“Every breath you take: the process of breathing explained”

January 8, 2018 | NursingTimes | source


“An inability to breathe normally is extremely distressing and the more distressed a person becomes, the more likely it is that their breathing will be compromised…we need to be able to get oxygen.”


“Breathing is central to life, as it allows the human body to obtain the energy it needs to sustain itself and its activities. But how does it work?


Breathing uses chemical and mechanical processes to bring oxygen to every cell of the body and to get rid of carbon dioxide. Our body needs oxygen to obtain energy to fuel all our living processes. Carbon dioxide is a waste product of that process. The respiratory system, with its conduction and respiratory zones, brings air from the environment to the lungs and facilitates gas exchange both in the lungs and within the cells. Nurses need a solid understanding of how breathing works, and of vital signs of breathing and breathing patterns, to be able to care for patients with respiratory problems and potentially save lives in acute situations.

Citation: Cedar SH (2018) Every breath you take: the process of breathing explained. Nursing Times [online]; 114: 1, 47-50.

Author: SH Cedar is associate professor and reader in human biology at the School of Health and Social Care, London South Bank University, and author of Biology for Health: Applying the Activities of Daily Living.

  • This article has been double-blind peer reviewed
  • Scroll down to read the article


The first question asked in an emergency situation is: “Is the person breathing?”. It is also often the first question asked about newborns and the last one asked about the dying. Why is breathing so important? What is in the breath that we need so much? What happens when we stop breathing? These might seem obvious questions, but the mechanisms of respiration are often poorly understood, and their importance in health assessments and diagnostics often missed. This article describes the anatomy and physiology of breathing.

Collaborating with green plants

We need energy to fuel all the activities in our bodies, such as contracting muscles and maintaining a resting potential in our neurons, and we have to work to obtain the energy we use.

Green plants take their energy directly from sunlight and convert it into carbohydrates (sugars). We cannot do that, but we can use the energy stored in carbohydrates to fuel all other reactions in our bodies. To do this, we need to combine sugar with oxygen. We therefore need to accumulate both sugar and oxygen, which requires us to work. As a matter of fact, we spend much of our energy obtaining the sugar and oxygen we need to produce energy.

We source carbohydrates from green plants or animals that have eaten green plants, and we source oxygen from the air. Green plants release oxygen as a waste product of photosynthesis; we use that oxygen to fuel our metabolic reactions, releasing carbon dioxide as a waste product. Plants use our waste product as the carbon source for carbohydrates.

Breaking chemical bonds

To obtain energy we must release the energy contained in the chemical bonds of molecules such as sugars. The foods we eat (such as carbohydrates and proteins) are digested in our gastrointestinal tract into molecules (such as sugars and amino acids) that are small enough to pass into the blood. The blood transports the sugars to the cells, where the mitochondria break up their chemical bonds to release the energy they contain. Cells need oxygen to be able to carry out that process. As every cell in our body needs energy, every one of them needs oxygen.

The energy released is stored in a chemical compound called adenosine triphosphate (ATP), which contains three phosphate groups. When we need energy to carry out an activity, ATP is broken down into adenosine diphosphate (ADP), containing only two phosphate groups. Breaking the chemical bond between the third phosphate group and ATP releases a high amount of energy.

Internal and external respiration

Our lungs supply oxygen from the outside air to the cells via the blood and cardiovascular system to enable us to obtain energy. As we breathe in, oxygen enters the lungs and diffuses into the blood. It is taken to the heart and pumped into the cells. At the same time, the carbon dioxide waste from the breakdown of sugars in the cells of the body diffuses into the blood and then diffuses from the blood into the lungs and is expelled as we breathe out. One gas (oxygen) is exchanged for another (carbon dioxide). This exchange of gases takes places both in the lungs (external respiration) and in the cells (internal respiration). Fig 1 summarises gas exchange in humans.

fig 1 gas exchange in humansSource: Peter Lamb

Bringing air into the lungs

Our respiratory system comprises a conduction zone and a respiratory zone. The conduction zone brings air from the external environment to the lungs via a series of tubes through which the air travels. These are the:

  • Nasal cavity;
  • Pharynx (part of the throat behind the mouth and nasal cavity),
  • Larynx (voice box),
  • Trachea (windpipe);
  • Bronchi and bronchioles.

Aside from conducting air to the lungs, these tubes also:

  • Warm the incoming air;
  • Filter out small particles from it;
  • Moisten it to ease the gas exchange in the lungs.

The nasal cavity has a large number of tiny capillaries that bring warm blood to the cold nose. The warmth from the blood diffuses into the cold air entering the nose and warms it.

The lining of the pharynx and larynx (which form the upper respiratory tract) and the lining of the trachea (lower respiratory tract) have small cells with little hairs or cilia. These hairs trap small airborne particles, such as dust, and prevent them from reaching the lungs.

The lining of the nasal cavity, upper respiratory tract and lower respiratory tract contains goblet cells that secrete mucus. The mucus moistens the air as it comes in, making it more suitable for the body’s internal environment. It also traps particles, which the cilia then sweep upwards and away from the lungs so they are swallowed into the stomach for digestion, rather than getting trapped in the lungs. This mechanism of moving trapped particles in this way is known as the mucociliary escalator.

The lungs are a little like balloons: they do not inflate by themselves, but only do so if air is blown into them. We can blow into the lungs and inflate them – which is one of the two techniques used for cardiopulmonary resuscitation – but that does not happen in the normal daily life of healthy people. We have to inhale and exhale air by ourselves. How do we do that?

Controlling the volume of air in the lungs

We have two lungs (right and left) contained in the thoracic cavity (chest). Surrounding the lungs are ribs, which not only protect them from damage but also serve as anchors for the intercostal muscles. Beneath the lungs is a very large dome-shaped muscle, the diaphragm. All these muscles are attached to the lungs by the parietal and visceral membranes (also called parietal and visceral pleura).”


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“An inability to breathe normally is extremely distressing and the more distressed a person becomes, the more likely it is that their breathing will be compromised… we need to be able to get oxygen.” Link





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