Animals have different types of breathing , such as lung and gill breathing. The types of breathing are directly related to the place where each animal lives. Gills, for example, are found in animals that need to extract oxygen from the water , while cutaneous, tracheal and pulmonary respiration are generally observed in terrestrial animals.
Respiration is essential for the survival of living beings , and in animals it guarantees the capture of oxygen, which will be used in the process of cellular respiration to, together with glucose , produce the energy needed to carry out their vital activities.
Types of animal breathing
Different types of breathing can be verified in animals, such as cutaneous, gill, tracheal and pulmonary. We will now explore each of these types better, looking at how they ensure the capture of oxygen and in which animals they are found.
Respiration by simple diffusion directly across the cell membrane
Diffusion is a process in which substances move from one environment, where they are more concentrated, to another, where they are in lower concentration .
In poriferans and cnidarians , oxygen passes from the water, by diffusion, to the interior of the cell , where it is less concentrated. Carbon dioxide travels in the opposite direction, passing from the cells to the water. In these animals, this is possible, because their body is relatively simple and the cells are very close to the external environment, favoring the rapid diffusion of gases to the cell.
In aquatic animals, the presence of gills is common. These, however, vary from one species to another. In crustaceans , for example, they are long and feathery and covered by an exoskeleton. In echinoderms , like the starfish, the gills are tubular projections from the skin. In the axolotl , they are external. The best known of these is the gill present in fish . In these animals, there is the presence of gill arches from which two rows of filaments start, formed by flattened plates called lamellae.
The fish are able, through the gills, to capture about 80% of the oxygen dissolved in the water as it passes through these structures. In these animals, water enters through the mouth and leaves through the gills. In the gills, the oxygen present in the water passes through the blood capillaries present in the lamellae.
It is important to note that not all fish have gill breathing exclusively. So-called lungfish have reduced gills . In this group, we see a kind of primitive lung , which is connected to the animal’s pharynx.
In some animals, such as earthworms and some amphibian species, gas exchange occurs through the skin, which is highly vascularized. The presence of a large network of capillaries located just below this body lining provides an exchange of gases between the external environment and the blood .
In insects , tracheal breathing is observed. In this respiratory system, we have tubular structures called tracheas, which open to the outside of the animal’s body. These windpipes branch throughout the body, reaching virtually the surface of every cell. At the tips of its ramifications, a moist epithelium can be seen, which allows gas exchange with the cells. In these animals, the involvement of the circulatory system in the transport of gases is not observed .
Filotracheal or foliate lung breathing
In arachnids it is possible to observe, in some species, the presence of structures called foliate lungs or phyllotrachea . These organs, adapted to carry out gas exchange, resemble the leaves of a book, being formed by several sheets contained in an internal chamber. This chamber communicates with the outside through an orifice, and hemolymph circulates between the sheets. The entry of air ensures oxygenation of the hemolymph.
Pulmonary breathing occurs in all terrestrial vertebrates. In amphibians , it can be seen that, in addition to pulmonary respiration, these organisms need gas exchange performed on the surface of their body (cutaneous respiration). In reptiles , birds , and mammals , however, all respiration takes place through the lungs. An exception to this statement is turtles, which have accessory respiration. In these animals, gas exchange is observed in organs such as the cloaca and the pharynx.
Although all terrestrial vertebrates have lungs, they have some differences from one group to another. In amphibians, for example, the lungs appear as simple sacs, having few divisions inside. In the other groups, however, they are more subdivided, having a larger surface for gas exchange.
In mammals , we observe a wide surface for gas exchange , the lung being formed by thousands of alveoli , which are species of small air sacs located at the end of the bronchioles. Gas exchange in these animals takes place at these sites, which are surrounded by several capillaries.
In birds, gas exchange takes place in channels called parabronchi and not in the alveoli, as in mammals. In the respiratory system of these animals , the presence of air sacs connected to the lungs is also observed, but not directly linked to the gas exchange. These bags act by providing greater air circulation in these organs. In birds, it is necessary to perform two cycles of inspiration and expiration for the air to pass through the entire respiratory system.