As we found out, the structure of the excretory system of fish (cartilaginous and bony) is somewhat different. The composition of the urine of these representatives of the fauna is also not the same. The main component of the liquid secretions of bony fish is ammonia. a substance that is toxic even in minimal concentrations. In cartilaginous, it is urea.
Metabolic products are delivered to the kidneys of the fish, which in fact are filter feeders, with the blood stream. The latter is preliminarily fed into the vascular glomeruli. It is in them that the filtration process takes place, as a result of which primary urine is formed. The vessels removed from the glomeruli entangle the excretory tubules. Joining together, they form the posterior cardinal veins.
In the middle part of the tubules (in the kidneys), the formation of secondary (final) urine occurs. Here, among other things, the absorption of substances necessary for the body takes place. This can be, for example, glucose, water, amino acids.
The kidneys are rather complex organs of the excretory system of fish. It is customary to distinguish three main departments:
- Anterior (head kidney);
The kidney sections of different fish species may not have the same shape. Unfortunately, it is rather difficult to consider the structure of this organ specifically for each class in one small article. Therefore, as an example, let’s figure out what a carp, pike and perch kidney looks like. In cyprinids, the right and left kidneys are located separately. Below they are connected into an unpaired tape. Well-developed middle section is strongly expanded and covers the swim bladder in the form of a ribbon.
In perch and pike, the kidneys have a slightly different structure: the middle sections are located separately, and the front and rear are connected.
The structure of the excretory system of fish is quite complex. The bladder is found in most species of these representatives of the aquatic fauna.
As you know, there are only two main classes of fish in nature:
The difference between them, first of all, lies in the structure of the skeleton. In the first case, it consists of cartilage, in the second, respectively, of bones. The class of cartilaginous fish is represented in nature by about 730 species. There are much more bony representatives of the aquatic fauna: about 20 thousand species.
The excretory system of fish (bone and cartilaginous) has a different structure. The former have a bladder, while the latter do not. Of course, the absence of this organ in cartilaginous fish does not mean that their VS is imperfect. It performs its functions just fine.
The excretory system of cartilaginous fish includes organs, the structure of which maximally prevents the uncontrolled flow of urine into the environment. Such representatives of the fauna usually emit very little “liquid waste” into the water.
Structure: which organs form the excretory system of the fish
For the removal of unnecessary and often toxic substances from the body, in these representatives of the aquatic fauna, as in humans, paired kidneys are responsible, which is a complex system of small wire tubules. The latter open into the common excretory duct. The bladder in most fish comes out in a separate opening.
The metabolic products formed in the kidneys through the ducts mainly enter the bladder.
Osmotic pressure in all such representatives of the fauna (both marine and freshwater) differs significantly from those of the environment. Mixins are the only exception to this rule. The concentration of salts in their body is the same as in sea water.
In cartilaginous fish, belonging to the isoosmotic group, the pressure is the same as in myxin and coincides with the water pressure. But the concentration of salts is an order of magnitude lower than in the external environment. The balance of pressure in the fish body is provided by the high m of urea in the blood. Concentration and removal of chloride ions and sodium ions from the body is performed by the rectal gland.
The excretory system of bony fish is well adapted to regulate the salt balance. The pressure of such representatives of the fauna is regulated in a slightly different way. Such fish do not belong to the isoosmotic class. Therefore, in the process of evolution, they have developed special mechanisms that control and regulate salts in the blood.
So, marine bony fish constantly losing water under the influence of osmotic pressure, to compensate for the losses, are forced to drink very often. Sea water in their bodies is constantly filtered from salts. The latter are excreted from the body in two ways:
- Calcium cations with chloride ions are released through the gill membranes;
- Magnesium cations with sulfate anions are excreted by the kidneys.
In bony freshwater fish, in contrast to sea fish, the concentration of salts in the body is lower than in the external environment. The representatives of the fauna equalize the pressure by capturing ions from the water through the gill membranes. In addition, a large amount of urea is produced in the body of such cold-blooded.
Understanding which organs form the excretory system of fish, we can conclude that the kidneys play a key role in its functioning.
In the evolutionary chain, fish are far from the first place. Biologists classify them as lower vertebrates. In terms of the complexity of the structure of organs, waterfowl are inferior to both amphibians and reptiles. Higher vertebrates, including humans, have pelvic kidneys. In fish, they are trunk.
The degree of complexity of the structure of the kidneys in any living creature is determined by:
- The number of tubules;
- The presence and structure of ciliated funnels.
In some representatives of the fauna, the buds are laid in the upper part and consist of 6-7 tubules. The ciliated funnel, which acts as a filter, in such organisms opens with one end into the ureter, the other into the body cavity. It is this structure that characterizes the kidneys of fry and some adult fish. These include eelpout, atherina, gobies and others. In other fish species, the primitive kidney is gradually transformed into a lymphoid blood-forming organ.
Kidneys of adult fish
In fry, in most cases, the kidney is located in the upper part of the body. In adult fish, this paired organ fills the space between the swim bladder and the spine. As already mentioned, the kidneys of these representatives of the water element belong to the trunk class and look like ribbon-like strands of maroon color.
The main functional element of the kidney of an adult fish is the nephron. The latter, in turn, consists of:
- Excretory tubules;
- Malpighian body.
The malpighian body in fish is formed by a capillary glomerulus and Shumlyansky-Bowman capsules, which are microscopic double-walled cups. The urinary canaliculi, extending from them, open into the collecting ones. The latter, in turn, merge into larger ones and fall into the ureters.
Ciliated funnels in the kidneys of most fish are absent, except for some species. Such functional elements, for example, are available in sturgeon and some cartilaginous.
Rectal gland of fish
As already mentioned, the excretory system of fish is responsible not only for the elimination of metabolic products, but also for maintaining a normal level of water-salt balance in the body. In fish, this function is performed by the rectal gland, which is a finger-like outgrowth that extends from the dorsal rectum. The glandular cells of the rectal gland secrete a special secret containing a large amount of NaCl. First of all, this organ removes excess salt from the body from food or sea water.
In addition to maintaining salt balance, the rectal gland of fish performs another very important function. During the breeding season, the secreted mucus follows the fish, attracting the characteristic smell of individuals of the opposite sex.
Excretory system of fish: features, structure and functions. What organs form the excretory system of fish?
The main function of the excretory system of any living creature, including fish, is to remove metabolic products from the body and maintain the water-salt balance in the blood and tissues. Of course, the excretory system of fish has a simpler structure than, for example, a human. The performance of functions occurs along a certain chain, for understanding which it is necessary to study the structure of the system as a whole and the work of its organs separately.
Long ago, almost 70 million years ago, the oceans were inhabited by invertebrates. But the fish, the first to acquire a brain, exterminated a significant number of them. Since then, they have dominated the water space. The modern fish brain is very complex. Indeed, it is difficult to follow any behavior without a program. The brain solves this problem using different options. Pisces preferred imprinting, when the brain is ready for the behavior that it sets at a certain point in its development.
For example, salmon have an interesting feature: they swim to spawn in the river in which they themselves were born. At the same time, they cover huge distances, and they have no map. This is possible due to this variant of behavior, when certain parts of the brain are like a camera with a timer. The principle of operation of the device is as follows: there comes a moment when the diaphragm is triggered. Images in front of the camera remain on the film. So it is with fish. They are guided in their behavior by images. Imprinting determines the personality of the fish. Given the same conditions, their different breeds will behave differently. In mammals, the mechanism of this mode of behavior, that is, imprinting, has been preserved, but the scope of its important forms has narrowed. A person, for example, has retained sexual skills.
It consists of two departments. One of them is the tectum roof. It is horizontal. Has the appearance of swollen visual lobes arranged in pairs. In fish with a high organization, they are better developed than in cave and deep-sea representatives with poor eyesight. Another department is located vertically, it is called the tegmentum. It contains the highest visual center. What functions does the midbrain perform??
- If you remove the visual roof from one eye, the other goes blind. The fish loses sight when the roof is completely removed, in which the visual grasping reflex is located. Its essence lies in the fact that the head, body, eyes of the fish move in the direction of food objects that are imprinted on the retina.
- The midbrain of the fish fixes the color. When you remove the top roof, the body of the fish brightens, and if you remove the eyes, it darkens.
- Has a connection with the forebrain and cerebellum. Coordinates the work of a number of systems: somatosensory, visual and olfactory.
- The middle part of the organ contains centers that regulate movement and maintain muscle tone.
- The fish brain makes reflex activity diverse. First of all, this affects the reflexes associated with visual and sound stimuli.
Parts of the brain in fish
This organ is small in this class. Does a fish have a brain? Yes, in a shark, for example, its volume is equal to thousandths of a percent of the total body weight, in sturgeon and bony fish. a hundredth, in small fish it is about one percent. The fish brain has a peculiarity: the larger the individual, the smaller it.
The family of stickleback fish, which live in Lake Miwan, Iceland, has a brain, the size of which depends on the sex of the individuals: it is smaller in the female, and larger in the male.
The fish brain has five sections. These include:
- Forebrain, consisting of two hemispheres. Each of them is in charge of the sense of smell and schooling behavior of fish.
- The midbrain, from which the nerves that react to stimuli branch off, which move the eyes. This is the center of the fish’s vision. It regulates body balance and muscle tone.
- The cerebellum is the organ responsible for movement.
- The medulla oblongata is the most important region. Performs many functions and is responsible for various reflexes.
Fish brain regions do not develop in the same way. This is influenced by the lifestyle of aquatic inhabitants and the state of the environment. So, for example, the pelagic species, possessing excellent skills in movement in water, have a well-developed cerebellum, as well as vision. The structure of the brain of fish is such that representatives of this class with a developed sense of smell are distinguished by an increased size of the forebrain, predators with good eyesight are medium, inactive representatives of the class are oblong.
This formation, which has an unpaired structure, is located in the back of the brain. The cerebellum partially covers the medulla oblongata. Consists of a middle part (body) and two ears (lateral sections).
Performs a number of functions:
- Coordinates movements and maintains normal muscle tone. If the cerebellum is removed, these functions are impaired, the fish begin to swim in a circle.
- Provides the implementation of motor activity. When the body of the cerebellum is removed, the fish begins to swing in different directions. If you also remove the damper, movements are completely disrupted.
- With the help of the cerebellum, metabolism is regulated. This organ affects other parts of the brain through the nucleoli located in the spinal cord and medulla oblongata.
The brain is oblong
He takes part in the formation of the trunk of the organ. The medulla oblongata of fish is designed in such a way that substances, gray and white, are distributed without a clear border.
Performs the following functions:
- Reflex. The centers of all reflexes are located in the brain, whose activity ensures the regulation of respiration, the work of the heart and blood vessels, digestion, and movement of the fins. Thanks to this function, the activity of the organs of taste is carried out.
- Conductor. It consists in the fact that the spinal cord and other parts of the brain conduct nerve impulses. The medulla oblongata is the site of the ascending paths from the dorsal to the head, which go to the descending paths connecting them.
He owes his education to the visual hillocks, which are also called thalamus. Their location is the central part of the brain. Thalamus have many formations in the form of nuclei, which transmit the received information to the brain of the fish. It has various sensations associated with smell, vision, hearing.
The main function of the thalamus is to integrate and regulate the sensitivity of the body. He also participates in the reaction that allows fish to move. If the thalamus is damaged, the sensitivity level decreases, coordination is impaired, and vision and hearing decrease.
It contains a mantle, as well as striped bodies. The mantle is sometimes called a cloak. The location is the top and sides of the brain. The cloak looks like thin epithelial plates. The striped bodies are located underneath. The forebrain of fish is designed to perform functions such as:
- Olfactory. If this organ is removed in fish, they lose the conditioned reflexes developed to stimuli. Physical activity decreases, attraction to the opposite sex disappears.
- Protective and defensive. It manifests itself in the fact that representatives of the Pisces class support a gregarious lifestyle, take care of their offspring.
Fish brain: structure and features
There are many classes of different animals in nature. One of them is fish. Many people do not even suspect that these representatives of the animal world have a brain. Read about its structure and features in the article.
Its location is the nerve arches (more precisely, their channels) of the spine of fish, consisting of segments. The spinal cord in fish is a continuation of the medulla oblongata. Nerves extend from it to the right and left between the pairs of vertebrae. They send irritating signals to the spinal cord. They innervate the surface of the body, trunk muscles and internal organs. What kind of brain does fish have? Head and dorsal. The gray matter of the latter is inside it, white is outside.
As fish hear. Ear device
The question of whether fish can hear has been debated for a long time. It has now been established that fish hear and make sounds themselves. Sound is a chain of regularly repeating compression waves of a gaseous, liquid or solid medium, i.e., in an aqueous medium, sound signals are just as natural as on land. Compression waves of an aqueous medium can propagate at different frequencies. Low-frequency vibrations (vibration or infrasound) up to 16Hz are not perceived by all fish. However, in some species, infrasound reception is brought to perfection (sharks). The spectrum of sound frequencies perceived by most fish lies in the range of 50-3000 Hz. The ability of fish to perceive ultrasonic waves (over 20,000 Hz) has not been convincingly proven to date.
The speed of sound propagation in water is 4.5 times higher than in air. Therefore, sound signals from the shore reach the fish in a distorted form. Hearing acuity in fish is not as developed as in land animals. Nevertheless, some species of fish have been experimenting with quite decent musical abilities. For example, a minnow at 400-800 Hz distinguishes 1/2 tone. The capabilities of other fish species are more modest. So, guppies and eels differentiate two octaves differing by 1 / 2-1 / 4 octaves. There are also completely musically incompetent species (bubbleless and labyrinth fish).
Hearing acuity is determined by the morphology of the acoustic-lateral system, which, in addition to the lateral line and its derivatives, includes the inner ear, the swim bladder and the Weberian apparatus (Fig.2.18).
Both in the labyrinth and in the lateral line, the so-called hairy cells act as sensitive cells. The displacement of a hair of a sensitive cell both in the labyrinth and in the lateral line leads to the same result. the generation of a nerve impulse entering the same acoustic-lateral center of the medulla oblongata. However, these organs also receive other signals (gravitational field, electromagnetic and hydrodynamic fields, as well as mechanical and chemical stimuli).
The auditory apparatus of fish is represented by a labyrinth, a swim bladder (in cystic fish), a Weber apparatus and a lateral line system. Labyrinth. Pair education. The labyrinth, or the inner ear of fish (Fig. 2.19), serves as an organ of balance and hearing. Auditory receptors are abundant in the lower two chambers of the labyrinth. Lagena and utriculus. The hairs of the auditory receptors are very sensitive to the movement of the endolymph in the labyrinth. A change in the position of the fish’s body in any plane leads to displacement of the endolymph, at least in one of the semicircular canals, which irritates the hairs.
In the endolymph of the saccula, utriculus and lagen, there are otoliths (pebbles) that increase the sensitivity of the inner ear.
Their total number is three on each side. They differ not only in location, but also in size. The largest otolith (pebble) is in a round bag. Lagen.
On otoliths of fish, annual rings are clearly visible, according to which the age of some fish species is determined. They also provide an estimate of the fish’s maneuvering efficiency. With the longitudinal, vertical, lateral and rotational movements of the fish body, some displacement of the otoliths and their irritation of sensitive hairs occur, which, in turn, creates a corresponding afferent flow. On them (otoliths) also the reception of the gravitational field, the assessment of the degree of acceleration of fish during throws.
An endolymphatic duct departs from the labyrinth (see Fig. 2.18.6), which is closed in teleost fishes, and open in cartilaginous fishes and communicates with the external environment. Weber’s apparatus. It is represented by three pairs of movably connected bones, which are called stapes (in contact with the labyrinth), incus and maleus (this bone is connected to the swim bladder). The bones of the Weberian apparatus are the result of the evolutionary transformation of the first trunk vertebrae (Fig. 2.20, 2.21).
With the help of the Weberian apparatus, the labyrinth contacts the swim bladder in all vesicular fishes. In other words, the Weberian apparatus provides a connection between the central structures of the sensory system and the sound-perceiving periphery.
1- perilymphatic duct; 2, 4, 6, 8. ligaments; 3. Stape; 5- incus; 7- maleus; 8. Swim bladder (vertebrae are indicated by Roman numerals)
Brain; 2. Utriculus; 3. Sakkula; 4- backing channel; 5. Lagena; 6- perilymphatic duct; 7-stapes; 8- incus; 9 maleus; 10- swim bladder
Swimming bladder. It is a good resonating device, a kind of amplifier for medium and low frequency vibrations of the medium. A sound wave from the outside leads to oscillations of the wall of the swim bladder, which, in turn, lead to a displacement of the chain of bones of the Weberian apparatus. The first pair of bones of the Weberian apparatus presses on the labyrinth membrane, causing displacement of the endolymph and otoliths. Thus, if we draw an analogy with higher land animals, the Weberian apparatus in fish performs the function of the middle ear.
However, not all fish have a swim bladder and Weber apparatus. In this case, fish exhibit low sensitivity to sound. In bubbleless fish, the auditory function of the swim bladder is partially compensated for by the air cavities associated with the labyrinth, and the high sensitivity of the lateral line organs to sound stimuli (waves of water compression).
Side line. It is a very ancient sensory formation that performs several functions simultaneously in evolutionarily young groups of fish. Taking into account the exceptional importance of this organ for fish, let us dwell in more detail on its morphological and functional characteristics. Different ecological types of fish show different variants of the lateral system. The location of the lateral line on the body of fish is often species-specific. There are fish species that have more than one lateral line. For example, a rasp has four lateral lines on each side, hence its second name. “eight-line chir”. In most teleost fishes, the lateral line stretches along the body (without interruption or interruption in some places), reaches the head, forming a complex system of canals. The lateral line canals are located either inside the skin (Fig.2.22), or openly on its surface.
An example of an open superficial arrangement of neuromasts. Structural units of the lateral line. The lateral line of the minnow appears. Despite the obvious diversity of the morphology of the lateral system, it should be emphasized that the observed differences relate only to the macrostructure of this sensory formation. The receptor apparatus of the organ itself (a chain of neuromasts) is surprisingly the same in all fish both morphologically and functionally.
The lateral line system reacts to compression waves of the aquatic environment, flowing currents, chemical stimuli and electromagnetic fields using neuromasts. Structures uniting several hair cells (Fig.2.23).
The neuromast consists of a muco-gelatinous part. Capsules in which hairs of sensitive cells are immersed. Closed neuromasts communicate with the external environment with small holes piercing the scales.
Open neuromasts are characteristic of the channels of the lateral system extending to the fish’s head (see Fig. 2.23, a).
Channel neuromasts extend from head to tail on the sides of the body, as a rule, in one row (in fish of the Hexagramidae family, six rows or more). The term “lateral line” in everyday life refers specifically to the channel neuromasts. However, in fish, neuromasts are also described, separated from the canal part and having the appearance of independent organs.
Channel and free neuromasts located in different parts of the fish body and the labyrinth do not duplicate, but functionally complement each other. It is believed that the sacculus and lagena of the inner ear provide the sound sensitivity of fish from a long distance, and the lateral system allows you to localize the sound source (albeit already near the sound source).
It has been experimentally proven that the lateral line perceives low-frequency vibrations, both sound and associated with the movement of other fish, i.e. Low-frequency vibrations arising from a fish’s tail hitting the water are perceived by other fish as low-frequency sounds.
Thus, the sound background of the reservoir is quite diverse and the fish have a perfect system of organs for the perception of wave physical phenomena under water.
Waves arising on the surface of the water have a noticeable effect on the activity of fish and the nature of their behavior. The reasons for this physical phenomenon are many factors: the movement of large objects (large fish, birds, animals), wind, tides, earthquakes. Excitement serves as an important channel for informing aquatic animals about events both in the water body and beyond. over, the excitement of the reservoir is perceived by both pelagic and bottom fish. There are two types of reaction to surface waves from the fish: the fish sinks to a great depth or is mixed to another part of the reservoir. The stimulus acting on the body of the fish during the period of the excitement of the reservoir is the movement of water relative to the body of the fish. The movement of water during its excitement is perceived by the acoustic-lateral system, and the sensitivity of the lateral line to waves is extremely high. So, for the appearance of afferentation from the lateral line, mixing of the cupula by 0.1 μm is sufficient. In this case, the fish is able to very accurately localize both the source of wave formation and the direction of wave propagation. The spatial diagram of fish sensitivity is species-specific (Fig. 2.26).
An artificial waveforming device was used in the experiments as a very strong stimulus. When its location changed, the fish unmistakably found the center of indignation. The response to a wave source consists of two phases.
First phase. Fading phase. It is the result of an orientation reaction (innate exploratory reflex). The duration of this phase is determined by many factors, the most significant of which are the wave height and the depth of the fish sinking. For carp fish (carp, crucian carp, roach) with a wave height of 2-12 mm and a fish immersion of 20-140 mm, the approximate reflex took 200-250 ms.
Second phase. Movement phase. The conditioned reflex reaction is developed in fish rather quickly. For intact fish, from two to six reinforcements are sufficient for its occurrence in blinded fish, after six combinations of wave formation of food reinforcement, a stable search food-procuring reflex was developed.
Small pelagic plankton-feeders are more sensitive to the surface wave, less. Large bottom fish. Thus, blinded verkhovki with a wave height of only 1–3 mm, already after the first presentation of the stimulus, demonstrated an orienting reaction. Seabed fish are sensitive to strong waves on the sea surface. At a depth of 500 m, their lateral line is excited when the wave height reaches 3 m and a length of 100 m. As a rule, waves on the sea surface generate rolling.Therefore, during excitement, not only the lateral line of the fish, but also its labyrinth comes into excitement. The results of the experiments showed that the semicircular canals of the labyrinth respond to rotational movements in which the body of the fish is drawn by the currents of water. The utriculus perceives the linear acceleration that occurs during the rolling process. During a storm, the behavior of both solitary and schooling fish changes. During a weak storm, pelagic species in the coastal zone descend into the bottom layers. With strong waves, fish migrate to the open sea and go to greater depths, where the influence of waves is less noticeable. Obviously, strong waves are assessed by fish as an unfavorable or even dangerous factor. It suppresses feeding behavior and forces fish to migrate. Similar changes in feeding behavior are observed in fish species living in inland waters. Anglers know that when the sea is rough, the fish stops biting.
Thus, the body of water in which the fish lives is source of various information transmitted through several channels. Such awareness of the fish about fluctuations in the external environment allows it to timely and adequately respond to them with locomotor reactions and changes in autonomic functions.
Fish signals. It is obvious that fish themselves are the source of various signals. They emit sounds in the frequency range from 20 Hz to 12 kHz, leave a chemical trace (pheromones, kairomones), and have their own electric and hydrodynamic fields. Fish create acoustic and hydrodynamic fields in different ways.
The sounds emitted by fish are quite diverse, however, due to the low pressure, they can be recorded only with the help of special highly sensitive equipment. The mechanism of formation of a sound wave in different fish species can be different (Table 2.5).
2.5. The sounds of fish and the mechanism of their reproduction
Digestive system of fish. Structure and function. Aqualover. Aquarium. aquarium for beginners, aquarium for amateurs, aquarium for professionals
The digestive tract of fish can be very diverse in structure, shape, length, which is explained by the types of nutrition of various species of fish (mainly predators, mainly herbivores; fish feeding on plankton, etc.), and by the peculiarities of digestion. But you can also highlight common points.
The digestive system of fish consists of the mouth and mouth, pharynx, esophagus, stomach, intestines (small, large, rectum, ending with the anus). Some fish have a cloaca in front of the anus: the cavity into which the rectum enters, the ducts of the urinary and reproductive systems.
The oral cavity of the fish is necessary for the primary intake and swallowing of food. There are no salivary glands in it, but there are taste buds (mouth buds of fish). Many fish have tongues and teeth in their mouths. Mostly herbivores, as a rule, do not have teeth. Teeth are usually rootless and are replaced with new ones over time. They can be found not only on the jaw, but also on other bones of the oral cavity, as well as on the tongue. In predatory fish, teeth can also be in the pharynx.
The process of absorption of food in fish is associated with respiration. Water, together with nutrient organisms, enters the mouth on inhalation, after which, on exhalation, the nutrient organisms are retained by the gill stamens, and then sent to the esophagus.
The esophagus often contains glandular cells that secrete mucus. In fish, it is usually short.
Not all fish have a stomach. For example, carp, many gobies, monkfish do not have it, but predators usually do. The stomach in different species of fish can be of different shapes: tubes, oval, letter V, etc., and also have a different structure. The gastric mucosa produces hydrochloric acid and pepsin, which are used to process food.
The intestine begins with the small intestine, into which the bile duct and the pancreatic duct flow. These two ducts deliver bile and enzymes to the intestine that break down proteins to amino acids, fats to glycerol and fatty acids, polysaccharides to sugars. In the intestine, in addition to the breakdown of nutrients, they are absorbed into the bloodstream, which proceeds most intensively in the posterior region. This is facilitated by the folded structure of the intestinal walls; the presence in them of outgrowths penetrated by capillaries and lymphatic vessels; the presence of cells that produce mucus; intestine length: in silver carp it is 16 times longer than body length.
The intestine ends with the anus, usually located in the back of the torso, in front of the genital and urinary openings.
In fish digestion, glands are also involved: liver, gallbladder and ducts, pancreas.
The liver is a large digestive gland, in sharks it has a mass of 14-25% of body weight, in teleost fish. 1-8% of body weight. The liver removes poisons and indigestible proteins from food. The gallbladder produces bile, which neutralizes the acidic reaction of gastric juice. The pancreas produces enzymes necessary for digestion.
Swim bladder fish
The buoyancy of fish (the ratio of the density of the fish’s body to the density of the water) can be neutral (0), positive or negative. In most species, buoyancy ranges from 0.03 to 0.03. With positive buoyancy, fish float, with neutral buoyancy, they hover in the water column, with negative buoyancy, they submerge.
Neutral buoyancy (or hydrostatic balance) in fish is achieved:
1) using the swim bladder;
2) watering the muscles and lightening the skeleton (in deep-sea fish)
3) accumulation of fat (sharks, tuna, mackerel, flounder, gobies, loaches, etc.).
Most fish have a swim bladder. Its occurrence is associated with the appearance of a bone skeleton, which increases the proportion of bony fish. In cartilaginous fish, the swim bladder is absent, from bony fishes it is absent in benthic (gobies, flounder, pinagor), deep-sea and some fast-swimming species (tuna, bonito, mackerel). An additional hydrostatic device in these fish is the lifting force, which is formed due to muscular efforts.
The swim bladder is formed by the bulging of the dorsal wall of the esophagus, its main function. Hydrostatic. The swim bladder also perceives pressure changes, is directly related to the organ of hearing, being a resonator and a reflector of sound vibrations. In loaches, the swim bladder is covered with a bone capsule, has lost its hydrostatic function, and acquired the ability to perceive changes in atmospheric pressure. In lungs and bony ganoids, the swim bladder performs the function of respiration. Some fish are capable of making sounds using their swim bladder (cod, hake).
The swimbladder is a relatively large elastic sac that sits under the kidneys. It happens:
1) unpaired (most fish);
2) paired (lung-breathing and mnogoper).
In many fish, the swim bladder is single-chambered (salmonids), in some species it is two-chambered (cyprinids) or three-chambered (error), the chambers communicate with each other. In a number of fish, blind processes extend from the swim bladder, connecting it to the inner ear (herring, cod, etc.).
The swim bladder is filled with a mixture of oxygen, nitrogen, and carbon dioxide. The ratio of gases in the swim bladder in fish differs and depends on the type of fish, depth of habitat, physiological state, etc. In deep-sea fish, the swim bladder contains much more oxygen than species living closer to the surface.
Fish with swimbladders are divided into open-vesicular and closed-vesicular.
In open-bladder fish, the swim bladder is connected to the esophagus by an air duct. These include. Diodes, polyperes, cartilaginous and bony ganoids, from bony. Herring-like, carp-like, pike-like. Atlantic herring, sprat, and anchovy have a second duct behind the anus, which connects the back of the swim bladder to the outside in addition to the usual air duct.
Closed-bubbly fish have no air duct (perch-like, cod-like, mullet-like, etc.).
The initial filling of the swim bladder with gases in fish occurs when the larva swallows atmospheric air. So, in carp larvae, this takes place 1-1.5 days after hatching. If this does not happen, the development of the larva is disrupted and it dies. In closed-vesicular fish, the swim bladder loses its connection with the external environment over time, in open-vesicular fishes the air duct remains throughout life.
The regulation of the volume of gases in the swim bladder in gallbladder fish occurs using two systems:
1) gaseous iron (fills the bladder with gases from the blood);
2) oval (absorbs gases from the bladder into the blood).
Gas gland. The system of arterial and venous vessels located in front of the swim bladder. Oval. A thin-walled area in the inner lining of the swim bladder surrounded by a muscular sphincter is located at the back of the bladder. When the sphincter relaxes, gases from the swim bladder flow to the middle layer of its wall, where there are venous capillaries and their diffusion into the blood occurs. The amount of absorbed gases is regulated by changing the size of the oval hole.
When closed-bubble fishes submerge, the volume of gases in their swim bladder decreases, and the fish acquire negative buoyancy, but upon reaching a certain depth, they adapt to it by releasing gases into the swim bladder through the gas gland. When the fish rises, when the pressure decreases, the volume of gases in the swim bladder increases, their excess is absorbed through the oval into the blood, and then through the gills is removed into the water.
In open-bubble fish, there is no oval; excess gases are removed to the outside through the air duct. Most open-bubble fish do not have a gas gland (herring, salmon). The secretion of gases from the blood into the bladder is poorly developed and is carried out with the help of the epithelium located on the inner layer of the bladder. Many open-bladder fish trap air before diving to provide neutral buoyancy at depth. However, during strong dives, it is not enough, and the filling of the swim bladder occurs with gases coming from the blood.
Ribosomes. structure and function
The structure and function of ribosomes should be known to any modern person. The functioning of a cell of a living organism is a complex process that continues throughout the life of an organism.
Ribosomes are cell organelles involved in a complex cellular mechanism for translating the genetic code into the amino acid chain. Long chains of amino acids are linked together to form proteins that perform various functions. The diagram of the structure of the ribosome is shown in the figure below.
What is the function of ribosomes?
The purpose of the described organoid in any cell is to carry out protein synthesis. Proteins are used by almost all cells:
- As catalysts, they speed up the reaction time;
- As fibers. provide cell stability;
- Many proteins have individual tasks.
The main storage of information in cells is a molecule of deoxyribonucleic acid (DNA). A special enzyme, RNA polymerase, binds to a DNA molecule and creates a “mirror copy”. matrix ribonucleic acid (mRNA), which freely moves from the nucleus to the cytoplasm of the cell.
The ribonucleic acid chain is processed as it exits the nucleus; RNA regions that do not encode proteins are removed; mRNA is used for further protein synthesis.
Each mRNA consists of 4 different nucleic acids, triplets of which make up codons. Each codon defines a specific amino acid. There are 20 amino acids in the body of all living things on Earth. The codons used to specify amino acids are nearly universal.
The codon that triggers all proteins is “AUG”, the nucleic acid sequence:
A special RNA molecule supplies amino acids for synthesis. transport RNA or tRNA. The tRNA carrying the corresponding amino acid approaches the active codon and associates with it. Formation of a peptide bond of a new amino acid with a protein under construction.
Where ribosomes are formed
The constituent parts of the organoid are formed in the nucleolus. The two subunits combine to start the chemical process of protein synthesis from the mRNA strand. The ribosome acts as a catalyst by forming peptide bonds between amino acids. Used tRNA is released back into the cytosol, and later it can bind to another amino acid.
The organoid will reach the mRNA stop codon (UGA, UAG and UAA), stopping the synthesis process. Special proteins (termination factors) will interrupt the amino acid chain, separating it from the last tRNA. protein formation will end.
Different proteins require some modifications to be transported to specific areas of the cell before they can function. The ribosome, attached to the endoplasmic reticulum, will place the newly formed protein inside, it will undergo additional modifications, and will be properly folded. Other proteins are formed directly in the cytosol, where they act as a catalyst for various reactions.
Ribosomes create the proteins the cells need, making up about 20 percent of the cell’s composition. There are approximately 10,000 different proteins in a cell, approximately a million copies each.
The ribosome is efficiently and quickly involved in synthesis, adding 3-5 amino acids to the protein chain per second. Short proteins containing several hundred amino acids can be synthesized in minutes.
Composition and structure of ribosomes
Ribosomes have a similar structure in the cells of all organisms on Earth and are indispensable for protein synthesis. At the beginning of the evolution of various life forms, the ribosome was accepted as a universal way of translating RNA into proteins. These organelles vary slightly in different organisms.
The described organelles consist of a large and small subunit located around the mRNA molecule. Each subunit is a combination of proteins and RNA called ribosomal RNA (rRNA).
The length of rRNA is different in different strands. RRNA is surrounded by proteins that make up the ribosome. RRNA holds mRNA and tRNA in the organoid and acts as a catalyst to accelerate the formation of peptide bonds between amino acids.
Ribosomes are measured in Svedberg units, which means how long it takes for a molecule to settle out of solution in a centrifuge. The larger the number, the larger the molecule.
The differences between prokaryotic and eukaryotic ribosomes are discussed in the table.
|Size in units of Svedberg||70S||80S|
|proteins and RNA||less protein and less RNA||more proteins and more RNA|
|RNA molecules||3 RNA molecules||4 RNA molecules|
Ribosomes are responsible for the process of protein synthesis. the motor force of the body and are one of the key organelles of a living cell, represented in all the variety of living things on Earth.
Functions of the gallbladder
In the human body, this organ performs several functions:
- Collects bile;
- Thickens and preserves it;
- Helps remove bile into the lumen of the small intestine;
- Protects the human body from irritating components.
A normal liver produces bile around the clock, resulting in a need for a reservoir to store it until it is needed. This reservoir is the gallbladder. But a lot of this secret is produced in the liver. from 1 to 2 liters, and the capacity of the gallbladder is ten times less. only 50–80 ml. How to fit this volume into such a small organ? It’s very simple. under the influence of various enzymes, water and some substances used in other processes are removed from bile. Simply put, its concentration occurs.
The bladder begins to contract within a few minutes after the food passes through the esophagus. The more fatty the food is eaten, the stronger the contraction will be, and the more gallbladder bile enters the small intestine. It is this type of concentrated bile that stimulates the peristalsis of the duodenum, helping the body to thoroughly digest heavy food. It takes approximately 2 hours from food enters the stomach to its passage into the first section of the small intestine.
The more food comes from the stomach, the more bile is needed to digest it. And if there is not enough gallbladder bile, the liver picks up the baton, and then hepatic bile begins to take an active part in digestion.
The mechanism for removing bile from the bladder is approximately as follows:
- The gallbladder contracts;
- The bladder valve opens;
- The sphincter of Oddi opens;
- Bile enters the intestines.
If a person’s gallbladder is removed, its function is taken over by the biliary tract. It is in the bile ducts that hepatic bile is concentrated, and remains until the moment when there is a need for it.
Overview of the Gallbladder
It is a hollow organ, shaped like a small pouch. It can be either completely empty (after ejection of a portion of bile into the intestines) or full. As a result, depending on the degree of filling, this organ can have either a pear-shaped or cylindrical or rounded shape. It is located, as well as the liver, in the right hypochondrium.
The gallbladder consists of the neck, body, and fundus. Directly from its neck comes the cystic duct, which, connecting with the hepatic duct, forms a common bile duct. Also in the extrahepatic biliary tract there are two sphincters, or valves, which are responsible for regulating the flow of bile directly into the gallbladder and intestines.
Functions of the gallbladder in the human body
It would seem, why does a person need a gallbladder? After all, bile can also come from the liver, because it is there that it is produced constantly. But if you look at it, everything turns out to be not so simple.
In order to understand why we need it, you also need to know how the gallbladder works.
Protective function of the gallbladder
Bile is a set of biologically active substances. This secretion contains bilirubin, bile acids, cholesterol, as well as a large amount of inorganic elements such as, for example, calcium, sodium, chlorine. Bile acids are cholesterol breakdown products, they are divided into primary and secondary. The effectiveness of this digestive secretion depends on the composition of acids and their salts. By their properties, they are hydrophobic. hepatotoxic (carcinogenic), and hydrophilic. hepatoprotective.
Excessive flow of bile from the liver into the small intestine increases the circulation of bile acids. This is especially true for patients whose bladder has been removed or filled with stones, due to which there is not enough space to collect and store secretions. The consequence can be the accumulation of dangerous hydrophobic acids in the liver cells, possibly the occurrence of reactive hepatitis. Bile synthesis is reduced or completely disrupted.
The concentration of the level of hydrophobic bile acids, as well as other toxic substances in the liver bile, increases the likelihood of chronic pancreatitis. Also, with this condition, it is possible to regularly throw the contents of the small intestine into the stomach. It increases the risk of developing bowel or pancreatic cancer.
The gallbladder, by collecting bile acids and thus reducing their concentration in the intestine, reduces the incidence of hepatotoxic acids in the small and large intestine. This protects the liver, stomach and colon from their effects.
So, the gallbladder is necessary for the human body not only in order to collect and store bile, it also removes excess bile from the circulation. An important function is also to protect the body from the irritating effects of bile.