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(Dr. G.M.Karajgaonkar)

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A brief Outline of Structure and functions of the Lungs

Lung comprise of two main zones :

1. Conducting Zone - Concerned with gas and blood transport; and,

2. Respiratory Zone - Where gas exchange takes place between alveolar air and blood in alveolar capillaries.

Conducting Zone

A C-shaped band of cartilage supports the trachea and the main bronchus. The gap at the posterior surface is spanned by muscles and dense longitudinal elastic strands. As the main bronchus enters the lung, the cartilaginous portion together with muscles surround the larger intrapulmonary branches.. The main bronchus divides in lobar branches, segmental branches, and end is bronchioles in the alveoli. The size of lumen of bronchus diminishes with each division.

Bronchi are defined as airways proximal to the last plate of cartilage and contain mucus glands in their walls. Most distal are respiratory bronchioles and are involved in gaseous exchange across alveolar capillary membrane.

Respiratory Zone

This consists of alveoli capillaries that together form a membrane across which exchange of oxygen and CO2 takes place. These are the basic functional units of the respiratory system (on the lungs) known as acinus.

Alveoli are tiny thin sacs, like tiny bubbles, whose walls contain numerous collagen and elastic tissue. Respiratory gas exchange takes place in the alveoli. Elastic, collagen, and reticular fibers form the basement membrane separating thin sqamous cell wall on the alveolar side and capillary endothelium on the other. Average diameter of alveolus is around 250 micrometers and total surface area of billions of alveoli is about 75 Sq. meters. Alveoli are somewhat larger in size at the top of the lungs as compared to the base.

Respiratory Function

Air flow into the lung when intrathoracic pressure falls due to contraction of respiratory muscles, diaphragm being the most important. Accessory muscles of respiration are activated when larger intrathoracic pressure develops, for example as during exercise.

Expiration is quiet and passive breathing phase that occurs die to elastic recoil of the lungs after the end of inspiration. This is possible due to surface tension and elastic fibers present in the lung and alveoli.

Additional volume of the air that can be inspired after normal inspiration is termed as inspiratory Reserve Volume, and the term Vital Capacity is used to denote the volume of air that can be expelled out completely after the end of full inspiration.

 

 

Pranayama and Respiratory Functions

The lungs and the unit structure alveolous are elastic in nature, which due to the action of respiratory muscles and the diaphragm. In normal respiration, in inspiration the air fills the alveoli and oxygen is taken up and carbon-di-oxide is expelled out. But there is residual air containing CO2 in the alveoli. This residual air dilutes the oxygen content of air we breathe in, in the next cycle of respiration.

 

 

The exchange of gases (O2 and C02) depends on :

  • *  Surface area,

  • *  Time,

  • *  Concentration or partial pressure of the gases (PO2 and PCO2)

Basically in Pranayama there are four steps:

1. Deep inspiration, known as Purak, where fresh air is taken inside.
2. Holding of the breath, Kumbhak,
3. Expiration of breath, Rechak, where the air from the lungs (alveoli) is thrown out through the nose or mouth; it may produce sound variations,
4. After full expiration, holding of breath is called as Shunyak.

Their ration in time frequency is roughly about 4:2:5:2.

In Purak, i.e. in deep inspiration, the unit structure alveolus gets stretched so the more surface area is made available for the absorption of O2 abd giving out of CO2.

In Kumbhak, i.e. holding og breath after inspiration, the inspired air remains for longer duration of time in alveoli so that more time is available for the exchange and diffusion of gases.

In Rechak, i.e. long expiration with sound in throat, the air is expelled more effectively and while making sound in the throat the respiratory muscles, accessory muscles of the respiration, and diaphragm are put in extra action resulting in complete expulsion of air from alveoli. Hence when fresh air is taken in, in the next breath oxygen concentration in the alveoli is not diluted due to residual gases.

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