The breathing Consists of the air absorption and expulsion. Once the air enters the organism of a living being, it takes in certain substances and then expels it, already modified due to the process.
Living beings breathe in air to receive oxygen that fixes in the blood and then exhales to eliminate carbon dioxide. This process of gas exchange is known as hematosis and it develops with different organs according to the species.
The gill respiration is one that is carried out through gills (Structures also known as “gills”). A large number of aquatic animals have these organs that allow them to absorb the oxygen found in the Water and remove carbon dioxide.
The fishes, in this way, they use the gills for the absorption of oxygen, which then passes into the blood and reaches the fabrics. The respiration process is completed when the animal expels the carbon dioxide that is produced in cellular respiration.
While the lungs what have the Humans and other mammals are internal, the gills are external. These respiratory organs serve to start a process that the tissues then continue, where at the cellular level the mitochondria (cellular organelles) work on the production of carbon dioxide that is finally eliminated.
The gills emerged along the evolution of aquatic species that acquired a certain size or considerable activity, since the others, those whose metabolic rate is not so great or their size is small, use the surface of their bodies to exchange gases. Are structures that specialize in the uptake of oxygen are those that organize the circulation of fluids, either in those species with a developed vascular system or in the rest, a group in which we can find mollusks, for example.
Why are the gills internal, as opposed to the tracheas and lungs? The answer lies in the characteristics of the movement of water by the body, since it is not very easy to carry out in such complex cavities, because it is a much denser element than air and because it rubs with greater intensity on the walls of the structures.
So that gases can be exchanged successfully, it is necessary that there are no barriers between the incoming water and the cells of the epidermis; for this reason, even in those species whose skin has strong scales, the gill tissues are fragile and soft. As for his anatomy, we can distinguish between two forms of gills:
* one that is made up of a large branch of appendages (relative to that of the animal). This is seen in annelids, larvae of newts and salamanders, mollusks and insect larvae;
* one that consists of slits that communicate the digestive tract with the outside, which we can observe in the aquatic vertebrates that we call fish. They look like sheets that overlap and run through the blood vessels.
Branchial respiration, however, develops in different ways according to the species. Fish that have a bony skeleton are responsible for pumping water from the oropharyngeal area to a cavity that is under the operculum(a fin that protects the gills thanks to its hardness, and that opens when the mouth is closed to allow the flow of water with little pressure). During this journey, the water passes through the gills that are responsible for the absorption of oxygen and its subsequent distribution throughout the body through the blood.