In amphibians, as in the first vertebrates to enter the air from the water, lungs appear as respiratory organs. At the same time, most species in the adult state lose their gills (in some tailed amphibians they remain). However, amphibian lungs do not have a surface area large enough to adequately provide tissues with oxygen. Therefore, the respiration of amphibians is carried out not only by the lungs, but also by the skin. Thus, we can say that in adult amphibians two organs are involved in respiration: the lungs and the skin. Moreover, through the skin, some species absorb up to 50% of oxygen.

The lungs of amphibians are a pair of oblong thin-walled sacs with folds inside. Their walls are penetrated by a dense network of capillaries. In the lungs, oxygen from the air enters the blood, and carbon dioxide is released from the blood into the air.

In the mechanism of pulmonary respiration in frogs, the oral cavity takes an active part, and the nostrils also participate in it. Inhalation occurs when lowering the bottom of the mouth. In this case, air is sucked in through the nostrils and enters the oropharyngeal cavity. Next, the nostrils close, the bottom of the mouth rises and the air is pushed into the lungs. To exhale, the bottom of the mouth falls again, the nostrils open, and the air leaves the lungs. Exhalation also involves some abdominal muscles. However, amphibians do not have a diaphragm, intercostal muscles, as in mammals. Therefore, the bottom of the pharynx plays a leading role in the suction and ejection of air from the lungs.

The lungs receive the most venous blood from the distributing chamber of the ventricle of the heart. Here the blood is saturated with oxygen, becomes arterial and returns to the left atrium of the heart. Thus, in amphibians, in connection with the appearance of lungs, a second circle of blood circulation occurs. It is also called small, or pulmonary.

Since amphibians also breathe through their skin, the blood that flows from the skin is also arterial and goes to the heart. But at the same time, it flows into the right atrium, where all the venous blood from the tissues of the body enters. Further, from both atria, the blood enters the ventricle of the heart, where it partially mixes, since there is only one ventricle in amphibians. Due to the fact that the organs and tissues of the body are not supplied with enough arterial blood, amphibians have a low metabolism, and they are cold-blooded animals.

The skin of amphibians is smooth. It does not have scales or other dense formations. Therefore, gases can easily penetrate through it. In addition, the skin is constantly moisturized, and this is important, since oxygen must first be dissolved in water in order to penetrate the skin into the bloodstream. If the frog dries out, it may suffocate.

Skin respiration is especially important when amphibians are underwater. Thanks to him, they can rise to the surface less often. Many frogs hibernate underwater in a state of torpor. At the same time, the metabolism slows down, and they do not need a lot of oxygen, and the one that is needed, they get from the water through the skin.

Tadpoles (larvae of frogs) and some species of amphibians have external or internal gills as respiratory organs. In tadpoles, external gills first appear, then they become internal. As it metamorphoses (turning it into a frog), lungs are formed, and the gills dissolve.

Amphibians(they are amphibians) - the first terrestrial vertebrates that appeared in the process of evolution. At the same time, they still retain a close relationship with the aquatic environment, usually living in it at the larval stage. Typical representatives amphibians - frogs, toads, newts, salamanders. Most varied in tropical forests because it's warm and damp. There are no marine species among amphibians.

General characteristics of amphibians

Amphibians are a small group of animals with about 5,000 species (according to other sources, about 3,000). They are divided into three groups: Tailed, Tailless, Legless. The frogs and toads familiar to us belong to the tailless ones, the newts belong to the tailed ones.

Amphibians have paired five-fingered limbs, which are polynomial levers. The forelimb consists of the shoulder, forearm, hand. Hind limb - from the thigh, lower leg, foot.

Most adult amphibians develop lungs as respiratory organs. However, they are not as perfect as in more highly organized groups of vertebrates. Therefore, skin respiration plays an important role in the life of amphibians.

The appearance of the lungs in the process of evolution was accompanied by the appearance of a second circle of blood circulation and a three-chambered heart. Although there is a second circle of blood circulation, due to the three-chambered heart, there is no complete separation of venous and arterial blood. Therefore, mixed blood enters most organs.

The eyes have not only eyelids, but also lacrimal glands for wetting and cleansing.

The middle ear appears with a tympanic membrane. (In fish, only the internal.) The eardrums are visible, located on the sides of the head behind the eyes.

The skin is naked, covered with mucus, it has many glands. It does not protect against water loss, so they live near water bodies. Mucus protects the skin from drying out and bacteria. The skin is made up of the epidermis and dermis. Water is also absorbed through the skin. The skin glands are multicellular, in fish they are unicellular.

Due to the incomplete separation of arterial and venous blood, as well as imperfect pulmonary respiration, the metabolism of amphibians is slow, like that of fish. They also belong to cold-blooded animals.

Amphibians breed in water. Individual development proceeds with transformation (metamorphosis). The frog larva is called tadpole.

Amphibians appeared about 350 million years ago (at the end Devonian period) from ancient lobe-finned fish. Their heyday occurred 200 million years ago, when the Earth was covered with huge swamps.

Musculoskeletal system of amphibians

In the skeleton of amphibians, there are fewer bones than in fish, since many bones grow together, while others remain cartilage. Thus, their skeleton is lighter than that of fish, which is important for living in an air environment that is less dense than water.

The brain skull fuses with the upper jaws. Only the lower jaw remains mobile. The skull retains a lot of cartilage that does not ossify.

Musculoskeletal system amphibians is similar to that of fish, but has a number of key progressive differences. So, unlike fish, the skull and spine are movably articulated, which ensures the mobility of the head relative to the neck. For the first time, the cervical spine appears, consisting of one vertebra. However, the mobility of the head is not great, frogs can only tilt their heads. Although they have a neck vertebra, they do not appear to have a neck in appearance.

In amphibians, the spine consists of more sections than in fish. If fish have only two of them (trunk and tail), then amphibians have four sections of the spine: cervical (1 vertebra), trunk (7), sacral (1), caudal (one tail bone in anurans or a number of separate vertebrae in tailed amphibians) . In tailless amphibians, the caudal vertebrae fuse into one bone.

The limbs of amphibians are complex. The anterior ones consist of the shoulder, forearm and hand. The hand consists of the wrist, metacarpus and phalanges of the fingers. The hind limbs consist of the thigh, lower leg and foot. The foot consists of the tarsus, metatarsus and phalanges of the fingers.

Limb belts serve as a support for the skeleton of the limbs. The belt of the forelimb of an amphibian consists of the scapula, clavicle, crow bone (coracoid), common to the belts of both forelimbs of the sternum. The clavicles and coracoids are fused to the sternum. Due to the absence or underdevelopment of the ribs, the belts lie in the thickness of the muscles and are not indirectly attached to the spine in any way.

The belts of the hind limbs consist of the ischial and ilium bones, as well as the pubic cartilages. Growing together, they articulate with the lateral processes of the sacral vertebra.

The ribs, if present, are short and do not form a chest. Tailed amphibians have short ribs, tailless amphibians do not.

In tailless amphibians, the ulna and radius are fused, and the bones of the lower leg are also fused.

The muscles of amphibians have a more complex structure than those of fish. The muscles of the limbs and head are specialized. Muscle layers break up into separate muscles, which provide movement of some parts of the body relative to others. Amphibians not only swim, but also jump, walk, crawl.

Digestive system of amphibians

General plan of the building digestive system amphibians is similar to fish. However, there are some innovations.

The anterior horse of the tongue of frogs adheres to the lower jaw, while the posterior one remains free. This structure of the tongue allows them to catch prey.

Amphibians have salivary glands. Their secret wets food, but does not digest it, as it does not contain digestive enzymes. The jaws have conical teeth. They serve to hold food.

Behind the oropharynx is a short esophagus that opens into the stomach. Here the food is partially digested. The first section of the small intestine is the duodenum. A single duct opens into it, where the secrets of the liver, gallbladder and pancreas enter. In the small intestine, food digestion is completed and nutrients are absorbed into the blood.

Undigested food remnants enter the large intestine, from where they move to the cloaca, which is an expansion of the intestine. The ducts of the excretory and reproductive systems also open into the cloaca. From it, undigested residues fall into external environment. Fish do not have a cloaca.

Adult amphibians feed on animal food, most often various insects. Tadpoles feed on plankton and plant matter.

1 Right atrium, 2 Liver, 3 Aorta, 4 Oocytes, 5 Large intestine, 6 Left atrium, 7 Heart ventricle, 8 Stomach, 9 Left lung, 10 gallbladder, 11 Small intestine, 12 Cloaca

Respiratory system of amphibians

Amphibian larvae (tadpoles) have gills and one circle of blood circulation (like in fish).

In adult amphibians, lungs appear, which are elongated sacs with thin elastic walls that have a cellular structure. The walls contain a network of capillaries. The respiratory surface of the lungs is small, so the bare skin of amphibians also participates in the breathing process. Through it comes up to 50% oxygen.

The mechanism of inhalation and exhalation is provided by raising and lowering the floor of the oral cavity. When lowering, inhalation occurs through the nostrils, when raised, air is pushed into the lungs, while the nostrils are closed. Exhalation is also carried out when the bottom of the mouth is raised, but at the same time the nostrils are open, and the air exits through them. Also, when exhaling, the abdominal muscles contract.

In the lungs, gas exchange occurs due to the difference in the concentrations of gases in the blood and air.

The lungs of amphibians are not well developed to fully provide gas exchange. Therefore, skin respiration is important. Drying out amphibians can cause them to suffocate. Oxygen first dissolves in the fluid covering the skin, and then diffuses into the blood. Carbon dioxide also first appears in the liquid.

In amphibians, unlike fish, nasal cavity became through and used for breathing.

Under water, frogs breathe only through their skin.

The circulatory system of amphibians

The second circle of blood circulation appears. It passes through the lungs and is called the pulmonary, as well as the pulmonary circulation. The first circle of blood circulation, passing through all organs of the body, is called large.

The heart of amphibians is three-chambered, consists of two atria and one ventricle.

The right atrium receives venous blood from the organs of the body, as well as arterial blood from the skin. Enters the left atrium arterial blood from lungs. The vessel that empties into the left atrium is called pulmonary vein.

Atrial contraction pushes blood into the common ventricle of the heart. This is where the blood mixes.

From the ventricle, through separate vessels, blood is directed to the lungs, to the tissues of the body, to the head. The most venous blood from the ventricle enters the lungs through the pulmonary arteries. Almost pure arterial goes to the head. The most mixed blood entering the body is poured from the ventricle into the aorta.

This separation of the blood is achieved by a special arrangement of vessels emerging from the distribution chamber of the heart, where blood enters from the ventricle. When the first portion of blood is pushed out, it fills the nearest vessels. And this is the most venous blood, which enters the pulmonary arteries, goes to the lungs and skin, where it is enriched with oxygen. From the lungs, blood returns to the left atrium. The next portion of blood - mixed - enters the aortic arches going to the organs of the body. The most arterial blood enters the distant pair of vessels (carotid arteries) and goes to the head.

excretory system of amphibians

The kidneys of amphibians are trunk, have an oblong shape. Urine enters the ureters, then flows down the wall of the cloaca into bladder. When the bladder contracts, urine flows into the cloaca and out.

The excretion product is urea. Removing it requires less water than to remove ammonia (which is formed in fish).

In the renal tubules of the kidneys, water is reabsorbed, which is important for its conservation in air conditions.

Nervous system and sense organs of amphibians

Key changes in nervous system amphibian versus fish did not occur. However, the forebrain of amphibians is more developed and is divided into two hemispheres. But their cerebellum is worse developed, since amphibians do not need to maintain balance in the water.

Air clearer than water therefore, vision plays a leading role in amphibians. They see further than fish, their lens is flatter. There are eyelids and nictitating membranes (or an upper fixed eyelid and a lower transparent movable one).

Sound waves travel worse in air than in water. Therefore, there is a need for a middle ear, which is a tube with a tympanic membrane (visible as a pair of thin round films behind the eyes of a frog). From the tympanic membrane, sound vibrations are transmitted through the auditory ossicle to the inner ear. The Eustachian tube connects the middle ear to oral cavity. This allows you to weaken the pressure drops on the eardrum.

Reproduction and development of amphibians

Frogs start breeding at about 3 years of age. Fertilization is external.

Males secrete seminal fluid. In many frogs, the males attach themselves to the backs of the females, and while the female spawns for several days, she is poured with seminal fluid.

Amphibians spawn less eggs than fish. Clusters of caviar are attached to aquatic plants or float.

The mucous membrane of the egg swells greatly in water, refracts sunlight and heats up, which contributes to the faster development of the embryo.

Development of frog embryos in eggs

An embryo develops in each egg (usually about 10 days in frogs). The larva that emerges from the egg is called a tadpole. It has many features similar to fish (two-chambered heart and one circle of blood circulation, breathing with the help of gills, lateral line organ). At first, the tadpole has external gills, which then become internal. The hind limbs appear, then the front. The lungs and the second circle of blood circulation appear. At the end of metamorphosis, the tail resolves.

The tadpole stage usually lasts several months. Tadpoles eat plant foods.

Instruction

Translated from the Greek language, the word "amphibian" means "double-living." The term "amphibian" is commonly used in scientific environment, and in ordinary life these creatures are called amphibians. It: Most of them feel great both on land and in water. Representatives of this simple class of animals include frogs, toads, newts, salamanders and their tadpoles. Currently, there are more than 4,500 species of various amphibians on Earth. In turn, they are divided into three detachments, which are clearly demarcated from each other. It is curious that representatives of one group practically do not look like their "neighbors", which leads to some doubts about their relationship.

The most numerous order of amphibians are tailless amphibians. They are also sometimes called jumpers. This group of animals includes more than 75% of all amphibian species. These include frogs and toads. The name of this detachment speaks for itself: these animals do not have a tail and move exclusively by jumping. The second, less numerous, detachment of amphibians was called the tailed amphibians. Its representatives appearance they resemble lizards, but with a frog head and frog-like skin. Representatives of this detachment in the process of evolution retained their tail. These include newts and salamanders.

The smallest and least studied detachment are amphibians. In appearance, these are very strange creatures that do not have not only a tail, but also all their limbs. These include worms (small-toothed worm, odd-toothed worm, etc.) and fish snakes. This order includes only 184 species of animals and is known for its existence in the early Jurassic period. These unique creatures are not as common as it might seem. Their distribution area is tropics and subtropics. South-East Asia, Latin America and Africa. Among the legless amphibians, there are species that are fully adapted to water, but these are already isolated cases.

The vast majority of all amphibians live in areas with high humidity and alternate their stay in the water with periodic attacks on land. But there are also such species of amphibians who spend the lion's share of their lives exclusively on trees (for example, tree frogs). As mentioned above, amphibians are the most primitive vertebrates in the world: they are not properly adapted to living exclusively on land, since the intensity of their metabolism (metabolism) is low. Their way of life is completely and entirely dependent on external factors: changing conditions environment plays a fatal role in the life of amphibians.

Amphibians, as a rule, are characterized by a change in the environment during development, since most of them retain the method of reproduction characteristic of fish in water by laying eggs and external fertilization. This most feature amphibians leads to the fact that they go to the reservoir during the breeding season.

Amphibian eggs, like fish, have only mucous membranes that protect against drying out only for a very short time, and the water necessary for the development of the embryo enters the developing egg from the environment. However, in amphibians, external fertilization has a number of features. The male always embraces the female in one way or another. How do males develop adaptations for a tighter grip?various outgrowths, spikes, "corns", etc., most often smoothing out or disappearing at the end of the breeding season. Males, in comparison with females, have a more developed musculature of the front legs and a heavy skeleton. Such mating of amphibians during external fertilization ensures the simultaneous release of eggs and sperm, which increases the percentage of egg fertilization.

Metamorphosis, like development in aquatic environment and external fertilization, to a certain extent, was inherited by amphibians from their fish-like ancestors. But, unlike fish, the respiratory, locomotion, and digestive organs of amphibian larvae are different from those of adults. This is due to the fact that in fish, an adult organism and a fry live in the same environment, while in amphibians, in the process of development, a change in habitat occurs.

In this regard, the larvae of amphibians, which have a number of characteristics of aquatic animals, already at the early stages of development, long before the end of metamorphosis, begin to develop signs characteristic of a terrestrial organism. In frogs, about a month before the end of metamorphosis, the rudiments of the fore and hind limbs appear. At the same time, the tadpoles already break through the internal nostrils, there is a glottis covered by the epiglottis, a larynx and paired thin-walled vascular sacs - lungs. Soon a septum appears in the atrium and a small circle of blood circulation is formed, etc. In other words, the completely aquatic larva already has the features of an adult terrestrial organism.

Among the living amphibians, due to the peculiarities of their organization and way of life, there is a significant diversity in the biology of reproduction.

Tests

704-01. What is missing in the skeleton of representatives of the class Amphibians?
A) shoulder girdle of limbs
B) bones of the hind limbs
B) chest
D) skull

Answer

704-02. Determine correct sequence processes characteristic of the development of the pond frog.
A) fertilization > laying eggs in water > egg maturation > release of a small frog
B) laying eggs in water > fertilization > development of a tadpole > appearance of a small frog
C) fertilization > moving eggs to land > development of the larva > development of the frog
D) laying of unfertilized eggs in water > development of the larva > development of the frog

Answer

704-03. Are the judgments about amphibians correct?
1. Amphibians include frogs, toads, lizards, newts.
2. Amphibians live in water, and only during the breeding season do they move to live on land.
A) only 1 is correct
B) only 2 is true
C) both statements are correct
D) both statements are wrong

Answer

704-04. Are judgments about the life processes of amphibians correct?
1. Lungs in amphibians are poorly developed, additional gas exchange occurs through moist skin.
2. With the appearance of lungs in amphibians, a second circle of blood circulation has formed.
A) only 1 is correct
B) only 2 is true
C) both statements are correct
D) both statements are wrong

Answer

704-05. In the process of evolution, the immediate ancestors of the representatives of the class to which the depicted animal belongs were the first to acquire

A) two circles of blood circulation
B) chord
B) internal skeleton
D) the brain

Answer

704-06. The heart of a tadpole is similar in structure to a heart.
A) fish
B) shellfish
B) an adult amphibian
D) an adult reptile

Answer

704-07. Amphibian larvae are similar to fish in that they have
A) pectoral fins
B) ventral fins
B) external gills
D) lateral line organs

Answer

704-08. To the class of amphibians not applicable animal, which is indicated by the letter in the figure

Answer

704-9. Toads, unlike frogs, can live away from a body of water. How can this be explained?
a) They breed on land.
B) They have better developed lungs and drier skin.
C) They have short hind limbs and long forelimbs.
D) They feed on terrestrial invertebrates.

Answer

704-10. Which organ in a frog is involved in respiration?
A) kidneys
B) skin
In the heart
D) stomach

Answer

704-11. Are the following judgments about the reproduction and development of amphibians correct?
1. After hibernation all amphibians accumulate in secluded places under snags and tree roots, where they reproduce.
2. At the larval stage of development, amphibians have a two-chambered heart and one circle of blood circulation.
A) only 1 is correct
B) only 2 is true
C) both statements are correct
D) both statements are wrong

Answer

704-12. Are judgments about the development of amphibians correct?
1. An amphibian larva does not look like an adult animal.
2. In the early stages of development, tadpoles have a lateral line, a two-chambered heart, and one circle of blood circulation.
A) only 1 is correct
B) only 2 is true
C) both statements are correct
D) both statements are wrong

Answer

704-13. Pulmonary respiration in amphibians is carried out by
A) swallowing movements
B) heart contractions
B) a change in the volume of the chest cavity of the body
D) stretching of the throat

Answer

704-14. The hearing organs of amphibians are represented
A) resonators
B) outer ear
B) middle ear
D) middle and inner ear

Answer

704-15. What pair of features distinguish representatives of the class Amphibians from other vertebrates?
A) pulmonary respiration and the presence of kidneys
B) the spine from several departments and the forelimbs
C) bare skin and development with transformation
D) a closed circulatory system and a three-chambered heart