Respiratory System in Humans: Parts, Function, Diagram, Anatomy

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Explanation About Respiratory System in humans

Respiration is the exchange of O2 and CO2 between the environment and cells of the body where organic nutrients are broken down enzymatically to release energy. Every cell needs the energy to stay alive. To get energy, every cell needs food and oxygen. Organisms take the food, digest it, and digested food is transported to each and every cell. Similarly, oxygen is taken from the air by a process called breathing and transported to all the cells.

Food is oxidized in the cells to produce energy along with carbon dioxide and water. This is called cellular respiration. This reaction takes place in the cytoplasm and mitochondria in the cell.

Glucose + Oxygen à Carbon dioxide + water + energy as ATP


Respiratory System in Humans Diagram

respiratory system diagram

When the breakdown of glucose occurs with the use of oxygen it is known as aerobic respiration.  Sometimes, and in some organisms, respiration takes place in the absence of oxygen. Such respiration is called anaerobic respiration. For example, yeast respires in the absence of oxygen. As a result, a little amount of energy is produced along with ethanol and carbon dioxide.

In our body also when energy demand increases and oxygen is in short supply (during heavy exercise, fast running), anaerobic respiration takes place in which lactic acid and carbon dioxide are produced. Lactic acid cause pain and fatigue in the muscles and on getting oxygen, it is converted back to carbon dioxide and water.

Breathing is an act of taking in air, absorbing oxygen from it, releasing carbon dioxide, giving out the air (with less oxygen and more carbon dioxide). Taking in of air is known as inhalation and giving out of the air is known as exhalation. Inhaled air contains about 21 percent oxygen and 0.04 percent carbon dioxide. The exhaled air contains 16.4 percent oxygen and 4.4 percent carbon dioxide.


Types of Respiration

Direct Respiration

Body cells exchange gases with the environment without the aid of any respiratory organ and transportation by blood.

Example: Unicellular organisms, roundworms, flatworms sponges, etc.

Indirect Respiration

There are respiratory surfaces and blood is involved in the transportation of gases between the respiratory surface and body cells. Organs having the respiratory surface is called respiratory organ.


Parts and Functions of Respiratory System in Humans

There are 8 major organs of the Respiratory system:

  • Nasal Cavity
  • Pharynx
  • Epiglottis
  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli
  • Diaphragm


Nasal Cavity

It is present in the nose and has small hair and mucous which filters the suspended impurities in the air and also warms up the air.


It is an opening into the esophagus and the windpipe. These pipes are covered with epiglottis. Inhaled air enters the pharynx and from there to the windpipe or trachea.


It ensures that air passes into the trachea, and food passes into the esophagus.


The trachea is a tube made of cartilage rings. The trachea is the passage through which air enters the lungs. Its walls are lined with cilia that prevent the suspended particles from being lodged in the lungs if any in the air.


It connects the trachea to the lungs. Air passes through them to a large number of bronchioles.


They are the small narrow tubes that cover the entire area of the lungs. Each bronchiole opens into an alveolus.


Alveoli are hollow, sac-like structures attached to the bronchioles. They have extremely thin walls. Every alveolus is covered by a network of capillaries. The exchange of oxygen and carbon dioxide takes place between blood and air in the alveoli through the walls of the alveoli and blood capillary.


The diaphragm is a muscular organ situated beneath the lungs. It is mainly responsible for the breathing mechanism. When it contracts and moves down, the intercostal muscles also contract, which moves the rib cage up and out.

The area inside the lungs increases creating a low-pressure zone forcing air from outside to get in which is called inhalation. The expression of the diaphragm makes it go up, and intercostal muscles expand to bring the rib cage back again. The lungs area is reduced and the extra air inside is pushed out which is called exhalation.


In between inhalation and exhalation, the gaseous exchange takes place between the lungs and the alveoli. Blood flows away from the lungs is rich in oxygen. It is sent through the heart to the cells of different parts of the body for cellular respiration to take place.

Most of the animals breathe through the lungs just like human beings. Cockroaches have spiracles through which air enters the body into a network of the trachea. Every cell gets oxygen from the trachea through diffusion. Earthworms breathe through their skin that is why their skin should always remain moist.

Frogs can breathe through their lungs as well as through their skin. Fishes have gills for breathing. They absorb oxygen dissolved in water.


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My Name is Mukesh Kumar. I am a Teacher, Blogger, Educational Content Writer, and Founder of CBSE Digital Education.

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