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Mechanism of Breathing: Definition, Diagram, Functions

Mechanism of Breathing: Definition, Diagram, Functions

Irshad AnwarUpdated on 02 Jul 2025, 06:40 PM IST

Breathing, or respiration, is the process of taking oxygen in and carbon dioxide. The mechanism of breathing contains two phases which are inhalation (inspiration), whereby the diaphragm contracts and the chest cavity expands, admitting air to the lungs and exhalation (expiration), whereby the diaphragm relaxes, forcing air out. The respiratory system coordinates this process for gas exchange. The understanding of the mechanism of respiration, especially in classes 10 and 11, helps explain how inspiration and expiration maintain the body's oxygen-carbon dioxide balance. This important topic from the Breathing Exchange of gases Chapter from Biology.

This Story also Contains

  1. What is Breathing?
  2. Process of Respiration
  3. Mechanism of Breathing
  4. Mechanism of Respiration
Mechanism of Breathing: Definition, Diagram, Functions
Mechanism of Breathing

What is Breathing?

Respiration is the physiological exercise through which gases, mainly oxygen and carbon dioxide are exhaled through the lungs of an organism. This is important for cellular respiration as this moves the oxygen required in aerobic respiration to reach the cells and at the same time takes out carbon dioxide, a waste product. Proper functioning of the lungs guarantees a constant supply of oxygen to the cells for their metabolism and regulates the proper distribution of gases, which are significant for the life process.

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Process of Respiration

The process of breathing involves the following steps:

Inhalation (Inspiration)

  • Inhalation is mainly characterised by the contraction of the diaphragm and the intercostal muscles to raise the ribs and expand the thoracic cavity.

  • This contraction generates a vacuum, or negative pressure within the thoracic cavity and air rushes into the lungs.

  • During the process of inhalation, contraction of the muscles surrounding the thoracic cavity increases the volume of this cavity and thus forces the air through the respiratory tract and into the alveoli to participate in the exchange of gases.

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Exhalation (Expiration)

  • Exhalation takes place when the diaphragm and intercostals decrease their size decreasing the volume of the thoracic cavity.

  • This relaxation leads to positive pressure in the thoracic cavity which in turn forces air out of the lungs and out of the respiratory tract.

  • The reduction of volume ejects the air laden with carbon dioxide ending the breathing cycle.

Process of Respiration

Mechanism of Breathing

The mechanism of breathing involves the following:

Diaphragm and Intercostal Muscles

  • The diaphragm functions as a muscle which is in the shape of a dome and is situated at the bottom part of the thoracic cavity and the intercostal muscles are located in between the ribs of an individual’s body.

  • Inhalation is done by the contraction of the diaphragm, which becomes flattened and the intercostal muscles that lift the ribs, expanding the thoracic cavity. By doing so, the pressure in the thoracic cavity is reduced enabling air to enter the lungs.

  • These muscles contract during inhalation and, at the same time, they relax during exhalation to narrow the thoracic cavity hence forcing air out of the lungs.

Lung Compliance and Elasticity

  • Lung compliance on the other hand deals with the ease with which the lungs can expand and dilate given some pressure.

  • High lung compliance means that the lungs can be expanded easily and can therefore fill up easily while low compliance means that the lungs are stiff and cannot be filled easily.

  • Accessibility of the lungs can be affected by the degree of elasticity of the lung tissues, and the quantity and nature of the surface tension-reducing agents. This leads to disorders in respiration.

  • Lung compliance is an index of work that the respiratory muscles need to do to achieve a certain level of ventilation.

Airway Resistance

  • Airway resistance is the opposition force within the respiratory tracts to the flow through them.

  • This depends on the dimensions like the diameter of the airway, mucus production, and bronchial constriction.

  • There is always the case of high resistance, this is because of the constriction of the tubes through which air has to pass, or the presence of an obstructing factor that makes it difficult to breathe.

  • It is important to deal with airway resistance if breathing properly and if fresh and expired air is going to get to the lungs.

Mechanism of Respiration

Some important mechanisms of respiration are discussed below:

Intrapleural Breathing

The pressure in the pleural cavity, the space between the lungs and pleura, is referred to as intrapleural breathing. This pressure is less than that of atmospheric pressure, known as negative pressure, which is very vital in the mechanics of respiration. The transpulmonary pressure or the pressure difference is accountable for the lung movement during breathing. The intrapleural pressure becomes more negative during inhalation and causes the lungs to expand. During expiration, the pressure increases, causing the lungs to recoil.

The lungs' elasticity and the surface tension of alveolar fluid pull the lungs inward, while the thoracic wall and pleural fluid create an opposing force. This balance results in negative intrapleural pressure, a key concept in the mechanism of breathing.

Respiratory Gas Transport

Respiratory gas transport refers to the transport of oxygen and carbon dioxide by the blood. Oxygen-rich blood from the lungs flows to the heart through pulmonary veins. The heart pumps this oxygenated blood to the rest of the body through the aorta.At the same time, deoxygenated blood with carbon dioxide is returned to the lungs by the pulmonary arteries for gas exchange. The whole process is repeated continuously so that oxygen, carbon dioxide, and carbon dioxide balance are maintained in the body.

This explanation of the mechanism of breathing, how to inspire and expire, helps to describe more precisely how the respiratory system works in a human being.

The gas exchange in the lungs involves the following:

Diffusion of Gases

  • In the alveoli oxygen from the inhaled air moves passively through the walls of the alveoli into the blood in capillaries, and at the same time, carbon dioxide diffuses active from the blood into the alveoli and thus is exhaled.

  • This exchange is driven by partial pressure gradients. Oxygen diffuses from the place that has high partial pressure in the alveoli relative to that found in blood and similarly for the diffusion of carbon dioxide.

Hemoglobin and Oxygen Transport

  • Oxygen on reaching the lungs gets attached to the haemoglobin molecules and forms oxyhemoglobin which is easily transported to the tissues.

  • The oxygen dissociation curve shows how the affinity of haemoglobin for oxygen varies with different concentrations of oxygen partial pressure.

  • At high partial pressures, for example in the lungs, haemoglobin grabs more oxygen than from the lower pressure found in tissues where oxygen is needed, for use by the cells.

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Frequently Asked Questions (FAQs)

Q: How does the pH of blood affect breathing rate?
A:
Blood pH is closely regulated by the respiratory system. When blood becomes too acidic (low pH), chemoreceptors in the brain and major blood vessels detect this change and signal the respiratory center to increase the breathing rate. This increased ventilation helps expel more CO2, which is acidic, thus raising blood pH. Conversely, if blood becomes too alkaline (high pH), the breathing rate decreases to retain more CO2 and lower the pH.
Q: How does positive pressure ventilation differ from normal breathing mechanics?
A:
Normal breathing relies on negative pressure created by the expansion of the thoracic cavity. In contrast, positive pressure ventilation, used in mechanical ventilation, pushes air into the lungs under pressure. This reverses the normal pressure gradients in the chest and can have several effects:
Q: What is the significance of the respiratory exchange ratio in exercise physiology?
A:
The respiratory exchange ratio (RER) is the ratio of CO2 produced to O2 consumed during respiration. In exercise physiology, RER provides insights into:
Q: How does the closing capacity of the lungs affect breathing, especially in older adults?
A:
Closing capacity is the lung volume at which small airways begin to close during exhalation. As people age, closing capacity increases due to loss of lung elasticity. This can lead to:
Q: What is the role of chemoreceptors in breathing regulation?
A:
Chemoreceptors are specialized cells that detect changes in blood chemistry and play a vital role in breathing regulation:
Q: How does the concept of dead space ventilation impact breathing efficiency?
A:
Dead space ventilation refers to the portion of each breath that doesn't participate in gas exchange. It includes:
Q: What is the significance of functional residual capacity in lung function?
A:
Functional residual capacity (FRC) is the volume of air remaining in the lungs after a normal exhalation. Its significance includes:
Q: What is the role of accessory muscles in breathing?
A:
Accessory muscles of respiration, such as the sternocleidomastoid, scalene, and pectoralis minor muscles, are not typically used during quiet breathing. However, during deep or labored breathing, these muscles contract to further expand the chest cavity. They assist in lifting the upper ribs and sternum, increasing thoracic volume and enhancing air intake. This is often seen during exercise or in individuals with respiratory difficulties.
Q: How does the Hering-Breuer reflex influence breathing?
A:
The Hering-Breuer reflex is a protective mechanism that prevents over-inflation of the lungs. Stretch receptors in the lungs detect excessive expansion and send signals to the respiratory center in the brain. This triggers the switch from inhalation to exhalation, preventing lung damage from over-inflation. The reflex helps regulate breathing depth and rate, particularly during deep breathing or in infants.
Q: How does the concept of compliance relate to breathing mechanics?
A:
Lung compliance refers to the lungs' ability to expand and contract in response to pressure changes. It's a measure of the lungs' stretchiness or elasticity. High compliance means the lungs expand easily with small pressure changes, while low compliance requires more effort to inflate the lungs. Factors affecting compliance include lung elasticity, surfactant function, and chest wall flexibility. Proper compliance is crucial for efficient breathing and gas exchange.
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