point of joining the pharynx and trachea. It is also termed as Adam’s apple or the voice box. It is the portion which rises and falls during swallowing of food particles. It generates sound as air passes through the hollow in the middle.


The nasal chambers open up into a wide hollow space termed as pharynx. It is a common path for both air and food. It functions by preventing the entry of food particles into the windpipe. The epiglottis is an elastic cartilage which serves as a switch between the larynx and the oesophagus by allowing the passage of air into the airway to the lungs, and food into the gastrointestinal tract.

Have you ever wondered why we cough when we eat or swallow?

Talking while we eat or swallow results in incessant coughing. The reason behind this reaction is the epiglottis. It is forced to open for the air to exit outwards and the food to enter into the windpipe, triggering a cough.


The trachea or the windpipe rises below the larynx and moves down to the neck. The walls of trachea comprise of C-shaped cartilaginous rings which give hardness to the trachea and maintain it by completely expanding. The trachea extends further down into the breastbone and splits into two bronchi, one for each lung.


The trachea splits into two tubes termed as bronchi, which enter each lung individually. The bronchi are divided into secondary, tertiary, and to bronchioles which is again further divided into small air-sacs called the alveoli. The alveoli are minute sacs of air with thin walls, and single-celled manner. It enables the exchange of oxygen and carbon dioxide molecules into or away from the bloodstream.


Lungs are the chief centres of the respiration process. They are located in the thoracic cavity of the chest near the backbone and on either side of the heart. They are the pair of large, spongy organs mainly involved in the exchange of gases between the blood and the air. Compared to the left lung, the right lung is quite bigger and heavier.

To learn about the respiratory system with video lessons, visit BYJU’S.

Practise This Question

Asthma is due to