Human Respiratory System

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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 a chemical process.

Every organism, from an individual bacterial 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.

Let us explore respiratory system notes to have a detailed understanding of the human respiratory system, its parts, functions and the process of respiration in humans.

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 the 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.

Also Read: Difference between trachea and esophagus

Respiratory System Parts and Functions

Let us have a detailed look at the different parts of the respiratory system and their functions.


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 the 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 in 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 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 divide 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 in humans and other vertebrates. 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 soundbox 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 discharge 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 may either be coughed 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.

Also read: Exchange Of Gases in Plants

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.

The 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 the brain.

Also Read: Respiratory System Disorders

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

Breathing is the first step in respiration for almost all organisms. The inhaling and exhaling of gas and its mechanism depend 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

Respiration is the process of taking in oxygen and giving out carbon dioxide. There are two types of respiration processes in humans:

  • External Respiration, that involves the inhalation and exhalation of gases.
  • Internal Respiration, that involves the exchange of gases between blood and body cells.

Respiration in humans takes place through the lungs. It is the largest organ of the human respiratory system. The air inhaled moves down the trachea into the lungs where oxygen is exchanged for carbon dioxide from the body tissues. Carbon dioxide is then exhaled out of the lungs through the mouth.

Also Read: Amphibolic Pathway

Learn more in detail about the human respiratory system, its structure, parts and functions, respiration process, respiration in humans and other related topics at BYJU’S Biology

To know more about Respiration, watch the video given below:

Frequently Asked Questions

What is the human respiratory system?

The human respiratory system is a system of organs responsible for inhaling oxygen and exhaling carbon dioxide in humans. The important respiratory organs in living beings include- lungs, gills, trachea, and skin.

What are the important respiratory system parts in humans?

The important human respiratory system parts include- Nose, larynx, pharynx, trachea, bronchi and lungs.

What is the respiratory tract made up of?

The respiratory tract is made up of nostril, nasal chamber, larynx, pharynx, epiglottis, trachea, bronchioles, bronchi, alveoli, and lungs.

What are the main functions of the respiratory system?

The important functions of the respiratory system include- inhalation and exhalation of gases, exchange of gases between bloodstream and lungs, the gaseous exchange between bloodstream and body tissues, olfaction and vibration of vocal cords.

What are the different types of respiration in humans?

The different types of respiration in humans include- internal respiration, external respiration and cellular respiration. Internal respiration includes the exchange of gases between blood and cells, external respiration is the breathing process, whereas cellular respiration is the metabolic reactions taking place in the cells to produce energy.

What are the different stages of aerobic respiration?

Aerobic respiration is the process of breaking down glucose to produce energy. It occurs in the following different stages- glycolysis, pyruvate oxidation, citric acid cycle or Krebs cycle, and electron transport system.

Why do the cells need oxygen?

Our body cells require oxygen to release energy. The oxygen inhaled during respiration is used to breakdown the food to release energy.

What is the main difference between breathing and respiration in humans?

Breathing is the physical process of inhaling oxygen and exhaling carbon dioxide in and out of our lungs. On the contrary, respiration is the chemical process where oxygen is utilized to breakdown glucose to generate energy to carry out different cellular processes.


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