The Gill respiration Consists of the exchange of gases and oxygen through the gills, also called gills. That is, while humans breathe with the help of the lungs, trachea, nasal passages and bronchi, this is the breathing of fish and other aquatic animals.
These organs called gills or gills are located at the back of the head of the aquatic animals, being practically small sheets that are one on top of others and that in its structure have multiple blood vessels.
Its function is to take the oxygen that is immersed in the water and expel the carbon dioxide gas to it.
How does it work?
In order for the gill respiration to be carried out, the animal needs to absorb the oxygen from the water, which can be done in different ways: either by the same water stream, or with the help of a small organ called an operculum, which helps To protect the marine respiratory apparatus and that leads the water towards the gills.
Oxygen taken from the medium, becomes part of the body and reaches the blood or other internal fluid such as hemolymph, and from there the oxygen passes to the organs that require the gas to perform cellular respiration, specifically performed by mitochondria .
Once the cellular respiration is performed, it is when carbon dioxide is obtained that needs to be expelled from the body of the animal, since it is highly toxic and could end in severe intoxication. At that moment is when the gas is expelled into the water.
Types of gills
In this sense, there are two types of gills at the anatomical level. Pérez and Gardey (2015) believe that the organs of breathing of the fish are a product of the same marine evolution, that over time began to increase or decrease their size, according to their activities.
For example, for aquatic animals that have a reduced metabolism, they can breathe with the external parts of their bodies and thus spread the rest of the fluids through the body.
External Branches
By the experts, from the evolutionary point of view they are the oldest gills, being the most common and seen in the marine world. They are made up of small sheets or large appendages in the upper part of their body.
The main disadvantages of this type of gills are that they can easily be injured, are more striking to predators and hinder movement and movement at sea.
Most of the animals that possess this type of gills are marine invertebrates, such as newts, salamanders, aquatic larvae, molluscs and annelids.
Internal gills
This is the second and last type of existing gills and represent a more complex system in every sense. Here the gills are located inside the animal, specifically below the pharyngeal clefts, orifices that communicate the interior of the animal's organism (the digestive tract) with its exterior.
In addition, these structures are traversed by blood vessels. Thus, water enters the body through the pharyngeal crevices and thanks to the blood vessels, oxygenates the circulating blood through the body.
This type of gills stimulated the appearance of the mechanism of ventilation present in animals with this type of gills, which translates into greater protection of the respiratory organs, in addition to representing a more elevated and useful aerodynamics.
The best known animals possessing this type of gills are vertebrates, that is, fish.
Examples
Perez and Gardey (2015) reflect on the difference between the human and aquatic respiratory systems, in our case the lungs and organs responsible for gas exchange are internal, and as already mentioned, fish have external structures.
The answer is that water is a heavier element than air, therefore, aquatic animals need the respiratory system on their surface so they do not have to carry water throughout the body, since the process is complicated .
Marine animals with external gills
The bivalve mollusk is a species with external gills. Specifically, they are located in their paleal cavity, thus offering a fairly wide respiratory surface.
It happens as follows: water enters this paleal cavity and, through the valves that are open for that moment, go up the front of the head, reaches the buccal palpos and the oxygen carried in the water crosses The branchial structure, finally leaving the H20 by the buttonhole.
This whole process facilitates and greatly helps the gas exchange and the conduction of the food.
Marine animals with internal gills
Earlier it was mentioned that the animals that possess this type of gills are denominated fish and its main characteristic is that they are vertebrates. The whole process of breathing happens as follows:
The gill structures, which in turn are composed of a skeletal axis, and the gill arch (formed by two rows of gill plates) are located in the gill chamber.
It all starts with the countercurrent flow, that is, that the oxygen circulation flows through the gill structures to the opposite direction of the flow of water and thus allows the maximum collection of oxygen.
Subsequently, the fish pumps the water through the mouth, taking it to the gill arches. In order to allow more water to enter the mouth, with each breath of the fish, the pharyngeal cavity is extended.
Thus, when the fish closes the mouth, the process is completed, as it exhales, and the water exits together with the carbon dioxide.
References
- Evans, D.H. (1987). The fish gill: site of action and model for toxic effects of environmental pollutants.Environmental Health Perspectives, 71, 47. Retrieved from: nlm.nih.gov.
- Evans, D.H., Piermarini, P.M., & Choe, K.P. (2005). The multifunctional fish gill: dominant site of gas exchange, osmoregulation, acid-base regulation, and excretion of nitrogenous waste.Physiological reviews, 85 (1), 97-177. Retrieved from: physrev.physiology.org.
- Hills, B.A., & Hughes, G. M. (1970). A dimensional analysis of oxygen transfer in fish gill. Respiration physiology, 9 (2), 126-140. Retrieved from: sciencedirect.com.
- Malte, H., & Weber, R.E. (1985). A mathematical model for gas exchange in the fish gill based on non-linear blood gas equilibrium curves.Respiration physiology, 62 (3), 359-374. Retrieved from: sciencedirect.com.
- Pérez, J and Gardey, A. (2015). Definition of gill respiration. Retrieved from: www.definicion.de.
- Perry, S. F., & Laurent, P. (1993). Environmental effects on fish gill structure and function. InFish Ecophysiology (pp. 231-264). Springer Netherlands. Retrieved from: link.springer.com.
- Randall, D. J. (1982). The control of breathing and circulation in fish during exercise and hypoxia. Exp. Biol, 100, 275-288. Retrieved from: researchgate.net.