The process of breathing usually occurs when there is a movement and exchange of air between the environment and the alveoli of the lungs.  It involves a very simple mechanism of two events: the first is inspiration, where the air is taken into the lungs, and the second is expiration, where the air is expelled out of the lungs into the atmosphere.  The entire process is known as respiration, which has four steps or parts: breathing, gas diffusion, gas transport, and regulatory process.  The pathway for the same is provided through airways that travel to and from the lungs to external orifices, which together form the Respiratory System, which is found to be in the chest cavity.

Key Facts About the Breathing Mechanism of Humans

The chest cavity or the thoracic cage and its walls in humans enclose the respiratory system and its various structures and have a very important function in pulmonary ventilation, the Breathing mechanism in humans.  The diaphragm and its supporting muscles are also involved in the function of breathing in humans.  The Respiratory centre that is located in the brain stem of the human brain is responsible for controlling the action or process of breathing in humans.

The Mechanical Components of the Breathing Mechanism 

The mechanical components of the breathing mechanism in humans include –

1. Thoracic Cage consists of the sternum, rib bones 12 in number, and 12 bones of the thoracic vertebrae. 
2. Inspiratory Muscles – includes the diaphragm and the intercostal muscles.

The Airways of the Breathing Mechanism 

The different airways involved in the Breathing mechanism include –

1. Conducting Airways – includes the nose, nasopharynx, larynx, tracheal tract, bronchi and bronchioles, 
2. Respiratory Zone – includes the respiratory bronchioles and alveoli

The Breathing Cycle 

The breathing cycle takes place in two distinct events.

1. Inspiration is the process of inhalation or taking air from the atmosphere into the lungs through the external nasal orifices.  This is facilitated by the diaphragm muscle, which contracts and pulls down; the intercostal muscles also contract, allowing the rib cage to expand to accommodate the lungs, which enlarge on taking in the air.
2. Expiration is the process of exhalation or expelling out air from the lungs into the atmosphere through the external orifices of the nose.  This is facilitated by the relaxation of the diaphragm, after which the muscle returns to its original position.  The intercostal muscles also relax, and the rib cage collapses on expelling out air. 

Respiratory Centre 

The respiratory centre of the Breathing Mechanism of Human consists of the neural and neuronal groups of the medulla oblongata and the brainstem’s pons structure. 

1. Dorsal Respiratory Group – it is the inspiratory centre of the respiratory system that controls the inspiration in the breathing mechanism.
2. Ventral Respiratory Group – it is responsible for forced respiration in the body.
3. The Pneumotaxic Centre is responsible for controlling the rate and depth of breathing in humans. 

Breathing Mechanism in Humans 

The key components discussed above play a vital role in carrying out the whole process of breathing and respiration.  The lungs are usually expanded and contracted or relaxed in two distinct ways.  The first method includes shortening and lengthening of the chest cavity of humans, and the second method involves an increase and decrease in the anteroposterior diameter of the chest cavity.  The two phases of breathing are Inspiration and Expiration.

Inspiration 

The process of inspiration involves the inhalation or taking in of air from the environment into your lungs.  It is an active process.  The diaphragm carries out normal and quiet noiseless inspiration by lengthening and shortening the chest cavity.  The diaphragm contracts and pulls the chest cavity lower, along with the elevation of the rib cage by the external intercostal muscles.

In cases where an individual needs to breathe in a deep and forced manner, the accessory muscles play an important role by increasing the thoracic or chest cavity size.  They pull the sternum further along with the first two rib bones.  These accessory muscles are the Scalene, Serati anterior muscles and the Sternocleidomastoid muscles. 

Expiration 

The process of expiration is very passive.  In this process, the external intercostal muscles and the diaphragm relax, and everything takes place in reverse order from that of inspiration.  The intrathoracic volume of the chest cavity decreases as the area of the chest cavity decreases on relaxation; simultaneously, the intrapulmonary pressure also increases because of which the air is expelled out from the lungs into the nostrils.  This expulsion of air is continued till the internal pressure of the lung does not equal the external pressure in the atmosphere, after which the process of inhalation or inspiration starts. 

Conclusion 

The respiratory system of humans performs many functions, including gaseous exchange, gas transfusion, transport of gases, breathing process, and the regulation of gases within the alveoli of lungs and the atmosphere.  The various cells and anatomy of the respiratory system are well equipped to carry out all essential functions of the breathing mechanism of humans. The chest cavity or the thoracic cage and its walls in humans enclose the respiratory system and its various structures and have a very important function in pulmonary ventilation, the Breathing mechanism in humans. The diaphragm and its supporting muscles are also involved in the function of breathing in humans.