Nile crocodile structure of the heart. Crocodiles use venous blood for digestion

A log floats on the river -
Oh, and it's wicked!
For those who fell into the river
Nose bit off...

(Crocodile.)

crocodiles

According to the general body structure, crocodiles resemble lizards in an enlarged form.

Types of crocodiles: 1 - gharial; 2 - Nile crocodile; 3 - Chinese alligator

However, this is purely superficial. Crocodiles differ from lizards not only in size, but also in essential features of the anatomical structure. They are assigned to a special group.

The huge mouth of crocodiles is armed with sharp teeth, which do not adhere to the jaw bones, as in all lower vertebrates, but sit in special recesses, cells, and in this respect resemble the teeth of mammals. The brain of crocodiles is well developed and in its structure approaches the more highly organized brain of birds. Lungs in crocodiles have a large volume and complex structure. Thanks to this, animals can stay under water for a long time. The skin of crocodiles, unlike the skin of frogs, is dressed in a horny cover that does not allow oxygen to pass through.

The heart of a crocodile is not three-chambered, like all other reptiles, but four-chambered. Not only the atrium, but also the ventricle is divided by a longitudinal septum into the right and left parts. The pure arterial blood coming from the pulmonary vessels to the left side of the heart does not mix here with the venous blood passing through the right atrium and right ventricle. Consequently, in this respect, crocodiles differ from both amphibians and other reptiles and approach higher vertebrates - birds and mammals, in which the heart is also four-chambered.

But still, the circulatory system of crocodiles differs from the circulatory system of higher - warm-blooded - animals: in the latter, only pure arterial blood from the left ventricle of the heart enters the arteries, and in crocodiles, venous blood also enters the main arterial trunk, and therefore, the arteries carry mixed blood throughout the body. blood. In this respect, crocodiles, despite their four-chambered heart, differ little from other reptiles. And only the head (brain!) receives pure arterial blood from crocodiles through the carotid arteries.

As a result, crocodiles, like all other reptiles, generally remain cold-blooded animals, and their vital activity is highly dependent on the surrounding temperature conditions.

So, the higher organization of crocodiles compared to other reptiles is expressed in the structure of the teeth, heart, lungs and brain. These features bring them closer to the animals of higher groups - mammals and birds.

Crocodiles are large and strong animals, active predators. The length of some species can reach 6 m. Crocodiles live in countries with a warm, tropical climate. Their life is closely connected with water bodies - on land they usually only bask and lay eggs, and they catch prey mainly in the water. Crocodiles are excellent swimmers and divers. Their long, muscular tail is laterally compressed and serves as a good mover, and the toes on the hind legs are partially interconnected by a swimming membrane. The body of crocodiles is dressed in a shell of horny scutes and scales, which are arranged in longitudinal and transverse rows. On the back, these shields ossify, making the shell more durable.

Having plunged into the water, the crocodile sticks out of it only the upper part of the head, where its somewhat raised nostrils and eyes are placed. Recall that in the same way a flattened head and a frog puts out of the water, this similarity is explained by the adaptation of both animals to similar living conditions. The main prey of crocodiles are fish and frogs. But they can also attack land animals that come to the watering place and swim across the pond. Large species of crocodiles are also dangerous to humans.

Crocodile skin has long been used to make suitcases, briefcases and other products. Crocodile meat is also edible.

The crocodile has always been an outlandish animal for us. Therefore, the interpreters of dreams attributed his appearance in a dream to a variety of reasons.

There is a version that seeing a crocodile in a dream and being happy is a sign that the girl will receive a favorable marriage proposal.

In general, the crocodile is a formidable and dangerous animal. If anything - no mercy.

Therefore, of course, to see him in a dream is a sign of a threat of a collision with a dangerous enemy that can cause you a lot of pain and trouble, or even take your life.

Sometimes such a dream means that close friends will betray you, after which you will stop believing in people altogether.

Often such a dream is an indication that you have made a mistake in your affairs, and your enemies will not fail to use it to grind you to powder.

Being dangerously close to a crocodile in a dream means that you will be drawn into an unpleasant story, fraught with bad consequences.

The peculiarity of such a dream is that in the situation in question, you will have to rely only on your own strength.

Seeing him at the zoo is a sign that you may soon find yourself in an unusual situation. Sometimes such a dream predicts a long journey.

If you dream that a crocodile is going to attack you, then the enemies are going to laugh at you.

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Dream Interpretation - Crocodile

A crocodile seen in a dream portends that you will soon be deceived by your closest friends. Yes, actually, and the enemies can be activated at the most unexpected moment.

I dreamed that you were walking along the back of a crocodile - you are in danger of trouble, with which you will fight hard, trying to get out of them on your own. You will succeed if you try to avoid excessive frankness in dealing with people.

Let me tell you a story that happened a few years ago. Now I am writing a school textbook of zoology according to the program, in which I participated myself. When this version of the program was just conceived, I convinced the ministerial worker that before a systematic study of individual groups, it was necessary to consider a fairly large topic, which would talk about animals in general.

"Okay, but where to start?" the official asked me. I said that the lifestyle of animals is determined primarily by what they eat and how they move. So, you need to start with a variety of ways to eat. “What are you talking about!” my interlocutor exclaimed. “How can I carry such a program to the minister? He will immediately ask why we inspire children that the most important thing is a gorge!”

I tried to argue. In general, the division of living organisms into kingdoms (animals, plants, fungi, and others) is associated primarily with the mode of nutrition, which, in turn, determines the features of their structure. Features of multicellular animals are a consequence of the fact that they need external sources of organic substances and at the same time do not absorb them through the surface of the body, but eat them in pieces. Animals are creatures that eat other organisms or parts of them! Alas, my interlocutor was adamant. The minister will be primarily interested in the educational aspect of the program.

Thinking about how to organize the prologue differently, I then made an unforgivable mistake. My next idea was the proposal to start the study of the course of zoology with a variety of life cycles. When my interlocutor realized that as "the main thing in life" I was going to consider not food, but reproduction, he seems to have decided that I was mocking him ... In the end, I wrote something that, as I hoped, no one won't shock. Then the Methodists conjured over this program, who corrected everything they did not understand in it, and replaced the formulations with those that were in use in historical epochs when these same Methodists studied in pedagogical institutes. Then officials corrected the unfortunate program, then rethought it in the spirit of new guidelines, then ... - in general, I am writing a textbook on my "own" program and do not get tired of cursing.

And I remembered this sad story because I was convinced once again: for animals, the most important thing is the notorious "zhrachka". When comparing different groups of our relatives with each other, we often do not realize what features led them to success or failure. Do you know, for example, what has become one of the main trump cards of mammals? A successful schoolboy will name the feeding of offspring with milk, warm-bloodedness, high development of the nervous system, or some other property that has become possible due to a sufficient amount of energy obtained from food. And one of the main trump cards of mammals is the structure of jaws and teeth!

Try to move your lower jaw: up and down, right and left, back and forth. Its "suspension" allows movement in all three planes! In addition, teeth sit on the jaws of mammals, the structure of which is determined by the task that is assigned to them - to pierce, crush, grind, cut, crush, bite off, tear, hold, gnaw, crush, pry, grind, scrape, etc. Our jaws are an evolutionary biomechanical masterpiece. Apart from mammals, almost no terrestrial vertebrates are capable of biting off food pieces! A few exceptions include the archaic tuatara, capable of sawing off the head of a petrel chick with its jaws, and turtles that have abandoned teeth in favor of a horny scissor-like beak. Both birds of prey and crocodiles do not bite off pieces of food, but simply tear them off - resting on their claws (the first) or spinning with their whole body (the second).

By the way, about crocodiles - this column is dedicated primarily to them. Thanks to sophisticated experiments, biologists from the University of Utah managed to learn something new about the functioning of the heart of these reptiles. But first, a few more words about school biology.

Some features of the presentation of biological material have been preserved from the time when the school was supposed to form a materialistic worldview, promoting evolution. Generally speaking, the fact of evolution has little to do with the "materialism-idealism" dilemma (refusing verbally from the mossy diamat, for some reason we still attach excessive importance to this dubious dichotomy). Alas, when some stale dogmas are taught instead of modern ideas about evolution, this only causes damage to the natural-scientific worldview. Among such dogmas is the linear idea of ​​evolution. Think of the history of vertebrates as a "bush" of many branches, each of which went its own way, adapted to its own way of life. And the school teacher, jumping from branch to branch of this bush, builds a progressive sequence of "typical representatives": lancelet-perch-frog-lizard-dove-dog. But the frog has never tried to become a lizard, it lives its own life, and without taking into account this life (and the background of frogs) it is impossible to understand it!

What will the school teacher tell about crocodiles? He uses them to illustrate the assertion that the most progressive are animals with a four-chambered heart and "warm-bloodedness" (homeothermic). And look, kids! - the crocodile has a four-chambered heart, almost, almost like that of mammals and birds, only one extra hole remains. We see with our own eyes how the crocodile wanted to become a man, but did not reach it, stopped halfway.

So, the crocodile has a four-chambered heart. From its right half, the blood goes to the lungs, from the left - to the systemic circulation (to the consumer organs of the oxygen received in the lungs). But between the bases of the vessels departing from the heart there is a gap - the panizzi foramen. In the normal mode of operation of the heart, part of the arterial blood passes through this hole from the left half of the heart to the right half and enters the left aortic arch (look at the figure so as not to get confused in the right-left relationship!). Vessels leading to the stomach depart from the left aortic arch. The right aortic arch departs from the left ventricle, feeding the head and forelimbs. And then the aortic arches merge into the dorsal aorta, which provides blood supply to the rest of the body. Why is it so difficult?

To begin with, let's figure out why two circles of blood circulation are needed at all. Fish manage with one thing: the heart - gills - consumer organs - the heart. Here the answer is clear. The lungs cannot withstand the pressure it takes to pump blood through the entire body. That is why the right (pulmonary) half of the heart is weaker than the left; that is why it seems to us that the heart is located on the left side of the chest cavity. But why does part of the blood flowing through the systemic circulation (from the left half of the heart) pass in crocodiles through the right, "pulmonary" part of the heart and the left aortic arch? In humans, incomplete separation of blood flows can be caused by heart disease. Why such a "vice" crocodiles? The fact is that the heart of a crocodile is not an unfinished human heart, it is "conceived" more complicated and can function in two different modes! When the crocodile is active, both aortic arches carry arterial blood. But if the panizzian opening is closed (and crocodiles "know how" to do this), venous blood will go into the left aortic arch.

Traditionally, such a device is explained by the fact that it supposedly allows a crocodile hiding at the bottom to turn off the pulmonary circulation. In this case, venous blood is sent not to the lungs (which are still impossible to ventilate), but immediately to a large circle - along the right aortic arch. Somewhat "better" blood will go to the head and to the front legs than to other organs. But if the lungs are disabled, what good is it to circulate the blood?

American biologists have figured out how to test the long-standing assumption that crocodiles transfer blood from one circulation to another not for the sake of hiding, but for the sake of better digestion of food (carbon dioxide is a substrate for the production of acid by the stomach glands). The researchers found that in healthy young alligators, in the process of digesting food, venous, carbonic acid-rich blood flows through the left aortic arch (the one that supplies blood to the digestive system). Then they began to interfere with the work of the heart of experimental crocodiles with surgical methods. In some of them, the transfer of venous blood to the left aortic arch was forcibly blocked; others underwent an operation simulating such an intervention. The effect was assessed by measuring the activity of gastric secretion and by X-ray observation of the digestion of bovine vertebrae swallowed by crocodiles. In addition, semiconductor sensors were placed in the unfortunate alligators, which made it possible to measure their body temperature. As a result of these manipulations, it was possible to convincingly confirm the hypothesis put forward - the transfer of venous blood to the systemic circulation enhances the production of acid in the stomach and accelerates the digestion of food.

Crocodiles are able to feed on fairly large prey, swallowing prey whole or in large pieces (remember what we said about the structure of the jaws?). The body temperature of these predators is unstable, and if they do not have time to digest the prey quickly enough, they will simply get poisoned by it. The complicated structure of the circulatory system and its ability to work in two different modes is a way to activate digestion. And the digestive system of crocodiles justifies its purpose: a series of x-rays shows how solid bull vertebrae “melt” in acid in the stomachs of predators!

So, now we know what is important in the life of crocodiles. What whole beings!

D. Shabanov. Heart of a crocodile // Computerra, M., 2008. - No. 10 (726). - pp. 36–37

Researchers from the University of Chicago explained the structural features of the circulatory system of crocodiles. In experiments with American alligators, they were able to show that the ability to let venous blood bypass the lungs to body tissues is necessary for them to digest food. The work of scientists was published in the journal Physiological and Biochemical Zoology.

Crocodiles, like other reptiles, have preserved the right and left aortic arches. However, unlike other reptiles, the crocodile's heart is four-chambered, that is, it is divided into two atria and two ventricles.

The right aortic arch departs from the left ventricle, through which oxygenated blood, after circulation through the lungs, goes to tissues and organs. The left aortic arch departs from the right ventricle and carries venous blood containing little oxygen. At the exit from the heart, there is a partial mixing of venous and arterial blood from two aortic arches. The mixing of venous and arterial blood is characteristic of the imperfect circulatory systems of amphibians and reptiles.

However, crocodiles can "block" the connection between the aortic arches. In this case, venous blood from the left arch does not mix with arterial blood from the right. That is, the main blood circulation proceeds according to the pattern characteristic of mammals.

The left aortic arch leads to the stomach of the crocodile. When the junction of the arches is "overlapped", the venous blood flowing through the left arch goes directly there. Scientists were able to show that in the glands located in the stomach, reactions occur with the participation of carbon dioxide in the blood, as a result of which bicarbonate and acid are formed, which helps the crocodile digest the bones of its victims. The concentration of acid in the stomach of a crocodile during active digestion is more than ten times higher than the concentration characteristic of mammals.

Crocodiles are known for being able to digest huge amounts of food - up to a quarter of their own weight. If venous blood is artificially prevented from entering the stomach bypassing the lungs, the crocodile's digestion is disturbed, and it cannot cope with the digestion of its usual food.

Scientists put forward several assumptions that explain such a high concentration of acid. Firstly, the acid prevents the growth of bacteria, which is especially important, given that underdigested food is in the crocodile's stomach for quite a long time. Secondly, bicarbonate is necessary for crocodiles to neutralize the large amount of lactic acid that is formed in the muscles when attacking the victim. If the blood is not "cleansed" in time, a dose of lactic acid can be fatal. "Siding" helps crocodiles do this.

As a third possible reason, scientists cite the need to quickly secrete a large amount of acid. This is especially important for young crocodiles. Digestion proceeds better in warmth, and warm places are also attractive to natural enemies, of which there are many young animals that have not entered full strength. As soon as the crocodile gets into heat, he must begin to digest food, and for this he needs to quickly secrete a lot of acid, for which he uses the "overlapping" of the aortic arches.

In their opinion, by directing venous blood instead of the lungs to the stomach, the reptile helps itself to digest food. And relieves the pain of aching muscles after a hard hunt.

The life of a crocodile can hardly be called measured. During dry periods, these toothy reptiles lie down for long periods in the last remaining puddles, slowly using up wisely prepared fat reserves. The sight is pitiful. But when the holiday comes to their street, crocodiles have few equals in the ability to instantly grab, drown or simply break the victim's neck. Not being able to chew prey with its powerful, but rather primitive jaws, the crocodile tears it into pieces in advance and sends it to the stomach in huge pieces.

The total mass of prey can be up to a fifth of the animal's own mass.
Of course, these reptiles are far from their related pythons, but it’s quite difficult to imagine a person capable of peeling 15–20 kilograms of raw meat in one sitting, and even with bones.

According to American biologists, the crocodile can thank its unique circulatory system for such amazing digestive abilities. The work of scientists from the University of Utah and the Salt Lake City Artificial Heart Institute has been accepted for publication in the March issue of the journal Physiological and Biochemical Zoology.

In the body of most vertebrates - including the crocodile - blood moves through the so-called two circles of blood circulation. In the small, or pulmonary, it, passing through the lungs, is enriched with oxygen and gets rid of carbon dioxide, in the large, or systemic, it nourishes all the organs of the body with oxygen. Actually, neither one nor the other is a full-fledged circle, since they close on each other: from the lungs, blood returns to the beginning of a large circle, and from the organs - a small one.

In the body of mammals and birds, these circles, however, are clearly separated. In a small circle, the blood saturated with carbon dioxide, arriving in the right atrium, drives the right ventricle into the lungs. The left ventricle, on the other hand, sends the oxygen-rich blood coming from the left atrium further throughout the body. In fact, a four-chambered heart is two pumps in one, and such a division even allows you to maintain significantly less pressure in a small circle than in a large one.

Amphibians and reptiles have a three-chambered heart - its atrium is divided in two, but there is only one ventricle, it sends blood further - both to the lungs and to the organs. It is clear that in this case, partial mixing of the blood is possible, which makes the system not very efficient. However, cold-blooded lizards and amphibians, for the most part leading a not too active lifestyle, can afford it.

The heart of a crocodile is a special case.

It has four chambers, but the circles of circulation are not completely separated. In addition, not only the pulmonary artery departs from the right ventricle, but also an additional, so-called left artery, through which most of the blood is sent to the digestive system, primarily to the stomach. Between the left and right arteries (the right one comes from the left ventricle) there is an opening of Panizza, which allows venous blood to enter the beginning of the systemic circulation - and vice versa.

In humans, this is an anomaly and is called congenital heart disease. The crocodile not only does not feel a vice here, but also has an additional mechanism that allows it to artificially pump oxygen-poor blood into the right artery. Or completely close the left artery, while his circulatory system will work almost the same as in mammals. This so-called tooth valve can be controlled by the crocodile at will.

The reasons that prompted nature to create such a remarkable mechanism have long occupied scientists. For a long time it was believed that the heart of a crocodile is a transitional stage on the way to a full-fledged four-chambered heart of warm-blooded mammals.

However, there was also an opposite point of view, according to which the crocodile is a descendant of a warm-blooded animal, for which, for evolutionary reasons, it became more profitable to live the life of a cold-blooded killer. In this case, the opening of Panizza and the notched valve are the adaptive mechanism that allowed the transition to a cold-blooded existence. For example, in 2004, Roger Seymour of the University of Adelaide in Australia showed with colleagues that such a structure of the heart can be very useful for a semi-submerged lifestyle: reducing the oxygen content in the blood can slow down metabolism, which helps in long dives when a predator is motionless waiting for its sacrifice.

Utah State University professor Colleen Farmer and her colleagues believe that thanks to such a complex system, the crocodile can quickly decompose the pieces of prey it swallowed.

And the crocodile cannot hesitate: if the fish, the monkey, and even the human leg, are not digested too quickly, the reptile will die. Either in the mouth of another predator due to its sluggishness, or from hunger and intestinal upset: in a hot climate, bacteria will multiply very quickly on a swallowed piece of meat in the belly of an animal.

Farmer believes that the point is not that the blood that has not passed through the lungs is poor in oxygen - to achieve this effect, a complex device of the heart is not needed, but it is enough to slow down breathing. In her opinion, the fact is that this blood is rich in carbon dioxide. When the crocodile sends rich CO2 blood to the stomach and other digestive organs, special glands use it to produce gastric juice, and the more carbon dioxide enters them, the more active the secretion. It is known that in the intensity of secretion of gastric juice by their glands, crocodiles are ten times superior to champions in this indicator among mammals. This allows not only to digest food, but also to suppress the growth of harmful bacteria in the stomach.

To prove their hypothesis, the scientists first studied the state of the circulatory system during periods of forced fasting and during the digestion of food by the crocodile. It turned out that in a crocodile that had just eaten for many hours, the valve really makes the blood flow mainly bypassing the lungs.

Next, the scientists surgically deactivated the valve, blocking the entrance to the left aorta, in a group of young crocodiles. The control group was also operated on for the purity of the experiment, but their aorta was not closed. As it turned out, after feeding in crocodiles whose left aorta was blocked, the production of gastric juice significantly decreased - despite the fact that the blood continued to flow to the digestive organs in sufficient quantities through the right aorta. At the same time, the ability of crocodiles to decompose bones, which make up a large part of their diet, also sharply decreased.

In addition to the function of transporting CO2 to the stomach, Farmer notes, allowing blood to bypass the lungs could play another important function that many gym goers would envy.

In a crocodile, a rich meal almost always follows a dash for prey, during which the usually clumsy animal instantly jumps out of the water, grabs the prey that gapes at the watering hole and drags it under the water. At this time, such an amount of toxic lactic acid is generated in the muscles (it is because of them that the muscles ache after physical exertion), which can cause the death of the animal. According to scientists from Utah, with the blood, this acid is also transferred to the stomach, where it is utilized.

As for the orifice of Panizza, its role is not only to direct oxygen-poor blood to other organs, slowing down the metabolism of the crocodile, but also to supply the digestive system with additional oxygen from the right aorta when needed. The toothed valve, on the other hand, helps to send carbon dioxide-rich blood from time to time not only to the stomach, but also to other internal organs that may need it.

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[[b]]Crocodiles (Crocodylia, or Loricata)[]

order of aquatic reptiles. The length of most crocodiles is 2-5 m, some - up to 6 m (combed crocodile, old males). The head is flat, with a long snout and a characteristically curved section of the mouth, the body is flattened, the tail is powerful, oar-like compressed from the sides, the legs are massive, relatively short. Eyes with a vertically slit pupil, set very high. The nostrils and ear openings are closed by valves.

The skin is thick, covered with large rectangular horny scutes on the upper and lower sides of the body and tail. Under the dorsal scutes, and in some species under the ventral scutes, there are thick bony plates that form the shell. The skull of a crocodile is characterized by the presence of two temporal arches and a fixed connection of the quadrate bone with the cranium. The nasopharyngeal passage is separated from the oral cavity by a secondary bony palate. The same type of conical teeth sit in separate cells and are replaced as they wear out. The vertebrae are anteriorly concave. The ribs articulate with the vertebrae with a double head and have a hook-shaped process. There are "abdominal ribs". The shoulder girdle consists only of the scapula and coracoid.

According to the development of the brain, crocodiles are higher than other reptiles. Of the sense organs, the organs of vision and hearing are especially well developed. The heart has 2 ventricles, completely separated by a septum (as in birds and mammals). At the intersection of two aortic arches, there is an opening between them through which blood can flow from one arch to another. Light large, complex structure. The fleshy tongue along the entire length is attached to the bottom of the oral cavity. The stomach has thick muscular walls. There is no bladder. Cloaca in the form of a longitudinal slit, in the back of which the unpaired genital organ is located in males, musky glands lie on the sides of it. The same glands are found on the underside of the jaw.

Crocoids are common in all tropical countries; live in rivers, lakes and deep swamps; some live in the coastal part of the seas. Active mainly at night. They feed mainly on fish, in addition, birds and mammals living near the water, as well as aquatic molluscs and crustaceans; on fords and watering holes they attack large mammals (even cattle). Large prey is dismembered on the shore with the help of powerful jaws and forelimbs and swallowed in parts. The voice of a crocodile is something between a bark and a roar, especially often heard during the breeding season.

The female lays her eggs in the sand on the shallows or buries them in a pile of rotting leaves of marsh plants. The number of eggs ranges from 20 to 100. The eggs have a dense white calcareous shell. Females of a number of species remain near the clutch for a long time, protecting the eggs, and then the young, from enemies. In some countries, during periods of drought, K. burrow into the silt of drying up reservoirs and hibernate until the onset of rains. K. cause some damage to animal husbandry. Large K. often attack a person. Crocodile meat is edible and is eaten by the population of many tropical countries. Leather, especially alligators, is used for various products (briefcases, suitcases, saddles, and the like).

The order of crocodiles includes 3 families: gharials, real crocodiles and alligators. Modern crocodiles are the remains of a large group of crocodiles (derived in the Late Triassic from thecodonts), which included up to 15 families, uniting about 100 genera; most of them died out by the beginning of the Cenozoic. Fossil remains of crocodiles have been found in Europe, Asia, North and South America.