Human Respiratory System

Table of Contents


What Is Respiratory System




Respiratory Tract


When we breathe, we inhale oxygen and exhale carbon dioxide. The so-called exchange of gases is necessary for metabolic activities and can be considered as a chemical process.

Every organism, from an individual bacteria cell to a mighty blue whale, undergoes respiration. This respiration is carried out by a system of organs known as the Respiratory System and the respiration in humans is carried out by the human respiratory system.

Respiratory System Definition

“Human Respiratory System is the organ system that involves inhaling of oxygen and exhaling of carbon dioxide to meet the energy requirements.”

What is Respiratory System?

The human respiratory system consists of a group of organs and tissues that help us to breathe. Lungs are the primary organs of the respiratory system which help in the exchange of gases. The other main parts of this system include a series of airways for air passages, blood vessels, and the muscles that facilitate breathing.

Also Read: Mechanism of Breathing

Human Respiratory System Diagram

The diagram of the human respiratory system shows different parts involved in the exchange of gases.

Human Respiratory System

Human Respiratory System Diagram showing different parts of the Respiratory Tract

Features of the human respiratory system

The respiratory system in humans has the following important features.

  • 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 System Parts

Let us have a detailed look at the different parts of the human respiratory system.


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.

Also Read: Respiration

Respiratory Tract

The respiratory tract in humans is made up of the following parts:

  • External nostrils – For the intake of air.
  • Nasal chamber – which is lined with hair and mucus to filter the air and remove dust and dirt.
  • Pharynx – It is a passage behind the nasal chamber and serves as the common passageway for both air and food.
  • Larynx – Also known as the sound box as it helps in the generation of sound and thus helps us in communicating.
  • Epiglottis – It is a flap-like structure that covers the glottis and prevents the entry of food into the windpipe.
  • Trachea – It is a long tube passing through the mid-thoracic cavity.
  • Bronchi – The trachea divides into left and right bronchi.
  • Bronchioles – Each bronchus is further  divided into finer channels known as bronchioles
  • Alveoli – The bronchioles end up into the balloon-like structures known as the alveoli
  • Lungs – We have a pair of lungs, which are sac-like structures and covered by a double-layered membrane known as pleura.

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 Functions

The human respiratory system functions are mentioned below:

Inhalation and Exhalation

The respiratory system helps in breathing, known as pulmonary ventilation. The air inhaled through the nose moves through the pharynx, larynx, and trachea into the lungs. The air is exhaled back through the same pathway. Changes in the volume and pressure in the lungs aid in pulmonary ventilation.

Exchange of Gases between Lungs and Bloodstream

Inside the lungs, the oxygen is exchanged for carbon dioxide waste through millions of microscopic sacs called alveoli. The inhaled oxygen diffuses into the pulmonary capillaries, binds to haemoglobin and is pumped through the bloodstream.

The carbon dioxide from the blood diffuses into the alveoli and is expelled through exhalation.

Exchange of Gases between Bloodstream and Body Tissues

The blood carries the oxygen from the lungs around the body and releases the oxygen when it reaches the capillaries. The oxygen is diffused through the capillary walls into the body tissues. The carbon dioxide also diffuses into the blood and is carried back to the lungs for release.

Vibration of the Vocal Cords

While speaking, the muscles in the larynx move the arytenoid cartilage. These cartilages push the vocal cords together. During exhalation, when the air passes through the vocal cords, it makes them vibrate and creates sound.

Olfaction or Smelling

During inhalation, when the air enters the nasal cavities, some chemicals present in the air bind to it and activate the receptors of the nervous system on the cilia. The signals are sent to the olfactory bulbs via brain.

Also Read: Respiratory System Disorders

Respiration is one of the metabolic processes which play an essential role in all living organisms.

Breathing is the first step in respiration for almost all organisms. The inhale and exhale of gas and its mechanism depends on the environment in which the organisms live.

For instance, the lower organisms like the unicellular take up oxygen and release carbon dioxide by the process of diffusion across their membrane. Annelids like earthworms have a moist cuticle which helps them in gaseous exchange. Respiration in fish and other aquatic organisms have special organs called gills, which help them in respiration. Most of the higher organisms possess a pair of lungs for breathing. Respiration in humans is carried out through the lungs.

To know more about what is respiratory system, its definition, parts, functions, respiration in humans and human respiratory system diagram, keep visiting BYJU’S website or download BYJU’S app for further reference.

Practise This Question

The serous membrane which covers the lungs is called