Introduction

All of us breathe day in and day out. It is an autonomous process; that is not in our control. We breathe when we sleep, we breathe when we exercise, and we breathe when we study and when we eat food. We breathe all the time irrespective of the work we do. Breathing is the most important vital function of the body which requires co-ordination of various organs known as the respiratory system.

Why do we breathe?

Our body is made up of cells which is the basic functional unit. Most of the higher organisms have evolved to obtain energy by using oxygen of the air as catalyst for the combustion of food in cells and production of metabolic energy in simpler words. Cells need oxygen to carry out all the metabolic processes and provide us energy. This energy is utilised for all other metabolic processes. Thus it makes the breathing most vital process without which we cannot survive.

What is respiratory system?

Respiratory system is a complex system which involves co-ordination of various organs. It has specialised tissues and cells that help in carrying oxygen rich air and later carbon-dioxide after gaseous exchange. Breathing starts through your nostrils but if congested or blocked as in common cold or as a habit people use mouth to breathe in air. Through your nostrils it travels down to trachea or wind-pipe and then through larynx or your voice box. The nasal cavity or mouth has a special function of warming and humidifying the cold and dry air that is breathed in as it irritates the lungs. The hair present in the nostrils entraps any foreign object that may cause irritation to lung mucosa. The saliva of mouth also acts in the same way. These particles are expelled either by coughing or sneezing.

Once the air has reached trachea, trachea divides into bronchi and bronchioles from which the air finally reaches lungs. Lungs are not just sac of air. They are formed of numerous small sacs alveoli just like bunch of grapes. These alveoli have numerous smaller blood vessels called capillaries. We have two lungs on either side of the sternum (breast bone). The left lung is a bit smaller than right lung to accommodate the heart. The lungs are further divided into five lobes. In some diseases removal of the affected lobe can bring relief and person can still breathe and lead a normal life. The lungs have rich blood supply. The blood vessels help in gaseous exchange. From here the oxygenated blood is taken to heart with the help of pulmonary veins from where it is taken to various parts of the body. Haemoglobin - the component which imparts red colour to the blood can bind four molecules of oxygen. Now this oxygenated blood is carried to heart from where it is taken to various parts of the body. When it reaches end organs oxygen is utilised by cytochrome oxidase a protein which utilises oxygen to produce energy. Carbon dioxide and water are the by-products. Water is used in another metabolic processes and carbon dioxide is again carried out by the haemoglobin as carboxy-haemoglobin to the heart where whole cycle is repeated again.

How breathing occurs?

To understand breathing process more accurately and clearly we can divide breathing process into two parts:

1. Inhalation or breathing in process
2. Exhalation or breathing out process

Inhalation

Inhalation is the process of breathing in air. To accommodate the inhaled air the diaphragm moves down by contracting. It increases the volume and gives away the space to expand lungs as the air is inhaled in. The intercostal muscles help enlarge the chest cavity by moving it upward or outward. When we breathe in air it is rich in oxygen. As the air is inhaled in through the nostrils it travels through the trachea and the bronchioles into the lungs. Once the air reaches the lungs and it then goes through the alveoli which has a very thin membrane and rich supply of capillaries. In the same time pulmonary arteries carry the carbon dioxide rich blood to the lung from heart. The gaseous exchange takes place through these capillaries as the haemoglobin has more affinity for oxygen than carbon-dioxide and oxygen rich blood is carried out to the heart by pulmonary veins. Once the oxygenated blood reaches heart it is carried to various parts of the body by heart.

Exhalation

The process of breathing out carbon dioxide rich air is called exhalation or breathing out process. For the air to be breathed out the diaphragm on contrary to inhalation relaxes and moves upward and hence causing a decrease in the volume of chest cavity. Chest cavity is also reduced by relaxation of intercostal muscles. It increases the pressure on lungs and air is exhaled out. The air that is exhaled out is rich in carbon dioxide. It travels out through the bronchioles, trachea, windpipe and nostrils. As compared to inhalation, exhalation is a passive process and does not utilise the energy of the body.

Control mechanism of breathing

Breathing is an autonomous process. It is controlled by the brain. Our brain has specialised respiratory centres located at the base of the brain. This respiratory centre sends signals to the various organs, nerves and muscles associated in the breathing mechanism. These signals maintain the rhythmicity of the breathing and maintain the regular interval at which lungs should contract or relax to breathe in and breathe out air. Though it is an automatic process still you can voluntarily alter your breathing rate by holding breath as in swimming or as in yoga practices. Your emotional and psychological state also affects your breathing rate by increased breathing in stress or panic.

The kind of physical activity you are involved in also affects the rate of breathing. Athletes and active sportsperson have higher breathing rate as compared to a person who has sedentary lifestyle. The physiological state of your body also affects the breathing rate. The respiratory regulatory sensor in brain regulates the rate of breathing by analysing oxygen demand of the body, the concentration of oxygen in blood, the pH of blood and oxygen consumption by different organs and muscles.

• The various sites regulate the breathing mechanism by giving a feedback to the regulatory system.
• Aorta and carotid artery check for the level of dissolved oxygen in blood.
• Irritants or foreign bodies are checked in airway itself and are expelled either by coughing or sneezing.
• The fluid accumulation in lungs is checked by the alveoli which as a result causes rapid and shallow breathing.
• In increased activity of the skeletal muscles, limbs and joints as in exercise, these cause for increased oxygen consumption and hence feedback for the faster breathing rate.

Now when we have understood the mechanism of breathing, we also know how important it is for us to breathe clean and fresh air. Breathing in clean and fresh early in the morning has many benefits. It is the time of day when pollution is least and oxygen concentration is most in the air. Breathing in fresh air rich in oxygen gives you a lot of energy and keeps you fresh throughout the day. So go out and have a long morning walk in the fresh air or practice breathing exercises in yoga.

Breathe fresh, stay fresh!