Which animal has one circle of blood circulation. Fish have one circle of blood circulation Cells have a thick cell wall

Date: 26.06.2020

Of course, fish and other aquatic inhabitants have a heart that has similar characteristics to a human, fulfilling its main function of supplying the body with blood. Unlike the human circulatory system, fish have only one circle, and that one is closed. In simple cartilaginous fish, the blood flow occurs in straight lines, and in higher cartilaginous fish - according to the shape of the English letter S. This difference is due to a more complex structure and different ones.At the beginning of the article, we will consider the heart of simple fish, and after that we turn to the amazing cartilaginous inhabitants of the aquatic world.

Important organ

The heart is the main and main organ of any fish, like humans and other animals, may seem strange, because fish are cold-blooded animals, unlike us. This organ is a muscle sac that constantly contracts, thereby pumping blood to the entire body.

What kind of heart a fish has and how the blood flows, you can find out by reading the information in this article.

Organ size

The size of the heart depends on the total body weight, so the larger the fish, the larger its "motor". Our heart is compared to the size of a fist; fish have no such opportunity. But as you know from biology lessons, a small fish has a heart only a few centimeters in size. But for large representatives of the underwater world, the organ can even reach twenty to thirty centimeters. These fish include catfish, pike, carp, sturgeon and others.

Where is the heart?

If someone is worried about the question of how many hearts a fish has, we will immediately answer - one thing. It is surprising that this question can arise at all, but as practice shows, it can. Very often, when cleaning fish, the hostesses do not even suspect that they can easily find the heart. Like humans, the heart of a fish is located in the anterior region of the body. More precisely, right under the gills. On both sides, the heart is protected by ribs, just like ours. In the picture below, the main organ of the fish is indicated by number one.

Structure

Considering the peculiarities of fish respiration and the presence of gills in them, the heart is arranged differently than that of land animals. Visually, the heart of a fish is similar in shape to ours. A small red sac, with a small pale pink sac underneath, is this organ.

The heart of cold-blooded aquatic creatures has only two chambers. Namely the ventricle and atrium. They are located in close proximity, or to be more precise, one above the other. The ventricle is located under the atrium and has a lighter shade. Fish have a heart made of muscle tissue, this is due to the fact that it acts as a pump and contracts continuously.

Circulation diagram

The heart of the fish is connected to the gills by arteries, which are located on either side of the main abdominal artery. It is also called the abdominal aorta, in addition, thin veins, through which blood flows, lead from all over the body to the atrium.

Fish blood is saturated with carbon dioxide, which must be processed in the following way. Passing through the veins, blood enters the heart of the fish, where it is pumped through the arteries to the gills with the help of the atrium. The gills, in turn, are equipped with many thin capillaries. These capillaries run through all the gills and help transport the pumped blood quickly. After that, it is in the gills that carbon dioxide mixes and changes to oxygen. That is why it is important that the water where the fish live is saturated with oxygen.

Oxygenated blood continues its journey through the fish's body and is directed to the main aorta, which is located above the ridge. Many capillaries branch off from this artery. In them, the circulation of blood begins, more precisely, the exchange, because as we remember, blood saturated with oxygen returned from the gills.

The result is the replacement of blood in the fish's body. Blood from the arteries, which usually looks deep red, changes to blood from the veins, which is much darker.

Direction of blood circulation

Fish are represented by the atrium and ventricle, which are equipped with special valves. It is due to these valves that the blood moves in only one direction, excluding the backflow. This is very important for a living organism.

Veins direct blood to the atrium, and from there it flows to the second chamber of the fish's heart, and then to special organs - the gills. The latter movement occurs with the help of the main abdominal aorta. Thus, you can see that the heart of the fish makes many endless contractions.

Heart cartilaginous fish

This particular one is characterized by the presence of a skull, spine and flat gills. The most famous representatives of this class are sharks and rays.

Like their cartilaginous relatives, the heart of cartilaginous fish has two chambers and one. The process of exchange of carbon dioxide for oxygen occurs in the same way as described above, with only a few peculiarities. These include the presence of a spray that helps water to enter the gills. And all because the gills of these fish are located in the abdominal region.

Another distinctive feature is the presence of such an organ as the spleen. She, in turn, is the final stop of the blood. This is necessary so that at the moment of special activity there is a rapid supply of the latter to the desired organ.

The blood of cartilaginous fish is more saturated with oxygen, due to the large number of red blood cells. And all because of the increased activity of the kidneys, where they are produced.

Blood performs numerous functions only when it moves through the vessels. The exchange of substances between blood and other tissues of the body takes place in the capillary network. Distinguished by its great length and branching, it has great resistance to blood flow. The pressure required to overcome the resistance of the vessels 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 significantly lower than that of land animals. Nevertheless, it copes with its tasks. The aquatic 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 a dense aquatic environment significantly neutralizes gravitational influences. A horizontally elongated body, a small blood volume, and the presence of only one circulatory system further facilitate the functions of the heart in fish.

§thirty. STRUCTURE OF THE HEART
The heart in fish is small, accounting for about 0.1% of body weight. There are, of course, exceptions to this rule. For example, in flying fish, heart weight reaches 2.5% of body weight.
All fish are characterized by a two-chambered heart. At the same time, there are species differences in the structure of this organ. In a generalized form, two schemes of the structure of the heart in the fish class 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 the teleosts and the arterial cone in the lamellibranchs (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 fibrous tissue with a spongy structure of the inner layer, but without valves.
In lamellibranchs, the arterial cone, in addition to fibrous tissue, also contains typical cardiac muscle tissue, therefore it has contractility. The cone has a system of valves that facilitate the unilateral 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 fish myocardium 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 fish, and is 6-7 microns, which is half as much as, for example, with a dog's myocardium. This myocardium is called spongy.
The reports on vascularization of the fish myocardium 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 Tibesian vessels. In the classical sense, fish have no coronary circulation. At least, cardiologists have this point of view. However, in the literature on ichthyology, the term "fish coronary circulation" is often found.
In recent 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 ray. On the side of the endocardium there is 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 provided with venous blood from the trabecular lacunae, and the compact layer receives arterial blood through the hypobronchial arteries of the second pair of branchials. 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 Tibesian vessels.
Another significant difference between teleosts and lamellibranchs is the morphology of the pericardium.
In teleosts, the pericardium resembles that of terrestrial animals. It is represented by a thin shell.
In lamellar-gill, the pericardium is formed by cartilaginous tissue; therefore, it is a kind of rigid, but elastic capsule. In the latter case, during the diastole period, a certain vacuum is created in the pericardial space, which facilitates the blood filling of the venous sinus and atrium without additional energy consumption.

§31. ELECTRIC PROPERTIES OF THE HEART
The structure of 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-gibranates is 70 mV, in myxines - 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 the 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 an extended 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 ensure 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 the initial level of minus 50 mV.
Fish heart myocytes, capable of generating potential, are localized in certain parts 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 conducting system, which in teleosts includes the center of the ear canal, a node in the atrioventricular septum, from which Purkinje cells stretch to typical cardiocytes of the ventricle.
The rate of conduction of excitation along the conducting 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 velocity of potential propagation was recorded in the structures of the ventricle.
The fish electrocardiogram resembles a human electrocardiogram in leads V3 and V4 (Fig. 7.2). However, the technique of overlapping leads for fish has not been developed in as much detail as for terrestrial vertebrates.

Rice. 7.2. Fish electrocardiogram
In trout and eel, the 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; in the lamellar-gillbranchs, in addition to the five classical teeth on the electrocardiogram, Bd waves are revealed between the S and T, as well as the Br wave between the teeth G and R. On the eel electrocardiogram, 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;
The T wave occurs in response to the repolarization of the cell membranes of the heart ventricle.

§32. WORK OF THE 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
Larva
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 ray was 20-40 beats per minute.
Of the many factors, the most pronounced effect on heart rate is the temperature of the environment. The following dependence was revealed by the method of telemetry on seabass and flounder (Table 7.1).

7.1. Dependence of heart rate on water temperature

Temperature, њС	Heart rate, beats per minute	Temperature, њС	Heart rate, beats per crumple
		11,5

The species sensitivity of fish to temperature changes has been established. So, in flounder, when the water temperature rises from g to 12 њС, the heart rate increases 2 times (from 24 to 50 beats per minute), in perch - only from 30 to 36 beats per minute.
The regulation of heart contractions is carried out with the help of the central nervous system, as well as intracardiac mechanisms. As in warm-blooded animals, tachycardia was observed in fish in in vivo experiments 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 rate of tachycardia.
Many humoral factors also have a chronotropic effect. A positive chronotropic effect was obtained with the introduction of atropine, adrenaline, eptatretin. Acetylcholine, ephedrine, and cocaine caused negative chronotropy.
Interestingly, the same humoral agent at different ambient temperatures can have exactly the opposite effect on the heart of fish. So, on an isolated heart of a trout at low temperatures (6 ° C), epinephrine causes a positive chronotropic effect, and against the background of elevated temperatures (15 ° C) of the perfusing 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, the dependence of cardiac output on the pressure of the perfusing fluid and the oxygen content in it was established in trout. However, under the same conditions, the minute volume did not change in the electric ray.
The researchers include more than a dozen components in the composition of the perfusate.
Trout heart perfusate composition (g / l)
Sodium chloride 7.25
Potassium chloride 0.23
Calcium fluoride 0.23
Magnesium sulfate (crystalline) 0.23
Sodium phosphate monobasic (crystalline) 0.016
Sodium phosphate disubstituted (crystalline) 0.41
Glucose 1.0
Polyvinyl pyrrole idol (PVP) colloidal 10.0

Notes:

I. The solution is saturated with a gas mixture of 99.5% oxygen, 0.5% carbon dioxide (carbon dioxide) or a mixture of air (99 5%) with carbon dioxide (0.5%).
2. The pH of the perfusate is adjusted to 7.9 at a temperature of 10 ° C using sodium bicarbonate.

Composition of perfusate for the heart of electric ray (g / l)
Sodium chloride 16.36
Potassium chloride 0.45
Magnesium chloride 0.61
Sodium sulfate 0.071
Sodium phosphate monobasic (crystalline) 0.14
Sodium bicarbonate 0.64
Urea 21.0
Glucose 0.9
Notes:

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

In such solutions, the isolated fish heart retains its physiological properties and functions for a very long time. When performing simple manipulations with the heart, the use of isotonic sodium chloride solution is allowed. However, you should not count on the long-term work of the heart muscle.

§33. CIRCLE OF CIRCULATION
As you know, fish have one circle of blood circulation. And, nevertheless, the blood circulates through it longer. It takes about 2 minutes for a complete circulation of blood in fish (in humans, blood passes through two circles of blood circulation in 20-30 s). From the ventricle, through the arterial bulb or arterial cone, blood enters the so-called abdominal aorta, which branches out from the heart in a cranial direction to the gills (Fig. 7.3).
The abdominal aorta is divided into left and right (according to the number of branchial arches) bearing branchial arteries. A petal artery extends from them to each branchial lobe, and from it to each lobe two arterioles extend, 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 petal artery. The petal arteries form the left and right efferent branchial arteries, through which arterial blood flows.

Rice. 7.3. Circulation diagram of bony fish:
1- abdominal aorta; 2 - carotid arteries; 3 - branchial arteries; 4- subclavian artery and vein; b - spinal aorta; 7- posterior cardinal vein; 8 - vessels of the kidneys; 9- tail vein; 10 - circulating vein of the kidneys; 11 - intestinal vessels, 12 - portal vein; 13 - liver vessels; 14 - hepatic veins; 15 - venous 16 - cuvier duct; 17- anterior cardinal vein

The carotid arteries extend 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 arteries.
The venous part of the circle begins with the capillaries of muscles and internal organs, which, when combined, form paired anterior and paired posterior cardinal veins. The cardinal veins, joining with two hepatic veins, form the Cuvier ducts that flow into the venous sinus.
Thus, the heart of the fish pumps and sucks in only venous blood. However, all organs and tissues receive arterial blood, since before filling the microcirculatory bed of the organs, the blood passes through the branchial apparatus, in which gases are exchanged between venous blood and the aqueous medium.

§34. BLOOD MOTION AND BLOOD PRESSURE
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 (causing 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. The pulse pressure for fish species varied 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 circle of blood circulation, the blood pressure on the walls of the vessels (in the cuvier ducts) did not exceed 10 mm Hg. Art.
The branchial system with its long and highly branched capillaries has the greatest resistance to blood flow. In carp and trout, the difference in systolic pressure in the abdominal and dorsal aortas, that is, at the entrance and exit from the branchial apparatus, is 40-50%. During hypoxia, the gills offer even greater resistance to blood flow.
In addition to the heart, other mechanisms contribute to the movement of blood through the vessels. Thus, the dorsal aorta, which has the shape 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 blood from flowing back. For venous blood flow, the contractions of the mice adjacent to the veins, which push the blood in the cardiac direction, are also of great importance.
Venous return and cardiac output are optimized by mobilizing the deposited blood. It has been experimentally proven that muscular load in trout leads to a decrease in the volume of the spleen and liver.
Finally, the movement of blood is facilitated by the mechanism of uniform filling of the heart and the absence of sharp systolic-diastolic fluctuations in cardiac output. Filling of the heart is provided already at diastole of the ventricle, when a certain vacuum is created in the pericardial cavity and the blood passively fills the venous sinus and atrium. The systolic stroke is damped by the arterial bulb, which has an elastic and porous inner surface.

Chapter 8. GAS EXCHANGE OF FISH
The oxygen concentration in the reservoir is the most unstable indicator of the fish habitat, which changes many times during the day. Nevertheless, the partial pressure of oxygen and carbon dioxide in the blood of fish is quite stable and refers to rigid homeostasis constants.
As a respiratory medium, water is inferior to air (Table 8.1).

8.1. Comparison of water and air as a breathing medium (at a temperature of 20 њС)

Given such unfavorable initial conditions for gas exchange, evolution has taken the path of creating additional mechanisms for gas exchange in aquatic animals, which allow them to tolerate dangerous fluctuations in the oxygen concentration in their environment. In addition to gills in fish, the skin, gastrointestinal tract, swim bladder, and special organs are involved in gas exchange.

§35. GILLS - EFFECTIVE ORGAN OF GAS EXCHANGE IN AQUATIC ENVIRONMENT
The main load in providing the fish organism with oxygen and removing carbon dioxide from it falls on the gills. They are doing tetanic work. If we compare the gill and pulmonary respiration, then we come to the conclusion that the fish needs to pump through the gills of the respiratory medium 30 times more in volume and 20,000 (!) Times more in mass.
A closer examination shows that the gills are well adapted to gas exchange in the aquatic environment. Oxygen passes into the capillary bed of the gills along the partial pressure gradient, which in fish is 40-100 mm Hg. Art. This is the same reason for the transfer of oxygen from the blood to the intercellular fluid in the tissues.
Here, the oxygen partial pressure gradient is estimated at 1-15 mm Hg. Art., the gradient of carbon dioxide concentration is 3-15 mm Hg.
Gas exchange in other organs, for example through the skin, is carried out according to the same physical laws, but the intensity of diffusion in them is much lower. The gill surface is 10-60 times the body area of the fish. In addition, the gills, organs highly specialized in gas exchange, even with the same area as other organs, will have great advantages.
The most perfect structure of the branchial apparatus is characteristic of bony fish. The basis of the branchial apparatus are 4 pairs of branchial arches. On the branchial arches there are well vascularized branchial lobes that form the respiratory surface (Fig. 8.1).
On the side of the branchial arch facing the oral cavity, there are smaller structures - the branchial stamens, which are more responsible for the mechanical purification of water as it flows from the oral cavity to the branchial lobes.
Microscopic branchial lobes are located transversely to the branchial lobes, which are the structural elements of the gills as respiratory organs (see Fig. 8.1; 8.2). The epithelium covering the petals has three types of cells: respiratory, mucous and supporting cells. The area of the secondary lamellae and, consequently, of the respiratory epithelium depends on the biological characteristics of the fish - lifestyle, basal metabolic rate, oxygen demand. So, in tuna with a mass of 100 g, the gill surface area is 20-30 cm 2 / g, in mullet - 10 cm 2 / g, in trout - 2 cm 2 / g, In roach - 1 cm 2 / g.
The branchial gas exchange can be effective only with a constant flow of water through the branchial apparatus. Water irrigates the gill lobes constantly, and this is facilitated by the oral apparatus. Water rushes from the mouth to the gills. Most fish species have this mechanism.

Rice. 8.1. The structure of the gills of teleost fish:
1- gill petals; 2- gill petals; 3-branchial artery; 4 -gill vein; 5-lobed artery; 6 - petal vein; 7-gill rakers; 8- branchial arch

However, it is known that large and active species, such as tuna, do not close their mouths, and they do not have respiratory movements of the gill covers. This type of ventilation of the gills is called "ram" ventilation; it is possible only at high speeds of movement in water.
For the passage of water through the gills and the movement of blood through the vessels of the branchial apparatus, a countercurrent mechanism is characteristic, providing a very high efficiency of gas exchange. Having passed through the gills, the water loses up to 90% of the oxygen dissolved in it (Table 8.2).

8.2. Efficiency of oxygen extraction from water by different forks of fish,%

Gill lobes and petals are very closely spaced, but due to the low speed of movement of water through them, they do not create much resistance to the flow of water. According to calculations, despite the large amount of work on moving water through the branchial apparatus (at least 1 m 3 of water per 1 kg of live weight per day), the energy consumption of fish is small.
Water injection is provided by two pumps - oral and branchial. In different fish species, one of them may prevail. For example, in high-speed mullet and horse mackerel, it is mainly the oral pump that operates, and in slow bottom fish (flounder or catfish), the gill pump.
The frequency of respiratory movements in fish depends on many factors, but two factors have the greatest influence on this physiological indicator - the temperature of the water and the oxygen content in it. The dependence of the respiratory rate on temperature is shown in Fig. 8.2.
Thus, gill respiration should be considered as a very effective mechanism of gas exchange in the aquatic environment from the point of view of the efficiency of oxygen extraction, as well as energy consumption for this process. In the event that the gill mechanism does not cope with the task of adequate gas exchange, other (auxiliary) mechanisms are activated.

Rice. 8.2. Respiration rate versus water temperature in underyearlings carp

§36. SKIN RESPIRATION
Cutaneous respiration is developed to varying degrees in all animals, but in some fish species it may be the main mechanism of gas exchange.
Cutaneous respiration is essential for species that lead a sedentary lifestyle in conditions of low oxygen content or leave the water body for a short time (eel, mud jumper, catfish). In an adult eel, skin respiration becomes the main one and reaches 60% of the total volume of gas exchange.

8.3. The proportion of cutaneous respiration in different fish species

The study of the ontogenetic development of fish indicates that cutaneous respiration is primary in relation to the branchial respiration. Fish embryos and larvae exchange gas with the environment through integumentary tissues. The intensity of skin respiration increases with an increase in water temperature, since an increase in temperature increases metabolism and reduces the solubility of oxygen in water.
In general, the intensity of cutaneous gas exchange is determined by the morphology of the skin. In acne, the skin is hypertrophied in comparison with other types of vascularization and innervation.
In other species, such as sharks, the proportion of skin respiration is insignificant, but their skin also has a rough structure with an underdeveloped blood supply system.
The area of blood vessels of the skin in different species of teleost fish ranges from 0.5 to 1.5 cm: / g of live weight. The ratio of the area of cutaneous capillaries and gill capillaries varies widely - from 3: 1 in loach to 10: 1 in carp.
The thickness of the epidermis, ranging from 31-38 microns in flounder to 263 microns in eels and 338 microns in loaches, is determined by the number and size of mucosal cells. However, there are fish with a very intense gas exchange against the background of an ordinary macro- and microstructure of the skin.
In conclusion, it should be emphasized that the mechanism of cutaneous respiration in animals is clearly insufficiently studied. An important role in this process is played by skin mucus, which contains both hemoglobin and the enzyme carbonic anhydrase.

§37. INTESTINAL RESPIRATION
In extreme conditions (hypoxia), intestinal respiration is used by many species of fish. However, there are fish in which the gastrointestinal tract has undergone morphological changes in order to efficiently exchange gas. In this case, as a rule, the length of the intestine increases. In such fish (catfish, gudgeon), air is swallowed and directed to a specialized section by peristaltic bowel movements. In this part of the gastrointestinal tract, the intestinal wall is adapted to gas exchange, firstly, due to hypertrophied capillary vascularization and, secondly, due to the presence of the respiratory column epithelium. The swallowed bubble of atmospheric air in the intestine is under a certain pressure, which increases the coefficient of oxygen diffusion into the blood. In this place, the intestine is provided with venous blood, therefore there is a good difference in the partial pressure of oxygen and carbon dioxide and the unidirectionality of their diffusion. Intestinal respiration is widespread in American catfish. Among them there are species with a stomach adapted for gas exchange.
The swim bladder not only provides the fish with neutral buoyancy, but also plays a role in gas exchange. It can be open (salmon) and closed (carp). An open bladder is connected by an air duct to the esophagus, and its gas composition can be rapidly renewed. In a closed bladder, a change in the gas composition occurs only through the blood.
There is a special capillary system in the wall of the swim bladder, which is commonly called the "gaseous gland". The capillaries of the gland form sharply curved countercurrent loops. The endothelium of the gas gland is able to secrete lactic acid and thereby locally change the pH of the blood. This, in turn, causes the hemoglobin to release oxygen directly into the blood plasma. It turns out that the blood flowing from the swim bladder is oversaturated with oxygen. However, the countercurrent mechanism of blood flow in the gaseous gland leads to the fact that this plasma oxygen diffuses into the cavity of the bubble. Thus, the bladder creates a supply of oxygen, which is used by the fish organism in unfavorable conditions.
Other devices for gas exchange are represented by a labyrinth (gourami, lalius, cockerel), a supra-gill organ (rice eel), lungs (lungs), an oral apparatus (creeper perch), pharyngeal cavities (Ophiocephalus sp.). The principle of gas exchange in these organs is the same as in the intestine or in the swim bladder. The morphological basis of gas exchange in them is a modified capillary blood circulation system plus thinning of the mucous membranes (Fig. 8.3).

Rice. 8.3. Varieties of supragillary organs:
1- slider perch: 2- heap; 3- snakehead; 4- nile sharmut

Morphologically and functionally, pseudobranchia are associated with the respiratory organs - special formations of the branchial apparatus. Their role is not fully understood. That. that oxygen-saturated blood flows from the gills to these structures indicates that. that they do not participate in the exchange of oxygen. However, the presence of a large amount of carbonic anhydrase on the membranes of pseudobranchia allows these structures to participate in the regulation of carbon dioxide exchange within the branchial apparatus.
Functionally associated with pseudobranchia is the so-called vascular gland, located on the back wall of the eyeball and surrounding the optic nerve. The vascular gland has a capillary network similar to that in the gas gland of the swim bladder. There is a point of view that the vascular gland ensures the supply of highly oxygenated blood to the retina with the lowest possible intake of carbon dioxide. It is likely that photoreception is demanding on the pH of the solutions in which it is carried out. Therefore, the pseudobranchia-vascular gland system can be considered as an additional buffer filter of the retina. If we take into account that the presence of this system is not associated with the taxonomic position of fish, but rather associated with the habitat (these organs are more often found in marine species living in water with high transparency, and in which vision is the most important channel of communication with the external environment) , then this assumption looks convincing.

§38. BLOOD GAS TRANSFER
There are no fundamental differences in the transportation of gases with blood. As in lung animals, in fish, the transport functions of blood are realized due to the high affinity of hemoglobin for oxygen, the relatively high solubility of gases in the blood plasma, and the chemical transformation of carbon dioxide into carbonates and bicarbonates.
The main transporter of oxygen in the blood of fish is hemoglobin. Interestingly, fish hemoglobin is functionally divided into two types - acid sensitive and acid insensitive.
Acid-sensitive hemoglobin loses its ability to bind oxygen when the blood pH drops.
Acid-insensitive hemoglobin does not respond to pH, and its presence is vital for fish, since their muscle activity is accompanied by large releases of lactic acid into the blood (a natural result of glycolysis under conditions of constant hypoxia).
Some Arctic and Antarctic fish species have no hemoglobin in their blood at all. In the literature, there are reports of the same phenomenon in carp. Experiments on trout have shown that fish does not experience asphyxia without functional hemoglobin (all hemoglobin was artificially bound with CO) at water temperatures below 5 ° C. This indicates that the oxygen demand of fish is much lower than that of land animals (especially at low water temperatures, when the solubility of gases in blood plasma increases).
Under certain conditions, one plasma copes with the transportation of gases. However, under normal conditions, gas exchange in the vast majority of fish without hemoglobin is practically excluded. Diffusion of oxygen from water into blood follows a concentration gradient. The gradient is maintained when oxygen dissolved in plasma is bound by hemoglobin, i.e. diffusion of oxygen from water proceeds until the hemoglobin is completely saturated with oxygen. The oxygen capacity of the blood ranges from 65 mg / l for stingray to 180 mg / l for salmon. However, saturation of the blood with carbon dioxide (carbon dioxide) can reduce the oxygen capacity of fish blood by 2 times.

Rice. 8.4. The role of carbonic anhydrase in the transport of carbon dioxide in the blood
The transport of carbon dioxide in the blood is different. The role of hemoglobin in the transport of carbon dioxide in the form of carbohemoglobin is insignificant. Calculations show that hemoglobin carries no more than 15% of carbon dioxide formed as a result of fish metabolism. The main transport system for the transport of carbon dioxide is blood plasma.
Getting into the blood as a result of diffusion from cells, carbon dioxide, due to its limited solubility, creates an increased partial pressure in the plasma and thus should inhibit the transition of gas from cells to the bloodstream. On the very grandfather, this does not happen. In plasma, under the influence of erythrocyte carbonic anhydrase, the reaction is carried out
CO 2 + H 2 O> H 2 CO 3> H + + HCO 3
Due to this, the partial pressure of carbon dioxide at the cell membrane from the side of the blood plasma is constantly decreasing, and the diffusion of carbon dioxide into the blood flows evenly. The role of carbonic anhydrase is schematically shown in Fig. 8.4.
The resulting bicarbonate with blood enters the branchial epithelium, which also contains carbonic anhydrase. Therefore, bicarbonates are converted into carbon dioxide and water in the gills. Further along the gradient of concentration of CO 2 from the blood diffuses into the water washing the gills.
The water flowing through the gill petals contacts the gill epithelium for no more than 1 s, therefore, the carbon dioxide concentration gradient does not change and it leaves the bloodstream at a constant rate. Approximately the same scheme is used to remove carbon dioxide in other respiratory organs. In addition, significant amounts of carbon dioxide formed as a result of metabolism are excreted from the body in the form of carbonates in the urine, in the pancreatic juice, bile and through the skin.

However, depending on the structure of the heart (four- or three-chambered), there are significant differences in the circulatory system. So, in animals with a four-chambered heart (birds and mammals), a small circle begins in the right ventricle of the heart, includes the pulmonary artery, capillaries of the lungs and the pulmonary vein; ends in the left atrium. The systemic circulation begins in the left ventricle of the heart with the aorta, includes arteries going to all cells of organs, capillaries, veins, and ends in the right atrium. In animals with a three-chambered heart (amphibians, reptiles), both circles begin from a single ventricle, therefore arterial blood mixes with venous blood, while in animals with a four-chambered heart, only venous blood flows through the right half of the heart, and only arterial blood through the left half. In all vertebrates, the brain is supplied only with arterial blood (through the carotid arteries).

Source: T. L. Bogdanova "A guide for applicants to universities"

Which animal has one circle of blood circulation and a two-chambered heart?

A) Nile crocodile

B) blue shark

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Which animal has one circle of blood circulation

In fish, the heart is two-chambered, consisting of one atrium and one ventricle. One circle of blood circulation: venous blood from the heart goes to the gills, there it becomes arterial, goes to all organs of the body, becomes venous and returns to the heart.

Amphibians (frogs and newts) have a three-chambered heart, consisting of one ventricle and two atria. Two circles of blood circulation:

Large circle: from the ventricle, mixed blood goes to all organs of the body, becomes venous, returns to the right atrium.
Small circle: from the ventricle, mixed blood goes to the lungs, becomes arterial, returns to the left atrium.
From the atria, blood enters the ventricle, where it mixes.

Three-chamber (appearance of the pulmonary circulation) contributed to the emergence of amphibians on land.

In reptiles (lizards, snakes, turtles), the circulatory system is the same as in amphibians, only an incomplete septum appears in the ventricle, which partially separates the blood: the most venous blood flows to the lungs, the most arterial blood to the brain, and mixed to all other organs. Crocodiles have a four-chambered heart, mixing of blood occurs in the arteries.

In mammals and birds, the circulatory system is the same as in humans.

Tests

26-01. Four-chambered heart in

26-02. In animals of which systematic group, the heart is two-chambered?

B) Flatworms

26-03. What trait characterizes the circulatory system in fish?

A) the heart is filled only with venous blood

B) there are two circles of blood circulation

C) three-chambered heart

D) the transformation of arterial blood into venous blood occurs in the spinal blood vessel

26-04. The formation of a three-chambered heart in amphibians during evolution led to the fact that their body cells began to be supplied with blood.

D) oxygen rich

26-05. The emergence of a three-chambered heart in amphibians contributed to

A) their going ashore

B) skin respiration

C) an increase in the size of their bodies

D) the development of their larvae in the water

26-06. Representatives of which of the given classes of chordates have one circle of blood circulation?

26-07. In the process of evolution, the appearance of the second circle of blood circulation in animals led to the emergence

A) gill breathing

B) pulmonary respiration

C) tracheal breathing

D) breathing with the entire surface of the body

26-08. Are the judgments about the circulatory system of fish correct?

1. Fish have a two-chambered heart, it contains venous blood.

2. In the gills of fish, venous blood is enriched with oxygen and converted into arterial blood.

A) only 1 is true

B) only 2 is true

C) both judgments are true

D) both judgments are wrong

26-09. Are the judgments about the circulatory system of amphibians correct?

1. The heart of amphibians consists of two chambers.

2. Venous blood from organs and tissues is collected in the veins and enters the right atrium, and then into the ventricle.

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The circulatory system of fish. Organs of hematopoiesis and blood circulation

From the atrium, it is pushed into the ventricle, then into the arterial cone, and then into the large abdominal aorta and reaches the gills, in which gas exchange takes place: the blood in the gills is enriched with oxygen and freed from carbon dioxide. Red blood cells of fish - erythrocytes contain hemoglobin, which binds oxygen in the gills, and carbon dioxide in organs and tissues.

The ability of hemoglobin in the blood of fish to extract oxygen differs from species to species. Fast swimming fish living in oxygen-rich flowing waters have hemoglobin cells, which are highly capable of binding oxygen.

Oxygen-rich arterial blood has a bright scarlet color.

After the gills, blood flows through the arteries to the head section and further to the dorsal aorta. Passing through the dorsal aorta, blood delivers oxygen to the organs and muscles of the trunk and tail. The dorsal aorta extends to the end of the tail; from it along the way, large vessels depart to the internal organs.

The venous blood of the fish, depleted in oxygen and saturated with carbon dioxide, has a dark cherry color.

After giving oxygen to the organs and collecting carbon dioxide, the blood flows through the large veins to the heart and atrium.

The fish organism has its own characteristics in blood formation:

Many organs can form blood: the branchial apparatus, intestines (mucous membrane), heart (epithelial layer and vascular endothelium), kidneys, spleen, vascular blood, lymphoid organ (accumulations of hematopoietic tissue - reticular syncytium - under the roof of the skull).

In the peripheral blood of fish, mature and young erythrocytes can be found.

Erythrocytes, unlike mammalian blood, have a nucleus.

Fish blood has an internal osmotic pressure.

To date, 14 systems of fish blood groups have been installed.

Which amphibians have a three-chambered heart?

The same organs in different species may differ in structure and functionality. Our own heart has four separate chambers, while frogs, toads, snakes and lizards can do with just three. You can learn about the functionality of three-chambered hearts in this article.

Classes of vertebrates and chambers of the heart

Vertebrates are represented by different classes: fish, amphibians, reptiles, mammals and birds. In vertebrates, the heart has the function of pumping blood throughout the body, this is called circulation. Although the circulatory systems are similar in many ways, the hearts of different classes of vertebrates have different numbers of chambers. These chambers determine how efficiently the heart carries the flow of oxygen-rich blood and carries oxygen-poor blood back to the heart.

Vertebrates can be classified by the number of chambers in the heart:

Two chambers: one atrium and one ventricle (fish)
Three chambers: two atria and one ventricle (amphibians, amphibians and reptiles)
Four chambers: two atria and two ventricles (birds and mammals)

Circulation

The most vital substance, oxygen, enters the bloodstream through the gills or lungs. To achieve more efficient use of oxygen, many vertebrates have two separate stages of circulation: pulmonary and systemic.

With chamber pulmonary circulation, the heart sends blood to the lungs to enrich it with oxygen. The process begins in the ventricle, from there, through the pulmonary arteries, it enters the lungs. Blood returns from the lungs through the pulmonary veins and flows into the left atrium. From there, it enters the ventricle, where the systemic circulation begins.

The circulation is the distribution of oxygen-rich blood throughout the body. The ventricle pumps blood through the aorta, a massive artery that branches off in all parts of the body. After oxygen is delivered to the organs and limbs, it returns through the veins that lead it to the inferior vena cava or superior vena cava. Then from these two main veins it enters the right atrium. Once there, oxygen-depleted blood returns to the pulmonary circulation.

The heart is a complex pump and the main organ of the circulatory system that provides the body with oxygen.

The heart consists of chambers: the atrium and the ventricle. One on each side, each with different functions. The left side provides systemic circulation, while the right side of the heart is responsible for pulmonary circulation, that is, for oxygenation.

Atria

The atria are the chambers through which blood flows to the heart. They are on the front of the heart, with one atrium on each side. Venous blood enters the right atrium through the superior vena cava and the inferior vena cava. The left one receives oxygenated blood from the lungs through the left and right pulmonary veins.

Blood flows into the atrium bypassing the valves. The atria relax and dilate as they fill with blood. This process is called diastole fibrillation, we call it pulse. The atria and ventricles are separated by a mitral and tricuspid valve. The atria pass near the atrial systole, creating short atrial contractions. They, in turn, push blood out of the atria through the valves and into the ventricles. The elastic tendons that attach to the ventricular valve relax during systole and go into ventricular diastole, but the valve closes during ventricular systole.

One of the defining characteristics of the atria is that they do not obstruct venous blood flow to the heart. The venous blood entering the heart has a very low pressure compared to arterial blood, and the valves take over the venous blood pressure. Atrial systole is incomplete and does not block the flow of venous blood through the atria to the ventricles. During atrial systole, venous blood continues to flow continuously through the atria to the ventricles.

Atrial contractions are usually minor; they only prevent significant backpressure that obstructs venous blood. The relaxation of the atria is coordinated with the ventricle to begin to relax before the ventricles begin to contract, which helps prevent too slow a pulse.

Ventricles

The ventricles are located at the back of the heart. The ventricle receives blood from the right atrium and pumps it through the pulmonary vein into the pulmonary circulation, which enters the lungs for gas exchange. Then he receives oxygen-enriched blood from the left atrium and pumps it through the aorta into the systemic circulation to supply the body tissues with oxygen.

The walls of the ventricles are thicker and tighter than those of the atria. The physiological stress that pumps blood throughout the body from the lungs is much greater than the pressure created to fill the ventricles. During ventricular diastole, the ventricle relaxes and fills with blood. During systole, the ventricle contracts and pumps blood through the semilunar valves into the systemic circulation.

Three-chambered heart

People are sometimes born with congenital abnormalities, in the form of a single ventricle with two atria. Rudimentary portions of the ventricular septum may be present, but not functional. The disease is called heart disease.

The only amphibian species that has 4 heart chambers is the common crocodile. A number of animals have three chambers, that is, two atria and one ventricle.

In nature, amphibians and most reptiles have a pre-chambered heart and consists of two atria and one ventricle. These animals also have separate chains of blood vessels, where separate chambers are responsible for oxygen saturation, and the venous one returns and flows into the right atrium. From there, blood is conducted to the ventricle and then pumped to the lungs. After being enriched with oxygen and free from carbon dioxide, the blood returns to the heart and flows into the left atrium. Then it enters the ventricle a second time and is then distributed throughout the body.

The fact that these are cold-blooded animals, their bodies do not expend a lot of energy to produce heat. Thus, reptiles and amphibians can survive with less efficient cardiac structures. They are also able to block the flow in the pulmonary artery to divert blood to the skin for cutaneous breathing during diving. They are also capable of bypassing the blood flow in the pulmonary artery system during a dive. This anatomical function is considered the most complex of the cardiac structure in vertebrates.

All vertebrates like fish, amphibians, reptiles, birds, mammals use oxygen from the air (or dissolved in water) to efficiently extract energy from food and release carbon dioxide as a waste product.

Any organism must deliver oxygen to all organs and collect carbon dioxide. We know this specialized system is called the circulatory system: it is made up of blood, it contains the cells that carry oxygen, the blood vessels (the tubes through which blood flows), and the heart (the pump that pumps blood through the blood vessels).

While everyone thinks fish only have gills, it's worth noting that many species also have lungs. In many fish, the circulatory system is a relatively simple cycle. The heart consists of two contractile chambers, the atrium and the ventricle. In this system, blood from the body enters the heart and is pumped through the gills, where it is enriched with oxygen.

To answer the question of how this phenomenon appeared, we must first understand what was behind the formation of such a complex shape of the heart and circulatory system during evolution.

For about 60 million years, from the early Carboniferous to the late Jurassic, amphibians were the dominant land animals on Earth. Soon, due to the primitive structure, they lost their place of honor. Although among the various families of reptiles that descended from amphibians, isolated groups were more resistant. For example, archosaurs (which eventually evolved into dinosaurs) and therapsids (who eventually evolved into mammals). The classic amphibian was the big-headed Eryops, which was about fourteen meters long from head to tail and weighed about two hundred kilograms.

The Greek word for “amphibian” means “both types of life,” and this pretty much sums up what makes these vertebrates unique: they lay their eggs in water because they require a constant source of moisture. And they can live on land.

Great progress in the evolution of vertebrates has given many species circulatory and respiratory systems that are highly efficient. According to these parameters, amphibians, amphibians and reptiles are located in the lower part of the oxygen-respiratory ladder: their lungs have a relatively small internal volume and cannot process as much air as the lungs of mammals. Fortunately, amphibians can breathe through the skin, which, when paired with a three-chambered heart, allows them, albeit with difficulty, to fulfill their metabolic needs.

Animal biology

Information about animals in the diversity of the animal world.

Class Amphibians (Amphibia)

General characteristics. Amphibians - four-legged vertebrates from the group Anamnia. Their body temperature is variable, depending on the temperature of the external environment. The skin is bare, with a large number of mucous glands. The forebrain has two hemispheres. The nasal cavity communicates with the oral internal nostrils - the choans. There is a middle ear, which contains one auditory ossicle. The skull is articulated with a single cervical vertebra by two condyles. The sacrum is formed by one vertebra. The respiratory organs of the larvae are the gills, and of the adults, the lungs. The skin plays an important role in respiration. There are two circles of blood circulation. The heart is three-chambered and consists of two atria and one ventricle with an arterial cone. Trunk kidneys. They reproduce by spawning. The development of amphibians takes place with metamorphosis. Eggs and larvae develop in water, have gills, they have one circle of blood circulation. After metamorphosis, adult amphibians become terrestrial lung-breathing animals with two circles of blood circulation. Only a few amphibians spend their entire life in water, retaining gills and some other signs of larvae.

More than 2 thousand species of amphibians are known. They are widespread on the continents and islands of the globe, but more numerous in countries with warm, humid climates.

Amphibians serve as chain objects of physiological experiments. While studying them, many outstanding discoveries were made. Thus, IM Sechenov, in experiments on frogs, discovered the reflexes of the brain. Amphibians are interesting as animals, phylogenetically related, on the one hand, with ancient fish, and on the other, with primitive reptiles.

Structure and vital functions. The appearance of amphibians is diverse (see Fig. 238). In tailed amphibians, the body is elongated, legs are short, of approximately the same length, a long tail remains throughout their life. In tailless amphibians, the body is short and wide, the hind legs are jumping, much longer than the front ones, the tail is absent in adults. Worms (legless) have a long, worm-like body without legs. In all amphibians, the neck is not expressed or is weakly expressed. Unlike fish, their head articulates with the spine in a flexible manner.

Veils. The skin of amphibians is thin, naked, usually covered with mucus secreted by numerous cutaneous glands. In larvae, the mucous glands are unicellular, in adults, they are multicellular. The secreted mucus prevents the skin from drying out, which is necessary for skin respiration. In some amphibians, skin glands secrete a poisonous or burning secret that protects them from predators. The degree of keratinization of the epidermis in different species of amphibians is far from the same. In larvae and those adults who lead mainly an aquatic lifestyle, keratinization of the surface layers of the skin is poorly developed, but in toads on the back, the stratum corneum makes up 60% of the entire thickness of the epidermis.

The skin is an important respiratory organ in amphibians, as evidenced by the figures for the ratio of the length of skin capillaries to the length of these vessels in the lungs; in the newt, it is 4: 1, and in toads with drier skin, it is 1: 3.

The coloration of amphibians is often patronizing. Some, like the tree tree frog, are capable of changing it.

The skeleton of amphibians consists of the spine, skull, limb bones and their belts (Fig. 233). The spine is divided into sections: cervical, consisting of one vertebra, trunk - from a number of vertebrae, sacral - from one vertebra and caudal. In tailless amphibians, the rudiments of the caudal vertebrae grow together into a long bone - the urostyle. In some caudate terrestrial aquatic vertebrae, the vertebrae are biconcave: the remnants of the notochord are preserved between them. In most amphibians, they are either convex in front and concave in the back, or, conversely, concave in front and convex in the back. The chest is missing.

Rice. 233. Frog skeleton:

/ - general form; // - vertebra from above; /// - front vertebra;

/ - cervical posture; 2 - sacral vertebra; 3 - urostpl; 4, 5 -sternum;

v - pre-sternum; 7 - coracoid; 8 - procoracoid; 9, 10 - paddle;

11 - ilium; 12 - gray bone; 13 - pubic brush; /-/ - brachial bone; 15 - forearm bones; 16 - wrist; 17 - metacarpus; 18 -20 - phalanges of the fingers; 21 - hip; 22 - shin bones; 23 - tarsus; 24 - metatarsus; 25

The skull is mainly cartilaginous, with a small number of overhead (secondary) and main (primary) bones. With the transition from gill respiration of aquatic ancestors of amphibians to pulmonary respiration, the visceral skeleton has changed. The skeleton of the branchial region has partially changed into the hyoid bone. The upper part of the hyoid arch is the pendant, to which the jaws are attached in lower fish, in amphibians, due to the fusion of the primary upper jaw with the skull, it has turned into a small auditory ossicle - a stirrup located in the middle ear.

The skeleton of the limbs and their belts consists of elements characteristic of the five-toed limbs of terrestrial vertebrates. The number of toes varies from species to species.

The musculature of amphibians, due to more varied movements and development of limbs adapted to movement on land, largely loses its metameric structure and becomes more differentiated. Skeletal muscles are represented by many individual muscles, the number of which in the frog exceeds 350.

The nervous system has undergone significant complications compared to that of fish. The brain is relatively larger (Fig. 234). The progressive features of its structure should be considered the formation of the forebrain hemispheres and the presence of nerve cells not only in the side walls, but also in the roof of the hemispheres. Due to the fact that amphibians are inactive, their cerebellum is poorly developed. The diencephalon Above it has an appendage - the pineal gland, and a funnel departs from the bottom, with which the pituitary gland is connected. The midbrain is poorly developed. Nerves extend from the brain and spinal cord to all organs of the body. There are ten pairs of head nerves. The spinal nerves form the brachial and lumbosacral connections that innervate the fore and hind limbs.

The sense organs of amphibians have received progressive development in the process of evolution. Due to the fact that the air medium is less sound-conducting, the structure of the inner ear in the hearing organs of amphibians became more complicated and the middle ear (tympanic cavity) with an auditory bone was formed. The middle ear is bounded outside by the tympanic membrane. It communicates with the pharynx canal (Eustachian tube), which makes it possible to balance the air pressure in it with the pressure of the external environment. Due to the peculiarities of vision in the air in amphibians, there have been changes in the structure of the eyes. The cornea of the eye is convex, the lens is lenticular, there are eyelids that protect the eyes. The olfactory organs have external and internal nostrils. The larvae and amphibians constantly living in the water retain the lateral line organs characteristic of fish.

Rice. 234. The brain of the frog:

/ - above; // - bottom; ///. on the side;

/ - hemispheres of the forebrain; 2 - olfactory lobes; ,3 - the olfactory nerve; 4

The digestive organs (Fig. 235). A wide mouth leads into a vast oral cavity: in many amphibians, small teeth are located on the jaws, as well as on the palate, which help to retain prey. Amphibians have tongues of various shapes; in frogs, it is attached to the front of the lower jaw and can be thrown out of the mouth; animals use this to catch insects. The inner nostrils of the choana open into the oral cavity, and the Eustachian tubes open into the pharynx. Interestingly, in the frog, the eyes take part in swallowing the piita; Having seized prey with its mouth, the frog draws its eyes into the depths of the oral cavity by muscle contraction, pushing the food into the esophagus. Through the esophagus, food enters the sac-like stomach, and from there - into the relatively short intestine, which is divided into small and thick intestines. departments. Bile produced by the liver and pancreatic secretions enter the beginning of the small intestine through special ducts. In the final part of the large intestine - the cloaca - the ureters, the bladder duct and the reproductive ducts open.

Rice. 235. Internal structure of the frog:

/ - heart; 2 -lung; 3, 4 - liver; 5 - gallbladder; 6 - stomach; 7 - pancreas; 8, 9 - small intestine; 10 - colon; 11 - spleen; 12 - cloaca; 13 - bladder; 14 - his hole in the cloaca; 15- bud; 16 - ureter;

17 - its hole in the cloaca; 18 - ovary; 19 - fatty body; 20, 21 - oviducts; 22 - uterine oviduct; 23- the opening of the oviducts in the cloaca; 24 -spinal aorta; 25 - posterior vena cava; 26

The respiratory organs change with the age of the animal. Amphibian larvae breathe with external or internal gills. In adult amphibians, lungs develop, although in some tailed amphibians the gills remain for life. The lungs look like thin-walled elastic bags with folds on the inner surface. Since amphibians do not have a chest, air enters the lungs by swallowing: when the bottom of the mouth is lowered, air enters it through the nostrils, then the nostrils close, and the bottom of the mouth rises, pushing air into the lungs. As indicated, gas exchange through the skin plays an important role in the respiration of amphibians.

This is a circulatory theme. In connection with air breathing, amphibians have two circles of blood circulation (Fig. 236). The amphibian heart is three-chambered, it consists of two atria and a ventricle. The left atrium receives blood from the lungs, and the right atrium receives venous blood from the whole body with an admixture of arterial blood coming from the skin. Blood from both atria flows into the ventricle through a common orifice with valves. The ventricle continues into a large arterial cone, followed by a short abdominal aorta. In tailless amphibians, the aorta is divided into three pairs of symmetrically departing vessels, which are modified giving branchial arteries of fish-like ancestors. The anterior pair - the carotid arteries, carry arterial blood to the head. The second pair - the arches of the aorta, bending to the dorsal side, merge into the dorsal aorta, from which arteries that carry blood to different organs and parts of the body depart. The third pair is the pulmonary arteries, through which venous blood flows into the lungs. On the way to the lungs, large cutaneous arteries branch off from them, heading into the skin, where they branch into many vessels, causing cutaneous respiration, which is of great importance in amphibians. From the lungs, arterial blood flows through the pulmonary veins into the left atrium.

Venous blood from the back of the body partially passes into the kidneys, where the renal veins break down into capillaries, forming the renal portal system. The veins leaving the kidneys form an unpaired posterior (inferior) vena cava. Another part of the blood from the posterior part of the body flows through two vessels, which, merging, form the abdominal vein. It goes, bypassing the kidneys, to the liver and participates, together with the portal vein of the liver, which carries blood from the intestine, in the formation of the portal system of the liver. After leaving the liver, the hepatic veins flow into the posterior vena cava, and the latter into the venous sinus (venous sinus) of the heart, which is the expansion of the veins. The venous sinus receives blood from the head, forelimbs, and skin. From the venous sinus, blood flows into the right atrium. In tailed amphibians, cardinal veins from aquatic ancestors have been preserved.

Rice. 236. The circulatory system of the frog:

1 - arterial; // - venous;

1 - the ventricle of the heart; 2 - right atrium; 3 - left atrium; 4 -arterial cone; 5 -7 - branches of the carotid arteries; 8 -- arch of the aorta; 9 - subclavian artery; 10 - pulmonary artery; 11 - large cutaneous artery; 12 - dorsal aorta; 13 - liver; 14 - gastric artery; 15 - intestinal artery; 16 - renal artery; 17 - night; 18 -seed; 19 -iliac artery; 20 - femoral vein; 21 - sciatic vein; 22 -iliac vein; 23 - abdominal vein; 24 - portal vein of the liver; 25 - hepatic vein; 26 - ovary; 27 - kidneys; 28 - posterior vena cava; 29 - large cutaneous vein; 30 -subclavian vein; 31, 32 - jugular veins; 33 - anterior vena cava; 34 - lung; 35 - pulmonary veins

The excretory organs in adult amphibians are represented by the trunk kidneys (see Fig. 235). A pair of ureters leaves the kidneys. The urine excreted by them first enters the cloaca, from there - into the bladder. With the contraction of the latter, urine again appears in the cloaca, and from it is excreted. Head buds function in amphibian embryos.

Reproductive organs. All amphibians are dioecious. Males have two testicles located in the body cavity near the kidneys. The vas deferens, passing through the kidney, flow into the ureter, represented by the wolf canal, which serves to excrete urine and sperm. In females, large paired ovaries lie in the body cavity. Ripe eggs enter the body cavity, from where they enter the funnel-shaped initial sections of the oviducts. Passing through the oviducts, the eggs are covered with a transparent thick mucous membrane. The oviducts open into the cloaca.

Rice. 237. Development of the frog:

/ -crystals in the mucous membrane; // - Vii- stages of tadpole development; VIII, IX- transformation of a tadpole into a frog; IVa- - the head of a tadpole with external gills; IV6 -

Development in amphibians takes place with a complex metamorphosis (Fig. 237). The eggs hatch into larvae that differ both in structure and lifestyle from adults. Amphibian larvae are real aquatic animals. Living in the aquatic environment, they breathe with gills. The gills of the larvae of tailed amphibians are external, branched; in the larvae of tailless amphibians, the gills are at first external, but soon become internal due to their overgrowth with folds of skin. The circulatory system of amphibian larvae is similar to that of fish and has only one circle of blood circulation. They have lateral line organs, like most fish. They move mainly due to the movement of a flattened tail, trimmed with a fin.

With the transformation of the larva into an adult amphibian, profound changes occur in most organs. Paired five-toed limbs appear, tailless amphibians have a reduced tail. Gill respiration is replaced by pulmonary respiration, and the gills usually disappear. Instead of one circle of blood circulation, two develop: large and small (pulmonary). In this case, the first pair of the bringing-in branchial arteries turns into carotid arteries, the second becomes aortic arches, the third is reduced to one degree or another, and the fourth is transformed into pulmonary arteries. In the Mexican amphibian amblystoma, neoteny is observed - the ability to reproduce at the larval stage, that is, to reach sexual maturity while maintaining the larval features of the structure.

Ecology and economic importance of amphibians. The habitats of amphibians are diverse, but most species adhere to wet places, and some spend their whole life in the water, without going out on land. Tropical amphibians - worms - lead an underground lifestyle. A peculiar amphibian - the Balkan Proteus lives in caves; his eyes are reduced, and his skin is devoid of pigment. Amphibians belong to the group of cold-blooded animals, that is, their body temperature is unstable and depends on the ambient temperature. Already at 10 ° C their movements become sluggish, and at 5-7 ° C they usually fall into a daze. In winter, in a temperate and cold climate, the vital activity of amphibians almost stops. Frogs usually hibernate at the bottom of reservoirs, and newts - in burrows, in moss, under stones.

Amphibians breed in most cases in spring. Females of frogs, toads, and many other tailless amphibians spawn eggs into the water, where males fertilize them with sperm. A kind of internal fertilization is observed in tailed amphibians. So, the male newt lays lumps of sperm in the mucous sacs-spermatophores on aquatic plants. The female, having found the spermatophore, captures it with the edges of the cloacal opening.

Fertility of amphibians varies widely. The common grass frog spawns 1-4 thousand eggs in the spring, and the green frog - 5-10 thousand eggs. The development of the common frog tadpoles in the egg lasts, depending on the water temperature, from 8 to 28 days. The transformation of a tadpole into a frog usually occurs at the end of summer.

Most amphibians, having laid eggs in water and fertilized them, do not take care of them. But some species take care of their offspring. So, for example, a male midwife toad, widespread in our country, reels the cords of fertilized eggs on its hind legs and swims with it until tadpoles hatch from the eggs. In a female South American (Surinam) pina toad, during spawning, the skin on the back thickens and softens greatly, the cloaca stretches out and becomes the ovipositor. After spawning and fertilization of eggs, the male puts it on the back of the female and presses them with his abdomen into the swollen skin, where the development of the young takes place.

Amphibians feed on small invertebrates, primarily insects. They eat a lot of pests of cultivated plants. Therefore, most amphibians are very useful for crop production. It is estimated that one grass frog can eat about 1.2 thousand insects harmful to agricultural plants during the summer. Toads are even more useful, because they hunt at night and eat a lot of nocturnal insects and slugs, inaccessible to birds. In Western Europe, toads are often released into greenhouses and hotbeds to exterminate pests. Newts are useful in that they eat mosquito larvae. At the same time, one cannot fail to note the harm that large frogs bring by the extermination of juvenile fish. In nature, many animals feed on frogs, including commercial ones.

The class Amphibians is divided into three orders: Tailed amphibians (Urodela), Tailless amphibians (Lpiga), Legless amphibians (Apoda).

Circles of blood circulation in animals

There are two circles of blood circulation - large and small. Venous blood from all internal organs is collected in two hollow veins - left and right, flowing into the right atrium. From the right atrium, venous blood passes in portions into the right ventricle, and from it through the pulmonary artery it enters the lungs, where it releases carbon dioxide through the lung tissue and is saturated with oxygen. Oxygenated blood flows through the pulmonary veins into the left atrium. The part of the circulatory system through which blood makes its way from the right ventricle through the lungs to the left atrium is called the small, or respiratory, circle. The purpose of the pulmonary circulation is to remove carbon dioxide from the blood and saturate it with oxygen.

From the left atrium, blood enters the left ventricle, and from there into the largest arterial vessel, the aorta. Arteries branch off from the aorta, branching into smaller ones. Organs and tissues are supplied with blood through the smallest blood vessels - arterial capillaries, which have very thin walls. Capillaries literally penetrate all tissues of the animal's body. By giving oxygen and accepting carbon dioxide and metabolic products in cells, the blood turns into venous and flows from tissues and organs, first through the venous capillaries, and then through the veins.

From the left ventricle, blood, moving through the arterial, and then through the venous vessels and, finally, entering the right atrium, passes the systemic circulation. The purpose of the systemic circulation is to supply blood, enriched with oxygen and nutrients, to all organs and tissues of the body.

As the blood moves in a closed system, it puts pressure on the walls of the blood vessels, and the pressure drops as the blood moves away from the left ventricle. For example, the pressure in the aorta is mm Hg. Art., in the arterial capillaries, and in the vena cava it is equal to zero. Therefore, damage to arteries, especially large ones, where blood flows under high pressure, is associated with danger, since the animal can lose a lot of blood.

In the human body, the circulatory system is designed to fully meet its internal needs. An important role in the advancement of blood is played by the presence of a closed system in which arterial and venous blood flows are separated. And this is done with the help of the presence of blood circulation circles.

History reference

In the past, when scientists did not yet have informative devices at hand capable of studying physiological processes in a living organism, the greatest scientists were forced to search for anatomical features in corpses. Naturally, the heart of a deceased person does not contract, so some of the nuances had to be conjectured on their own, and sometimes simply fantasized. So, back in the second century AD Claudius Galen, student on the works of himself Hippocrates, assumed that the arteries contain air in their lumen instead of blood. Over the next centuries, many attempts have been made to combine and link together the available anatomical data from the standpoint of physiology. All scientists knew and understood how the circulatory system works, but how does it work?

Scientists have made a colossal contribution to the systematization of data on the work of the heart Miguel Servet and William Harvey in the 16th century. Harvey, the scientist who first described the large and small circles of blood circulation , in 1616 determined the presence of two circles, but how the arterial and venous channels are connected, he could not explain in his writings. And only later, in the 17th century, Marcello Malpighi, one of the first who began to use the microscope in his practice, discovered and described the presence of the smallest capillaries invisible to the naked eye, which serve as a connecting link in the blood circulation.

Phylogenesis, or the evolution of the circulation

Due to the fact that, with evolution, animals of the class of vertebrates became more and more progressive in anatomical and physiological terms, they required a complex structure of the cardiovascular system. So, for a more rapid movement of the liquid internal environment in the body of a vertebrate animal, it became necessary to have a closed blood circulation system. In comparison with other classes of the animal kingdom (for example, with arthropods or with worms), the rudiments of a closed vascular system appear in chordates. And if a lancelet, for example, lacks a heart, but there is an abdominal and dorsal aorta, then fish, amphibians (amphibians), reptiles (reptiles) have a two- and three-chambered heart, respectively, and birds and mammals have a four-chambered heart, a feature of which is the focus in it of two circles of blood circulation, not mixing with each other.

Thus, the presence in birds, mammals and humans, in particular, of two separated circles of blood circulation is nothing more than the evolution of the circulatory system necessary for better adaptation to environmental conditions.

Anatomical features of the circulatory system

The circulatory system is a collection of blood vessels, which is a closed system for the supply of oxygen and nutrients to the internal organs through gas exchange and the exchange of nutrients, as well as for the removal of carbon dioxide and other metabolic products from cells. The human body is characterized by two circles - the systemic, or large circle, as well as the pulmonary, also called the small circle.

Video: circulatory circles, mini-lecture and animation

A large circle of blood circulation

The main function of the great circle is to ensure gas exchange in all internal organs, except for the lungs. It starts in the left ventricular cavity; represented by the aorta and its branches, the arterial bed of the liver, kidneys, brain, skeletal muscles and other organs. Further, this circle continues with the capillary network and the venous bed of the listed organs; and by the confluence of the vena cava into the cavity of the right atrium ends in the latter.

So, as already mentioned, the beginning of the great circle is the cavity of the left ventricle. This is where the arterial blood stream is directed, which contains more oxygen than carbon dioxide. This flow enters the left ventricle directly from the circulatory system of the lungs, that is, from the small circle. The arterial flow from the left ventricle through the aortic valve is pushed into the largest great vessel - the aorta. The aorta can be figuratively compared to a kind of tree, which has many branches, because arteries extend from it to internal organs (to the liver, kidneys, gastrointestinal tract, to the brain - through the carotid artery system, to skeletal muscles, to subcutaneous fat fiber, etc.). Organ arteries, also having numerous ramifications and bearing the names corresponding to the anatomy, carry oxygen to each organ.

In the tissues of internal organs, arterial vessels are subdivided into vessels of smaller and smaller diameters, and as a result, a capillary network is formed. Capillaries are the smallest vessels that practically do not have a middle muscle layer, but are represented by an inner membrane - an intima lined with endothelial cells. The gaps between these cells at the microscopic level are so large compared to other vessels that they allow proteins, gases and even formed elements to freely penetrate into the intercellular fluid of the surrounding tissues. Thus, between the capillary with arterial blood and the liquid intercellular medium in one organ or another, there is an intense gas exchange and the exchange of other substances. Oxygen penetrates from the capillary, and carbon dioxide, as a product of cell metabolism, enters the capillary. The cellular stage of respiration is carried out.

After more oxygen has passed into the tissues, and all carbon dioxide has been removed from the tissues, the blood becomes venous. All gas exchange is carried out with each new flow of blood, and during the period of time while it moves along the capillary towards the venule - a vessel that collects venous blood. That is, with each cardiac cycle in one or another part of the body, oxygen is supplied to the tissues and carbon dioxide is removed from them.

These venules are combined into larger veins, and a venous bed is formed. Veins, similar to arteries, bear the names in which organ they are located (renal, cerebral, etc.). From the large venous trunks, tributaries of the superior and inferior vena cava are formed, and the latter then flow into the right atrium.

Features of blood flow in the organs of a large circle

Some of the internal organs have their own characteristics. So, for example, in the liver there is not only the hepatic vein, which "carries" the venous flow from it, but also the portal vein, which, on the contrary, brings blood to the hepatic tissue, where the blood is purified, and only then the blood is collected into the tributaries of the hepatic vein to get to the big circle. The portal vein brings blood from the stomach and intestines, so everything that a person has eaten or drunk must undergo a kind of "cleaning" in the liver.

In addition to the liver, certain nuances exist in other organs, for example, in the tissues of the pituitary gland and kidneys. So, in the pituitary gland, the presence of the so-called "miraculous" capillary network is noted, because the arteries that bring blood to the pituitary gland from the hypothalamus are divided into capillaries, which are then collected into venules. Venules, after the blood with molecules of releasing hormones is collected, are again divided into capillaries, and then veins are formed that carry the blood from the pituitary gland. In the kidneys, the arterial network is divided twice into capillaries, which is associated with the processes of excretion and reabsorption in the kidney cells - in the nephrons.

Small circle of blood circulation

Its function is to carry out gas exchange processes in the lung tissue in order to saturate the "spent" venous blood with oxygen molecules. It begins in the cavity of the right ventricle, where from the right atrial chamber (from the "end point" of the great circle) venous blood flow enters with an extremely small amount of oxygen and a high content of carbon dioxide. This blood moves through the valve of the pulmonary artery into one of the large vessels called the pulmonary trunk. Further, the venous flow moves along the arterial bed in the lung tissue, which also breaks down into a network of capillaries. By analogy with capillaries in other tissues, gas exchange takes place in them, only oxygen molecules enter the lumen of the capillary, and carbon dioxide penetrates into the alveolocytes (alveolar cells). Air from the environment enters the alveoli with each act of breathing, from which oxygen penetrates through the cell membranes into the blood plasma. With the exhaled air during exhalation, the carbon dioxide that has entered the alveoli is removed to the outside.

After saturation with O 2 molecules, the blood acquires arterial properties, flows through the venules and eventually reaches the pulmonary veins. The latter, consisting of four or five pieces, open into the left atrial cavity. As a result, venous blood flow flows through the right half of the heart, and arterial blood flows through the left half; and normally these streams should not mix.

The lung tissue has a double network of capillaries. With the help of the first, gas exchange processes are carried out in order to enrich the venous flow with oxygen molecules (interconnection directly with the small circle), and in the second, the lung tissue itself is nourished with oxygen and nutrients (interrelation with the large circle).

Additional circles of blood circulation

With these concepts, it is customary to distinguish the blood supply to individual organs. So, for example, to the heart, which needs oxygen more than others, arterial inflow is carried out from the branches of the aorta at its very beginning, which are called the right and left coronary (coronary) arteries. Intensive gas exchange occurs in the capillaries of the myocardium, and venous outflow is carried out into the coronary veins. The latter are collected in the coronary sinus, which opens directly into the right atrial chamber. In this way, cardiac, or coronary circulation.

coronary (coronary) circle of blood circulation in the heart

Circle of willis is a closed arterial network of cerebral arteries. The brain circle provides additional blood supply to the brain in case of disturbance of cerebral blood flow through other arteries. This protects such an important organ from a lack of oxygen, or hypoxia. The cerebral circulation is represented by the initial segment of the anterior cerebral artery, the initial segment of the posterior cerebral artery, the anterior and posterior communicating arteries, and the internal carotid arteries.

Circle of Willis in the brain (classic version of the structure)

Placental circulation functions only during gestation by a woman and performs the function of "breathing" in a child. The placenta forms from 3-6 weeks of gestation and begins to function at full strength from the 12th week. Due to the fact that the lungs of the fetus do not work, the flow of oxygen into its blood is carried out through the flow of arterial blood into the umbilical vein of the child.

fetal circulation before birth

Thus, the entire human circulatory system can be conditionally divided into separate interconnected areas that perform their functions. The correct functioning of such areas, or circles of blood circulation, is the key to the healthy functioning of the heart, blood vessels and the whole organism as a whole.