On the Rein-Cords Fixed to the Chariot of the Sun

 The lungs is, essentially, the hierarchy of bronchial conduits. Starting from the level of the primary bronchus down to the level of the acinus, there are, broadly speaking, three classes of conduits – the bronchi, the bronchioles and the respiratory bronchioles. Now, the "sun" of the Puranas, strictly speaking, is the neural entity innervating this network of conduits. The nerves trunks emanating from this chief innervating entity coursing along the  bronchi are imagined by the ancient anatomists, those keen watchers of the landscape of the microcosm, as the "sun" himself traveling in his resplendent (bronchial) chariot.

Now, as previously noted, a chariot has a carriage which is connected to components that enable it to move. Thus we have a wheel and the horses which do the job of pulling (extending) the carriage and moving it forward. In the context of the bronchial chariot, these would be the lower order bronchi or could even be the bronchioles. The idea sought to be conveyed, through a very sophisticated metaphor, is that the lungs is essentially a set of interconnected entities; the lower order bronchi and the bronchioles extend the bronchial conduit and carry the innervating entity to the furthest and deepest (distalmost)  regions of the lung. Of course, the wheel and the horses do not pull and move the carriage directly. They are fitted to two other components of the chariot, the axle and the yoke. The former connects the wheel while to the latter the horses are fitted. 

In the following lines taken from the Brahmanda Purana, this bronchial chariot is said to have two "rein-cords" fastened to it, at the extremities of the axle and the yoke. These are the pulmonary arteries. They are said, further, to "revolve" in Dhruva which we have identified previously as the pulmonary trunk, but which may, in a more strict sense, stand for a particular neural entity. 

"Revolving" is used by the Puranic authors in the sense of "enclosing." An entity (such as a conduit) is said to "revolve" around another entity if it "encloses" it  or travels along all its "sides" or "directions." The lower order bronchial conduits, in this manner, "revolve" around the higher order bronchi, accompanied by their respective pulmonary arterial conduits which remain fixed, ultimately, in Dhruva, the pulmonary trunk. 

76. There are two rein-cords [pulmonary arterial conduits] fixed to the extremities of the yoke and the axis [bronchial conduits] of the chariot. Those two rein-cords revolve in Dhruva [pulmonary trunk] (and perform the function) of a pair of wheels. 

79. The extremities of the yoke and the axis [bronchial conduits] of the chariot revolve all round along with the rein-cords [pulmonary arterial conduits] like the rope fixed to a peg.

It must be noted that the pulmonary arterial conduits are not literally fixed to the bronchial conduits. It is only at the level of the alveoli that there is some sort of a direct connection. What the author seeks to indicate here, perhaps, is the physiological interdependence of these two entities. Anatomically, this "fixing" can only be in the sense of "as it were."

The Wind Named "Parivaha"

 According to the Brahmanda Purana, the name of the "wind" transporting the Ganga of the "sky" – the deoxygenated pulmonary flow originating from the heart (pulmonary trunk) and arriving into the lungs from the "outer space" of the mediastinum and traveling to the respiratory zone by means of the pulmonary arterial conduit and its branches – is "parivaha." Further, this "wind" is the (physiological) support of Parjanya and the dik gajas:

The sixth wind [conduit of circulation] named Parivaha is their support. This powerful (wind) holds up the Ganga of the firmament [...] The Ganga is situated in the path of Sviti (i.e. firmament) in three currents.

The Progress of the Ganga

 The progress of the Ganga described in the passages is clearly from the central axial region of the primary (Meru) and secondary bronchus (its base) to the "filament" region (segmental bronchus) to the region of the "petals," the sub-segmental region in which Bharata is situated. 

The Sun Sucks the Water of the Entire World

 According to the Brahmanda Purana (chapter 22, 12), "Presided over by Dhruva, the sun takes up water and showers it."  

 The lungs suck, as it were, the "water" of deoxygenated blood coming in to the heart from the systemic circulation. This oxygen-deprived flow enters the lungs by means of the pulmonary trunk ("presided over by Dhruva"). The deoxygenated blood of the body enters into pulmonary circulation. The sun (lungs), in this manner, sucks the water of the entire world:

With the mass of his rays [bronchial conduits] and accompanied by the wind [pulmonary artery] all round, the sun takes away the water of the entire world.

This "water" of deoxygenated blood is reoxygenated in the lungs – in the acinar region – and the "water" now returns to the heart for re-entering into systemic circulation as a rich and vivifying liquid. It is the pulmonary vein – the moon of the Puranas – that does this work of completing the pulmonary circulatory loop. 

The moon [pulmonary veins] transmits the entire water [flow of blood] drunk by the sun [lungs].

Therefore the function of the lung is not to change the volume of the "water" coming into it but to change the character of the liquid flowing through it: 

There is no total destruction of water. The same water gets transformed.

The terms "usna" (hot) and "sita" (cold) undoubtedly refer to deoxygenated and oxygenated blood respectively. The deoxygenated flow is always imagined as "deadly," as "fierce," "fiery" and "hot" – the pulmonary arterial conduit, as noted elsewhere, is given the code of "fire" – while the polar opposites of these concepts are associated with the oxygenated flow. 

The Usna (hot virility) [deoxygenated blood] oozes out of the sun [bronchial tree], and the Sita (chill virility) [oxygenated blood] functions from the moon [pulmonary veins].

The next few lines declare the supreme fact that this entire apparatus of the lungs is a peerless – almost magical – creation of the Lord:

 It is for the sake of sustenance of all the worlds [bodies / regions of the body] that this cosmic Maya has been created (by the lord).

Cloud Formation 

But the "sun" does not merely take up "water" and shower it (v. 12 above). Before such showering can take place, the "clouds" need to be formed. There is a process of combining of entities. The bronchial conduit and the pulmonary arterial conduit taken together, are referred to as "cloud" and it is the showering of these two entities in unison that gives rise to "rain" (oxygenated blood). 

The concept of "cloud," properly speaking, pertains to the respiratory zone (the acinus) and not the conducting zone. However, reading the extracts from the Puranas, one gets the impression that even the conduits in the conducting zone are referred to as "clouds." 

For clouds to be formed, both the bronchial conduits and the pulmonary arterial flows would need to be "vaporized." This means that the bronchial tubes have now, at the acinus, become so thin and wispy that they have become as subtle as vapor. Correspondingly the pulmonary flows  too have become extremely "emaciated."

The pulmonary arterial conduit is seen as a great cosmic heater (in contrast to the pulmonary veins which are imagined as a cooler) which is transforming the liquid poured into it – the deoxygenated blood – into smoke. 

At the same time, by virtue of its close proximity to the bronchial tree, it is also seen as incinerating the entire creation. We will see later how this image forms the basis of the practice of the yajna. 

The bronchial tree comprises both weighty conduits like the bronchi which are relatively unmoving. These make up the "immobiles" of the creation (such as the mountains and the giant trees). On the other end, we have the smaller bronchial conduits divested of cartilage – the bronchioles and the respiratory bronchioles – which are like birds. They are light and relatively "moving" – they dilate and constrict much. These are the "mobiles" of the creation. 

22. (The Ganga), the great rivers [pulmonary arterial flows] beginning with Bhadrasoma and the waters [ deoxygenated blood] (humids) that flow within the bodies [bronchial conduits] of all living beings mobile and immobile, become smoke (i.e. vapour).

23. When the mobiles and immobiles [bronchi and the bronchioles] get heated (and burnt) they spread everywhere as vapour.

As a result of this "vaporization" of conduits within the lungs, the clouds are formed in the respiratory zone: 

24. Clouds are formed thereby. It is remembered that the abode (waters) is full of clouds (or, is in the form of clouds).

It may be because the respiratory zone of the lung is full of "clouds" that it is referred to as the "waters" in the Puranic texts.This line seems to give the definition of the "waters."

Deciphering the Clouds

 

"Clouds" rain in the acinar region 

The central axes, 7-8 in number, as we have seen already in the chapter on geography, are referred to as the Meru and the heavenly regions. These regions are Ramyaka, Kimpurusa and the rest. In these regions, it is said that Indra never pours down rain. Therefore there can be no question of sighting clouds in this portion of the bronchial lotus. Therefore it is said that the sun merely draws the water from these places, through the pulmonary artery. This is the heavenly water that is being drawn and the pulmonary flow is given the name of the heavenly Ganga or Ganga in the sky. It is only in the levels of the bronchial tree following these levels that the clouds are imagined. This would be the bronchiolar region; from this region onwards, the sun (bronchial conduit) no longer sucks but only pours. Different kinds of clouds are imagined. 

Movements Along the Bronchial Conduit : Creation, Destruction, Day and Night

 The bronchial conduit is regarded as the sun in the same sense as it is regarded as a dik gaja. It is in the sense of "anatomical compass." The bronchial conduits illuminate the interior of the lung, as it were, by making clear the "directions." As the bronchial lotus expands and unfolds, we have the movement of day synonymous with vivification and creation; and as it contracts and folds back, we have the movement of destruction and expiration of the universe. 

The movement of day which is from the hilum of the lung to the region of the acinus, is also the path taken by the oxygen molecules to reach the respiratory zone and, therefore, matches beautifully with all the vivifying aspects associated with "day;" while the movement of night which is from the acinus to the hilum – the path taken by the molecules of carbon-dioxide to exit from the lung – is fittingly described as a movement of destruction. Not only does this movement finish off the bronchial tree anatomically but, physiologically also, it is associated with the carrying of a deadly substance (carbon-dioxide). It also ends a cycle of inspiration and expiration; and the creation of a "new" world is set to begin with a new cycle. 

The Three Divisions of the Ganga

The deoxygenated pulmonary flow, the Ganga, first travels through the "sky," the foremost part of the pulmonary arterial conduit network. Then it is borne by the "wind" in the secondary division of the pulmonary arterial tree (corresponding to the bronchioles?). And, finally, this flow, assuming the name of "Sita," enters the "fire" at the level of the acinus.

She is three-fold as the river of sky, earth, and the lower regions, tripathaga, trilokaga, etc.

Sita's Entering Fire in Lanka 

The deoxygenated flow, enters the "fire" of the pulmonary arterial conduit in the "lower" regions –the acinus –and becomes exceedingly pure.