“Breathing in, I calm body and mind. Breathing out, I smile. Dwelling in the present moment I know this is the only moment.”
― Thich Nhat Hanh, Being Peace
In yoga everything begins with the breath. We initiate each movement with an inhalation or exhalation and are constantly reminded by our teachers to take our awareness to our breathing. We even practice different forms of pranayama (breathing techniques) that create incredible changes throughout our bodies. By looking at how the respiratory system functions we can answer questions like ‘Why do we breathe through our nose in yoga?”. But first let’s tackle the basic question ‘How does the respiratory system work?’.
Our breathing relies on the principle that air always moves from an area of higher pressure to lower pressure. The catalyst for pressure change within our bodies is the diaphragm. The diaphragm is located at the top of the abdominal (stomach) cavity and the bottom of the thoracic (chest) cavity. Its range of motion is relatively from the nipple to navel.
When we inhale, the diaphragm contracts and lowers down towards the abdomen. This increases the volume of the chest cavity. As volume increases, pressure decreases as there is more room for the air to move about freely. Air outside of our bodies is at a higher pressure relative to the air within our chest cavity so it begins to flow into our chests, attracted to this area of lower pressure. Conversely, when we exhale our diaphragms relax and press upwards towards the lungs and heart, decreasing the volume of our chest cavity. As a result the pressure within our chest becomes greater than the air outside. Air rushes out of our bodies, attracted by the lower pressure outside.
As the diaphragm lowers, air enters our nostrils or mouth and makes its way down to our windpipe, called the trachea. (To learn why nostril breathing is much more effective than mouth breathing continue reading the next section.) From the trachea, air splits into two bronchi, leading to the right and left lobes of the lungs. These bronchi branch off into smaller bronchioles which eventually lead to millions (around 300 million!) of tiny air sacs called alveoli. These alveoli are surrounded by very tiny blood vessels called capillaries.
Red blood cells coursing through the capillaries exchange carbon dioxide picked up from their travels through the body for fresh oxygen. This exchange occurs through the process of diffusion. Once the hemoglobin within the red blood cells has received fresh oxygen, the blood travels back to the left side of the heart where it is pumped to the rest of the body where the oxygen is used wherever needed.
Diffusion requires gases to dissolve into liquids before transferring membranes. Water is the main component of our blood and is necessary for the exchange of oxygen and carbon dioxide.
Sea animals such as fish do not need lungs in order to exchange oxygen and carbon dioxide because they are surrounded by water. This presence of water allows them to extract oxygen from their surroundings with only gills. Similarly, a newt does not contain lungs, but a newt needs to be near a water supply to keep its skin moist to allow for respiration. If you were to take a newt and mistakenly place it in a terrarium without water as a pet, it would slowly start to suffocate because the requirement of liquid for respiring is not met.
The human body is made primarily of water and we have our own air humidifying systems within our nostrils. Our nostrils are specifically designed for respiration in many different ways, making them more ideal for breathing than our mouths as we will see in the following post.