BRANCHIAL RESPIRATION: OPERATION, TYPES AND EXAMPLES - BIOLOGY - 2025

The breathing branchial is gas exchange and oxygen through the gills, also called gills. That is, while human beings breathe with the help of the lungs, trachea, nostrils and bronchi, this is the respiration carried out by fish and other aquatic animals.

These organs called gills or gills are located at the back of the head of aquatic animals, practically being small sheets that are one on top of the other and that in their 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 branchial respiration work?

For the gill respiration process to take place, the animal needs to absorb oxygen from the water, which can be done in different ways: either thanks to the same stream of water, or with the help of a small organ called the operculum, which helps to protect the marine respiratory system and that conducts the water towards the gills.

The oxygen taken from the environment, becomes part of the body and reaches the blood or another internal fluid such as hemolymph, and from there the oxygen passes to the organs that require gas to carry out cellular respiration, specifically carried out by the mitochondria.

Once cellular respiration has been carried out, it is when the carbon dioxide that needs to be expelled from the animal's body is obtained, since it is highly toxic and could end in serious poisoning. This 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 breathing organs of fish are a product of the same marine evolution, which over time began to increase or decrease in size, according to their mostly carried out 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 throughout the body.

External gills

According to experts, from an 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 appendages in the upper part of its body.

The main disadvantages of this type of gill is that they can be easily injured, are more conspicuous to predators and make movement and transfer difficult in the sea.

Most of the animals that have this type of gill are marine invertebrates, such as newts, salamanders, aquatic larvae, mollusks and annelids.

Internal gills

This is the second and last type of existing gill and they represent a more complex system in every way. Here the gills are located inside the animal, specifically under the pharyngeal fissures, orifices that are responsible for communicating the interior of the animal's body (the digestive tract) with its exterior.

In addition, these structures are crossed by blood vessels. Thus, water enters the body through the pharyngeal fissures and, thanks to the blood vessels, oxygenates the circulating blood in the body.

This type of gill stimulated the appearance of the ventilation mechanism present in animals with this type of gill, which translates into greater protection of the respiratory organs, in addition to representing a higher and more useful aerodynamics.

The best known animals that have this type of gill are vertebrates, that is, fish.

Examples

Pérez 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 to avoid having to transport 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 its paleal cavity, thus offering a fairly wide respiratory surface.

It happens as follows: the water enters this paleal cavity and, through the valves that are open for that moment, goes up the front of the head, reaches the buccal palps and the oxygen carried in the water passes through the gill structure, the H20 finally emerging through the eyelet.

All this process facilitates and helps in a great way the gas exchange and the conduction of the food.

Marine animals with internal gills

It was already mentioned earlier that animals that have this type of gill are called fish and their main characteristic is that they are vertebrates. The whole breathing process happens as follows:

The branchial structures, which in turn are composed of a skeletal axis, and the branchial arch (formed by two rows of gill plates) are located in the branchial chamber.

It all begins with the countercurrent flow, that is, the circulation of oxygen runs through the gill structures in the opposite direction to the flow of water, thus allowing maximum oxygen harvesting.

Subsequently, the fish pumps the water through its mouth, carrying it towards the gill arches. In order to allow the greatest entry of water through the mouth, with each fish breath, the pharyngeal cavity extends.

Thus, when the fish closes its mouth, the process is completed, since it exhales, and the water comes out along with the carbon dioxide.

References

1. Evans, DH (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.
2. Evans, DH, Piermarini, PM, & Choe, KP (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. Recovered from: physrev.physiology.org.
3. Hills, BA, & Hughes, GM (1970). A dimensional analysis of oxygen transfer in the fish gill. Respiration physiology, 9 (2), 126-140. Recovered from: sciencedirect.com.
4. Malte, H., & Weber, RE (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. Recovered from: sciencedirect.com.
5. Pérez, J and Gardey, A. (2015). Definition of branchial respiration. Recovered from: www.definicion.de.
6. Perry, SF, & Laurent, P. (1993). Environmental effects on fish gill structure and function. InFish ecophysiology (pp. 231-264). Springer Netherlands. Recovered from: link.springer.com.
7. Randall, DJ (1982). The control of respiration and circulation in fish during exercise and hypoxia. exp. Biol, 100, 275-288. Recovered from: researchgate.net.