What is Breathing? Steps, Mechanism, Diagram, and More
Breathing is one of the most fundamental activities our bodies perform every second. It operates automatically to ensure a continuous supply of oxygen while expelling carbon dioxide. Although it might seem simple, the mechanism of breathing is a highly coordinated process that involves our respiratory organs, skeletal muscles, and the nervous system. This article will not only discuss the mechanism of breathing. but will also explain the mechanism of breathing in humans step by step, highlighting every crucial detail that helps us maintain life.
What is Breathing?
Breathing, often referred to as external respiration, is the physical exchange of gases—oxygen and carbon dioxide—between an organism and its environment. When we inhale, oxygen from the atmosphere is taken into the lungs. When we exhale, we release carbon dioxide, a waste product of metabolism, back into the environment.
Breathing involves the inhalation and exhalation process, which is primarily controlled by the diaphragm (a dome-shaped muscular sheet at the base of the thoracic cavity) and the intercostal muscles (muscles situated between the ribs). Together, these muscles alter the volume and pressure inside the thorax, enabling air to move in and out of our lungs.
Also Read: Difference Between Breathing and Respiration
Steps of the Breathing Mechanism
What are the steps of the breathing mechanism? Let us break down the two main phases involved:
1. Inhalation (Inspiration)
Muscular Contraction: During inhalation, the diaphragm contracts and flattens, moving downwards. Simultaneously, the external intercostal muscles contract, pulling the rib cage up and out.
Volume and Pressure Changes: As the chest cavity expands, the volume inside the thorax increases. This drop in pressure within the lungs relative to the external air pressure causes air to rush in.
Air Entry: Oxygen-rich air then enters through the nose or mouth, passes the pharynx, trachea, and bronchi, eventually reaching the alveoli—tiny air sacs where gas exchange begins.
2. Exhalation (Expiration)
Muscular Relaxation: In exhalation, the diaphragm relaxes and moves upwards into a dome shape. The external intercostal muscles also relax while the internal intercostal muscles may contract slightly to aid forceful expiration.
Volume and Pressure Changes: With the decrease in thoracic volume, the pressure inside the lungs becomes higher than the atmospheric pressure.
Air Exit: Carbon dioxide-rich air is pushed out of the lungs, through the airways and finally released into the atmosphere.
These two steps—inhalation and exhalation process—constitute the mechanism of breathing. To understand this even better, let us explore a simplified mechanism of breathing flow chart below.
Mechanism of Breathing Flow Chart
Start
|
Diaphragm + External Intercostal
Muscles Contract (Inspiration)
|
Thoracic Cavity Volume Increases
|
Pressure in Lungs Decreases
|
Air Rushes In
|
Gas Exchange
|
Diaphragm + Intercostal Muscles Relax
(Expiration Begins)
|
Thoracic Cavity Volume Decreases
|
Pressure in Lungs Increases
|
Air is Expelled
|
End
This mechanism of breathing flow chart visually represents how changes in pressure and volume result in the inward and outward movement of air.
Mechanism of Respiration
Although breathing is vital, it is only one component of respiration. The mechanism of respiration covers both breathing (external respiration) and the actual use of oxygen in the cells (internal or cellular respiration). Here, we will focus on the external and internal transport of gases that underpin our survival.
Oxygen Transport
Oxygen from the alveoli diffuses into the blood, binding primarily to haemoglobin (forming oxyhaemoglobin).
This oxygenated blood travels through the pulmonary veins to the heart, which then pumps it to tissues all over the body.
Internal Respiration
Inside the tissues, oxyhaemoglobin releases oxygen for cellular metabolic activities.
Cells use oxygen to break down glucose and generate energy (ATP). As a by-product, carbon dioxide is produced.
Carbon Dioxide Transport
Carbon dioxide is transported from the tissues back to the lungs in three ways:
Dissolved in blood plasma as carbonic acid.
Converted to bicarbonate ions.
Bound to haemoglobin to form carbaminohaemoglobin.
Eventually, carbon dioxide is released into the alveoli and exhaled.
When you explain the mechanism of breathing in humans, it is essential to include these gas transport steps, because breathing alone does not complete the whole picture of how cells receive oxygen and expel carbon dioxide.
Intrapleural Pressure and Lung Movement
Sometimes referred to as intrapleural breathing, this aspect deals with the pressure in the pleural cavity (the space between the lungs and the chest wall). This pressure is typically negative compared to atmospheric pressure, ensuring the lungs stay inflated.
Transpulmonary Pressure: The difference between intra-alveolar (inside the lungs) and intrapleural pressures. This gradient keeps the lungs expanded.
During Inhalation: The intrapleural pressure becomes more negative, increasing the transpulmonary pressure and allowing the lungs to expand.
During Exhalation: The pressure in the pleural cavity becomes less negative, causing the lungs to recoil and push air out.
Respiratory Gas Transport
After breathing brings oxygen into the lungs, the next phase is distributing these gases throughout the body. Oxygen and carbon dioxide travel via the bloodstream, aided by:
Haemoglobin in red blood cells, which binds oxygen.
Bicarbonate formation in plasma for carbon dioxide transport.
Protein Bonding (e.g., carbaminohaemoglobin) for additional CO₂ transport.
This distribution, combined with the mechanism of breathing diagram (which illustrates changes in lung volume and pressure), ensures every cell gains access to oxygen and eliminates carbon dioxide efficiently.
Key Takeaways
Breathing is the physical process of air intake (inhalation) and air release (exhalation).
The mechanism of breathing relies on pressure differences created by the contraction and relaxation of the diaphragm and intercostal muscles.
The mechanism of respiration expands on breathing by explaining how gases are exchanged at the alveoli and transported to and from body tissues.
Negative intrapleural pressure helps keep the lungs inflated, making inhalation easier.
Proper gas exchange ensures cells receive adequate oxygen and dispose of carbon dioxide effectively.
Mnemonics for Easy Recall
A handy mnemonic to remember the phases of the inhalation and exhalation process is “DI-EG (Diaphragm – Intercostal, Expand – Gas in)” and “DI-CR (Diaphragm – Intercostal, Contract – Release gas)”:
DI-EG:
D – Diaphragm contracts
I – Intercostal muscles contract
E – Expansion of thoracic cavity
G – Gas (air) flows in
DI-CR:
D – Diaphragm relaxes
I – Intercostal muscles relax
C – Contraction of the thoracic cavity
R – Release of gas (air)
Quiz Time!
Which muscles are primarily involved in expanding the rib cage during inhalation?
A. Internal intercostal muscles
B. External intercostal muscles
C. Abdominal muscles
D. None of the above
What are the steps of the breathing mechanism?
(a) Inspiration followed by expiration
(b) Expiration followed by inspiration
(c) Only inspiration
(d) Only expiration
Which of these is NOT a way by which carbon dioxide is transported in the blood?
A. Bicarbonate ions
B. Carbaminohaemoglobin
C. Carbonic anhydrase
D. Dissolved in plasma
Answers to Quiz
B, 2. (a), 3. C
FAQs on Mechanism of Breathing: Inhalation, Exhalation & Respiration Explained
1. How can I illustrate the mechanism of the breathing diagram at home?
You can sketch a simple diagram showing the diaphragm, ribs, lungs, and arrows indicating airflow during inhalation and exhalation. Label the pressure changes and volume changes for clarity.
2. What is the mechanism of breathing in humans if someone has asthma or other respiratory conditions?
In respiratory conditions like asthma, the airways narrow or become inflamed, making inhalation and exhalation more difficult. However, the fundamental pressure and volume principles remain the same, though airflow is restricted.
3. Which factor triggers us to breathe more frequently—lack of oxygen or build-up of carbon dioxide?
An increase in blood carbon dioxide concentration is the primary trigger for an increased breathing rate. Low oxygen can also stimulate breathing but is usually a secondary mechanism.
4. Why do athletes often have a lower resting breathing rate?
Athletes’ bodies are more efficient at oxygen uptake and carbon dioxide removal. Their respiratory muscles are stronger, and their tissues use oxygen more effectively, reducing the need for rapid breaths at rest.
5. Does holding your breath affect the mechanism of respiration?
Holding your breath temporarily stops the exchange of gases, causing carbon dioxide levels to rise and oxygen levels to fall. This triggers the urge to breathe, compelling you to resume normal respiration.
