Mammalian immersion reflex: what it is and what it is for

It is summer and one of the greatest pleasures at this time is to immerse ourselves in the peace and calm of the sea or the pool. Although humans are not marine animals, we certainly miss being able to dive when the colder months arrive.

This calm when immersing ourselves in cold waters has an evolutionary reason and we share it with other animals, especially mammals. This phenomenon is the immersion reflex of mammals. and it turns out to be essential for the survival of many marine animals.

Next we are going to learn what triggers this reflex, what changes at an organic level it implies and how diving training influences its appearance.

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Mammalian immersion reflex: definition

Sea or pool water gives us peace. It is entering that cold water that we begin to feel deep calm. This sensation is ancestral and has a very important evolutionary origin and is shared with the rest of the mammalian species. It is called the mammalian diving reflex and

just dip in cold water or throw it on your face to start activating pleasant sensations.

Although this reflex is a very striking link with other mammalian species, it is especially present in mammals aquatic, such as seals, otters or dolphins, in which their appearance is a fundamental condition for their survival. In humans it appears in a very weakened form, but even so it implies a whole series of changes to organic level that means that we can spend more time than expected submerged in water, be it fresh or salty.

Although it is called a mammal, it also seems to manifest in marine animals such as penguins, which has led to the assumption that its true origin would be in a common ancestor between birds and mammals. It would be a mechanism that demonstrates the theory that birds and mammals come from the same ancestor and that they must have lived in the water.

How does it manifest?

The mammalian diving reflex It occurs as long as it comes into contact with water that is at a low temperature, normally less than 21ºC. The lower the temperature, the greater the effect.

Also It is necessary that, for this mechanism to be activated, the water falls on the face, since that is where the trigeminal nerve is located, made up of the ophthalmic, maxillary and mandibular nerves. It is these three nerve branches that can only be located on the face that, when activated, initiate the reflex, which implies the following processes following this same order.

1. bradycardia

Bradycardia is a slowing of the heart rate.. When we are diving it is necessary that we reduce the oxygen consumption and, for this reason, the heart begins to reduce the beats per minute between 10 and 25%.

This phenomenon depends directly on the temperature, meaning that the lower it is, the fewer beats are made. There have been cases of people who have only made between 15 and 5 beats per minute, something very low considering that the normal is 60 or more.

2. peripheral vasoconstriction

Peripheral vasoconstriction or redistribution of blood involves taking it to more important organslike the brain and the heart. The blood capillaries are selectively closed, while those of the major vital organs are kept open.

The first capillaries to contract are those of the toes and hands, to then give way to the feet and hands in their extension. Finally, those in the arms and legs contract, cutting off blood circulation and leaving more blood supply to the heart and brain.

In this way, the possible damage caused by low temperatures is minimized and survival is increased in case of prolonged oxygen deprivation. The adrenaline hormone plays a leading role in this process., and it is the one that would be behind the fact that, when we wash our faces with very cold water, we wake up faster.

• You may be interested in: "The theory of biological evolution"

3. Introduction of blood plasma

Blood plasma is drawn into the lungs and other parts of the rib cage, causing the alveoli to fill with this plasma, which is reabsorbed when exited into a pressurized environment. This way, organs in this region are prevented from being crushed by high water pressures.

Blood plasma is also produced within the lungs. When diving in low depths, in a more mechanical way, part of the blood enters the pulmonary alveoli. This protects them by increasing resistance against pressure.

This phase of the immersion reflex has been observed in humans, as would be the case of the freediver Martin Stepanek, during apneas greater than 90 meters deep. In this way, people can survive longer without oxygen under cold water than on dry land..

4. contraction of the spleen

The spleen is an organ located behind and to the left of the stomach, whose main function is the reserve of white and red blood cells. This organ contracts when the immersion reflex of mammals occurs, causing it to release part of its blood cells into the blood, increasing the capacity to transport oxygen. Thanks to this, temporarily increases hematocrit by 6% and hemoglobin by 3%.

It has been seen that in trained people, such as the Ama, some Japanese and Korean divers who are dedicated to collecting of pearls, the increases in these cells are around 10%, percentages close to what happens to marine animals such as seals.

Conclusion

The immersion reflex of mammals is a mechanism that human beings possess, evidence ancestral evidence that we have a common ancestor between birds and other mammals that had to live in environments aquatic. Thanks to this reflex, we can survive submerged for a more or less long period of time, trainable as would be the case of the Japanese and Korean ama or, also, the Bajau of the Philippines, populations dedicated to underwater fishing.

Although human beings cannot be considered marine animals, the truth is that we can train our immersion capacity. We can get to be submerged for 10 minutes and there are even cases of people who have exceeded 24 minutes or more. Not only can you endure a long time underwater, but you can reach depths close to 300 meters.

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