Gill arches of fish. Functions of gill arches

The way of breathing in fish is of two types: air and water. These differences arose and improved in the process of evolution, under the influence of various external factors. If the fish have only a water type of respiration, then this process is carried out with the help of skin and gills. In fishes with an air type, the respiratory process is carried out with the help of the supragastric organs, the swim bladder, the intestine and through the skin. The main respiratory organs, of course, are the gills, and the rest are auxiliary ones. However, not always auxiliary or additional bodies are of secondary importance, most often they are the most important.

Species of respiration of fish

Cartilage and bony fish have a different structure of gill cover. Thus, the first have septa in the gill slits, which allows the opening of the gills outward through separate apertures. These septa are covered with branchial petals, which, in turn, are lined with a network of blood vessels. This structure of the gill cover is clearly seen in the example of rays and sharks.

At the same time, in bony species, these septa are reduced as superfluous, since the gill covers are mobile in themselves. Gill arches of fish perform the function of support, on which the gill petals are located.

Functions of gills. Gill arches

The most important function of the gills is, of course, gas exchange. With their help, oxygen is absorbed from the water, and carbon dioxide (carbon dioxide) is released into it. But few know that the gills also help the fish to exchange water-salt substances. So, after processing into the environment, urea, ammonia is removed, salt exchange takes place between water and the fish body, and first of all it concerns sodium ions.

In the process of evolution and modification of fish subgroups, the gill apparatus also changed. So, in teleosts, the gills have the form of scallops; in the cartilaginous fish they consist of plates, and the cycloths have bag-shaped gills. Depending on the structure of the respiratory apparatus, the structure is different, as well as the functions of the gill arch of fish.

Structure

Gills are located along the sides of the corresponding cavities of bony fishes and protected by lids. Each gill consists of five arcs. Four gill arches are formed completely, and one - rudimentary. On the outer side, the branchial arch is more convex, in the sides of the arches the branchial petals depart, based on the cartilaginous rays. Gill archs serve as a support for fastening the petals, which are supported by their base with their base, and the free edges diverge inward and outward at an acute angle. On the gill lobes themselves are the so-called secondary plates, which are located across the petal (or petals, as they are also called). On the gills there is a huge number of petals, in different fishes they can be from 14 to 35 per millimeter, with a height of not more than 200 microns. They are so small that their width does not reach up to 20 microns.

The main function of the gill arches

Gill arches of vertebrates perform the function of a filtering mechanism with the help of gill rakers located on an arc that faces the mouth of fish. This makes it possible to hold suspensions in the mouth in the water column and various nutrient microorganisms.

Depending on what the fish eats, the gill rakers also changed; They are based on bone plates. So, if the fish is a predator, then its stamens are located less frequently and are lower, and in fish that feed exclusively on plankton, living in the water column, the gill rakers are tall and thicker. In those fish that are omnivorous, the stamens have an average location between predators and planktonophages.

Circulatory system of the small circle of blood circulation

Gills of fish have a bright pink color due to the large amount of blood enriched with oxygen. This is due to the intensive circulatory process. Blood, which must be enriched with oxygen (venous), is collected from all over the body of the fish and enters the gill arch along the abdominal aorta. The abdominal aorta splits into two bronchial arteries, followed by a gill arterial arch, which in turn is divided into a large number of petal arteries enveloping the gill petals located along the inner edge of the cartilaginous rays. But this is not the limit. The petal arteries themselves are divided into a huge number of capillaries, enveloping the inner and outer parts of the petals with a dense mesh. The diameter of the capillaries is so small that it is equal to the size of the erythrocyte itself, which carries oxygen through the blood. Thus, the gill arches serve as a support for the stamens that provide gas exchange.

On the other side of the petals, all marginal arterioles merge into a single vessel that flows into a vein that carries blood, which in turn passes into the bronchial and then into the dorsal aorta.

If we examine in more detail the gill arches of fish and conduct a histological study, it is best to study the longitudinal section. Thus, not only stamens and petals will be seen, but also respiratory folds, which are a barrier between the aquatic environment and blood.

These folds are lined with only one layer of epithelium, and inside - with capillaries, supported by the pilar-cells (supporting). The barrier from the capillaries and respiratory cells is very vulnerable to the external environment. If there are impurities of toxic substances in water, these walls swell, detachment occurs, and they thicken. This is fraught with serious consequences, since the gas exchange in the blood is difficult, which ultimately leads to hypoxia.

Gas exchange in fish

The production of oxygen by fish occurs by passive gas exchange. The main condition for enriching the blood with oxygen is the constant water flow in the gills, and for this it is necessary that the gill arch and the whole apparatus retain its structure, then the function of the gill arches in fish will not be disturbed. The diffuse surface must also maintain its integrity for proper enrichment of hemoglobin with oxygen.

To carry out passive gas exchange, the blood in the capillaries of the fish moves in the opposite direction to the blood flow in the gills. This feature contributes to the almost complete extraction of oxygen from water and the enrichment of blood. In some individuals, the enrichment index of blood relative to the composition of oxygen in water is 80%. The current of water through the gills occurs by pumping it through the gill cavity, while the main function is performed by the movement of the oral apparatus, as well as the gill covers.

What determines the frequency of respiration of fish?

Due to the characteristic features, it is possible to calculate the respiration rate of fish, which depends on the movement of the gill covers. The concentration of oxygen in the water and the carbon dioxide content in the blood affect the respiratory rate of the fish. Moreover, these aquatic animals are more sensitive to a small concentration of oxygen than a large amount of carbon dioxide in the blood. The frequency of breathing is also influenced by the water temperature, pH and many other factors.

Fish have a specific ability to extract foreign substances from the surface of gill arches and from their cavities. This ability is called a cough. Gill covers are periodically covered, and with the help of the reverse movement of water, all suspensions located on the gills are washed out with a current of water. This manifestation in fish is most often observed if the water is contaminated with suspensions or toxic substances.

Additional functions of the gills

In addition to the main respiratory, the gills perform osmoregulatory and excretory functions. Fish are ammoniotic organisms, in fact, like all animals that live in water. This means that the final product of the decomposition of nitrogen containing in the body is ammonia. It is thanks to the gills that it is released from the body of fish in the form of ammonium ions, while purifying the body. In addition to oxygen, through the gills into the blood, as a result of passive diffusion, salts, low-molecular compounds, and a large number of inorganic ions in the water column enter. In addition to gills, absorption of these substances is carried out with the help of special structures.

This number includes specific chloride cells that perform osmoregulatory function. They are able to move ions of chlorine and sodium, while moving in the direction opposite to the large diffusion gradient.

Movement of chloride ions depends on the habitat of fish. Thus, in freshwater individuals, monovalent ions are transferred by chloride cells from water to the blood, replacing those that were lost as a result of the functioning of the excretory system of fish. But in marine fishes the process takes place in the opposite direction: the release is from the blood to the environment.

If the concentration of harmful chemical elements is markedly increased in the water, the auxiliary osmoregulatory function of the gills may be impaired. As a result, the amount of substances that is needed is not flowing into the blood, but much more in concentration, which can have a detrimental effect on the condition of the animals. This specificity is not always negative. So, knowing this feature of the gills, one can fight many diseases of fish, introducing medicinal preparations and vaccines directly into the water.

Dermal respiration of various fish

Absolutely all fish have the ability to skin breathing. But only to what extent it is developed - depends on a large number of factors: this is the age, and environmental conditions, and many others. So, if the fish lives in pure running water, then the percentage of cutaneous respiration is insignificant and is only 2-10%, while the respiratory function of the embryo is carried out exclusively through the skin, as well as the vascular system of the gallbladder.

Intestinal Breathing

Depending on the habitat, the method of breathing fish changes. So, tropical catfish and wader fishes actively breathe with the help of the intestine. The air, when swallowed, enters there and already penetrates the blood with the help of a dense network of blood vessels. This method began to develop in fish in connection with specific environmental conditions. Water in their reservoirs, due to high temperatures, has a small concentration of oxygen, which is exacerbated by turbidity and lack of flow. As a result of evolutionary transformations, fish in such reservoirs have learned to survive, using oxygen from the air.

Additional function of the swim bladder

The swim bladder is designed for hydrostatic regulation. This is its main function. However, in some species of fish the swim bladder is adapted for breathing. It is used as a reservoir for air.

Types of the structure of a swim bladder

Depending on the anatomical structure of the swim bladder, all fish species are divided into:

• Open-bubble;
• Closed-bubble.

The first group is the most numerous and is the main one, while the group of closed-bladder fish is very insignificant. To her belong, percids, mullet, cod, stickleback, etc. In open-bladder fish, on the basis of the name, the swim bladder is open for communication with the main intestinal stream, and in closed-bladder, respectively - no.

Carps also have a specific structure of the swim bladder. It is divided into the back and front chambers, which are connected by a narrow and short channel. The walls of the anterior chamber of the bladder consist of two membranes, outer and inner, while in the back chamber there is no outer shell.

The swim bladder is lined with one row of flat epithelium, after which there is a row of loose connective, muscular and layer of vascular tissue. The swim bladder has only its pearly reflection, which is provided by a special dense connective tissue, which has a fibrous structure. To ensure the strength of the bladder outside, both chambers are covered with an elastic serous membrane.

Labyrinth organ

A small number of tropical fish develops a specific organ, such as labyrinth and nadzhiberny. This species includes macropods, gourami, roosters and snakeheads. The formation can be observed in the form of a change in the pharynx, which is transformed into the suprabranchial organ, or the gill cavity (the so-called labyrinth organ) protrudes. Their main purpose is the possibility of obtaining oxygen from the air.