In this article “Mechanics of Respiration or Breathing” we will discuss the respiration process in detail. Read this article to know how humans breathe. This article includes:

Introduction to Respiration

Respiration is a very important process in all living things, including humans. It helps us exchange gases with the air around us. We breathe in oxygen from the air, which our cells need to stay alive and do their work. At the same time, we breathe out carbon dioxide, which is a waste product of the cells. This process is crucial for our survival because it gives us the oxygen we need and gets rid of the carbon dioxide we don’t need. So, we can say respiration is like the “breathing” that keeps us alive and healthy. In this article, we will learn the mechanism of respiration.

Overview of the Respiratory System

The respiratory system is a complex network of organs and tissues responsible for the exchange of gases between the body and the external environment. It can be divided into two main parts: the upper respiratory tract and the lower respiratory tract, let’s discuss them:

human respiratory system

1. Upper Respiratory Tract

The upper respiratory tract comprises the nose, nasal cavity, sinuses, and pharynx (throat), let’s discuss them:

  • Nose and Nasal Cavity: The nose serves as the main entry point for air into the respiratory system. It contains small hair-like structures called cilia and mucous-producing cells that help filter, humidify, and warm the inhaled air, protecting the delicate lung tissues from harmful particles and pathogens.
  • Sinuses: These are air-filled spaces within the bones of the face, and they help to lighten the skull and add resonance to the voice. The sinuses are connected to the nasal cavity through small openings.
  • Pharynx: The pharynx acts as a common pathway for both the respiratory and digestive systems. It is involved in directing air from the nasal cavity into the lower respiratory tract and food from the mouth into the esophagus.

2. Lower Respiratory Tract

The lower respiratory tract includes the larynx (voice box), trachea (windpipe), bronchi, bronchioles, and lungs:

  • Larynx (Voice Box): The larynx is responsible for producing sound and protecting the lower respiratory tract from food aspiration by closing during swallowing.
  • Trachea (Windpipe): The trachea is a rigid tube that connects the larynx to the bronchi. It is lined with cilia and mucus-producing cells, which continue the filtration and moistening of the air as it travels further down.
  • Bronchi and Bronchioles: The trachea branches into two main bronchi—one leading to each lung—and further divide into smaller bronchioles. These airways continue to branch throughout the lungs, ultimately reaching the microscopic structures called alveoli.
  • Lungs: The lungs are a pair of spongy, elastic organs responsible for gas exchange. Within the lungs, the bronchioles terminate in tiny air sacs called alveoli. It is here that the exchange of oxygen and carbon dioxide takes place, as the oxygen diffuses into the bloodstream while carbon dioxide is removed from the blood and exhaled.

In the next section, we will discuss the Mechanics of Respiration.

Mechanics of Respiration

The process of breathing, also known as respiration, is a fundamental physiological function that ensures the exchange of oxygen and carbon dioxide in our bodies. It involves two main phases: inspiration and expiration. Let’s explore the mechanics of each phase in detail to understand how our respiratory system facilitates this crucial process:

breathing process


When we breathe in, our chest expands, and our lungs fill with air. This happens because our diaphragm moves down, creating more room in our chest for the air to enter. Let’s discuss inspiration in detail:

  1. Diaphragmatic Contraction: When we inhale, the diaphragm, a dome-shaped muscle located at the base of the lungs, contracts and moves downward. This action creates more space in the chest cavity, allowing the lungs to expand.
  2. Intercostal Muscles’ Role: In addition to the diaphragm, the intercostal muscles, located between the ribs, play a vital role in inspiration. They contract to lift the ribcage upward and outward, further increasing the thoracic cavity’s volume.
  3. Enlargement of Thoracic Cavity: The combined action of the diaphragm and intercostal muscles results in the enlargement of the thoracic cavity. This expansion reduces the air pressure within the lungs compared to the atmospheric pressure outside, creating a pressure gradient that drives air into the lungs.
  4. Intrapleural Pressure Changes: During inspiration, the intrapleural pressure (pressure between the lung’s outer surface and the chest wall) decreases. This reduction in intrapleural pressure helps keep the lungs adhered to the chest wall and prevents lung collapse.


During expiration, we breathe out by relaxing our breathing muscles, like the diaphragm and intercostal muscles. This relaxation reduces the space in our chest, causing air to be pushed out of our lungs. Let’s discuss it in detail:

  1. Passive vs. Active Expiration: Expiration can occur in two ways: passively and actively. Passive expiration primarily involves the relaxation of the diaphragm and intercostal muscles, allowing the chest cavity to recoil and decrease in size. In contrast, active expiration involves the use of additional muscles, such as the abdominal muscles, to forcefully compress the abdominal contents and push air out of the lungs.
  2. Relaxation of Diaphragm and Intercostal Muscles: During passive expiration, the diaphragm and intercostal muscles relax, returning to their resting positions. This action reduces the volume of the thoracic cavity, increasing the air pressure within the lungs.
  3. Decrease in Thoracic Cavity Size: As the thoracic cavity decreases in size, the air pressure inside the lungs becomes higher than the atmospheric pressure outside. This pressure gradient causes air to flow out of the lungs, facilitating expiration.
  4. Intrapleural Pressure Changes During Expiration: During expiration, the intrapleural pressure increases back to its original value. This slight increase in pressure helps maintain the close relationship between the lungs and the chest wall, preventing lung collapse and ensuring the optimal functioning of the respiratory system.

In the next section, we will discuss the Factors Affecting Respiratory Mechanics.

Factors Affecting Respiratory Mechanics

Respiratory mechanics is all about how we breathe and the important things that affect our breathing. Three main factors play a big role in this process and can affect how well we can breathe and stay healthy. Let’s delve into the three key factors affecting respiratory mechanics: Lung Elasticity, Airway Resistance, and Surface Tension, let’s discuss them in detail:

  1. Lung Elasticity: Lung elasticity is how our lungs can stretch and bounce back when we breathe. It’s like a rubber band that helps us breathe easily. When our lungs are healthy, they work well. But in some lung problems, they become stiff, making breathing harder.
  2. Airway Resistance: Airway resistance is like a roadblock for the air in our breathing tubes. Usually, the air can flow easily through these tubes, but in conditions like asthma or bronchitis, they become narrow, making it difficult for air to move in and out.
  3. Surface Tension: Surface tension is a force that tries to collapse the tiny air sacs in our lungs when we breathe. But our body has a special substance called surfactant that prevents this collapse, helping us breathe without any trouble.

In the next part, we will discuss the Respiratory Disorders Related to Mechanics.

Respiratory Disorders Related to Mechanics

Respiratory disorders are medical conditions that affect the normal functioning of the respiratory system, including the mechanics of breathing. Three common respiratory disorders related to mechanics are asthma, chronic obstructive pulmonary disease (COPD), and restrictive lung diseases. Each of these conditions impacts the respiratory mechanics in different ways, leading to various symptoms and challenges in breathing. Let’s discuss them in detail:

1. Asthma

Asthma is a long-term breathing problem that affects the tubes inside our lungs. These tubes are called airways. When someone has asthma, their airways become inflamed (swollen) and narrower, making it hard for them to breathe. The key features of asthma include:

asthma inflamed bronchial tube
  • Bronchoconstriction: The narrowing of the airways due to the contraction of smooth muscles.
  • Inflammation: Swelling and increased mucus production in the airways, further narrowing the passages.
  • Triggers: Asthma symptoms can be triggered by various factors such as allergens, respiratory infections, exercise, cold air, and stress.

2. Chronic Obstructive Pulmonary Disease (COPD)

COPD is a lung problem that usually happens to older people. It’s caused by breathing in harmful things like cigarette smoke or pollution for a long time. This leads to the following aspects:

Chronic obstructive pulmonary disease
  • Chronic Bronchitis: This involves inflammation and excessive mucus production in the bronchial tubes, leading to persistent cough and difficulty in clearing the airways.
  • Emphysema: Destruction of the air sacs (alveoli) reduces the surface area available for gas exchange, resulting in decreased oxygen uptake and carbon dioxide removal.
  • Shortness of Breath: Gradually worsens over time, making simple activities like walking or climbing stairs challenging.

3. Restrictive Lung Diseases

Restrictive lung diseases are a group of disorders that restrict lung expansion, leading to reduced lung volume. Unlike obstructive lung diseases like asthma and COPD, where airway obstruction occurs, restrictive lung diseases affect the lung tissue’s ability to expand properly. Common features include:

  • Interstitial Lung Diseases: Inflammation and scarring of the lung tissue, which hampers lung expansion.
  • Neuromuscular Conditions: Diseases affecting the nerves and muscles involved in breathing, causing weakness and reduced lung expansion.
  • Chest Wall Abnormalities: Structural abnormalities in the chest wall that limit lung expansion, such as scoliosis.
  • Symptoms: Shortness of breath, reduced exercise tolerance, and difficulty in fully expanding the lungs.


In the article “Mechanics of Respiration or Breathing,” we explored various aspects. Respiration is essential for all living things, including humans. It helps us exchange gases with the air around us. When we breathe in, our chest expands, and our lungs fill with air (inspiration). The diaphragm and intercostal muscles play a role in this process. When we breathe out, our chest gets smaller, and the air is pushed out of our lungs (expiration). Factors like lung elasticity, airway resistance, and surface tension affect how well we can breathe. Some respiratory disorders, like asthma and COPD, can make breathing difficult. Taking care of our respiratory system is vital for staying healthy.

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