The special structure of the crocodile's heart can help him in digestion. Heart of a crocodile External structure of a crocodile

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 directs 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 rush to 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 after physical activity aching muscles), 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 opening 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 digestive system supplemental 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. Bladder no. 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 long time remain near the masonry, 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.

Crocodiles are vertebrate cold-blooded animals that lead a semi-aquatic lifestyle. Water is their favorite medium, being more constant in terms of temperature. It was thanks to her that the ancestors of crocodiles survived during the global cooling of the climate on Earth. The body shape of crocodile is lizard-shaped. The large head is flattened in the dorsal-abdominal 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 and broken ones. The teeth are strengthened in separate bone cells of the jaws, the base of the tooth is hollow inside; The bite of a crocodile is arranged in such a way that opposite the largest teeth of the lateral edge of one jaw are the smallest teeth of the other. This design was able to turn the dental apparatus into a perfect weapon for attack. In narrow-faced fish-eating gharials, the jaws can be compared to the jaws of tweezers, which allow them to grab small moving prey in the water with a lateral movement of the head.

The jaw system is arranged differently in Chinese alligators (Alligator sinensis), common in East China along the lower reaches of the Yangtze River. These are Small reptiles (maximum length 1.5 m), feeding mainly on bivalves, water snails, crustaceans, as well as frogs and slow-moving fish species. Grind such rough food closely planted posterior teeth with a flat surface of the crown. Rinsing their mouths in the water, the profited alligators get rid of fragments of crushed shells and shells.

At the end of the crocodile muzzle are bulging nostrils, the eyes are also raised and are located on the upper side of the head. This feature of the structure of the skull determines the favorite posture 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, four on their hind limbs, they are connected by an interdigital swimming membrane. The tail is long, laterally compressed, very powerful and multifunctional: it is a “steering” and “engine” when swimming, a support when moving on land, and when hunting, it is like a stunning mace. During 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 for large mammals at a watering hole, a huge combed 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 tamp the tail brought for the nest " construction material”, slap them on the water, spraying the nest with masonry.

The entire surface of the crocodile's body is covered with large, regular-shaped horny scales. The dorsal shields are thicker and bear convex, spiny ridges that merge into barbs on the tail. Each of the scales develops independently and grows at the expense of its underlying layers. Under the large shields of the skin on the back and tail, a real shell of bone plates, the osteoderm, develops. The shields are elastically connected to each other, due to which they do not restrict the movements of the animal. The shape and pattern of the shell surface is individual for each species. On the head, osteoderms fuse with the bones of the skull. Thus, the animal wears a 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 pierced by air-bearing outgrowths of the middle ear cavity. Most of the posterior bones of the skull contain cavities of a strongly overgrown and complexly branching system of the Eustachian tubes. The bones of the long muzzle and palate also contain significant voids: blind outgrowths of the nasal passage enter them. Scientists believe that the systems of air cavities and passages, penetrating almost the entire huge crocodile skull, significantly facilitate it, allowing you to keep your head above the surface of the water without significant expenditure of muscle energy (for silent and imperceptible immersion, it is enough for a crocodile to lower the pressure in the chest cavity and direct part of the air from the air cranial passages).

All species of crocodiles have highly organized sense organs. Unlike snakes, they hear perfectly - the range of auditory sensitivity is very large and is 100-4000 Hz. At the same time, crocodiles are deprived of Jacobson's special "snake" organ, which allows creepers to distinguish taste and smell with great accuracy. The eyes of crocodilians are adapted for night vision, but they 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 able to narrow in the light into a narrow vertical slit, and at night the alligator's eyes have a reddish-pink sheen, which is often taken as invariable evidence of its bloodthirstiness. It should be said that although the hunting instincts of crocodiles are aggravated at night, the 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 in animals of a special pigment - rhodopsin - on the retina, illuminated by reflected light. Under water, the eyes of crocodiles are protected by a transparent nictitating membrane that closes them when immersed.

Everyone knows the expression "to shed crocodile tears." Indeed, crocodiles cry, but not from grief, pain or the desire to treacherously lull someone's vigilance. Thus, animals are freed from excess organic salts contained in the body. Their cloudy tears are unusually salty, but devoid of emotion. Salt glands are located in representatives of the family of real 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 when the animal dives. The lungs have a complex structure compared to the baggy lungs of snakes and are able to accommodate a large supply of air. As a result, for example, a young Nile crocodile only 1 meter long is able to stay under water for about 40 minutes, and without the slightest harm to its own health. As for large adults, the duration of their “diving” can reach 1.5 hours. At the same time, it should be noted that scaled reptiles they are not able to absorb oxygen through rough skin, as thin-skinned amphibians (frogs, newts) do.

The air inhaled through the nostrils passes through the paired nasal passages, separated from the oral cavity by a secondary bony palate, which serves as a kind of protection of 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. In front of the choanas (internal nostrils), a muscular veil descends from above, which is pressed 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, due to its anatomical structure, the 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 change in volume chest produced by the movement of the ribs, then the volume of the lungs in crocodiles also changes with the movement of the liver. The latter is moved forward by contraction of the transverse abdominal muscles, causing an increase in pressure in the lungs and exhalation, and then moves backward by the longitudinal diaphragmatic muscles that connect the liver with the pelvis, causing a decrease in pressure in the lungs and, accordingly, inspiration. As researchers K. Hans and B. Clark proved, in crocodiles in water, it is the movements of the liver that play the main role in lung ventilation.

The heart of crocodiles consists of four chambers and is much more perfect than the three-chambered heart of other reptiles: oxygen-enriched 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 retains two aortic arches with an anastomosis (bridge) at the intersection. Thus, despite the fact that the body temperature, metabolic rate, motor activity and appetite of crocodiles significantly depend on the ambient temperature, the process of gas exchange in their cells proceeds more efficiently 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 gastroliths), which the animals deliberately 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 center of gravity of the crocodile down in front, giving greater stability when swimming and facilitating diving, or they contribute to grinding food while contracting the walls of the stomach, as in birds.

Crocodiles do not have a bladder, which is apparently associated with life in the water. Urine is excreted along with feces through a special organ that removes waste products located on the ventral side of the animal (it is called the cloaca). The cloaca has the form of a longitudinal slit, while in lizards and turtles it is of a transverse type. In the back of it, males have an unpaired genital organ. The female lays fertilized eggs, protected from the outside by a dense calcareous shell, and from 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 the lower jaw of crocodiles, there are large paired glands that secrete a brown secret with a strong smell of musk. The secretion of these glands is especially activated during the breeding season, helping sexual partners find each other.

More interesting articles

Fish

In the heart of fish there are 4 cavities connected in series: sinus venosus, atrium, ventricle and arterial cone/bulb.

• The venous sinus (sinus venosus) is a simple extension of the vein into which blood is collected.
• In sharks, ganoids, and lungfish, the arterial cone contains muscle tissue, several valves, and is able to contract.
• In bony fish, the arterial cone is reduced (it does not have muscle tissue and valves), therefore it is called the "arterial bulb".

The blood in the fish heart is venous, from the bulb/cone it flows to the gills, there it becomes arterial, flows to the organs of the body, becomes venous, returns to the venous sinus.

Lungfish

In lungfish, a "pulmonary circulation" appears: from the last (fourth) gill artery, blood goes through the pulmonary artery (LA) to the respiratory sac, where it is additionally enriched with oxygen and returns through the pulmonary vein (PV) to the heart, to left part of the atrium. Venous blood from the body flows, as it should, into the venous sinus. To limit the mixing of arterial blood from the "pulmonary circle" with venous blood from the body, there is an incomplete septum in the atrium and partly in the ventricle.

Thus, arterial blood in the ventricle is before venous, therefore it enters the anterior branchial arteries, from which a direct road leads to the head. Smart fish brain receives blood that has passed through the gas exchange organs three times in a row! Bathed in oxygen, rogue.

Amphibians

The circulatory system of tadpoles is similar to that of bony fish.

In an adult amphibian, the atrium is divided by a septum into the left and right, in total 5 chambers are obtained:

• venous sinus (sinus venosus), in which, like in lungfish, blood flows from the body
• left atrium (left atrium), into which, as in lungfish, blood flows from the lung
• right atrium (right atrium)
• ventricle
• arterial cone (conus arteriosus).

1) Arterial blood from the lungs enters the left atrium of amphibians, and venous blood from organs and arterial blood from the skin enters the right atrium, thus, mixed blood is obtained in the right atrium of frogs.

2) As can be seen in the figure, the mouth of the arterial cone is displaced towards the right atrium, so the blood from the right atrium enters there in the first place, and from the left - to the last.

3) Inside the arterial cone there is a spiral valve (spiral valve), which distributes three portions of blood:

• the first portion of blood (from the right atrium, the most venous of all) goes to the pulmocutaneous artery, to be oxygenated
• the second portion of blood (a mixture of mixed blood from the right atrium and arterial blood from the left atrium) goes to the organs of the body through the systemic artery
• the third portion of blood (from the left atrium, the most arterial of all) goes to the carotid artery (carotid artery) to the brain.

4) In lower amphibians (tailed and legless) amphibians

• the septum between the atria is incomplete, so the mixing of arterial and mixed blood is stronger;
• the skin is supplied with blood not from the skin-pulmonary arteries (where the most venous blood is possible), but from the dorsal aorta (where the blood is medium) - this is not very beneficial.

5) When a frog sits underwater, venous blood flows from the lungs into the left atrium, which, in theory, should go to the head. There is an optimistic version that the heart at the same time starts to work in a different mode (the ratio of the phases of the pulsation of the ventricle and the arterial cone changes), complete mixing of the blood occurs, due to which not completely venous blood from the lungs enters the head, but mixed blood, consisting of venous blood of the left atrium and mixed right. There is another (pessimistic) version, according to which the brain of the underwater frog receives the most venous blood and becomes dull.

reptiles

In reptiles, the pulmonary artery (“to the lung”) and two aortic arches emerge from the ventricle, which is partially divided by a septum. The division of blood between these three vessels occurs in the same way as in lungfish and frogs:

• the most arterial blood (from the lungs) enters the right aortic arch. To make it easier for children to learn, the right aortic arch starts from the leftmost part of the ventricle, and it is called the "right arch" because it goes around the heart on right, it is included in the composition of the spinal artery (how it looks - you can see in the next and following figure). The carotid arteries depart from the right arc - the most arterial blood enters the head;
• mixed blood enters the left aortic arch, which goes around the heart on the left and connects to the right aortic arch - the spinal artery is obtained, carrying blood to the organs;
• the most venous blood (from the organs of the body) enters the pulmonary arteries.

crocodiles

Crocodiles have a four-chambered heart, but they still mix blood through a special foramen of Panizza between the left and right aortic arches.

True, it is believed that mixing does not occur normally: due to the fact that there is a higher pressure in the left ventricle, blood from there flows not only into the right aortic arch (Right aorta), but also - through the foramen panicia - into the left aortic arch (Left aorta), thus, the organs of the crocodile receive almost completely arterial blood.

When a crocodile dives, the blood flow through its lungs decreases, the pressure in the right ventricle increases, and the flow of blood through the foramen panicia stops: blood from the right ventricle flows along the left aortic arch of an underwater crocodile. I don’t know what the point is: all the blood in the circulatory system at this moment is venous, why redistribute where? In any case, blood from the right aortic arch enters the head of the underwater crocodile - when the lungs are not working, it is completely venous. (Something tells me that the pessimistic version is also true for underwater frogs.)

Birds and mammals

The circulatory systems of animals and birds in school textbooks are set out very close to the truth (all other vertebrates, as we have seen, are not so lucky with this). The only trifle that is not supposed to be said at school is that in mammals (C) only the left aortic arch has been preserved, and in birds (B) only the right one (under the letter A is the circulatory system of reptiles in which both arches are developed) - there is nothing else interesting in the circulatory system of either chickens or humans. Is that the fruit ...

Fruit

Arterial blood, received by the fetus from the mother, comes from the placenta through the umbilical vein (umbilical vein). Part of this blood enters the portal system of the liver, part bypasses the liver, both of these portions eventually flow into the inferior vena cava (interior vena cava), where they mix with the venous blood flowing from the organs of the fetus. Once in the right atrium (RA), this blood is once again diluted with venous blood from the superior vena cava (superior vena cava), thus, in the right atrium, the blood is completely mixed. At the same time, a little venous blood from non-working lungs enters the left atrium of the fetus - just like a crocodile sitting under water. What are we going to do, colleagues?

The good old incomplete septum comes to the rescue, over which the authors of school textbooks on zoology laugh so loudly - the human fetus has an oval hole (Foramen ovale) right in the septum between the left and right atrium, through which mixed blood from the right atrium enters the left atrium. In addition, there is a ductus arteriosus (Dictus arteriosus), through which mixed blood from the right ventricle enters the aortic arch. Thus, mixed blood flows through the fetal aorta to all its organs. And to the brain too! And we molested frogs and crocodiles !! But themselves.

testiki

1. Cartilaginous fish lack:
a) swim bladder
b) spiral valve;
c) arterial cone;
d) chord.

2. The circulatory system in mammals contains:
a) two aortic arches, which then merge into the dorsal aorta;
b) only the right aortic arch
c) only the left aortic arch
d) only the abdominal aorta, and the aortic arches are absent.

3. As part of the circulatory system in birds there is:
A) two aortic arches, which then merge into the dorsal aorta;
B) only the right aortic arch;
C) only the left aortic arch;
D) only the abdominal aorta, and the aortic arches are absent.

4. The arterial cone is present in
A) cyclostomes;
B) cartilaginous fish;
B) cartilaginous fish;
D) bony ganoid fish;
D) bony fish.

5. Classes of vertebrates in which blood moves directly from the respiratory organs to the tissues of the body, without first passing through the heart (select all the correct options):
A) bone fish;
B) adult amphibians;
B) reptiles
D) Birds;
D) mammals.

6. The heart of a turtle in its structure:
A) three-chamber with an incomplete septum in the ventricle;
B) three-chamber;
B) four-chamber;
D) four-chamber with a hole in the septum between the ventricles.

7. The number of circles of blood circulation in frogs:
A) one in tadpoles, two in adult frogs;
B) one in adult frogs, tadpoles do not have blood circulation;
C) two in tadpoles, three in adult frogs;
D) two in tadpoles and in adult frogs.

8. In order for the carbon dioxide molecule, which passed into the blood from the tissues of your left foot, to be released into environment through the nose, it must pass through all of the following structures in your body except:
A) right atrium
B) pulmonary vein;
B) alveoli of the lungs;
D) pulmonary artery.

9. Two circles of blood circulation have (select all correct options):
BUT) cartilaginous fish;
B) ray-finned fish;
B) lungfish
D) amphibians;
D) reptiles.

10. A four-chambered heart has:
A) lizards
B) turtles;
B) crocodiles
D) birds;
D) mammals.

11. Before you is a schematic drawing of the heart of mammals. Oxygenated blood enters the heart through the vessels:

A) 1;
B) 2;
AT 3;
D) 10.

12. The figure shows arterial arches:
A) lungfish
B) tailless amphibian;
B) tailed amphibian;
D) reptile.

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 a ministerial worker [Not a Russian ministry, don't worry!] that before a systematic study of individual groups, a rather large topic should be considered, which will 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 diversity 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 ill-fated 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". 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 the sophisticated experiments of biologists from the University of Utah, they 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-ka. 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 figured out how to test the long-standing assumption that crocodiles transfer blood from one circle of blood circulation to another not in order to hide, but for the sake of better digestion of food (carbon dioxide is a substrate for the production of acid by the stomach glands). Researchers have seen that healthy young alligators in the process of digesting food through the left aortic arch (the one that supplies blood to the digestive system) flows venous, carbonic acid-rich blood. 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!

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. Mixing of venous and arterial blood is characteristic of imperfect circulatory systems 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 cause scientists call 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.