Conducting Part of Respiratory System. The part of respiratory system, starting with the external nostrils up to the terminal bronchioles, constitutes the conducting part. The conducting part transports the atmospheric air to the alveoli, clears it from foreign particles, humidifies and also brings the air to body temperature.

In some industries, workers may inhale harmful dust. For example, workers in stone crushing plant may inhale silica dust. When there is long term exposure to such situations, lungs can develop inflammation, which leads to fibrosis and ultimately to serious damage to lungs.

Respiratory rhythm centre is primarily responsible for regulation of respiration. This centre is present in the medulla. Pneumotaxic centre, present in the pons region, also coordinates respiration. Apart from them, receptors associated with aortic arch and carotid artery, can also recognize changes in CO₂ and H⁺ concentration and send signal to the rhythm centre for proper action.

Alveoli are the primary sites of exchange of gases. Exchange of gases also occur between blood and tissues. O₂ and CO₂ are exchanged in these sites by simple diffusion mainly based on pressure/ concentration gradient. Solubility of the gases as well as the thickness of the membranes involved in diffusion are also some of the important factors that can affect the rate of diffusion. Pressure contributed by an individual gas in a mixture of gases is called partial pressure and is represented as pO₂ for oxygen and pCO₂ for carbon dioxide.

Alveoli are the primary sites of exchange of gases. Exchange of gases also occur between blood and tissues. O₂ and CO₂ are exchanged in these sites by simple diffusion mainly based on pressure/ concentration gradient. Solubility of the gases as well as the thickness of the membranes involved in diffusion are also some of the important factors that can affect the rate of diffusion. Pressure contributed by an individual gas in a mixture of gases is called partial pressure and is represented as pO₂ for oxygen and pCO₂ for carbon dioxide.

Steps of Respiration:
(i) Breathing or pulmonary ventilation by which atmospheric air is drawn in and CO₂ rich alveolar air is released out.
(ii) Diffusion of gases (O₂ and CO₂)across alveolar membrane.
(iii) Transport of gases by the blood.
(iv) Diffusion of O₂ and CO₂ between blood and tissues.
(v) Utilisation of O₂ by the cells for catabolic reactions and resultant release of CO₂

Anatomically, thoracic chamber is an air-tight chamber. The thoracic chamber is formed dorsally by the vertebral column, ventrally by the sternum, laterally by the ribs and on the lower side by the dome-shaped diaphragm. The anatomical setup of lungs in thorax is such that any change in the volume of the thoracic cavity will be reflected in the lung (pulmonary) cavity. Such an arrangement is essential for breathing, as we cannot directly alter the pulmonary volume.

Hypoxia is a pathological condition in which the body as a whole (generalized hypoxia) or a region of the body (tissue hypoxia) is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise. A mismatch between oxygen supply and its demand at the cellular level may result in a hypoxic condition. Hypoxia in which there is complete deprivation of oxygen supply is referred to as anoxia.

Inspiration is initiated by the contraction of diaphragm which increases the volume of thoracic chamber in the anteroposterior axis. The contraction of external intercostal muscles lifts up the ribs and the sternum causing an increase in the volume of the thoracic chamber in the dorsoventral axis. The overall increase in the thoracic volume causes a similar increase in pulmonary volume. An increase in pulmonary volume decreases the intra-pulmonary pressure to less than the atmospheric pressure which forces the air from outside to move into the lungs, i.e., inspiration.

The respiratory process is regulated by certainly specialised cebtres present is hindbrain.Amongst them, pneumotaxis centre is located in the dorsal part of pons varoli of the brain, can reduce the duration of inspiration and thus, alter the respiratory rate.

A person sleeping in such room gets carbon monoxide poisonong.CO combines with Hb more readily than oxygen forming carboxyhaemoglobin.This reduce the amount of free Hb available for carrying O₂ .Thus, the tissue is starved of O₂ .this is the reason why it is not advisable to sleep in closed rooms warmed with coals

Large number of chemoreceptors are located in the carotid bodies (lie bilaterally in the bifurcations of the common carotid arteries).
Their afferent nerve fibers pass through glossophatyngeal cranial nerve and thus to dorsal respiratory area of the medulla oblongta, sizeable number of chemoreceptors are also located in the aortic bodies (which lie along the arch of aorta)
Their afferent nerve fibres pass through the vagus cranial nerve and thus, to dorsal respiratory group of neurons

A specialised centre present in the medulla region of the brain called respiratory rhythm centre is primarily responsible for the regulation of respiration.Another centre present in the pons region of the brain called pneumotaxic centre can moderate the functions of the respiratory rhythm centre.Neural signal from this centre can reduce the duration of inspiration and thereby, alter the respiratory rate.

The foul air follows the route given below
Alveoli\(\rightarrow \)Alveolar ducts\(\rightarrow \)Bronchioles\(\rightarrow \)Bronchi\(\rightarrow \)Trachea\(\rightarrow \)Larynx\(\rightarrow \)Glottis\(\rightarrow \)Pharynx\(\rightarrow \)Internal nares\(\rightarrow \)Nasal chambers\(\rightarrow \)External nares\(\rightarrow \)Atmosphere.
The tidal volume increases 4-10 times during excitment and activity.