Circulatory systems of vertebrates (complex). Anatomical structure of a crocodile What kind of heart does an alligator have?
The life of a crocodile can hardly be called measured. During dry periods these toothy reptiles lie for a long time in the last remaining puddles, slowly using up wisely stored reserves of fat. It's a pitiful sight. But when a holiday comes to their street, crocodiles have few equals in their 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 into the stomach in huge pieces.
The total mass of prey can be up to a fifth of the animal’s own weight.
Of course, these reptiles are far from their relatives, pythons, but it’s hard to imagine a person capable of peeling 15-20 kilograms in one sitting raw meat, and even with bones, it’s quite difficult.
According to American biologists, the crocodile can thank its unique circulatory system for such amazing digestive abilities. Job scientists from the University of Utah and the Institute artificial heart in Salt Lake City has been accepted for publication in the March issue of the Journal of Physiological and Biochemical Zoology.
In the body of most vertebrates - including crocodiles - blood moves through the so-called two circles of 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 supplies oxygen to all organs of the body. Actually, neither one nor the other are full-fledged circles, since they are closed on each other: from the lungs, blood returns to the beginning of the large circle, and from the organs - to the small one.
In the body of mammals and birds, these circles, however, are clearly separated. In a small circle, blood saturated with carbon dioxide, arriving at the right atrium, is driven into the lungs by the right ventricle. The left ventricle sends oxygen-rich blood coming from the left atrium further throughout the body. In fact, a four-chamber heart is two pumps in one, and this division even allows you to maintain significantly lower pressure in the small circle than in the large circle.
Amphibians and reptiles have a three-chambered heart - its atrium is divided in two, but there is only one ventricle, which 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 effective. However, cold-blooded lizards and amphibians, for the most part leading not too active image life, can afford it.
The crocodile heart 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, most of blood through which is directed to the digestive system, primarily to the stomach. Between the left and right arteries (the right one comes from the left ventricle) there is a foramen of Panizza, which allows venous blood to enter the systemic circulation - and vice versa.
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Structure of the crocodile heart (RV - right ventricle, LV - left ventricle, FP - foramen of Panizza, RA - right aorta, LA - left aorta, PA - pulmonary aorta)
// pharyngula.org/Gazeta.Ru
In humans, this is an anomaly and is called birth defect hearts. The crocodile not only does not feel the defect 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 its circulatory system will work almost the same as in mammals. The crocodile can control this so-called toothed valve 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 was a transitional stage on the way to a full-fledged four-chambered heart of warm-blooded mammals.
However, there was an opposite point of view, according to which the crocodile is a descendant of a warm-blooded animal, which, for evolutionary reasons, became more profitable to live the life of a cold-blooded killer. In this case, the Panizza foramen and the serrated valve turn out to be an adaptation mechanism that allowed the transition to a cold-blooded existence. For example, in 2004, Roger Seymour from the Australian University of Adelaide and his colleagues showed that such a heart structure can be very useful for a semi-underwater lifestyle: a decrease in oxygen in the blood can slow down the metabolism, which helps in long dives when a predator is motionless waiting for its kill. sacrifice.
Utah State University professor Colleen Farmer and her colleagues consider, that thanks to such a complex system, a crocodile can quickly decompose pieces of prey it has swallowed.
But a crocodile cannot hesitate: if a fish, a monkey, or even human leg, are not digested too quickly, the reptile will die. Either in the mouth of another predator due to its clumsiness, or from hunger and intestinal upset: in a hot climate, bacteria 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 such an effect, you do not need a complex heart structure, but rather slowing down your breathing. In her opinion, the fact is that this blood is rich in carbon dioxide. When a crocodile sends blood rich in CO 2 to the stomach and other digestive organs, special glands use it to produce gastric juice, and the more carbon dioxide they receive, the more active the secretion. It is known that in the intensity of secretion of gastric juice by their glands, crocodiles are ten times higher than the champions in this indicator among mammals. This allows you not only to digest food, but also to suppress the growth of harmful bacteria in the stomach.
To prove their hypothesis, scientists first studied the condition 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 actually causes the blood to flow predominantly bypassing the lungs.
Next, the scientists surgically deactivated the valve, closing the entrance to the left aorta, in a group of young crocodiles. For the purity of the experiment, the control group was also operated on, but their aorta was not closed. As it turned out, after feeding in crocodiles whose left aorta was blocked, the production of gastric juice was significantly reduced - despite the fact that blood continued to flow to digestive organs in sufficient quantities through the right aorta. At the same time, the ability of crocodiles to decompose bones, which make up a significant part of their diet, also sharply decreased.
In addition to the function of transferring CO 2 to the stomach, Farmer notes, the release of blood bypassing the lungs could also play another role important function, the presence of which will be the envy of many gym visitors.
For 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 is gaping 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 after physical activity muscle aches), which can cause the death of the animal. According to scientists from Utah, this acid is also transported through the blood to the stomach, where it is utilized.
As for the foramen of Panizza, its role is not only to direct oxygen-poor blood to other organs, slowing down the crocodile’s metabolism, but also, on the contrary, to supply the digestive system with additional oxygen from the right aorta when needed. The toothed valve helps from time to time send blood rich in carbon dioxide not only to the stomach, but also to other internal organs that may need it.
Among the most dangerous predators in the world, crocodiles occupy one of the first places ( Latin name– Crocodilia) are the only surviving descendants of dinosaurs, which belong to the order of aquatic vertebrates. Average length an adult individual is from 2 to 5.5 meters, and the mass of a crocodile can reach 550-600 kilograms.
External structure of a crocodile
The structural features of crocodiles, both internal and external, help them survive in incredible conditions. It is interesting that, despite the long process of evolution, these reptiles retained almost all the features of their ancestors, in particular crocodile body, adapted to aquatic environment a habitat:
Few people know that the body of a crocodile can have different colors, although, as a rule, the color of the crocodile is greenish-brown. The upper part of the skin consists of rows of extremely strong and tightly connected horny plates that grow with the individual itself, so that they do not shed. The color that crocodile skin acquires can change depending on external factors, and more precisely temperature environment. These animals are cold-blooded, therefore normal temperature The crocodile's body angle varies between 30 and 35 degrees.
Crocodile teeth
Representatives of this species are often confused with alligators, although in reality they have a number of differences, the main of which is the location and structure of the dentition. For example, if the jaws of a crocodile are closed, you can see the 4th tooth from the bottom, whereas in an alligator they are all closed. Total number A crocodile has 64 to 70 teeth, depending on the variety, and they have the same conical shape and a hollow inner surface where new incisors develop. On average, each crocodile's fang is replaced once every two years, and over the course of a lifetime there can be up to 45-50 such updates. In turn, the crocodile’s tongue is completely fused to the lower jaw, so some generally think that reptiles do not have this organ. 
Despite the fact that the crocodile's mouth looks very scary, in fact its teeth are not designed for chewing food, so it swallows its prey in large pieces. The crocodile's digestive system has a number of specific features For example, the stomach has very thick walls, and to improve digestion it contains stones (gastroliths). Their additional function is to change the center of gravity to improve swimming performance.
Features of the internal structure of crocodiles
Generally, internal structure The crocodile has similarities in structure to other reptiles, but there are some unusual features. For example, the skeleton of a crocodile is very similar to the structure characteristic of dinosaurs: two temporal arches, a diapsid skull, etc. The most vertebrae are found in the tail (up to 37), while in the cervical region and trunk there are only 9 and 17, respectively. For additional protection, there are ribs in the abdominal part that are not connected to the spine.
The crocodile's respiratory system is designed in such a way that the animal feels comfortable both on land and under water. The crocodile's respiratory organs are represented by the choanae (nostrils), the nasopharyngeal passage with a secondary bony palate, the palatine curtain, the trachea and the lungs with the diaphragm. The very powerful and complex lungs of a crocodile are capable of holding a large volume of air, while the animal can, if necessary, adjust its center of gravity. To prevent the crocodile's breathing from interfering with its ability to move quickly, there are special muscles in the diaphragm area. 
The crocodile’s circulatory system is unique in its own way, which is much more advanced than that of other reptiles. Thus, the crocodile’s heart is four-chambered (2 atria and 2 ventricles), and a special mechanism for mixing blood from arteries and veins makes it possible to regulate the blood supply process. If you need to speed up the digestion process, the structure of the crocodile’s heart allows you to change arterial blood to venous blood, which is more saturated with carbon dioxide and promotes the production of additional gastric juice. It should also be noted that crocodile blood has a high content of antibiotics, and hemoglobin is saturated with oxygen and works independently of red blood cells.
By the way, Bladder these predators do not, but to search for a mate during the breeding season there are special glands on the lower half of the jaw, which emit a musky odor.
Their nervous system is very developed, in particular, the crocodile’s brain (or rather, the cerebral hemispheres) is covered with a cortex, and among the sensory organs, hearing and vision are especially developed. We can say with confidence that the crocodile’s memory is very good, since it manages to remember the paths along which other animals go to the watering hole.
Crocodiles are cold-blooded vertebrates that lead a semi-aquatic lifestyle. Water is their favorite medium, being more constant in temperature. It was thanks to her that the ancestors of crocodiles survived the global cooling of the Earth's climate. The body shape of crocodiles is lizard-like. The large head is flattened in the dorso-ventral direction, the muzzle is elongated or long, with strong elongated jaws, seated with sharp conical “fangs” up to 5 cm long, which grow throughout the life of the animal, replacing worn out and broken ones. The teeth are strengthened in individual bone cells of the jaws, the base of the tooth is hollow inside; The crocodile's bite is designed in such a way that opposite the largest teeth on the lateral edge of one jaw are the smallest teeth of the other. This design could turn the dental apparatus into a perfect weapon for attack. In narrow-snouted fish-eating gharials, the jaws can be compared to the jaws of tweezers, allowing them to grab small mobile prey in the water with a lateral movement of the head.
The jaw system of Chinese alligators (Alligator sinensis), common in Eastern China along the lower reaches of the Yangtze River, is structured differently. These are small reptiles (maximum length 1.5 m), feeding mainly bivalves, water snails, crustaceans, as well as frogs and slow-moving fish species. Such coarse food is ground by the closely set back teeth with a flat crown surface. By rinsing their mouths in water, the fed alligators get rid of fragments of crushed shells and shells.
At the end of the crocodile's snout there are convex nostrils, and the eyes are also raised and located on the upper side of the head. This structural feature of the skull determines the favorite pose of the aquatic reptile: the body is blissful in the water - only the eyes and nostrils are visible from the outside.
Crocodiles have five fingers on their forelimbs and four on their hind limbs; they are connected by an interdigital membrane. The tail is long, laterally compressed, very powerful and multifunctional: it is a “steering control” and an “engine” when swimming, a support when moving on land, and when hunting it is like a stunning mace. When swimming, the limbs of crocodiles are laid back, the front ones are pressed to the sides, and the powerful flattened tail, bending, describes S-shaped movements. Lying in wait large mammals at the watering hole, huge saltwater crocodile(Crocodylus porosus) attacks suddenly, grabbing a zebra or antelope by the head and breaking its neck, or knocking the victim down with a terrible blow of the tail. During the breeding season, females use their tail to compact what they have brought for the nest. construction material", splash it in the water, spraying the nest with clutches.
The entire surface of the crocodile's body is covered with large, regular-shaped horny scales. The dorsal scutes are thicker and bear convex spiny ridges that turn into serrations on the tail. Each scale develops independently and grows due to the underlying layers. Under the large scutes of skin on the back and tail, a real shell of bone plates, osteoderms, develops. The shields are elastically connected to each other, so they do not restrict the animal’s movements. The shape and surface pattern of the shell is individual for each species. On the head, osteoderms are fused with the bones of the skull. Thus, the animal wears real “armor” that effectively protects vital internal organs and the brain.
The structure of the skull is very unusual. The quadrate and articular bones are penetrated by air-bearing outgrowths of the middle ear cavity. Most of the posterior bones of the skull contain cavities of a highly expanded and complex branching system of eustachian tubes. Bones long muzzle and the palate also contain significant voids: the blind outgrowths of the nasal passage enter them. Scientists believe that the systems of air cavities and passages that penetrate almost the entire huge skull of the crocodile significantly lighten it, allowing it to hold its head above the surface of the water without significant expenditure of muscle energy (for a silent and imperceptible dive, it is enough for the crocodile to reduce the pressure in the chest cavity and direct part of it into the lungs air from the air cranial passages).
All types of crocodiles have highly organized sense organs. Unlike snakes, they hear perfectly - the range of auditory sensitivity is very large and amounts to 100-4000 Hz. At the same time, crocodiles are deprived of the special “snake” Jacobson’s organ, which allows creepers to distinguish taste and smell with great accuracy. The eyes of crocodiles are adapted for night vision, but also serve well during the day. The retina of the eye contains mainly rod receptors that capture light photons. The pupil, like a cat’s, is capable of narrowing in the light into a narrow vertical slit, and at night the alligator’s eyes have a red-pink glow, which is often taken as constant proof of its bloodthirstiness. It should be said that although the hunting instincts of crocodiles are exacerbated in dark time days, ferocious predatory eyes are only a consequence of the anatomical structure of the visual analyzer. In the dark, the vertical pupil dilates, and the bloody color is provided by the presence of a special pigment in animals - rhodopsin - on the retina, illuminated by reflected light. Underwater, the eyes of crocodiles are protected by a transparent nictitating membrane, which closes them when diving.
Everyone knows the expression “shed crocodile tears.” Indeed, crocodiles cry, but not from grief, pain or the desire to treacherously lull someone’s vigilance. In this way, animals are freed from excess organic salts contained in the body. Their muddy tears are unusually salty, but devoid of emotion. Salt glands are located in representatives of the family of true crocodiles, even under the tongue.
The respiratory system of crocodiles also has its own characteristics. The nostrils, like the external auditory openings, can be tightly closed by muscles - they automatically contract as soon as the animal dives. The lungs have a complex structure compared to the baggy lungs of snakes and are capable of holding a large supply of air. As a result, for example, young Nile crocodile only 1 meter long, it can stay under water for about 40 minutes, and without the slightest harm to its own health. As for large adult individuals, the duration of their “diving” can reach 1.5 hours. It should be noted that scaly reptiles are not able to absorb oxygen through their rough skin, as thin-skinned amphibians (frogs, newts) do.
The air inhaled through the nostrils passes through paired nasal passages, separated from the oral cavity by the secondary bony palate, which serves as a kind of protection for the skull from the inside. In the case when a crocodile tries to swallow a large and severely mutilated victim, bone fragments and desperate resistance, jerks and blows of the doomed animal are not able to injure the vault of the oral cavity and damage the brain. Just before the choanae (inner nostrils), a muscular curtain descends from above, which presses against a similar outgrowth at the base of the tongue and forms a valve that completely separates the oral cavity from the respiratory tract. Thus, thanks to its anatomical structure, a crocodile is able to drown, tear and swallow prey without the risk of choking itself.
The mechanism of ventilation of the lungs is peculiar and unusual in crocodiles. If for most higher vertebrates the volume of the chest changes through the movement of the ribs, then the volume of the lungs in crocodiles also changes with the movement of the liver. The latter moves forward by reducing the transverse abdominal muscles, causing an increase in pressure in the lungs and exhalation, and then moves backward by the longitudinal diaphragmatic muscles connecting the liver to the pelvis, causing a decrease in pressure in the lungs and, accordingly, inhalation. As researchers K. Hans and B. Clark proved, in crocodiles in water, the main role in ventilation of the lungs is played by the movements of the liver.
The heart of crocodiles consists of four chambers and is much more advanced than the three-chambered heart of other reptiles: oxygenated arterial blood does not mix with venous blood, which has already given oxygen to organs and tissues. The heart of crocodiles differs from the four-chambered heart of mammals in that the latter retain two aortic arches with an anastomosis (bridge) at the crossover. Thus, despite the fact that body temperature, metabolic rate, motor activity and appetite of crocodiles significantly depend on the ambient temperature, the process of gas exchange in their cells is more efficient than in lizards and turtles.
The digestive system of crocodiles is distinguished primarily by the absence of saliva in the oral cavity. In addition, there is another amazing adaptation: in the thick-walled muscular stomach of most adult crocodiles there is a certain amount of stones (the so-called gastrolites), which the animals specifically swallow. In Nile crocodiles, the weight of stones in the stomach reaches 5 kg. The role of this phenomenon is not entirely clear; it is assumed that the stones play the role of ballast and move the crocodile’s center of gravity in front downwards, giving greater stability when swimming and making it easier to dive, or they contribute to the grinding of food when the walls of the stomach contract, as in birds.
Crocodiles do not have a bladder, which is apparently due to life in water. Urine is excreted along with feces through a special organ that removes waste products, located on the abdominal side of the animal (it is called the cloaca). The cloaca has the appearance of a longitudinal slit, while in lizards and turtles it is of a transverse type. In its posterior part, males have an unpaired genital organ. The female lays fertilized eggs, protected on the outside by a dense calcareous shell, and on the inside by primary reserves of food and moisture sufficient for the development of the embryo.
On the sides of the cloaca, as well as under lower jaw Crocodiles have large paired glands that secrete a brown secretion with a strong musky odor. The secretion of these glands is especially activated during the breeding season, helping sexual partners find each other.
More interesting articles
I'll tell you a story that happened a few years ago. Now I am writing a school textbook on zoology according to a program in which I myself participated. When this version of the program was first conceived, I convinced the ministerial official that before systematically studying individual groups, it was necessary to consider enough big topic, where we will talk about animals in general.
“Okay, where should I start?” - the official asked me. I said that the way animals live is determined primarily by what they eat and how they move. This means we need to start with a variety of ways of eating. “What are you talking about!” my interlocutor exclaimed. “How can I take such a program to the minister? He will immediately ask why we instill in children that the most important thing is food!”
I tried to argue. In general, the division of living organisms into kingdoms (animals, plants, fungi and others) is associated primarily with the method of nutrition, which, in turn, determines the features of their structure. The characteristics of multicellular animals are a consequence of the fact that they need external sources organic matter and at the same time they do not absorb them through the surface of the body, but eat them in pieces. Animals are creatures that eat other organisms or their parts! Alas, my interlocutor was adamant. The minister will be primarily interested in the educational aspect of the program.
Thinking about how to organize the introductory part differently, I then made an unforgivable mistake. My next idea was the proposal to start studying the zoology course with diversity life cycles. When my interlocutor realized that I was going to consider reproduction, not food, as the “main thing in life”, he seemed to think that I was making fun of him... In the end I wrote something that, as I hoped, no one won't be shocking. Then methodologists worked their magic on this program, corrected everything in it that they did not understand, and replaced the formulations with those that were in use in historical eras, when these same methodologists studied at pedagogical institutes. Then the ill-fated program was corrected by officials, then it was rethought in the spirit of new guidelines, then... - in general, I’m writing a textbook on my “own” program and I don’t get tired of swearing.
And I remembered this sad story because I was once again convinced: the most important thing for animals is the notorious “food”. Comparing different groups our relatives with each other, we often do not realize what characteristics led to their success or failure. Do you know, for example, what has become one of the main trump cards of mammals? A successful schoolchild will name feeding offspring with milk, warm-bloodedness, high development of the nervous system, or some other property that became possible due to a sufficient amount of energy obtained from food. And one of the main trump cards of mammals is the structure of the jaws and teeth!
Try moving your lower jaw: up and down, left and right, back and forth. Its “suspension” allows movement in all three planes! In addition, on the jaws of mammals there are teeth, the structure of which is determined by the task assigned to them - to pierce, crush, grind, cut, crush, bite, tear, hold, gnaw, crush, pry, grind, scrape, etc. Our jaws are an evolutionary biomechanical masterpiece. Apart from mammals, almost no land vertebrates are capable of biting off pieces of food! A few exceptions include the archaic hatteria, which can saw off the head of a petrel chick with its jaws, and turtles, which abandoned teeth in favor of a horny scissor-shaped beak. AND predator birds, and crocodiles do not bite off pieces of food, but simply tear them off - resting with 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 were able 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 times when the school was supposed to form a materialistic worldview, promoting evolution. Generally speaking, the fact of evolution has no special relation to the “materialism-idealism” dilemma (while we verbally reject the mossy dichotomy, for some reason we still attach excessive importance to this dubious dichotomy). Alas, when instead modern ideas some stale dogmas are taught about evolution, this only causes damage to the natural science worldview. Such dogmas include the linear view of evolution. Think about it, the history of vertebrates is a “bush” of many branches, each of which followed its own path, adapted to its own way of life. A 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 never tried to become a lizard, it lives its own life, and without taking into account this life (and the backstory of frogs) it is impossible to understand it!
What will the school teacher tell you about crocodiles? He uses them to illustrate the statement that the most progressive animals are those with a four-chambered heart and “warm-blooded” (homeothermic). And - look, children! - a crocodile has a four-chambered heart, almost like those of mammals and birds, but there is only one extra hole left. We see with our own eyes how the crocodile wanted to become a man, but did not get there, stopping halfway.
So, the crocodile has a four-chambered heart. From its right half, blood goes to the lungs, from the left - to the systemic circulation (to the organs that consume the oxygen received in the lungs). But between the bases of the vessels extending from the heart there is a gap - the foramen of Panizzia. During the normal 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 picture 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, supplying 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?
First, let’s figure out why we need two circles of blood circulation at all. Fish make do with one thing: heart - gills - consumer organs - heart. Here the answer is clear. The lungs will not be able to withstand the pressure required to pump blood through the entire body. This 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 in 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 through the right, “pulmonary” part of the heart and the left aortic arch in crocodiles? In humans, incomplete separation of blood flows can be caused by heart disease. Why do crocodiles need such a “vice”? The fact is that the heart of a crocodile is not an unfinished human heart, it is “conceived” more complex and can function in two different modes! When the crocodile is active, both aortic arches carry arterial blood. But if the foramen of Panizzia is closed (and crocodiles “know how” to do this), venous blood will flow into the left aortic arch.
Traditionally, such a device is explained by the fact that it supposedly allows a crocodile hidden at the bottom to turn off the pulmonary circulation. In this case, venous blood is sent not to the lungs (which cannot be ventilated anyway), but immediately to the 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, is there much use in circulating the blood?
American biologists have figured out how to test the long-standing assumption that crocodiles transfer blood from one circulation to another not in order to hide, but for the sake of better digestion of food ( carbon dioxide- substrate for the production of acid by the glands of the stomach). Researchers have verified that in healthy young alligators, in the process of digesting food, venous, carbon dioxide-rich blood flows through the left aortic arch (the one that supplies blood to the digestive system). Then they began to interfere with the heart function of experimental crocodiles using surgical methods. In some of them, the transfer of venous blood to the left aortic arch was forcibly blocked; others underwent surgery simulating such an intervention. The effect was assessed by measuring the activity of gastric secretions and by X-ray observation of the digestion of bovine vertebrae swallowed by crocodiles. In addition, semiconductor sensors were placed in the unfortunate alligators, allowing them 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 into the systemic circulation increases the production of acid in the stomach and accelerates the digestion of food.
Crocodiles are capable of feeding on fairly large prey, swallowing the 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 their prey quickly enough, they will simply be 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 your purpose digestive system justifies crocodiles: a series of x-rays shows how solid bovine vertebrae “melt” in acid in the stomachs of predators!
So, now we know what is important in the life of crocodiles. What integral beings they are!
D. Shabanov. Heart of a crocodile // Computerra, M., 2008. – No. 10 (726). - pp. 36–37
A log floats down the river -
Oh, how furious it is!
To those who fell into the river,
The nose will be bitten off...
(Crocodile.)
Crocodiles
By general warehouse The bodies of crocodiles resemble lizards in an enlarged form.
Types of crocodiles: 1 - gharial; 2 - Nile crocodile; 3 - Chinese alligator
However it is clean external resemblance. Crocodiles differ from lizards not only in size, but also in significant features of their anatomical structure. They are allocated to a special squad.
The huge mouth of crocodiles is armed with sharp teeth, which do not grow to the jaw bones, like 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 its structure is similar to the more highly organized brain of birds. The lungs of 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 covered with a horny cover that does not allow oxygen to pass through.
The crocodile's heart is not three-chambered, like all other reptiles, but four-chambered. Not only the atrium, but also the ventricle are divided by a longitudinal septum into right and left parts. Pure arterial blood coming from the pulmonary vessels to the left side of the heart does not mix here with venous blood passing through the right atrium and right ventricle. Consequently, in this respect, crocodiles differ from amphibians and other reptiles and are closer to higher vertebrates - birds and mammals, which also have a four-chambered heart.
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 life activity is highly dependent on the surrounding temperature conditions.
So, more high organization crocodiles compared to other reptiles is expressed in the structure of the teeth, heart, lungs and brain. These features bring them closer to 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 warm, tropical climate. Their life is closely connected with bodies of water - on land they usually only bask and lay eggs, and catch prey mainly in the water. Crocodiles are excellent swimmers and divers. Their long, muscular tail is laterally compressed and serves as a good propulsion device, and the toes on the hind legs are partially connected 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 scutes ossify, making the shell more durable.
Having plunged into the water, the crocodile emerges from it only top part head, where he has slightly raised nostrils and eyes. Let us remember that the frog also raises its flattened head out of the water in the same way; 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 water and swim across a body of water. Large species Crocodiles are also dangerous to humans.
Crocodile skin has long been used to make suitcases, briefcases and other products. Crocodile meat is also edible.