GGG0604C

The Mammals That Live
In The Sea

In guide 4, we are going to learn about the 5 more common kinds of respiration you can find. As you have learned, all mammals breathe through their lungs and in the alveoli is where gas exchange takes place. But there was a group of animals that a long- long time ago returned to the sea after having constructed lungs and a life on earth. Those animals are dolphins and whales; among others, and they have some adaptations in their respiratory system in order to survive.

Dolphins, like other mammals, need air to survive, especially oxygen. Oxygen is one of the main sources of energy in the body and every living thing cannot make it without it. Unlike fish, dolphins have to rise to the surface frequently to breathe. When they are underwater, they hold their breath; when they are out of breath, they return to the surface to take in more fresh air.

Unlike other mammals who breathe through their nostrils and mouth, dolphins breathe through the blowhole, which is situated on the top on its head. A reason for this difference is that the blowhole will facilitate the breathing at the surface of the water. Since the blowhole is at the top of the head, only a small region of the head is required to break the surface of the water to inhale air.

The dolphin starts to exhale before reaching the surface and this helps to reduce the amount of time spent breathing at the surface. Dolphins can catch a breath about five times in a minute before diving again, without hindering the progress of their swim. Usually, a dolphin breathes two to four times each minute when it is swimming near the surface. It can hold its breath for seven minutes or more when it is diving.

The lungs of dolphins are not significantly larger or smaller than the land mammals. Obviously, the size of the lungs does not determine the amount of oxygen that can be stored and utilized.

However, the dolphin lungs contain a lot more alveoli (air cells) than human lungs do. Dolphin lungs are made up of two layers of capillaries, and this arrangement increases the efficiency of gas exchange since most mammals have only one layer of capillaries. Therefore, this means that the surface area of the lungs have been greatly increased and gas exchange can occur more quickly.

As mentioned in the earlier section on lungs, the size of the lungs is not the main reason for the dolphin's diving prowess. Even if the lungs are totally filled with air, it will not enable the dolphin to sustain dives as long as fifteen minutes. The main reason why dolphins can hold their breath so long is because of the adaptations made in the circulatory system. These adaptations have greatly increased their capacity to store oxygen and improved the efficiency of oxygen usage.

They have to be prepared to deep diving, they have to reduce their respiration needs and also have the nose in the top of their heads so that they can breathe more easily.

In this picture you can observe the Respiratory system of the dolphins.

Whales are mammals who breathe air into their lungs. Blowholes are a whale's nostrils and are located on the top or back of the whale's head. Blowholes are covered by muscular flaps that keep water from entering them when the whale is under water. In the relaxed state, the flap covers the blowhole. A blowhole leads to the whale's trachea and then to its lungs. Unlike us, whales cannot breathe through their mouth; they only breathe throught their blowholes.

Baleen whales (like humpbacks, blue whales, gray whales, bowhead whales, etc.) have two blowholes, located side by side. Toothed whales (like sperm whales, beluga whales, dolphins, etc.) have one blowhole.

At the surface of the water, whales open their blowhole(s) and exhale air explosively through their blowhole. This exhaled air from the blowhole is called the blow and usually forms a gusher or a bushy stream of misty air and vapor. This is immediately followed by inhalation of fresh air, and the blowhole(s) close again. (Blowholes are in a closed position when the whale relaxes.) This breathing pattern takes only a fraction of a second for small cetaceans (dolphins and tortoises), but it may take a few seconds for larger whales.

Just before a whale dives underwater, strong muscles surrounding the blowhole relax and the protective flap covers the blowhole.

Whales cannot breathe through their mouths (like people can). Their trachea (the tube to the lungs) and esophagus (the tube to the stomach) are not connected.

Fish can breathe inside the water by a very different manner: They have gills that help them to exchange gases.

The gills are the primary respiratory organ of the fish. The gill epithelium of the fish is the major site of gas exchange. These functions are vital not only to the quality of its life, but for the very existence of the fish. Therefore, when fish are exposed to enivronmental pollutants, these vital functions could be in jeopardy. Several studies have been alone on the effects of such pollutants as ammonia, posticides, metals, nitrites and petroleum hydrocarbons, and all showed that gills are damaged often exposure to such pollutants.