Vertebrates with a three-chambered heart whose reproduction. Vertebrate animals with a three-chambered heart, the reproduction of which is closely. Evolutionary development of organisms
The same organs different types may differ in structure and function. Our own heart has four separate chambers, while frogs, toads, snakes and lizards can get by with just three. You can learn about the functionality of three-chambered hearts in this article.
Vertebrate classes and chambers of the heart
Vertebrate animals are represented by different classes: fish, amphibians, reptiles, mammals and birds. At vertebrate heart performs blood pumping function throughout the body this is called circulation. Although the circulatory systems are similar in many ways, the hearts of different classes of vertebrates have different numbers of chambers. These chambers determine how efficiently the heart carries oxygen-rich blood and oxygen-poor blood back to the heart.
Vertebrates can be classified according to the number of heart chambers:
- Two chambers: one atrium and one ventricle (fish)
- Three chambers: two atria and one ventricle (amphibians, amphibians and reptiles)
- Four chambers: two atria and two ventricles (birds and mammals)
Circulation
The most vital substance - oxygen, enters the bloodstream through the gills or lungs. To achieve a more efficient use of oxygen, many vertebrates have two separate stages of circulation: pulmonary and systemic.
In chambered pulmonary circulation, the heart sends blood to the lungs to enrich it with oxygen. The process begins in the ventricle, from there, through the pulmonary arteries, it enters the lungs. Blood returns from the lungs through the pulmonary veins and flows into the left atrium. From there, it enters the ventricle, where the systemic circulation begins.
The circulation is the distribution of oxygen-rich blood throughout the body. The ventricle pumps blood through the aorta, a massive artery that branches off to all parts of the body. After oxygen is delivered to the organs and limbs, it returns through the veins that lead it to the inferior vena cava or superior vena cava. Then from these two main veins enters the right atrium. Once there, the oxygen-depleted blood returns to the pulmonary circulation.
The heart is a complex pump and main body circulatory system to provide oxygen to the body.
The heart is made up of chambers: atrium and ventricle. One on each side, each with different functions. Left-hand side provides systemic circulation, while the right side of the heart is responsible for pulmonary circulation, that is, for oxygen enrichment.
atrium
The atria are the chambers through which blood enters the heart. They are on the front side of the heart, one atrium on each side. Venous blood enters the right atrium through the superior vena cava and inferior vena cava. The left receives oxygenated blood from the lungs via the left and right pulmonary veins.
Blood flows into the atrium, bypassing the valves. The atria relax and expand as they fill with blood. This process is called diastolic fibrillation, we are with you call it pulse. The atria and ventricles are separated by the mitral and tricuspid valves. The atria pass near atrial systole, creating short cuts atria. They, in turn, push the blood out of the atria through the valves and into the ventricles. The elastic tendons that attach to the ventricular valve relax during systole and transition into ventricular diastole, but the valve closes during ventricular systole.
One of the defining characteristics of the atria is that they do not interfere with venous blood flow in the heart. The venous blood entering the heart has a very low pressure compared to the arterial blood, and the valves take over the venous blood pressure. Atrial systole is incomplete and does not block the flow of venous blood through the atria into the ventricles. During atrial systole, venous blood continues to flow continuously through the atria into the ventricles.
Atrial contractions are usually minor, they only prevent significant backpressure that impedes venous blood flow. Relaxation of the atria is coordinated with the ventricle to begin to relax before the ventricular contraction begins, which helps prevent the pulse from being too slow.
Ventricles
The ventricles are at the back of the heart. The ventricle receives blood from the right atrium and pumps it through the pulmonary vein into the pulmonary circulation which enters the lungs for gas exchange. It then receives oxygen-enriched blood from the left atrium and pumps it through the aorta into the systemic circulation to supply body tissues with oxygen.
The walls of the ventricles are thicker and stronger than those of the atria. The physiological stress that pumps blood throughout the body from the lungs is much greater than the pressure created to fill the ventricles. During ventricular diastole, the ventricle relaxes and fills with blood. During systole, the ventricle contracts and pumps blood through the semilunar valves into the systemic circulation.
People are sometimes born with congenital anomalies, in the form of a single ventricle with two atria. Vestigial parts of the ventricular septum may be present but not functional. The disease is called heart disease.
The only amphibian species that has 4 heart chambers is the common crocodile. A number of animals have three chambers, that is, two atria and one ventricle.
- amphibians
- amphibians
- reptiles.
In nature, amphibians and most reptiles have a prechamber heart and consist of two atria and one ventricle. These animals also have separate chains of blood vessels, where separate chambers are responsible for oxygen saturation, and the venous chamber returns and flows into the right atrium. From there, blood is conducted to the ventricle and then pumped to the lungs. After enrichment with oxygen and release from carbon dioxide, the blood returns to the heart and flows into the left atrium. Then it enters the ventricle a second time and is further distributed throughout the body.
The fact that they are cold-blooded animals, their bodies do not expend much energy to produce heat. Thus, reptiles and amphibians can survive with less efficient cardiac structures. They also able to block the flow in the pulmonary artery to divert blood to the skin for skin respiration while diving. They are also capable of shunting the blood flow in the pulmonary artery system during a dive. This anatomical function is considered the most complex of the cardiac structures in vertebrates.
All vertebrates like fish, amphibians, reptiles, birds, mammals use oxygen from the air (or dissolved in water) to efficiently extract energy from food and release carbon dioxide as a waste product.
Any organism must deliver oxygen to all organs and collect carbon dioxide. We know that this specialized system is called the circulatory system: it is made up of blood, it contains cells that carry oxygen, blood vessels (the tubes through which blood flows), and the heart (the pump that pumps blood through the blood vessels).
Although everyone thinks that fish only have gills, it is worth noting that many species also have lungs. In many fish, the circulatory system is a relatively simple cycle.. The heart consists of two contractile chambers, the atrium and the ventricle. In this system, blood from the body enters the heart and is pumped through the gills, where it is enriched with oxygen.
To answer the question of how this phenomenon appeared, we must first understand what was behind the formation of such a complex form of the heart and circulatory system during evolution.
About 60 million years, from the beginning of the Carboniferous period to the end jurassic, amphibians were the dominant land animals on the ground. Soon, due to the primitive structure, they lost their place of honor. Although among the various families of reptiles that descended from amphibian isolated groups, there were more persistent ones. For example, archosaurs (which eventually evolved into dinosaurs) and therapsids (which eventually evolved into mammals). The classic amphibian was the big-headed Eryops, which was about fourteen meters long from head to tail and weighed about two hundred kilograms.
Word "amphibian" in Greek means "both kinds of life", and that pretty much sums up what makes these vertebrates unique: they lay their eggs in water because they need a constant source of moisture. And they can live on land.
Great progress in the evolution of vertebrates has given many species circulatory and respiratory systems, highly efficient. According to these parameters, amphibians, amphibians, reptiles are located at the bottom of the oxygen-respiratory ladder: their lungs have a relatively small internal volume and cannot process as much air as the lungs of mammals. Fortunately, amphibians can breathe through their skin, which, coupled with a three-chambered heart, allows them, albeit with difficulty, to fulfill their metabolic needs.
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The appearance of a four-chambered heart in birds and mammals was the most important evolutionary event, thanks to which these animals were able to become warm-blooded. A detailed study of the development of the heart in lizard and turtle embryos and its comparison with the available data on amphibians, birds, and mammals showed that changes in the regulatory gene played a key role in the transformation of a three-chambered heart into a four-chambered one. Tbx5, which functions in the initially single rudiment of the ventricle. If a Tbx5 it is expressed (works) evenly throughout the rudiment, the heart turns out to be three-chambered, if only on the left side it is four-chambered.
The emergence of vertebrates on land was associated with the development of pulmonary respiration, which required a radical restructuring of the circulatory system. Fish breathing with gills have one circle of blood circulation, and the heart, respectively, is two-chambered (consists of one atrium and one ventricle). Terrestrial vertebrates have a three- or four-chambered heart and two circulations. One of them (small) drives the blood through the lungs, where it is saturated with oxygen; then the blood returns to the heart and enters the left atrium. The large circle sends oxygen-enriched (arterial) blood to all other organs, where it gives off oxygen and returns through the veins to the heart, entering the right atrium.
In animals with a three-chambered heart, blood from both atria enters a single ventricle, from where it then goes to the lungs and all other organs. Wherein arterial blood to some extent mixed with venous. In animals with a four-chambered heart during embryonic development initially a single ventricle is subdivided by a septum into left and right halves. As a result, the two circles of blood circulation are completely separated: venous blood enters only the right ventricle and goes from there to the lungs, arterial blood only goes to the left ventricle and goes from there to all other organs.
The formation of a four-chambered heart and the complete separation of the circulation circles was a necessary prerequisite for the development of warm-bloodedness in mammals and birds. The tissues of warm-blooded animals consume a lot of oxygen, so they need “clean” arterial blood, maximally saturated with oxygen, and not mixed arterial-venous blood, which cold-blooded vertebrates with a three-chambered heart are content with (see: Phylogeny of the circulatory system of chordates).
A three-chambered heart is characteristic of amphibians and most reptiles, although in the latter there is a partial division of the ventricle into two parts (an incomplete intraventricular septum develops). The true four-chambered heart developed independently in three evolutionary lines: in crocodiles, birds, and mammals. This is considered one of the clearest examples of convergent (or parallel) evolution (see: Aromorphoses and parallel evolution; Parallelisms and homological variability).
A large group of researchers from the USA, Canada and Japan, who published their results in the latest issue of the journal Nature, set out to find out the molecular genetic basis of this most important aromorphosis.
The authors studied in detail the development of the heart in the embryos of two reptiles - red-eared turtle Trachemys scripta and anole lizards ( Anolis carolinensis). Reptiles (except crocodiles) are of particular interest for solving the problem, since the structure of their heart in many ways is intermediate between a typical three-chamber (such as in amphibians) and a real four-chamber, like in crocodiles, birds and animals. Meanwhile, according to the authors of the article, for 100 years no one has seriously studied the embryonic development of the heart of reptiles.
Studies performed on other vertebrates have not yet given an unequivocal answer to the question of what genetic changes caused the formation of a four-chambered heart during evolution. However, it has been observed that the regulatory gene Tbx5, coding for a transcriptional regulator (see transcription factors), works (expressed) differently in the developing heart in amphibians and warm-blooded animals. In the former, it is evenly expressed throughout the future ventricle; in the latter, its expression is maximum in the left part of the anlage, from which the left ventricle is later formed, and minimum on the right. It was also found that a decrease in activity Tbx5 leads to defects in the development of the septum between the ventricles. These facts allowed the authors to suggest that changes in the activity of the gene Tbx5 may have played some role in the evolution of the four-chambered heart.
During the development of the lizard heart, a muscular fold develops in the ventricle, partially separating the outlet of the ventricle from its main cavity. This ridge was interpreted by some authors as a structure homologous to the intergastric septum of vertebrates with a four-chambered heart. Based on the study of the growth of the ridge and its fine structure, the authors of the article under discussion reject this interpretation. They pay attention to the fact that the same roller briefly appears during the development of the heart of a chicken embryo - along with a real septum.
The data obtained by the authors indicate that, apparently, no structures homologous to the true intergastric septum are formed in the lizard. In the turtle, on the other hand, an incomplete septum is formed (along with a less developed muscular ridge). The formation of this partition in the turtle begins much later than in the chicken. Nevertheless, it turns out that the heart of a lizard is more "primitive" than that of a turtle. The turtle heart is intermediate between the typical three-chambered heart (such as those of amphibians and lizards) and the four-chambered hearts of crocodiles and warm-blooded animals. This is contrary to generally accepted ideas about the evolution and classification of reptiles. On the basis of anatomical features, turtles have traditionally been considered the most primitive (basal) group among modern reptiles. However, comparative DNA analysis by a number of researchers has repeatedly pointed to the closeness of turtles to archosaurs (a group that includes crocodiles, dinosaurs and birds) and to the more basal position of squamates (lizards and snakes). The structure of the heart confirms this new evolutionary pattern (see figure).
The authors studied the expression of several regulatory genes in the developing turtle and lizard heart, including the gene Tbx5. In birds and mammals, already at the very early stages of embryogenesis, a sharp gradient in the expression of this gene is formed in the ventricular anlage (expression rapidly decreases from left to right). It turned out that in the lizard and turtle in the early stages of the gene Tbx5 expressed in the same way as in a frog, that is, evenly throughout the future ventricle. In the lizard, this situation persists until the end of embryogenesis, while in the turtle, at the later stages, an expression gradient is formed, essentially the same as in the chicken, only less pronounced. In other words, in the right part of the ventricle, the activity of the gene gradually decreases, while in the left part it remains high. Thus, according to the nature of gene expression Tbx5 the turtle also occupies an intermediate position between the lizard and the chicken.
It is known that the protein encoded by the gene Tbx5, is regulatory - it regulates the activity of many other genes. Based on the data obtained, it was natural to assume that the development of the ventricles and the laying of the interventricular septum are under the control of the gene Tbx5. It has been previously shown that a decrease in activity Tbx5 in mouse embryos leads to defects in ventricular development. This, however, was not enough to consider the "leading" role of Tbx5 in the formation of a four-chambered heart.
To obtain stronger evidence, the authors used several lines of genetically modified mice, in which, during embryonic development, the gene Tbx5 could be turned off in one or another part of the heart germ at the request of the experimenter.
It turned out that if a gene is turned off in the entire ventricular bud, then the bud does not even begin to divide into two halves: a single ventricle develops from it without any traces of an intergastric septum. Characteristic morphological features, by which one can distinguish the right ventricle from the left one, regardless of the presence of a septum, are also not formed. In other words, mouse embryos with a three-chambered heart are obtained! Such embryos die on the 12th day of embryonic development.
The next experiment was that the gene Tbx5 turned off only in the right part of the rudiment of the ventricles. Thus, the concentration gradient of the regulatory protein encoded by this gene was sharply shifted to the left. In principle, it could be expected that in such a situation, the intergastric septum would begin to form more to the left than it should be. But this did not happen: the septum did not begin to form at all, but there was a division of the rudiment into the left and right parts according to other morphological features. This means that the expression gradient Tbx5 is not the only factor controlling the development of a four-chambered heart.
In another experiment, the authors succeeded in making the gene Tbx5 expressed uniformly in the entire ventricular anlage of the mouse embryo, approximately the same as in a frog or a lizard. This again led to the development of mouse embryos with a three-chambered heart.
The results obtained show that changes in the work of the regulatory gene Tbx5 indeed could play an important role in the evolution of the four-chambered heart, and these changes occurred in parallel and independently in mammals and archosaurs (crocodiles and birds). Thus, the study once again confirmed that changes in the activity of genes that regulate individual development play a key role in the evolution of animals.
Of course, it would be even more interesting to design such genetically modified lizards or turtles that have Tbx5 would be expressed as in mice and chickens, that is, in the left side of the ventricle it is strong, and in the right it is weak, and see if this makes their heart look more like a four-chamber. But this is not yet technically feasible: the genetic engineering of reptiles has not yet advanced that far.
Tests
706-01. Vertebrate animals with a three-chambered heart, whose reproduction is closely related to water, are combined into a class
A) bony fish
B) Mammals
B) reptiles
D) Amphibians
Answer
706-02. What class do animals belong to, the diagram of the structure of the heart of which is shown in the figure?
A) insects
B) Cartilaginous fish
B) amphibians
D) Birds
Answer
706-03. The characteristic that distinguishes amphibians from fish is
A) cold-bloodedness
B) the structure of the heart
B) development in water
D) closed circulatory system
Answer
706-04. Amphibians differ from fish in having
A) the brain
B) a closed circulatory system
C) paired lungs in adults
D) sense organs
Answer
706-05. Which feature among the listed distinguishes most animals of the class Amphibians from Mammals?
B) external fertilization
B) sexual reproduction
D) use for habitation of the aquatic environment
Answer
706-06. Reptiles in the process of evolution acquired, unlike amphibians,
A) a closed circulatory system
B) high fertility
B) a large egg with embryonic membranes
D) three-chambered heart
Answer
706-07. If, in the process of evolution, an animal has formed a heart, shown in the figure, then the respiratory organs of the animal must be 
A) lungs
B) skin
B) lung sacs
D) gills
Answer
706-08. In which group of animals does reproduction not depend on water?
A) non-cranial (lancelets)
B) bony fish
B) amphibians
D) reptiles
Answer
706-09. In which animals does the development of the embryo complete inside the egg?
A) bony fish
B) tailed amphibians
B) tailless amphibians
D) reptiles
Answer
706-10. Vertebrate animals with a three-chambered heart, whose reproduction is not associated with water, are combined into a class
A) bony fish
B) Mammals
B) reptiles
D) Amphibians
Answer
706-11. Vertebrates with variable body temperature, pulmonary respiration, a three-chambered heart with an incomplete septum in the ventricle are classified as
A) bony fish
B) amphibians
B) reptiles
D) cartilaginous fish
Answer
706-12. Reptiles, unlike amphibians, tend to
A) external fertilization
B) internal fertilization
C) development with the formation of a larva
D) division of the body into head, trunk and tail
Answer
706-13. Which of the following animals is cold-blooded?
A) a lizard
B) Amur tiger
B) steppe fox
D) common wolf
Answer
706-14. What class do animals with dry skin with horny scales and a three-chambered heart with an incomplete septum belong to?
A) reptiles
B) Mammals
B) amphibians
D) Birds
Answer
706-15. Birds differ from reptiles in having
A) internal fertilization
B) central nervous system
B) two circles of blood circulation
G) constant temperature body
Answer
706-15. What structural feature is similar in modern reptiles and birds?
A) bones filled with air
B) dry skin, devoid of glands
B) caudal region in the spine
D) small teeth in the jaws
Answer
706-16. What animal has gas exchange between atmospheric air and the blood goes through the skin?
A) killer whale
B) triton
B) crocodile
D) pink salmon
Answer
706-17. Which group of animals has a two-chambered heart?
A) fish
B) amphibians
B) reptiles
D) mammals
Answer
706-18. The development of the baby in the uterus occurs in
A) birds of prey
B) reptiles
B) amphibians
D) mammals
Answer
706-19. What class of chordates is characterized by cutaneous respiration?
A) amphibians
B) Reptiles
B) birds
D) Mammals
Answer
706-20. A sign of the amphibian class is
A) chitinous cover
B) bare skin
B) live birth
D) paired limbs
Answer
706-21. How do members of the class Amphibians differ from other vertebrates?
A) spine and free limbs
B) pulmonary respiration and the presence of a cloaca
C) bare mucous skin and external fertilization
D) a closed circulatory system and a two-chambered heart
Answer
706-22. Which feature among the listed distinguishes animals of the class Reptiles from animals of the class Mammals?
A) a closed circulatory system
B) fluctuating body temperature
C) development without transformation
D) use of the ground-air environment for habitation
They have a different body structure. Everyone has a common building plan. This proves descent from the same ancestor. However, the complexity of the body structure varies. It is believed that the complication of the structure went in the course of evolution. That is, more primitive organisms first appeared.
Evolutionary development of organisms
The course of evolution of vertebrates began with the lancelet.
This organism already has a notochord and a neural tube. And also the most primitive heart for vertebrates: a pulsating abdominal vessel.
Further complication of organization led to the formation of fish. Gill-breathing organisms and one circle of blood circulation.
Amphibians and most reptiles have a three-chambered heart. It also increases their vitality.
Birds and mammals are at the pinnacle of evolution. The heart is made up of four chambers. There are no openings between the atria, as well as between the ventricles. The two circles of blood circulation are completely separated. Therefore, birds and mammals have warm-bloodedness, which sharply distinguishes them from other animals. Of course, humans also belong to this group.
Three-chambered heart
In amphibians and reptiles, the heart has three chambers: two atria and one ventricle. Scientists have found that it is precisely this structure of the muscular organ that is suitable for the life of these animals.
The presence of two circles of blood circulation provides a fairly high level of vital activity. Animals with a three-chambered heart live on land, they are quite mobile (especially reptiles). They can tolerate a slight drop in temperature without falling into a stupor. Tritons, for example, are the first to emerge from winter shelters when the snow has not yet melted. Spring makes you wake up very early. These amphibians hop across the snow in search of a breeding partner.
The presence of a three-chambered heart makes it possible for amphibians to fall into a stupor when frost sets in. Circulatory system allows not to spend a lot of energy for pumping blood, which would be observed in the presence of a heart with four chambers and a complete separation of the two circles of blood circulation.
reptile heart
Reptiles have a three-chambered heart with an incomplete septum. It can be seen that their mobility increases dramatically compared to amphibians. Agile lizards are actually very mobile. They are quite difficult to catch, especially in warm weather. However, body temperature still depends on environment. Reptiles are cold-blooded organisms.
Crocodiles have an unusual heart structure. Scientists classify crocodiles as animals with a four-chambered heart. The septum between the right and left ventricles is large area. However, there is a hole in this wall. Therefore, crocodiles remain cold-blooded creatures. Blood saturated with an oxidizing element mixes with oxygen-poor blood. In addition, the special structure of the crocodile blood system is expressed in the presence of the left artery. It departs from the right ventricle along with the pulmonary. The left artery carries blood to the crocodile's stomach. This structure contributes to faster digestion of food. This is necessary, as the reptile swallows large pieces of meat, which can begin to rot if left in the digestive tract for a long time.
Four-chambered heart
Birds and animals that feed their young with milk have a heart with four chambers. These are the most highly organized organisms. Birds are capable of long flight, while mammals are capable of fast running. All of them have warm blood. They remain active in cold weather, which cold-blooded representatives cannot afford.
Only those organisms that cannot provide themselves with food in winter fall into hibernation. The bear, which has not gained enough weight in autumn, wakes up and wanders through the snow in search of food.
Thus, the four-chambered heart maximized the vital activity of organisms. Warm-blooded animals do not go into a state of torpor. Their motor activity does not depend on the ambient temperature. Such vertebrates feel great on land in conditions of strong gravity.
Animals with a three-chambered heart have already acquired two circles of blood circulation. However, the large and small circles are not completely separated. Blood rich in the element of oxidation mixes with blood rich in carbon dioxide. Despite this, the three-chambered heart ensures the life of organisms on land.
