Mammalian dipping reflex: what it is and what it is used for.

A summary of the characteristics of the mammalian immersion reflex.

It's summertime and one of the greatest pleasures of the season is to immerse ourselves in the peace and calm of the sea or the swimming pool. Although we humans are not marine animals, we certainly miss being able to dive when the colder months arrive.

This calmness when submerging in cold waters has an evolutionary reason and we share it with other animals, especially mammals. This phenomenon is the mammalian submersion reflex and it turns out to be fundamental for the survival of many marine animals.

Below we will learn what awakens this reflex, what changes at the organic level it implies and how dive training influences its appearance.

Mammalian immersion reflex: definition

Sea or pool water brings us peace. It is when we enter this cold water that we begin to feel a deep sense of calm. This sensation is ancestral and has a very important evolutionary origin shared with the rest of the mammalian species. It is called the immersion reflex of mammals and it is It is enough to immerse oneself in cold water or to splash it on the face to start activating pleasant sensations..

Although this reflex is a very striking link with other mammalian species, it is especially present in aquatic mammals, such as seals, otters or dolphins, in which its appearance is a fundamental condition for their survival. In humans it is present in a very weakened form, but even so it involves a whole series of changes at the organic level that allow us to spend more time than expected submerged in water, whether fresh or salt.

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

How does it manifest itself?

The mammalian immersion reflex occurs whenever it comes into contact with water that is at a low temperature, usually below 21ºC.. The lower the temperature, the greater the effect.

Also It is also necessary that, in order for this mechanism to be activated, the water must be on the faceThe trigeminal nerve, composed of the ophthalmic, maxillary and mandibular nerves, is located there. These three nerve branches can only be located on the face and, when activated, initiate the reflex, which involves the following processes in the same order.

Bradycardia

Bradycardia is the slowing of the heart rate.. When we are diving it is necessary to reduce 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, so that the lower the temperature, the less the heart beats. There have been cases of people who have made only 15 to 5 beats per minute, which is very low considering that the normal is 60 or more.

2. Peripheral vasoconstriction

Peripheral vasoconstriction, or redistribution of blood, involves moving Blood to more important organs, such as the brain and heart.such as the brain and 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 fingers, and then give way to the feet and hands in their extension. Finally, the arms and legs contract, cutting off blood circulation and leaving more blood supply to the heart and brain.

This minimizes the possible damage caused by low temperatures and increases survival in case of prolonged oxygen deprivation. The adrenaline hormone plays a major role in this process, and is the hormone that may be behind this process.The adrenaline hormone is the one behind the fact that when we wash our face with very cold water we wake up faster.

3. Introduction of blood plasma

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

Blood plasma is also produced inside the lungs. When diving at shallow depths, more mechanically, some of the blood is introduced into the pulmonary alveoli. This protects them by increasing resistance against pressure.

This phase of the dive reflex has been observed in humans, as in the case of freediver Martin Stepanek, during apneas deeper than 90 meters. Thus, people can survive longer without oxygen under cold water than on land..

4. Spleen contraction

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 mammalian immersion reflex occurs, causing it to release part of its blood cells into the blood, increasing its capacity to transport oxygen. Thanks to this, it temporarily increases the hematocrit by 6% and the hemoglobin by 3%..

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

Conclusion

The mammalian immersion reflex is a mechanism that we humans possess, ancestral evidence that we have a common ancestor among birds and other mammals that had to live in aquatic environments. Thanks to this reflex, we can survive submerged for a more or less long period of time, trainable as would be the caseThanks to this reflex, we can survive submerged for a more or less long period of time, as in 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 as marine animals, the truth is that we can train our immersion capacity. We can be submerged for 10 minutes and there are even cases of people who have exceeded 24 minutes or more. Not only can we endure a long time underwater, but we can reach depths close to 300 meters.

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