The odontoceti have in common a single blowhole to breath. It is actually the ancestor of the nasal orifices. During the cetacean evolution, their nostrils have migrated to the top of the skull. Thus they do not need to get the head out of water while resurfacing to fill in their lungs with air.

With the killer whale, the single blowhole ‘s purpose is the shutting of the respiratory ways when the animal is under water. Alongside the 2 nasal pipes, cavities (nasals) or vestibular bags are found. A tubular pipe creates a link between this bag and a new pocket (called pre maxilla bag). At a lower level, the nasal pipes will merge to end up in the larynx. 3 shutting down level can be found, the blowhole, each nasal pipe and finally the sphincter (peri laryngeal).

For the duration of the immersion, the blowhole stays shut thanks to powerful muscles. During the resurfacing, the body is slightly tilted and the blowhole will be the first to be in contact with the surface. Only then the killer whale decides (it is a voluntary action, not an automatic one) to open the blowhole, then it will expulse the hot air contained in its lungs.

This expulsion is quick and powerful, similar to a geyser. In fact, the hot air creates condensation when in contact with the colder ambient air. It becomes then small water drop (steam). Furthermore, in calm water, the killer whale sometimes expulses the air before being completely at the surface. This reinforces the geyser effect and creates a very characteristic noise. This vapour also contains micro drops of secretion used in the internal organ lubrication (pipe and blowhole) passed during the expulsion of the hot air.
Warning to the curious, the expulsed air is far from being nice and fresh.

The larynx is simple and efficient. The epiglottis creates a link, in a tube shaped between the nasal cavity and the trachea. The air admission in the lung is controlled by the peri laryngeal sphincter, which, by relaxing during the inhalation allows the larynx to open. Note that this sphincter crosses the pharynx (digestive system).
CAREFUL: do not mix up larynx (breathing) and pharynx (digestion).

Therefore the respiratory circuit is totally autonomous from the digestive circuit creating major advantage

• The air cannot pass into the stomach
• In immersion, water cannot pass into the lungs nor the nasal cavities
• In semi immersion, the killer whale can breath and/or hold on a prey, feed itself

The trachea is made of very strong cartilaginous rings.

The lungs are not too much more developed than terrestrial mammals (of similar sizes). The breathing surface is therefore similar.It is actually the ramification that is very developed, like a tree with numerous branches to increase the number of leaves. We also have 2 levels of capillary respiratory. Like the trachea, the bronchial tubes and bronchioles have cartilaginous rings. The tissues are abundant. The pleura is very thick, the elastic pulmonary alveolus are bigger.

But how can the killer whale stock so much oxygen. In fact, it can renew 80% of its air in one breath compared to 20% for human. When it dives at a certain depth, its heartbeat reduces to limit the oxygen requirements. The air does not remain in the lungs. It moves around the bronchial tubes and bronchioles (which are numerous), leading to the respiratory alveolus. This has the tremendous advantage of reducing the gas exchange with the tissues, thus avoiding decompression when coming up rapidly. Killer whales’ oxygen reserve is in the muscle. The latter are very rich in myoglobin (protein found in the muscle cells). Hence blood becomes a secondary oxygen reserve, half of the oxygen is stored there. However the killer whale has much more haemoglobin than the human and its myoglobin is much more concentrated. Therefore an enormous amount of oxygen can be stocked. The dive can consequently be longer. On top of that, the animal’s tissues can tolerate high carbon dioxide accumulation. The lactic acid, which is a metabolism waste from glucose, is stored in the muscles as well in order to make it harmless during the dives.
It is important to note that it is not the lack of oxygen that triggers the coming up to renew the air, it is the high rate of CO2 that will force it (toxicity).

Another interesting phenomenon. If you dive in a swimming pool, after having breathed in, you will realise that you exhale your air under water, go up to the surface and then inhale violently to fill in your lungs with air. If you observe the killer whale, they exhale the air, not in the water but out of water. Then they fill their lungs in with fresh air. The exhaling action before inhaling allows the nitrogen to regain its normal state, gaseous, and to be eliminated by the respiratory ways. The nitrogen is not dissolved in the blood, which would be fatal to the killer whale. Humans have this nitrogen bubble in the blood problem that causes numerous deaths to careless divers.

Finally, a complex network of blood vessels, called the admirable network (retia mirabilia), allows the storing of oxygen as well as the blood distribution to the vital organs, thus avoiding brain and heart suffocation (see cardio vascular).

It is important to note that unlike terrestrial mammals, killer whales have lost their sense of smell. Their nostrils, when migrating to the top of the head became the blowhole. The contact with the air being rarefied, the olfactory organs have progressively been atrophied.
The blowhole and nasal cavity only have a breathing function… (see origin).