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In order to keep living our cells need the oxygen, available in the air we breath and that the body takes constantly and cycle-wise through breathing. Each cycle is made of two steps:  inhalation, when the air gets into the body full of oxygen, and exhalation, when the air gets out of the body full of carbon dioxide produced through our metabolic process. The air we breath gets out of our body with an average rate of 13/16 cycles per minute. The alternation between inhalation and exhalation is controlled by the respiratory centre, that is located in the medulla oblongata at the base of the skull.

The centre gets signals by the chemoreceptors about the level of carbon dioxide in our body: when such a level increases over a certain amount it gives the impulse to the respiratory apparatus to inhale and exhale again. Let’s briefly see which are the components of the respiratory apparatus following the path of the incoming air. 

Starting from the top we find the upper respiratory tracts: the two nostrils, the nasal cavities, the pharynx, the larinx and the trachea, splitting itself in the two bronchus that go down to the two lungs. Inside the lungs the bronchus  branch out in bronchioles ending up in alveoli, little cells where the gas exchanges do take place.

The lungs within the thorax are wrapped into the pleura, a double layer membrane allowing them to easily slide during the expansion and the contraction of the ribcage. The latter is made by 12 pairs of ribs, 10 of which are linked to the sternum (the first 7 pairs directly, from the 9th to the 10th through cartilages, the last two instead are fluctuant). The ribs are linked on the rear part to the dorsal vertebrae. The lungs are separated from the abdominal cavity by a cupola shake muscle that is fundamental in the biomechanical respiratory process, called diaphragm.

It is connected through a net of ligaments to the ribcage and to the spine up to the base of the skull, while in the lower part it is supported by the so called pillars of the diaphragm,two fleshy bundles connected to the lumbar vertebrae.

These are the parts of which the respiratory apparatus is composed, but how do they work during the respiratory act?


The cyclic alternation of inhalation and exhalation takes place tank to the activity of several muscles working right for the same aim. The most important one is the diaphragm, sinergically working with the ribcage muscles ant not only. The lungs in fact, per definition are passive organs, they cannot move autonomously to let air in and out, but they are expanded during inhalation, by the action of the diaphragm and the thorax inhalation muscles, or they are compressed by the exhalation muscles and by the abdominal muscles in case of forced exhalations.

The diaphragm is essentially an inhalation muscle: when its fibres contract, they lower it taking with them the lower portions of the lungs that expand and let air in.

Just to have an idea of what happens we can think the diaphragm as the piston of a syringe, while it goes down it sucks the air through the respiratory tract that in this example would represent the structure of the syringe.                                 

The diaphragm however does not work alone. During inhalation (fig: 2) it works together with the external and middle intercostal muscles that in synergy with other thorax muscles (scalenus, sternocleidomastoideus) are destined to the expansion and the contraction of the ribcage, increasing the thorax volume and by consequence the quantity of air within the lungs.

The rib motions are essentially two: one called “bucket handle”, expanding the thorax, and the other called “pump lever”, raising the ribcage. In the exhalation phase the diaphragm de-contracts going back its original cupola shape, the thorax muscles relax, the ribs lower and the thorax gets back to its original volume (fig. 3). During the exhalation there should not be a massive muscle action as it all happens by relaxation.

However there are some exhalation muscles playing a key role in case of forced exhalation or activities for which an increased air volume is needed. In particular the abdominals during the exhalation can help diaphragm to raise more, compressing the lower portion of the lungs while the thorax muscles (inner intercostals) get the ribs closer reducing the ribcage volume and further compressing the lungs, this way a larger quantity of air gets out during exhalation.

How much air do we breath?


Into the lungs always remains at the end of a maximum exhalation, a little quantity of air requested to keep the pressure balance with the environment, called residual volume (average 1000-1200 ml),  while the functional volume (average 300 to 500 ml) is the quantity of air going in and out at each respiratory act.

The inspiratory reserve volume is instead the  quantity of air that at the end of a normal inhalation, a person can stock in his lungs. Then the expiratory reserve volume defines the quantity of air that at the end of a normal expiration a person can let out of the lungs with a forced expiration. The sum of the inspiration and expiration reserve volume gives the vital capacity. By adding the residual volume to this value we obtain the Total Lung Capacity.

For all freedivers it is important to increase the vital capacity so  being able to use all the inspiration muscles, first of all the diaphragm, in order to have a greater quantity of air available to hold the breath longer. Let’s do not forget that also the expiratory muscles are equally important. Letting a greater quantity of air out allows to change that stock of air always present in the lungs. In practice by learning how to manage efficiently also the expiration phase we allow more oxygen in our lungs.

Do we all breath the same way?


Introduzione alla respiraione    jkdslfhkds

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