gills . They are unsuitable for life in the air , as once they have been removed from the water , the gill filaments fold and stick together. A fish out of water quickly suffocates despite the abundance of oxygen around it; In addition, in the aerial environment, the gills offer a wide surface that would favor the loss of water.
Summary
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- 1 Position
- 1 Internal gills
- 2 External gills
- 2 Gill respiration
- 3 Structure of the gills of fish
- 4 General characteristics
- 5 Sources
Position
internal gills
- They are organs formed by numerous gill filaments that are located, for example, in the windows of the larynx of bony fish (commonly called gills). They have high vascularization, hence their reddish color. Internal gills are also present inside the mantle of octopusesand squids.
external gills
- In those vertebrates that have external gills, these appear as highly vascularized branched filaments that emerge on each side of the animal’s neck; in tailless amphibians ( toadsand [[Rana|frogs), only during the tadpole stage, in aquatic salamanders in the adult stage.
gill respiration
The respiratory structures are the gills, in the form of integumentary folds or very fine structures that are highly irrigated and surrounded by water. They can be external gills, little evolved, or internal, more evolved, since being inside they are more protected. However, they need a mechanism to produce movement in the water that bathes them. The gills appear in many animals of aquatic life, such as annelids, molluscs, crustaceans, fish and amphibians. They are also found in terrestrial crustaceans, such as pillbugs and beach fleas.
Fish support and extend the gills by means of gill arches. In sharks and rays there are five arches (six in the least evolved) and four arches in bony fish. A bony structure called the operculum protects these gill arches. The water circulates from the mouth to the gill slits, pressed by the tongue and creating a current that favors gaseous exchange between the gill and the water.
Structure of the gills of fish
Respiratory system – Fish
The gills of fish are very thin, vascularized laminar structures, grouped in bony arches called gill arches.
Two rows of gill filaments emerge from each gill arch, and each filament carries a series of gill lamellae where gas exchange takes place.
In fish, gas exchange is produced by a mechanism called the countercurrent exchange system: the blood, in the gills, circulates in the opposite direction to the water, which allows the maximum extraction of oxygen by diffusion.
General characteristics
The gills are external organs, unlike the lungs or tracheas of subaerial animals, because the complex cavity-shaped organs are not suitable for the intensive movement of a liquid such as water, with a density much greater than that of air. , and by the friction involved. Effective gas exchange requires barrier-free contact between the epidermal cells of the gill and the surrounding water, as well as in the lungs, so that even in animals with reinforced integuments, such as the scaly skin of fish , the gills are always at least covered with soft and fragile tissues.
Anatomically the gills occur in two forms. The most common is that of branched appendages with a large relative surface area. Thus they occur, for example, in molluscs, annelids and aquatic larvae of salamanders and newts, or aquatic larvae of insects. The other form is the one observed in the heterogeneous group of aquatic vertebrates called fish.
In these, the gills are specialized structures organized between the pharyngeal slits, or gill slits, holes that laterally communicate the digestive tube with the outside. The water that enters through the mouth comes out through the cracks, oxygenating the blood that circulates through vessels that run through the partitions located between them, which are the gills. In sharks , the lateral gill slits are easily seen.
In both anatomical modalities, the gills can be more or less protected within an open cavity through which the water is circulated. This is the case, for example, of molluscs (cephalopods, gastropods, bivalves, etc.) where the pallial cavity containing the gills exchanges water with the environment only through conduits called siphons. This is also the case in bony fish, where the gills are externally protected by an extension of the body wall called the operculum. The term gill in these fish refers to the gills, but colloquial usage often applies to the operculum. In sharks, by contrast, the gill slits are externally visible.
In bony fishes, water is actively pumped, with rhythmic movements, from the oropharyngeal cavity into the cavity below the operculum, passing between the gills. It has been said about sharks, but now we know that it is not exact, that they just swim with their mouths open, so that the water flows constantly through the gills.
In vertebrates and insects with aquatic juvenile stages, such as amphibians and mayflies, the larvae are equipped with gills, although the adults breathe through aerial organs. The gills are related to the circulatory system that reaches them from the body carrying CO2 and returns to the body from them loaded with O2. Gas exchange is called hematosis.
Many people might think that fish breathe oxygen from the molecule that makes up water (H2O), but this deduction is not true. Fish breathe dissolved oxygen in the water. As is well known, water is the “universal solvent” since it can contain almost the majority of the compounds that exist in nature. In the case of sea water, more than 80 elements are dissolved in it. On the other hand, the level of oxygen dissolution in the water is never the same, on the one hand, the amount of elements that are dissolved in the water influences it.
Sea water contains much less oxygen than fresh water due to the large amount of dissolved salts. The temperature also affects the amount of oxygen that the water can contain dissolved, the concentration of this being lower the higher the temperature. Finally, the state in which the water is found, whether at rest or in agitation, also affects the oxygen level. The greater the movement of this, the higher the level of oxygen it houses.
Therefore, a pool of stagnant water exposed to the summer sun does not contain the same level of oxygen as a mountain river with numerous waterfalls, as the water of the North Atlantic sea, as marshes or intertidal pools. The amount of oxygen is always different, and fish have the ability to adapt to different types of oxygen levels in the water through specialization derived from natural selection.
Each species of fish adapts to a different system in water conditions, conditions that also have changes in other types of factors such as pH, density, alkalinity, temperature, etc.
To do this, fish along with numerous other marine organisms have developed a somewhat special breathing mechanism called gills.
From a definitional point of view, it could be said that the gills are epithelial appendages 1 in the form of threads, lamellar and arborescent, which are richly endowed with capillary vessels.
The gills do not have to be internal. Many organisms have them externally and can even protrude freely from the body, as is the case, for example, in polychaete worms and marine nudibranchs. They can also be protected as in gastropod and cephalopod molluscs that are housed in the pallial cavity (where the mantle is in molluscs). In the case of fish they are inside the cavity called “brachial chamber”.
Inside the water, the Gills are shown as a tremendously effective element for respiration, although they are totally ineffective outside of it since, lacking support and due to their direct exposure, they would suffer serious dehydration.
For the proper functioning of the gills, they must be in permanent contact with the water, this is because the level of oxygen in it is always scarce, which is why the living beings that use them have devised numerous systems for moving water through through them. From molluscs that have a series of vibrating filaments that promote circulation, through cephalopods such as cuttlefish or squid that perform movements very similar to inspiration and expiration of lung-bearing animals, to crustaceans that use a kind of spatula to push water through them.
In the case of fish, the maximum sophistication is reached since these are inside the body, being very highly vascularized. In the case of fish whose habitat is the open sea or are considered good swimmers. The same movement of the animal favors the water to pass quickly through the gills.
In the case of more sedentary fish, it is achieved through coordinated movements between the mouth and the opercula. In addition, the blood circulates in the opposite direction to the circulation of the water, in this way a countercurrent exchange system is carried out that significantly increases the efficiency of the system.
At the same time that this happens, the carbon dioxide present in the animal crosses the gill membranes in the opposite direction and is returned to the water.
