Vertebrates with a three-chambered heart whose reproduction. The heart of amphibians, detailed description and characteristics
“Forms of reproduction” - Sexual reproduction. No, spores of all higher plants are formed by meiosis. 6. Polyembryony. Bacteria reproduce through mitotic divisions. A form of asexual reproduction characteristic of many groups of plants. Can sexual reproduction occur without the participation of gametes? Topic: “Forms of reproduction of organisms.”
“Reproduction and development of animals” - Platypus. Cubs are an adult animal. Insects. Grasshopper development. Eggs. Mammals. Butterfly development. They lay eggs. Butterfly. They lay eggs. Caviar --- fry --- fish. Egg --- baby --- adult animal. Reproduction and development of animals. Groups of animals. Stickleback. Larva. Reptiles.
“Sexual reproduction of animals” - Reproductive organs. What features characterize a hermaphroditic organism? The basis for the existence of species is reproduction. Parthenogenesis - in bees. How many individuals participate in sexual reproduction? The advantage of parthenogenesis is an increase in the rate of reproduction. Parthenogenesis is the development of an individual from an unfertilized egg.
“Vertebrate Birds” - III.Reflection. Letter to the editor of the newspaper "Friends of Nature". Understanding. I.Challenge Game “Believe it or not.” Each person writes only one sentence. The letter is passed around the circle only once. Work with text. Group writing letter. Working with the text “Birds of the Red Book”. Let's compare our assumptions with the material in the text.
“Reproduction and development of amphibians” - We will record the results of our work in a notebook. How are tadpoles and fish similar? Mating season. Evolution of amphibians. Reproduction of amphibians. The tadpole is very similar to a fish. Conclusions. Summarize. What are the similarities between the development of frogs and fish? The influence of seasonal changes on the life of amphibians. An ancient lobe-finned fish.
“Classes of vertebrates” - Class mammals or animals. Most are herbivores, fleeing from predators. The body of most fish is covered with mucus and scales. Only oviparous mammals lay eggs. They have 1 or 3 fingers on their limbs. Squad of rodents. They feed on both plant and animal foods. Rodents include: squirrel, muskrat, gopher, hamster, mice, rats.
The same organs in different species may differ in structure and functionality. Our own heart has four separate chambers, while frogs, toads, snakes and lizards can get by with just three. You can learn about the functionality of three-chambered hearts in this article.
Vertebrate classes and cardiac chambers
Vertebrates are represented by various classes: fish, amphibians, reptiles, mammals and birds. In vertebrates, the heart performs blood pumping function throughout the body this is called blood 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 divided by 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 blood through the gills or lungs. To achieve more efficient use of oxygen, many vertebrates have two separate stages of blood circulation: pulmonary and systemic.
In chamber pulmonary circulation, the heart sends blood to the lungs to enrich it with oxygen. The process begins in the ventricle, from there, through the pulmonary arteries, it enters the lungs. Blood returns from the lungs through the pulmonary veins and flows into the left atrium. From there it enters the ventricle, where the systemic circulation begins.
The circulatory system distributes oxygen-rich blood throughout the body. The ventricle pumps blood through the aorta, a massive artery that branches throughout the body. Once oxygen is delivered to the organs and limbs, it is returned through the veins, which lead it to the inferior vena cava or superior vena cava. Then from these two main veins it enters the right atrium. Once there, the oxygen-depleted blood returns to the pulmonary circulation.
The heart is a complex pump and the main organ of the circulatory system, ensuring the enrichment of the body with oxygen.
The heart is made up of chambers: atrium and ventricle. One on each side, each with different functions. The left side provides systemic circulation, while the right side of the heart is responsible for pulmonary circulation, that is, for oxygenation.
Atria
The atria are the chambers through which blood enters the heart. They are located on the front side of the heart, with one atrium on each side. The right atrium receives venous blood through the superior vena cava and the inferior vena cava. The left one receives oxygenated blood from the lungs through the left and right pulmonary veins.
Blood flows into the atrium, bypassing the valves. The atria relax and dilate as they fill with blood. This process is called diastole fibrillation, we are with you we call it pulse. The atria and ventricles are separated by the mitral and tricuspid valves. The atria pass around atrial systole, creating brief atrial contractions. They, in turn, push blood from the atria through the valves and further into the ventricles. The elastic tendons that attach to the ventricular valve relax during ventricular systole and move 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 to the heart. Venous blood entering the heart has very low pressure compared to arterial blood, and the valves absorb 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, only preventing the significant backpressure that prevents venous blood from flowing. Atrial relaxation is coordinated with the ventricle to begin relaxing before the ventricles begin to contract, which helps prevent the heart rate from becoming too slow.
Ventricles
The ventricles are located at the back of the heart. The ventricle receives blood from the right atrium and pumps it through the pulmonary vein into the pulmonary circulation, which enters the lungs for gas exchange. It then receives oxygen-rich blood from the left atrium and pumps it through the aorta into the systemic circulation to supply the body’s tissues with oxygen.
The walls of the ventricles are thicker and stronger than those of the atria. The physiological loads that pump blood throughout the body from the lungs are 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. Rudimentary parts of the ventricular septum may be present but not functional. The disease is called heart disease.
The only species of amphibian that has 4 chambers of the heart 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 being enriched with oxygen and freed 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 these are cold-blooded animals, their bodies do not expend much energy to produce heat. Thus, reptiles and amphibians can survive with less efficient heart structures. They also capable of blocking the flow in the pulmonary artery to divert blood to the skin for cutaneous respiration during diving. They are also capable of shunting blood flow in the pulmonary artery system during a dive. This anatomical function is considered the most complex among cardiac structures in vertebrates.
All vertebrate animals such as fish, amphibians, reptiles, birds, and mammals use oxygen from the air (or dissolved in water) to effectively extract energy from food and emit 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 shape of the heart and circulatory system during evolution.
About 60 million years, from the beginning of the Carboniferous period until the end of the Jurassic period, amphibians were the dominant land animals on the ground. Soon, due to their primitive structure, they lost their place of honor. Although among the various families of reptiles that descended from amphibians, isolated groups were more resilient. 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 approximately fourteen meters long from head to tail and weighed about two hundred kilograms.
Word "amphibian" in Greek means "both types of life", and that pretty much sums up what makes these vertebrates unique: they lay their eggs in water because they require a constant source of moisture. But 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 and 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.
They have different body structures. Everyone has a common building plan. This proves descent from one ancestor. However, the complexity of the body's structure varies. It is believed that the complication of the structure occurred in the course of evolution. That is, more primitive organisms appeared first.
Evolutionary development of organisms
The 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 complexity of the organization led to the formation of fish. Organisms that breathe with gills and one circle of blood circulation.
Amphibians and most reptiles have a three-chambered heart. This also increases their vital energy.
Birds and mammals are at the pinnacle of evolution. The heart is formed by four chambers. There are no openings between the atria, nor between the ventricles. The two circles of blood circulation are completely separated. Therefore, birds and mammals have warm blood, which sharply distinguishes them from other animals. Humans, of course, 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 this particular structure of the muscular organ is suitable for the life of these animals.
The presence of two circles of blood circulation ensures a fairly high level of vital activity. Animals with a three-chambered heart live on land and are quite mobile (especially reptiles). They can tolerate a slight drop in temperature without going into torpor. Newts, 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 gallop through the snow in search of a breeding partner.
The presence of a three-chambered heart allows amphibians to fall into torpor when frost sets in. The circulatory system allows you to avoid spending a lot of energy to pump blood, which would be observed if there was a heart with four chambers and complete separation of the two circles of blood circulation.
Heart of reptiles
Reptiles have a three-chambered heart with an incomplete septum. You can notice that their mobility increases sharply compared to amphibians. Agile lizards are actually very active. They can be quite difficult to catch, especially in warm weather. However, body temperature still depends on the 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 has a large area. However, there is a hole in this wall. Therefore, crocodiles remain cold-blooded creatures. Blood rich in an oxidizing element mixes with blood poor in oxygen. In addition, the special structure of the crocodile's blood system is reflected in the presence of the left artery. It arises from the right ventricle along with the pulmonary one. The left artery carries blood to the crocodile's stomach. This structure promotes faster digestion of food. This is necessary, since 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, and mammals are capable of fast running. All of them are warm-blooded. They remain active even in cold weather, which cold-blooded representatives cannot afford.
Only those organisms that cannot provide themselves with food in winter hibernate. A bear that has not gained enough weight in the fall 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 fall into a state of torpor. Their motor activity does not depend on the ambient temperature. Such vertebrates thrive 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 oxidation element mixes with blood rich in carbon dioxide. Despite this, the three-chambered heart ensures the life of organisms on land.
Tests
706-01. Vertebrates with a three-chambered heart, whose reproduction is closely related to water, are grouped into the class
A) Bony fish
B) Mammals
B) Reptiles
D) Amphibians
Answer
706-02. What class do animals belong to, the diagram of the heart structure 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) structure of the heart
B) development in water
D) closed circulatory system
Answer
706-04. Amphibians differ from fish in having
A) brain
B) closed circulatory system
B) paired lungs in adults
D) sense organs
Answer
706-05. Which characteristic among those listed distinguishes most animals of the class Amphibians from Mammals?
B) external fertilization
B) sexual reproduction
D) use of the aquatic environment for habitat
Answer
706-06. In the process of evolution, reptiles acquired, unlike amphibians,
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 the heart shown in the figure, then the animal’s respiratory organs should be
A) lungs
B) skin
B) lung sacs
D) gills
Answer
706-08. In which group of animals does reproduction not involve water?
A) skullless (lancelets)
B) bony fish
B) amphibians
D) reptiles
Answer
706-09. In which animals does the embryo develop completely inside the egg?
A) bony fish
B) tailed amphibians
B) tailless amphibians
D) reptiles
Answer
706-10. Vertebrates with a three-chambered heart, whose reproduction is not associated with water, are grouped into the class
A) Bony fish
B) Mammals
B) Reptiles
D) Amphibians
Answer
706-11. Vertebrates with unstable body temperature, pulmonary breathing, 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
B) development with the formation of a larva
D) division of the body into head, torso and tail
Answer
706-13. Which of the following animals is cold-blooded?
A) quick lizard
B) Amur tiger
B) steppe fox
D) common wolf
Answer
706-14. Which class include animals that have dry skin with horny scales and a three-chambered heart with an incomplete septum?
A) Reptiles
B) Mammals
B) Amphibians
D) Birds
Answer
706-15. Birds differ from reptiles by having
A) internal fertilization
B) central nervous system
B) two circles of blood circulation
D) constant body temperature
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. In which animal does gas exchange between atmospheric air and blood occur through the skin?
A) killer whale
B) triton
B) crocodile
D) pink salmon
Answer
706-17. Which group of animals has a heart consisting of two chambers?
A) fish
B) amphibians
B) reptiles
D) mammals
Answer
706-18. The development of the baby in the uterus occurs at
A) birds of prey
B) reptiles
B) amphibians
D) mammals
Answer
706-19. Representatives of which class of chordates are characterized by cutaneous respiration?
A) Amphibians
B) Reptiles
B) Birds
D) Mammals
Answer
706-20. The sign of the amphibian class is
A) chitinous cover
B) bare skin
B) live birth
D) paired limbs
Answer
706-21. By what characteristics do representatives of the class Amphibians differ from other vertebrates?
A) spine and free limbs
B) pulmonary breathing and the presence of a cloaca
B) bare mucous skin and external fertilization
D) closed circulatory system and two-chamber heart
Answer
706-22. Which feature among the listed distinguishes animals of the class Reptiles from animals of the class Mammals?
A) closed circulatory system
B) unstable body temperature
C) development without transformation
D) use of the ground-air environment for habitat
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 heart development in lizard and turtle embryos and comparison with available data on amphibians, birds and mammals showed that changes in the functioning of a 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 ventricular rudiment. If Tbx5 is expressed (works) evenly throughout the entire embryo, the heart turns out to be three-chambered, if only on the left side - four-chambered.
The emergence of vertebrates onto land was associated with the development of pulmonary respiration, which required a radical restructuring of the circulatory system. Fish that breathe with gills have one blood circulation, and the heart, accordingly, is two-chambered (consists of one atrium and one ventricle). Terrestrial vertebrates have a three- or four-chambered heart and two circuits of blood circulation. One of them (small) drives blood through the lungs, where it is saturated with oxygen; the blood then returns to the heart and enters the left atrium. The large circle directs oxygenated (arterial) blood to all other organs, where it releases oxygen and returns through the veins to the heart, ending up in the right atrium.
In animals with a three-chambered heart, blood from both atria enters a single ventricle, from where it is then sent to the lungs and all other organs. In this case, arterial blood is mixed to one degree or another with venous blood. In animals with a four-chambered heart, during embryonic development, the initially single ventricle is divided 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 enters the left ventricle and goes from there to all other organs.
The formation of a four-chambered heart and complete separation of the blood circulation 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 “pure” arterial blood, maximally saturated with oxygen, and not mixed arterial-venous, 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 evolved independently in three evolutionary lineages: crocodiles, birds, and mammals. This is considered one of the striking 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 published their results in the latest issue of the journal Nature, set out to find out the molecular genetic basis of this important aromorphosis.
The authors studied in detail the development of the heart in the embryos of two reptiles - the red-eared turtle Trachemys scripta and anole lizards ( Anolis carolinensis). Reptiles (except crocodiles) are of particular interest for solving this problem, since the structure of their heart in many ways is intermediate between a typical three-chambered heart (such as that of amphibians) and a true four-chambered one, like that of crocodiles, birds and animals. Meanwhile, according to the authors of the article, no one has seriously studied the embryonic development of the reptile heart for 100 years.
Studies carried out on other vertebrates have not yet given a clear answer to the question of what genetic changes caused the formation of a four-chambered heart during evolution. It was, however, observed that the regulatory gene Tbx5, encoding a protein that is a transcription regulator (see transcription factors), works (is expressed) differently in the developing heart of amphibians and warm-blooded animals. In the former, it is uniformly expressed throughout the entire future ventricle; in the latter, its expression is maximum in the left part of the rudiment, from which the left ventricle is subsequently formed, and minimal on the right. It was also found that the 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 gene activity Tbx5 may have played some role in the evolution of the four-chambered heart.
During the development of the lizard's heart, a muscular ridge 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. The authors of the article under discussion, based on a study of the growth of the ridge and its fine structure, reject this interpretation. They draw attention to the fact that the same ridge appears briefly during the development of the heart of the chick embryo - along with the real septum.
The data obtained by the authors indicate that the lizard apparently does not form any structures homologous to the real intergastric septum. In the turtle, on the contrary, an incomplete septum is formed (along with a less developed muscle ridge). The formation of this septum in a turtle begins much later than in a chicken. Nevertheless, it turns out that the lizard has a more “primitive” heart than the turtle. The turtle heart occupies an intermediate position between the typical three-chambered heart (such as that of amphibians and lizards) and the four-chambered one such as that of crocodiles and warm-blooded animals. This contradicts generally accepted ideas about the evolution and classification of reptiles. Based on 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 stubbornly to the proximity 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 heart of turtles and lizards, including the gene Tbx5. In birds and mammals, already at very early stages of embryogenesis, a sharp gradient of expression of this gene is formed in the ventricular primordium (expression quickly decreases from left to right). It turned out that in lizards and turtles in the early stages the gene Tbx5 expressed in the same way as in the frog, that is, evenly throughout the entire future ventricle. In the lizard, this situation persists until the end of embryogenesis, while in the turtle, at 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 gene activity gradually decreases, while in the left it remains high. Thus, according to the pattern 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 formation of the interventricular septum are controlled by the gene Tbx5. It has previously been shown that a decrease in activity Tbx5 in mouse embryos leads to defects in ventricular development. This, however, was not enough to consider the “leadership” role proven. Tbx5 in the formation of a four-chambered heart.
To obtain more compelling evidence, the authors used several lines of genetically modified mice in which, during embryonic development, the gene Tbx5 it was possible to turn off in one or another part of the cardiac rudiment at the request of the experimenter.
It turned out that if you turn off the gene in the entire ventricular primordium, the primordium does not even begin to divide into two halves: a single ventricle develops from it without any traces of the intergastric septum. Characteristic morphological features by which one can distinguish the right ventricle from the left, regardless of the presence of a septum, are also not formed. In other words, the result is mouse embryos with a three-chambered heart! 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 ventricular primordium. Thus, the concentration gradient of the regulatory protein encoded by this gene was sharply shifted to the left. In principle, one could expect that in such a situation the intergastric septum would begin to form to the left than expected. But this did not happen: the septum did not begin to form at all, but there was a division of the rudiment into left and right parts according to other morphological characteristics. 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 managed to ensure that the gene Tbx5 was uniformly expressed throughout the ventricular primordium of the mouse embryo - approximately the same as in a frog or lizard. This again led to the development of mouse embryos with three-chambered hearts.
The results obtained show that changes in the functioning of the regulatory gene Tbx5 may indeed have played 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 construct genetically modified lizards or turtles that Tbx5 would be expressed like in mice and chickens, that is, in the left part of the ventricle strongly, and in the right - weakly, and see if this would make their heart more like a four-chambered one. But this is not yet technically feasible: genetic engineering of reptiles has not yet advanced that far.
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