Fish heart. The cardiovascular system of fish. The structure of the heart of cold-blooded inhabitants of reservoirs

The sturgeon belongs to the class of ray-finned animals, a subclass of cartilaginous ganoids. The sturgeon is a rather large fish, the length of the body can reach up to 6 meters. Weight Limit reaches 816 kilograms. However, the average sturgeon that goes into the fishery reaches a weight of 12 to 16 kilograms.

The skeleton consists of cartilage, the spine is absent. It retains the notochord throughout its life. The structure of the body is very interesting, has the following forms:

• The body is spindle-shaped, elongated, devoid of scales. The body has five rows of diamond-shaped lamellar scutes. Along the ridge, one such row contains from 10 to 20 scutes.
• Sturgeon head small size, the muzzle is elongated cone-shaped. At the end of the muzzle are four antennae without a fringe. The mouth is protruding, the lips are fleshy, the teeth are missing. The fry grow small teeth, but then fall out.
• On the body of the sturgeon are randomly scattered bone plates in the form of stars. The pectoral fin is very rigid, the anterior ray resembles a spine. The dorsal fin has 27 to 51 rays that run towards the caudal fin.
• The swim bladder is well developed.
• The color of the sturgeon is mostly grey. However, the back may be lighter shades or grayish-black. It has brown sides and a white belly.

Is one of the longest living fish on earth. On average, lives from 40 to 60 years. Some representatives of the sturgeon species have lived for more than 100 years.

Varieties of sturgeon fish

The sturgeon genus includes 17 species of fish. Most of them are on the verge of extinction and are in the Red Book.

The bulk of representatives of fish of this species begins its spawning at a fairly late age. Males are ready to breed at the age of 5 to 18 years, females from 8 to 21 years. The habitat of the fish affects the time of maturation of the fish - the further north the fish lives, the later it will begin to reproduce offspring. Reproduction in these fish does not occur every year, spawning of females occurs every 3-5 years. The spawning migration of anadromous fish extends considerably in time and lasts from the beginning of spring to the beginning of November. The peak is in the middle of summer.

For spawning, they prefer rivers with a strong current, with a rocky bottom and rarely sandy. Egg laying in stagnant water is not observed. Spawning occurs at a depth of 4 to 25 meters, at a water temperature of 15 to 20 degrees, depending on the habitat. High temperatures adversely affect the development of embryos. At the same time, if the temperature rises above 22 degrees, the game dies.

Females lay their game in crevices on the bottom or between large stones. This is a very prolific fish: a large individual lays more than a million eggs, which makes up to 25% of its body weight. Sturgeons have sticky caviar, it keeps well on the surface where it was reflected. Embryo development lasts approximately 2-4 days. The incubation period is 10 days. The larva hatches and it weighs only 10 grams. Newborn fish have poor vision and swim very poorly, at first they hide in shelters.

The yolk sac resolves within 10-14 days. The fry during this time grow up to 1.5-2 centimeters and begin to feed. Usually, fry prefer planktonic crustaceans for food. When they grow up, they switch to crustaceans and mysids. At first, small fish live in fresh water, staying in salt water is deadly for them.

The benefits and harms of sturgeon

The calorie content of sturgeon meat is 160 calories per 100 grams of product. Contains easily digestible proteins, due to which the product is digested very quickly. Often sturgeon meat is used in various kinds of diets, as meat contains a large amount of rare beneficial acids. Meat includes vitamins of groups "B", "C", "A" and "PP". Delicious sturgeon meat contains useful macroelements of potassium, phosphorus, calcium, magnesium, as well as sodium, iron, chromium, nickel, iodine and fluorine.

Sturgeon caviar is saturated with protein and lipids. The calorie content of caviar is more than meat and is 200 calories per 100 grams. Therefore, the product is recommended for use by people after serious illnesses.

Regular consumption of sturgeon meat beneficial effect on the heart vascular system human. Reduces cholesterol levels and the risk of myocardial infarction. The product affects the growth and strengthening of bone tissue, and also improves skin condition.

Despite the obvious benefits of sturgeon products, they can also be harmful. Caviar and sturgeon itself can be infected with the causative agent of botulism, so you need to buy products only from trusted sellers. When buying, pay attention to appearance and smell.

Should be used with caution in people who are ill diabetes as well as obese people.

Despite the fact that fish are cold-blooded creatures, they also have a heart in their body. They need it for the same functions as the human heart, that is, its main function is to ensure the movement of blood through the vessels.

The heart is one of the most important organs of the body, not only in humans, but also in animals. Fish are no exception, although they are cold-blooded creatures.

The fish's heart

By itself, this organ in them is a small sac that performs the main function in the body - that is, through contraction, it performs the function of pumping blood throughout the body.

The heart size of these waterfowl directly depends on their size. Thus, the larger the size of the fish, the larger this important organ will be. Therefore, such a parameter as the size of a heart with a fist for a fish is completely unsuitable. Vedas, very small individuals can have such an organ only a few centimeters in size. The largest representatives of this species of animals can have this organ up to thirty centimeters in size. These fish include:

• sturgeon;
• pike
• catfish;
• carp, etc.

Fish heart location

Some people ask: how many hearts does a fish have? Of course, there is only one correct answer. is one heart. Many housewives do not even have a clue that they can easily find this important organ in fish when they are cleaning it.

So where is he? Everything is very simple. Like a person or any other animal, these cold-blooded creatures have it in the anterior part of the peritoneum. More precisely, its location is directly under the gills. On both sides of it, like a person, there are ribs that protect it.

The structure of the heart of cold-blooded inhabitants of reservoirs

Since fish live in water, for their life gills needed. In this regard, the structure of their heart differs from the structure of this organ in the terrestrial inhabitants of the planet. If we evaluate it purely externally, then it resembles a human organ. A small red sac, with a small pale pink sac at the bottom, is that organ.

The fish heart consists of only two chambers, that is, it is two-chambered. This is the main feature of its structure. Its components are the ventricle and atrium, which are in close proximity to each other. Namely, they are located one above the other. The chambered ventricle is located slightly below the atrium and can be distinguished by its lighter shade. In fish, the heart consists of muscle tissue, due to the fact that it acts as a pump, that is, it constantly contracts.

Found in the ventricle of the fish heart differences in the structure of the myocardium. It is generally accepted that the myocardium of fish is more special and is represented by a homogeneous heart tissue, which is evenly penetrated by trabeculae and capillaries. The diameter of muscle fibers in fish is smaller than in warm-blooded ones, and is approximately 6-7 microns. These values ​​are half as much when compared with other animals, for example, with the myocardium of a dog. This myocardium has a name - spongy.

The heart of cold-blooded inhabitants of water bodies is connected to the gills with the help of arteries. And they, in turn, are located on both sides of the main abdominal artery. This artery is also called the abdominal aorta. It is worth noting that in addition to these vessels, thin veins run throughout the body of such waterfowl, which lead to the atrium. These veins carry blood.

The blood of fish is saturated with carbon dioxide.. This gas is processed in a special way.

From this it follows that the water in which the fish live must be saturated with oxygen.

This continues the circulation process. . Oxygenated blood, moves further through the body and enters the main aorta, located above the ridge. Many capillaries diverge from this artery to the sides. They circulate blood.

In view of this, it turns out that in the fish body there is a constant replacement of blood. Arterial blood, which has a rich red tint, changes to venous blood, which looks darker.

Veins carry blood to the atrium and from there goes to the second chamber. Then it moves to the gills with the help of the abdominal aorta. From this it can be seen that the heart of the fish makes many contractions that continue all the time.

In the circulatory system of fish, in comparison with lancelets, a real heart appears. It consists of two chambers, i.e. double chambered fish heart. The first chamber is the atrium, the second chamber is the ventricle of the heart. Blood first enters the atrium, then is pushed into the ventricle by muscle contraction. Further, as a result of its contraction, it pours into a large blood vessel.

The heart of fish is located in the pericardial sac located behind the last pair of gill arches in the body cavity.

Like all chords, closed circulatory system of fish.

This means that nowhere along the path of its passage, the blood does not leave the vessels and does not pour into the body cavity. To ensure the exchange of substances between the blood and the cells of the whole organism, large arteries (vessels that carry blood saturated with oxygen) gradually branch into smaller ones. The smallest vessels are capillaries. Having given up oxygen and taken in carbon dioxide, the capillaries again unite into larger vessels (but already venous).

Fish only one circle of blood circulation.

With a two-chambered heart, it cannot be otherwise. In more highly organized vertebrates (starting with amphibians), a second (pulmonary) circle of blood circulation appears. But these animals also have a three-chambered or even four-chambered heart.

Venous blood flows through the heart that gives oxygen to the cells of the body.

Does a fish have a heart?

Further, the heart pushes this blood into the abdominal aorta, which goes to the gills and branches into the afferent branchial arteries (but despite the name "arteries" they contain venous blood). In the gills (specifically, in the gill filaments), carbon dioxide is released from the blood into the water, and oxygen seeps from the water into the blood.

This happens as a result of the difference in their concentration (dissolved gases go to where they are less). Enriched with oxygen, the blood becomes arterial. The efferent branchial arteries (already with arterial blood) flow into one large vessel - the dorsal aorta.

It runs under the spine along the body of the fish and smaller vessels originate from it. The carotid arteries also depart from the dorsal aorta, going to the head and supplying blood, including the brain.

Before entering the heart, venous blood passes through the liver, where it is cleared of harmful substances.

There are slight differences in the circulatory system of bony and cartilaginous fish. Mostly it's about the heart. In cartilaginous fish (and some bony fish), the dilated portion of the abdominal aorta contracts along with the heart, while in most bony fish it does not.

The blood of fish is red, it contains red blood cells with hemoglobin, which binds oxygen.

However, fish erythrocytes are oval in shape, not disc-shaped (as, for example, in humans). The amount of blood flowing through the circulatory system is less in fish than in terrestrial vertebrates.

The heart of fish does not beat often (about 20-30 beats per minute), and the number of contractions depends on temperature environment(the warmer, the more often).

Therefore, their blood does not flow as fast and therefore their metabolism is relatively slow. This, for example, affects the fact that fish are cold-blooded animals.

In fish, the hematopoietic organs are the spleen and the connective tissue of the kidneys.

Despite the fact that the described circulatory system of fish is characteristic of the vast majority of them, it differs somewhat in lungfish and lobe-finned fish.

In lungfish in the heart appears incomplete septum and a semblance of a pulmonary (second) circulation appears. But this circle does not pass through the gills, but through the swim bladder, turned into a lung.

Through the heart of fish passes a) arterial blood b) mixed blood c) venous blood?

What does the heart of a fish look like?

Pike fish heart photo.
Does the fish have a heart, of course.


Photo of pike fish with heart.
The blood in the heart of fish passes in the same way as in others, providing organs with everything necessary for life.
How many hearts a fish has, only one river.

Where the fish has a heart, in the region of the larynx and in pike it continues to beat for some time even after it is removed from the fish.
What kind of blood is in the heart of fish, the blood in the heart of a pike fish is of the same red color, which noticeably darkens when cleaning.


Photo of blood in the heart of a fish.
Useful fish for the heart, almost all are river, only the size of the heart itself is too small for gastronomic use.

Blood performs numerous functions only when it moves through the vessels. The exchange of substances between the blood and other tissues of the body occurs in the capillary network. Differing in great length and branching, it has great resistance to blood flow. The pressure necessary to overcome vascular resistance is created mainly by the heart. The structure of the heart of fish is simpler than that of higher vertebrates. The performance of the heart in fish as a pressure pump is much lower than in terrestrial animals.

Nevertheless, it copes with its tasks. The water environment creates favorable conditions for the work of the heart. If in terrestrial animals a significant part of the work of the heart is spent on overcoming the forces of gravity, vertical movement of blood, then in fish water environment significantly eliminates gravitational influences.

The body elongated in a horizontal direction, a small volume of blood, and the presence of only one blood circulation circuit additionally facilitate the functions of the heart in fish.

The structure of the heart of fish

The heart of fish is small, accounting for approximately 0.1% of body weight. There are, of course, exceptions to this rule. For example, in flying fish, the mass of the heart reaches 2.5% of body weight.

All fish have a two-chambered heart. However, there are species differences in the structure of this organ.

In a generalized form, two schemes of the structure of the heart in the class of fish can be presented. In both the first and second cases, 4 cavities are distinguished: the venous sinus, the atrium, the ventricle, and a formation that vaguely resembles the aortic arch in warm-blooded animals, the arterial bulb in teleosts and the arterial cone in lamellar gills (Fig. 7.1). The fundamental difference between these schemes lies in the morphofunctional features of the ventricles and arterial formations.

In teleosts, the arterial bulb is represented by a fibrous tissue with a spongy structure of the inner layer, but without valves.

In lamellar gills, the arterial cone, in addition to fibrous tissue, also contains typical cardiac muscle tissue, therefore it has contractility.

The cone has a valve system that facilitates the one-way movement of blood through the heart.

Rice. 7.1. Diagram of the structure of the heart of fish

Differences in the structure of the myocardium were found in the ventricle of the fish heart.

It is generally accepted that the myocardium of fish is specific and is represented by a homogeneous cardiac tissue, evenly penetrated by trabeculae and capillaries. The diameter of muscle fibers in fish is smaller than in warm-blooded ones, and is 6-7 microns, which is half as much as, for example, in the myocardium of a dog. Such a myocardium is called spongy.

What kind of blood passes through the heart of a fish?

Reports of fish myocardial vascularization are rather confusing. The myocardium is supplied with venous blood from the trabecular cavities, which, in turn, are filled with blood from the ventricle through the Thebesian vessels. In the classical sense, fish do not have a coronary circulation. At least, cardiologists adhere to this point of view. However, in the literature on ichthyology, the term "coronary circulation of fish" occurs frequently.

IN last years researchers have found many variations in myocardial vascularization. For example, C. Agnisola et. al (1994) reports the presence of bilayer myocardium in trout and electric rays. From the side of the endocardium lies a spongy layer, and above it is a layer of myocardial fibers with a compact, ordered arrangement.

Studies have shown that the spongy layer of the myocardium is supplied with venous blood from trabecular lacunae, while the compact layer receives arterial blood through the hypobronchial arteries of the second pair of gill vents.

In elasmobranchs, the coronary circulation differs in that arterial blood from the hypobronchial arteries reaches the spongy layer through a well-developed capillary system and enters the ventricular cavity through the vessels of Tibesia.

Another significant difference between teleosts and lamellar gills lies in the morphology of the pericardium.

In teleosts, the pericardium resembles that of land animals. It is represented by a thin shell.

In lamellar gills, the pericardium is formed cartilage tissue therefore, it is like a rigid, but elastic capsule.

In the latter case, during the period of diastole, some rarefaction is created in the pericardial space, which facilitates the blood filling of the venous sinus and atrium without additional energy expenditure.

Electrical properties of the fish heart

The structure of the myocytes of the cardiac muscle of fish is similar to that of higher vertebrates.

Therefore, the electrical properties of the heart are similar. The resting potential of myocytes in teleosts and lamellar gills is 70 mV, in myxines it is 50 mV. At the peak of the action potential, a change in the sign and magnitude of the potential is recorded from minus 50 mV to plus 15 mV. Depolarization of the myocyte membrane leads to excitation of sodium-calcium channels. First, sodium ions and then calcium ions rush into the myocyte cell. This process is accompanied by the formation of a stretched plateau, and the absolute refractoriness of the heart muscle is functionally fixed.

This phase in fish is much longer - about 0.15 s.

The subsequent activation of potassium channels and the release of potassium ions from the cell provide rapid repolarization of the myocyte membrane.

In turn, membrane repolarization closes potassium channels and opens sodium channels. As a result, the potential of the cell membrane returns to its original level of minus 50 mV.

The myocytes of the fish heart, capable of generating potential, are localized in certain areas of the heart, which are collectively combined into the "cardiac conduction system". As in higher vertebrates, in fish, the initiation of cardiac systole occurs in the sinatrial node.

Unlike other vertebrates in fish, the role of pacemakers is played by all structures of the conduction system, which in teleosts includes the center of the ear canal, a node in the atrioventricular septum, from which Purkinje cells stretch to typical ventricular cardiocytes.

The rate of conduction of excitation along the conduction system of the heart in fish is lower than in mammals, and it is not the same in different parts of the heart.

The maximum speed of potential propagation was registered in the structures of the ventricle.

The fish electrocardiogram resembles that of a human in leads V3 and V4 (Fig.

7.2). However, the technique for imposing leads for fish has not been developed in as much detail as for terrestrial vertebrates.

Rice. 7.2. fish electrocardiogram

In trout and eel, P, Q, R, S, and T waves are clearly visible on the electrocardiogram. Only the S wave looks hypertrophied, and the Q wave unexpectedly has a positive direction; T, as well as the Vg wave between the G and R teeth.

On the electrocardiogram of acne, the P wave is preceded by the V wave. The etiology of the teeth is as follows: the P wave corresponds to the excitation of the ear canal and the contraction of the venous sinus and atrium; the QRS complex characterizes the excitation of the atrioventricular node and ventricular systole; T wave occurs in response to repolarization cell membranes cardiac stomach.

The work of the fish heart

The heart of fish works rhythmically.

The heart rate in fish depends on many factors.

Heart rate (beats per minute) in carp at 20 °C

Juveniles weighing 0.02 g 80

Underyearlings weighing 25 g 40

Two-year-olds weighing 500 g 30

In experiments in vitro (isolated perfused heart), the heart rate in rainbow trout and electric skate was 20-40 beats per minute.

Of the many factors, environmental temperature has the most pronounced effect on heart rate.

The telemetry method on sea bass and flounder revealed the following relationship (Table 7.1).

Species sensitivity of fish to temperature changes has been established.

So, in flounder, when the water temperature rises from g to 12 ° C, the heart rate increases by 2 times (from 24 to 50 beats per minute), in perch - only from 30 to 36 beats per minute.

The heartbeat is controlled by the central nervous system, as well as intracardiac mechanisms.

As in warm-blooded animals, tachycardia was observed in fish in experiments in vivo with an increase in the temperature of the blood flowing to the heart. A decrease in the temperature of the blood flowing to the heart caused bradycardia. Vagotomy reduced the level of tachycardia. Many humoral factors also have a chronotropic effect. A positive chronotropic effect was obtained with the introduction of atropine, adrenaline, eptatretin. Negative chronotropy was caused by acetylcholine, ephedrine, cocaine.

Interestingly, the same humoral agent different temperature environment can have the exact opposite effect on the heart of fish.

So, on an isolated trout heart with low temperatures(6aC) epinephrine causes a positive chronotropic effect, and against the background elevated temperatures(15°C) of the perfusion fluid - a negative chronotropic effect.

The cardiac output of blood in fish is estimated at 15-30 ml/kg per minute. The linear velocity of blood in the abdominal aorta is 8-20 cm/s.

In vitro on trout, the dependence of cardiac output on the pressure of the perfusion fluid and the oxygen content in it was established. However, under the same conditions, the minute volume of the electric ray did not change. Researchers include more than a dozen components in the perfusate.

Composition of perfusate for trout heart (g/l)

Sodium chloride 7.25

Potassium chloride 0.23

Calcium fluoride 0.23

Magnesium sulfate (crystalline) 0.23

Sodium phosphate monosubstituted (crystalline) 0.016

Sodium phosphate disubstituted (crystalline) 0.41

Glucose 1.0

Polyvinyl pyrrole idol (PVP) colloidal 10.0

Notes:

The solution is saturated with a gas mixture of 99.5% oxygen, 0.5% carbon dioxide (carbon dioxide) or a mixture of air (995%) with carbon dioxide (0.5%).

2. The pH of the perfusate is adjusted to 7.9 at 10°C using sodium bicarbonate.

The composition of the perfusate for the heart of the electric skate (g / l)

Sodium chloride 16.36

Potassium chloride 0.45

Magnesium chloride 0.61

Sodium sulfate 0.071

Sodium phosphate monosubstituted (crystalline) 0.14

Sodium bicarbonate 0.64

Urea 21.0

Glucose 0.9

Notes:

The perfusate is saturated with the same gas mixture. 2.pH 7.6.

In such solutions, the isolated heart of fish retains physiological properties and works for a very long time. When performing simple manipulations with the heart, it is allowed to use isotonic solution sodium chloride. However, do not count on long work heart muscle.

Circle of blood circulation of fish

Fish, as you know, have one circle of blood circulation. And, nevertheless, the blood circulates through it longer.

It takes about 2 minutes for a complete blood circulation in fish (in a person, blood passes through two circles of blood circulation in 20-30 seconds). From the ventricle, through the arterial bulb or arterial cone, blood enters the so-called abdominal aorta, which departs from the heart in a cranial direction to the gills (Fig.

The abdominal aorta is divided into left and right (according to the number of gill arches) afferent branchial arteries. A petal artery departs from them to each gill petal, and two arterioles depart from it to each petal, which form a capillary network of the thinnest vessels, the wall of which is formed by a single-layer epithelium with large intercellular spaces.

The capillaries merge into a single efferent arteriole (according to the number of petals). The efferent arterioles form the efferent lobular artery. Petal arteries form the left and right efferent branchial arteries, through which arterial blood flows.

Rice. 7.3. Diagram of the circulatory system of bony fish

The carotid arteries branch from the efferent branchial arteries to the head. Further, the branchial arteries merge to form a single large vessel - the dorsal aorta, which stretches throughout the body under the spine and provides arterial systemic circulation.

The main outgoing arteries are the subclavian, mesenteric, iliac, caudal and segmental. The venous part of the circle begins with capillaries of muscles and internal organs, which, when combined, form paired anterior and paired posterior cardinal veins. The cardinal veins, uniting with two hepatic veins, form the Cuvier ducts, which flow into the venous sinus.

Thus, the heart of fish pumps and sucks only venous blood.

all organs and tissues receive arterial blood, since before filling the microcirculatory bed of organs, blood passes through the gill apparatus, in which gases are exchanged between venous blood and the aquatic environment.

Blood movement and blood pressure in fish

Blood moves through the vessels due to the difference in its pressure at the beginning of the circle of blood circulation and at its end.

When measuring blood pressure without anesthesia in the ventral position (causes bradycardia) in salmon in the abdominal aorta, it was 82/50 mm Hg. Art., and in the dorsal 44/37 mm Hg. Art. The study of anesthetized fish of several species showed that anesthesia significantly reduces systolic pressure - up to 30-70 mm Hg. Art.

Pulse pressure at the same time by species of fish ranged from 10 to 30 mm Hg. Art. Hypoxia led to an increase in pulse pressure up to 40 mm Hg. Art.

At the end of the circulation circle, the blood pressure on the walls of the vessels (in the Cuvier ducts) did not exceed 10 mm Hg. Art.

The greatest resistance to blood flow is provided by the gill system with its long and highly branched capillaries.

In carp and trout, the difference in systolic pressure in the abdominal and dorsal aorta, i.e., at the entrance and exit from the gill apparatus, is 40-50%. In hypoxia, the gills provide even greater resistance to blood flow.

In addition to the heart, other mechanisms also contribute to the movement of blood through the vessels.

Thus, the dorsal aorta, which has the form of a straight tube with relatively rigid (compared to the abdominal aorta) walls, has little resistance to blood flow. The segmental, caudal, and other arteries have a system of pocket valves similar to those of large venous vessels.

This valve system prevents backflow of blood. For venous blood flow great importance also have contractions adjacent to the veins of the mouse, which push the blood in the cardiac direction. Venous return and cardiac output are optimized by the mobilization of the deposited blood. It has been experimentally proven that muscle load in trout leads to a decrease in the volume of the spleen and liver.

Finally, the mechanism of uniform filling of the heart and the absence of sharp systolic-diastolic fluctuations in cardiac output contribute to the movement of blood. The filling of the heart is already provided during ventricular diastole, when a certain rarefaction is created in the pericardial cavity and blood passively fills the venous sinus and atrium. The systolic shock is damped by the arterial bulb, which has an elastic and porous inner surface.

The cardiovascular system of fish consists of the following elements:

Circulatory system, lymphatic system and hematopoietic organs.

The circulatory system of fish differs from other vertebrates in one circle of blood circulation and a two-chambered heart filled with venous blood (with the exception of lungfish and crossopterans). The main elements are: Heart, blood vessels, blood (Fig. 1b

Figure 1. The circulatory system of fish.

Heart in fish is located near the gills; and is enclosed in a small pericardial cavity, and in lampreys - in a cartilaginous capsule. The fish heart is two-chambered and consists of a thin-walled atrium and a thick-walled muscular ventricle. In addition, adnexal sections are also characteristic of fish: the venous sinus, or venous sinus, and the arterial cone.

The venous sinus is a small thin-walled sac in which venous blood accumulates. From the venous sinus, it enters the atrium, and then into the ventricle. All openings between the sections of the heart are equipped with valves, which prevents the backflow of blood.

In many fish, with the exception of teleosts, an arterial cone adjoins the ventricle, which is part of the heart. Its wall is also formed by cardiac muscles, and on the inner surface there is a system of valves.

In bony fish, instead of an arterial cone, there is an aortic bulb - a small formation white color, which is an enlarged part of the abdominal aorta. Unlike the arterial cone, the aortic bulb consists of smooth muscles and has no valves (Fig. 2).

Fig.2. Scheme circulatory system sharks and the structure of the heart of sharks (I) and bony fishes (II).

1 - atrium; 2 - ventricle; 3 - arterial cone; 4 - abdominal aorta;

5 - afferent gill artery; 6 - efferent gill artery; 7- carotid artery; 8 - dorsal aorta; 9 - renal artery; 10 - subclavian artery; I - tail artery; 12 - venous sinus; 13 - Cuvier duct; 14 - anterior cardinal vein; 15 - tail vein; 16 - the portal system of the kidneys; 17 - posterior cardinal vein; 18 - lateral vein; 19 - subintestinal vein; 20-portal vein of the liver; 21 - hepatic vein; 22 - subclavian vein; 23 - aortic bulb.

In lungfish, due to the development of pulmonary respiration, the structure of the heart has become more complicated. The atrium is almost completely divided into two parts by a septum hanging from above, which continues in the form of a fold into the ventricle and arterial cone. Arterial blood from the lungs enters the left side, venous blood from the venous sinus enters the right side, so more arterial blood flows in the left side of the heart, and more venous blood flows in the right side.

Fish have a small heart. Its mass is different types fish varies and ranges from 0.1 (carp) to 2.5% (flying fish) of body weight.

The heart of cyclostomes and fish (with the exception of lungfish) contains only venous blood. The heart rate is specific for each species, and also depends on the age, physiological state of the fish, water temperature and is approximately equal to the frequency of respiratory movements. In adult fish, the heart contracts rather slowly - 20-35 times per minute, and in juveniles much more often (for example, in sturgeon fry - up to 142 times per minute). When the temperature rises, the heart rate increases, and when it decreases, it decreases. In many fish during the wintering period (bream, carp), the heart contracts only 1-2 times per minute.

The circulatory system of fish is closed. The vessels that carry blood away from the heart are called arteries, although venous blood flows in some of them (abdominal aorta, bringing gill arteries), and the vessels that bring blood to the heart - veins. Fish (except lungfish) have only one circle of blood circulation.

In bony fish, venous blood from the heart through the aortic bulb enters the abdominal aorta, and from it through the afferent branchial arteries to the gills. The teleosts are characterized by four pairs of afferent and as many efferent gill arteries. Arterial blood through the efferent branchial arteries enters the paired supra-gill vessels, or roots of the dorsal aorta, passing along the bottom of the skull and closing in front, forming a head circle, from which vessels depart to different parts of the head. At the level of the last branchial arch, the roots of the dorsal aorta, merging together, form the dorsal aorta, which runs in the trunk region under the spine, and in the caudal region in the hemal canal of the spine and is called the caudal artery. The arteries that supply arterial blood to organs, muscles, and skin are separated from the dorsal aorta. All arteries break up into a network of capillaries, through the walls of which there is an exchange of substances between blood and tissues. Blood is collected from the capillaries into the veins (Fig. 3).

The main venous vessels are the anterior and posterior cardinal veins, which, merging at the level of the heart, form transversely running vessels - the Cuvier ducts, which flow into the venous sinus of the heart. The anterior cardinal veins carry blood from the top of the head. From the lower part of the head, mainly from the visceral apparatus, blood is collected in the unpaired jugular (jugular) vein, which stretches under the abdominal aorta and near the heart is divided into two vessels that independently flow into the Cuvier ducts.

From the caudal region, venous blood is collected in the caudal vein, which passes in the hemal canal of the spine under the caudal artery. At the level of the posterior edge of the kidneys, the tail vein divides into two portal veins of the kidneys, which stretch along the dorsal side of the kidneys for some distance, and then branch into a network of capillaries in the kidneys, forming the portal system of the kidneys. The venous vessels leaving the kidneys are called the posterior cardinal veins, which run along the underside of the kidneys to the heart.

On their way, they receive veins from the reproductive organs, the walls of the body. At the level of the posterior end of the heart, the posterior cardinal veins merge with the anterior ones, forming paired Cuvier ducts, which carry blood into the venous sinus.

From the digestive tract, digestive glands, spleen, swim bladder, blood is collected in the portal vein of the liver, which, after entering the liver, branches into a network of capillaries, forming the portal system of the liver. From here, blood flows through the paired hepatic veins into the venous sinus. Therefore, fish have two portal systems - the kidneys and the liver. However, the structure of the portal system of the kidneys and the posterior cardinal veins in bony fish is not the same. So, in some cyprinids, pike, perch, cod, the right portal system of the kidneys is underdeveloped and only a small part of the blood passes through the portal system.

Due to the great diversity of the structure and living conditions of various groups of fish, they are characterized by significant deviations from the outlined scheme.

Cyclostomes have seven afferent and as many efferent gill arteries. The supragillary vessel is unpaired, there are no aortic roots. The portal system of the kidneys and the Cuvier ducts are absent. One hepatic vein. There is no inferior jugular vein.

Cartilaginous fish have five afferent gill arteries and ten efferent ones. There are subclavian arteries and veins that provide blood supply to the pectoral fins and shoulder girdle, as well as lateral veins starting from the ventral fins. They pass along the side walls of the abdominal cavity and merge with the subclavian veins in the region of the shoulder girdle.

The posterior cardinal veins at the level of the pectoral fins form extensions - the cardinal sinuses.

In lungfish, more arterial blood, concentrated in the left side of the heart, enters the two anterior branchial arteries, from which it is sent to the head and dorsal aorta. More venous blood from the right side of the heart passes into the two posterior branchial arteries and then into the lungs. During air breathing, the blood in the lungs is enriched with oxygen and enters the left side of the heart through the pulmonary veins (Fig. 4).

In addition to the pulmonary veins, lungfish have abdominal and large cutaneous veins, and instead of the right cardinal vein, the posterior vena cava is formed.

Lymphatic system. The lymphatic system, which is of great importance in metabolism, is closely connected with the circulatory system. Unlike the circulatory system, it is open. Lymph is similar in composition to blood plasma. During the circulation of blood through the blood capillaries, part of the plasma containing oxygen and nutrients leaves the capillaries, forming tissue fluid that bathes the cells. Part of the tissue fluid containing metabolic products re-enters the blood capillaries, and the other part enters the lymphatic capillaries and is called lymph. It is colorless and contains only lymphocytes from the blood cells.

The lymphatic system consists of lymphatic capillaries, which then pass into the lymphatic vessels and larger trunks, through which the lymph slowly moves in one direction - to the heart. Consequently, the lymphatic system carries out the outflow of tissue fluid, complementing the function of the venous system.

The largest lymphatic trunks in fish are paired subvertebrals, which stretch along the sides of the dorsal aorta from tail to head, and lateral, which pass under the skin along the lateral line. Through these and head trunks, lymph flows into the posterior cardinal veins at the Cuvier ducts.

In addition, fish have several unpaired lymphatic vessels: dorsal, ventral, spinal. There are no lymph nodes in fish, however, in some species of fish, under the last vertebrae, there are pulsating paired lymphatic hearts in the form of small oval pink bodies that push lymph to the heart. The movement of the lymph is also facilitated by the work of the trunk muscles and respiratory movements. Cartilaginous fish do not have lymphatic hearts and lateral lymphatic trunks. In cyclostomes, the lymphatic system is separate from the circulatory system.

Blood. The functions of the blood are diverse. It carries nutrients and oxygen throughout the body, frees it from metabolic products, connects the endocrine glands with the relevant organs, and also protects the body from harmful substances and microorganisms. The amount of blood in fish ranges from 1.5 (stingray) to 7.3% (scad) of the total mass of fish, while in mammals it is about 7.7%.

Rice. 5. Fish blood cells.

Fish blood consists of blood fluid, or plasma, formed elements - red - erythrocytes and white - leukocytes, as well as platelets - platelets (Fig. 5). Compared to mammals, fish have a more complex morphological structure of blood, since in addition to specialized organs, the walls of blood vessels also participate in hematopoiesis. Therefore, there are shaped elements in the bloodstream at all phases of their development. Erythrocytes are ellipsoidal and contain a nucleus. Their number in different fish species ranges from 90 thousand / mm 3 (shark) to 4 million / mm 3 (bonito) and varies in the same species B: depending on the sex, age of the fish, as well as environmental conditions.

Most fish have red blood, which is due to the presence of hemoglobin in red blood cells, which carries oxygen from the respiratory system to all cells of the body.

Rice. 6. Antarctic whitefish

However, in some Antarctic whitefish, which include icefish, the blood contains almost no red blood cells, and therefore hemoglobin or any other respiratory pigment. The blood and gills of these fish are colorless (Fig. 6). In conditions of low water temperature and high oxygen content in it, respiration in this case is carried out by diffusion of oxygen into the blood plasma through the capillaries of the skin and gills. These fish are inactive, and their lack of hemoglobin is compensated by the increased work of a large heart and the entire circulatory system.

The main function of leukocytes is to protect the body from harmful substances and microorganisms. The number of leukocytes in fish is high, but variable

in and depends on the species, gender, physiological state of the fish, as well as the presence of a disease in it, etc.

A sculpin bull, for example, has about 30 thousand / mm 3, a ruff has from 75 to 325 thousand / mm 3 leukocytes, while in humans there are only 6-8 thousand / mm 3. A large number of leukocytes in fish indicates a higher protective function of their blood.

Leukocytes are divided into granular (granulocytes) and non-granular (agranulocytes). In mammals, granular leukocytes are represented by neutrophils, eosinophils, and basophils, while non-granular leukocytes are represented by lymphocytes and monocytes. There is no generally accepted classification of leukocytes in fish. The blood of sturgeons and teleosts differs primarily in the composition of granular leukocytes. In sturgeon they are represented by neutrophils and eosinophils, while in teleosts they are represented by neutrophils, pseudoeosinophils and pseudobasophils.

Non-granular fish leukocytes are represented by lymphocytes and monocytes.

One of the features of the blood of fish is that the leukocyte formula in them, depending on the physiological state of the fish, varies greatly, therefore not all granulocytes characteristic of this species are always found in the blood.

Platelets in fish are numerous, and larger than in mammals, with a nucleus. They have importance in blood coagulation, which is facilitated by the mucus of the skin.

Thus, the blood of fish is characterized by signs of primitiveness: the presence of a nucleus in erythrocytes and platelets, a relatively small number of erythrocytes, and a low content of hemoglobin, which cause a low metabolism. At the same time, it is also characterized by features of high specialization: a huge number of leukocytes and platelets.

Hematopoietic organs. If in adult mammals hematopoiesis occurs in the red bone marrow, lymph nodes, spleen and thymus, then in fish that do not have either bone marrow or lymph nodes, various specialized organs and foci participate in hematopoiesis. So, in sturgeons, hematopoiesis mainly occurs in the so-called lymphoid organ located in the head cartilages above the medulla oblongata and cerebellum. All types of shaped elements are formed here. In bony fish, the main hematopoietic organ is located in the recesses of the outer part of the occipital region of the skull.

In addition, hematopoiesis in fish occurs in various foci - the head kidney, spleen, thymus, gill apparatus, intestinal mucosa, walls of blood vessels, as well as in the pericardium of teleosts and the endocardium of sturgeons.

head kidney in fish, it is not separated from the trunk and consists of lymphoid tissue, in which erythrocytes and lymphocytes are formed.

Spleen fish have a variety of shapes and locations. Lampreys do not have a formed spleen, and its tissue lies in the sheath of the spiral valve. In most fish, the spleen is a separate dark red organ located behind the stomach in the folds of the mesentery. In the spleen, red blood cells, white blood cells and platelets are formed, and the destruction of dead red blood cells occurs. In addition, the spleen performs a protective function (phagocytosis of leukocytes) and is a blood depot.

thymus(goiter, or thymus, gland) is located in the gill cavity. It distinguishes the surface layer, cortical and cerebral. Here lymphocytes are formed. In addition, the thymus stimulates their formation in other organs. Thymus lymphocytes are capable of producing antibodies involved in the development of immunity. It reacts very sensitively to changes in the external and internal environment, responding by increasing or decreasing its volume. The thymus is a kind of guardian of the body, which, under adverse conditions, mobilizes its defenses. It reaches its maximum development in the younger fish. age groups, and after they reach puberty, its volume decreases markedly.

Fish are cold-blooded aquatic vertebrates that live in both salt and fresh water. Like mammals, fish have a closed circulatory system, meaning blood is always in the blood vessels unless they are damaged. Their circulatory system is quite simple. It is made up of the heart and blood vessels. The heart is a primitive muscular structure that is located behind the gills.

The circulatory system of fish consists of the heart and blood vessels.

Anatomy and function

The question of what kind of blood is in the heart of fish, and what is the heart of fish, was asked by many early researchers, since it is believed that the two-chamber heart played a vital role in the progressive evolution of four-chamber cardiac and vascular circuits.

In fish, this organ is also called the gill heart, because it its main function is to pump venous blood into the abdominal aorta and into the gills, and then into the somatic vascular system, so the blood in it is venous.

The structure of the heart of fish is simpler than that of mammals, amphibians, and some terrestrial vertebrates. This organ is enclosed in a pericardial membrane or pericardium and consists of four parts:

Although the heart of these animals consists of four parts, it is considered two-chambered, since the four parts of the heart do not form a single organ. They are usually found one after the other. Gill and systemic blood vessels are located in series with the heart.

In adults, the four compartments are not arranged in a straight row, but instead form an S-shape with the last two compartments above the previous two. This relatively simpler pattern is found in cartilaginous and ray fish. In bony fish, the cone arteriosis is very small and can be more accurately described as part of the aorta rather than the cardiac organ proper.

Body work

The work of the fish heart is mainly dependent on two factors: heart rate and stroke volume. With each heartbeat, the ventricle pumps out blood. The volume is called stroke volume and the heart rate time is known as heart rate.

The atrium of the fish is filled with suction created by the rigidity of the pericardium and surrounding tissue. Venous blood returning to the atrium is accompanied by contraction of the ventricle in systole, which causes a drop in intrapercardial pressure, which is transmitted through the thin wall of the atrium to create aspiration effect or font effect.

Fish have a circulatory system in which blood passes through the heart only once during each complete cycle. Deprived of oxygen, it from the tissues of the body reaches the heart, from where it is pumped into the gills.

Gaseous exchange takes place inside the gills, and oxidized blood from the gills circulates throughout the body.

Blood and cardiovascular system

Fish blood contains plasma (fluid) and blood cells. Red cells - red blood cells contain hemoglobin, a protein that carries oxygen throughout the body. White cells form an integral part of the immune system. Platelets perform functions that are equivalent to the role of platelets in the human body.

Mechanism of blood circulation

Although the circulatory system in fish is simple compared to other mammals, it serves an important purpose in illustrating the various stages in the evolution of the circulatory system in animals. The cardiovascular system of fish includes:

• heart;
• veins;
• arteries;
• thin capillaries.

Capillaries are microscopic vessels that form a network called the capillary layer where arterial and venous blood merges. Capillaries have thin walls that facilitate diffusion, the process by which oxygen and other nutrients are carried into cells.

Capillaries are microscopic vessels

The capillaries congregate into small veins called venules, which in turn drain into larger veins. Veins carry blood to the sinus vein, which is like a small chamber.

The sinus vein has pacemaker cells that are responsible for initiating contractions so that blood moves into a thin walled atrium with very few muscles.

The atrium creates weak contractions to force blood into the ventricle. The ventricle is a thick-walled structure with many heart muscles. It generates enough pressure to pump blood flow throughout the body and into the bulbus, a small chamber with elastic components.

The ventricle is a thick-walled structure with many heart muscles

While bulbus arteriosus- this is the name of the chamber in bony fish, in fish with a cartilaginous skeleton, this chamber is called conus arteriosus. The conus arteriosus has many valves and muscles, while the bulbus arteriosus has no valves. The main function of this structure is to reduce the pulse pressure generated by the ventricle in order to avoid damaging the thin-walled gills.

The outflow tract to the ventral aorta consists of tubular cone arteriosis, arteriosis bulbus, or both. Cone arteriosis, commonly found in more primitive fish species, constricts to aid blood flow to the aorta. The ventral aorta delivers blood to the gills, where it is oxygenated, and flows through the dorsal aorta to the rest of the body. (In tetrapods, the ventral aorta is divided into two parts: one half forms the ascending aorta, and the other forms the pulmonary artery).