The digestive system consists of 4 departments(oropharyngeal cavity, esophagus, stomach, intestines)
Characteristic general lengthening of the digestive tract compared to other groups of vertebrates and its more developed differentiation, significant development also occurs digestive glands
Developing symbiotic digestion
The mouth opening is surrounded by soft lips
Teeth differentiated by function, sit in the alveoli
When food enters the oral cavity, it is chewed by the teeth and moistened saliva(contains enzymes), from the oral cavity enters throat, and from there to esophagus and stomach
Stomach in most mammals it is simple (unilocular), but in some. there are several sections (stomachs)
Intestines divided into thin and thick (the latter is attached to the cecum)
Most of it is digested in small intestine, through the walls of which nutritional substances are absorbed into the blood, the remainder enters colon where fermentation processes involving bacteria occur
Undigested residues are eliminated through anal hole
There are digestive glands that facilitate digestion and secrete various enzymes
Digestive system of a mammal.
1 - liver,
2 - gallbladder,
3 - bile duct,
4, 12 - large intestine,
5 - cecum,
6 - rectum,
7 - esophagus,
8 - stomach,
9 - pylorus of the stomach,
10 - pancreas,
11 - small intestine,
13 - anus.
Origin of mammals.
Mammals appeared in Upper Carboniferous from animal-like reptiles that had a number of primitive characteristics: amphicoelous vertebrae, mobile cervical and lumbar ribs, etc.
For a long time, animal-like reptiles existed little, differing from their ancestors and retaining many of the organizational features of amphibians (this can explain the large number of skin glands in mammals)
According to modern ideas, mammals evolved from synapsid from the group cynodonts, released at the end of the Triassic period. The most advanced cynodonts already strongly resembled mammals - such as Oligokyphus from the family Tritylodontidae with its developed coat, living in the Late Triassic and Early Jurassic.
At the same time, the initial mammal divergence: Fossil remains of Cuneotherium and Haramiids were found in Late Triassic sediments. The latter are usually considered as early representatives of the subclass (or infraclass) of allotherium, which also includes polytubercles - the most diverse and numerous of the Mesozoic orders of mammals, which existed for over 100 million years. As for morganucodonts, they are extremely close in appearance and structure to the supposed ancestor of all later mammals.
In the Upper Triassic, other main lineages of mammals emerged, the known remains of which date back to a later time: a lineage including monotreme; line three conodonts(Jurassic - Cretaceous); finally, the line to which the marsupials and placentals belong, which separated from each other in the Jurassic period.
Cynodont Oligokyphus(modern reconstruction)
Morganucodon- Triassic prototype of later mammals
Origin of birds.
The origin of birds has long been the subject of lively debate. Over the foreseeable period of time, several scientific versions of the origin and kinship of birds and the emergence of flight in them have been put forward, and for more than a hundred years they were purely hypothetical.
The theory of the evolution of birds from reptiles first arose after the discovery of fossilized remains in Germany in 1860 Archeopteryx- an animal that lived about 150 million years ago in the Upper Jurassic. It had the characteristics of a typical reptile - a special structure of the pelvis and ribs, teeth, clawed paws and a long tail, like a lizard. At the same time, the fossils had well-preserved imprints of the flight wings, similar to those of modern birds. For many decades, the history of birds was viewed as an evolutionary group that developed from Archeopteryx.
It was on his study that all the first hypotheses and theories about the origin and family relationships of birds were based: wood theory("down from the trees" Marsh, 1877) and running theory(“from the ground up”, Williston, 1879) the emergence of flight in birds. The origin of the birds themselves was interpreted in accordance with these ideas - from Triassic thecodonts (archosauromorphs) under the arboreal theory, or from Jurassic running theropod dinosaurs under the terrestrial theory.
Currently, Archeopteryx is no longer considered as the common ancestor of all modern birds. However, it is probably closely related to their real ancestor. The exact position of Archeopteryx in the evolutionary tree is difficult to determine. According to cladistic analysis by Chinese paleontologists Archeopteryx may represent a parallel dead-end branch on the common trunk of dinosaurs. However, a more thorough phylogenetic analysis did not confirm the placement of Archeopteryx among Deinonychosaurs, and therefore it continues to be considered the oldest and most primitive bird (as part of the group Avialae).
However, older fossil remains have been discovered that may also be classified as a treasure. Avialae, although at the moment they are considered to be dinosaurs: Anchiornis, Xiaotingia And Aurornis.
Archeopteryx (reconstruction) and its archaeological imprint
Origin of reptiles.
The remains of the most ancient reptiles are known from Upper Carboniferous(approx. 300 million years ago)
However, the separation of reptiles should have occurred a little earlier (about 320 million years), when from primitive stegocephalians, forms were isolated that apparently had greater terrestriality
In the Middle Carboniferous, a new branch arose from similar forms - seymuriomorph, they occupy a transitional position from amphibians to mammals, while having many reptilian features
It is not yet clear when the pattern of reproduction and egg development inherent in amniotes in the air took shape, but it can be assumed that this happened in the Carboniferous during the formation of cotylosaurs. The roof of their skull was solid, the formation of the atlas and epistropheus was completed
The main ancestral group that gave rise to all the diversity of modern reptiles were cotylosaurs
Origin of chordates.
Attempts to work out the evolutionary relationships of chordates have led to the birth of several hypotheses. The current consensus is that chordates are descendants of a single common ancestor, which itself is a chordate, and its closest relatives vertebrates(lat. Vertebrata) are cephalochordates(lat. Cephalochordata).
All discovered fossils of fossil chordates were found in Early Cambrian and include two species of vertebrates classified as fish. Because chordate fossils are poorly preserved, only the method of molecular phylogenetics offers a reasonable prospect of investigating their origin. However, the use of molecular phylogenetics to study evolutionary processes is controversial.
Bilaterian animals are divided into two large taxa - protostomes and deuterostomes. Chordata are deuterostomes. It is very likely that the fossil kimberella, who lived 555 million years ago, belonged to protostomes. Ernietta, who lived 549-543 million years ago in the Ediacaran region, was already clearly a deuterostome animal. Thus, protostomes and deuterostomes must have separated before the time of the existence of these animals, that is, before the beginning of the Cambrian period.
The first known fossils of two groups closely related to chordates—echinoderms and hemichordates—are discovered from the Early and Middle Cambrian, respectively. On the other hand, fossils of other chordates are quite rare because they do not have hard body parts.
Research into the relationships of chordates began in the 90s of the 19th century. These were based on anatomical, embryological and paleontological data and resulted in different phylogenetic trees. For some time, hemichordates were considered to be the closest relatives of chordates, but this hypothesis has now been rejected. The combination of these classical methods with data from the analysis of rRNA gene sequences led to the hypothesis that tunicates are living representatives of a group basal to other deuterostomes. Regarding relationships within chordates, some scientists believe that the closest relatives of vertebrates are cephalochordates, but there is reason to consider tunicates as such.
The time of origin of chordates, based on the molecular clock method, has been estimated at 896 Ma.
Reproduction and development of reptiles
Reptiles - dioecious animals, bisexual reproduction.
The male reproductive system consists of couplestestes, which are located on the sides of the lumbar spine. Derived from each testis seminal canal, which flows into wolf channel. With the appearance of the trunk bud in wolf reptiles, the canal in males acts only as a vas deferens and is completely absent in females. The Wolff Canal opens in cloaca, forming seminal vesicle.
The female reproductive system is presented ovaries, which are suspended on the mesentery to the dorsal side of the body cavity on the sides of the spine. Oviducts(Müllerian canals) are also suspended on the mesentery. The oviducts open into the anterior part of the body cavity with slit-like openings - funnels. The lower end of the oviduct opens into the lower section cloaca on her dorsal side.
Development - fertilization internal. Development of the embryo occurs in egg with a leathery or calcareous shell, along with this there is ovoviviparity and (less often) true live birth. In reptiles, direct postembryonic development.
For many representatives it is characteristic caring for offspring, in particular, female crocodiles carry offspring from the laying site to bodies of water in the oral cavity, although in some cases they can eat the cub.
Mammals are animals that feed their young with milk. They are the most highly organized. The excretory, reproductive, digestive, respiratory and circulatory systems of mammals are most complex in structure compared to representatives of other systematic units. But special attention needs to be paid to the structure
Nutrition and Digestion
Nutrition is one of the main characteristics of living organisms. This process consists of the intake of substances into the body, their transformation and the removal of unprocessed food residues. Digestion occurs in specialized organs - the breakdown of complex organic substances (proteins, lipids, carbohydrates) into simple ones that can be absorbed into the blood. Why do biopolymers break down into their component parts? The fact is that their molecules are very large, and they cannot penetrate from the digestive tract into the bloodstream. mammals are no exception. It has a number of features that distinguish them from other chordates.
The structure of the digestive system of mammals
This organ system consists of two parts: the canal and the glands. In the first, food is digested, absorbed into the blood, and its unprocessed remains come out. The alimentary canal includes the following sections: oral cavity, pharynx, esophagus, stomach, small and large intestines, ending in the anus. Through it, undigested residues are removed. The structural features of the mammalian digestive system also include the presence of glands. These are special organs that contain enzymes - biological catalysts that promote the process of breaking down biopolymers.
Features of digestion in the oral cavity
The organs of the mammalian digestive system, or rather the canal, begin with the oral cavity. The cheeks and lips form the preoral cavity. This is where two types of food processing occur. Mechanical is carried out using differentiated teeth and tongue, chemical - enzymes of the salivary glands. Here they break down only one type of organic substances - complex carbohydrates, polysaccharides, into simple, monosaccharides.
The differentiation of teeth depends on the type of food and the method of obtaining it. Predators have the most developed incisors, herbivores have flat-shaped molars, and whales have no teeth at all.
Digestion in the stomach
The bolus of food from the oral cavity moves through the esophagus into the stomach - the most expanded part of the entire canal. Its muscle walls begin to contract and the food is mixed. Here it is also subjected to chemical treatment. Digestive, closely interrelated. Gastric juice breaks down proteins and lipids into monomers - their constituent parts. Only in this form will they enter the bloodstream.
Digestion in the intestines
The digestive system of mammals continues with the intestines: small and thick. Partially digested food in the stomach enters the first section in small portions. Here the final breakdown and absorption of substances into the blood and lymph occurs. The first section of the small intestine is called the duodenum. The ducts of the pancreas and liver open into it. The large intestine is the final section of the digestive system. Here most of the water is absorbed and feces are formed, which are reflexively removed from the rectum.
Digestive glands
The digestive system of mammals is characterized by the presence of glands. These are the organs that contain enzymes. There are three pairs in the oral cavity. They secrete a colorless mucous substance. Includes water, enzymes amylase and maltase and mucin. Each of them performs its own function. Water moistens food, lysozyme neutralizes microorganisms and heals wounds, amylase and maltase break down carbohydrates, mucin has an enveloping effect.
The composition of gastric juice includes hydrochloric acid, which delays putrefactive processes and stimulates motor activity. Additional substances are lipase, which, accordingly, break down proteins and lipids. Hydrochloric acid is a chemically active substance; it can corrode the gastric mucosa. It is protected from this action by mucus (mucin).
The pancreas produces digestive juice consisting of the enzymes trypsin, lipase and amylase. They finally break down all organic substances.
The role of the liver is also great. Bile is constantly produced in it. Once in the small intestine, it emulsifies fats. The essence of this process is the breakdown of these biopolymers into small droplets. In this form, they are quickly broken down and absorbed by the body. Activation of enzymes, increased intestinal motility, stopping putrefactive processes are also functions of the liver.
What are enzymes
And now more about the nature and mechanism of action of enzymes. As biological catalysts, they speed up chemical reactions. The mammalian digestive tract is essentially just a site of enzyme action.
Mammalian nutritional features
The totality of chemical transformations of substances from the moment they enter the body until they are excreted is called metabolism. This is a necessary condition for the growth, development and simply existence of any living organism. Different groups of mammals have adapted differently to foraging. Predators attack weaker animals. To do this, they have well-developed teeth, namely incisors and canines. There are also many herbivorous and insectivorous species. Ruminant animals are of particular interest. Their digestive system is especially complex. The incisors on top are completely absent, they are replaced by a transverse dental ridge, and the canines are underdeveloped. This teeth structure is necessary to chew grass - cud. Giraffes, cows and deer are typical representatives of this group of animals. Their stomach consists of four sections. They are called tripe, mesh, book, abomasum. In the first two, chewed food breaks down into solid and liquid parts. The gum is regurgitated from the stomach back into the mouth and chewed again. Then the carefully processed food immediately goes into the third section - the book, and from there - into the abomasum. In this last section, it is already exposed to gastric juice and is finally broken down.
Non-ruminant animals, such as wild boars, pigs and hippopotamuses, have a simple single-chamber stomach and a standard digestive system.
Some mammals use their limbs to grab food. Thus, an elephant places food in its mouth using its trunk. And bats that feed on nectar have a flattened muzzle and a brush-shaped tongue. There is also a special device for storing food. Many rodents store grains in their cheek pouches.
The digestive system of mammals has a complex structure, the features of which depend on the nature of the food and the habitat of the animals.
Mammals are one of the classes of animals. There are more than 5,000 species of mammals, and humans (Homo sapiens species) are also included in this class.
The structure of the digestive system is very similar in all species, but some have differences. These differences are due to the fact that mammals populated all living environments - soil, land, surface layers of the atmosphere, sea and fresh water bodies. That's why their diet is different.
The digestive system has many parts. Food travels a long way through the body of mammals - starting from the oral cavity and ending with the rectum. During this entire path, it passes through different parts of the body: the mouth, larynx, esophagus, stomach and intestines. Each performs its own function.
The oral cavity contains teeth, which according to their purpose are divided into incisors, canines and molars. The teeth crush the food, after which the crushed pieces are well moistened with saliva and thanks to this they easily pass from the oral cavity to the stomach through the esophagus.
Many mammals have a single-chambered stomach, but there are animals with a multi-chambered stomach. For example, such animals include goats, sheep, cows and other ruminant artiodactyls. This type of stomach is needed to digest coarser plant food.
After the stomach, food enters the intestines. Typically, in mammals, the intestine consists of a large intestine, a small intestine, and a rectum. However, most animals (such as rabbits) also have a cecum. It attaches to the end of the small intestine. In some animals, the appendix comes out of it.
The cecum is needed in order to change poorly digestible substances in food. After this, the food is completely digested in the small intestine. There, nutrients are absorbed into the blood, and what remains passes into the large intestine, from where it exits through the rectum.
There are very few, but there are still mammals whose intestines open into the cloaca. These include the platypus and echidna.
The digestive system consists of 4 departments(oropharyngeal cavity, esophagus, stomach, intestines)
Characteristic general lengthening of the digestive tract compared to other groups of vertebrates and its more developed differentiation, significant development also occurs digestive glands
Developing symbiotic digestion
The mouth opening is surrounded by soft lips
Teeth differentiated by function, sit in the alveoli
When food enters the oral cavity, it is chewed by the teeth and moistened saliva(contains enzymes), from the oral cavity enters throat, and from there to esophagus and stomach
Stomach in most mammals it is simple (unilocular), but in some. there are several sections (stomachs)
Intestines divided into thin and thick (the latter is attached to the cecum)
Most of it is digested in small intestine, through the walls of which nutritional substances are absorbed into the blood, the remainder enters colon where fermentation processes involving bacteria occur
Undigested residues are eliminated through anal hole
There are digestive glands that facilitate digestion and secrete various enzymes
Digestive system of a mammal.
1 - liver,
2 - gallbladder,
3 - bile duct,
4, 12 - large intestine,
5 - cecum,
6 - rectum,
7 - esophagus,
8 - stomach,
9 - pylorus of the stomach,
10 - pancreas,
11 - small intestine,
13 - anus.
Origin of mammals.
Mammals appeared in Upper Carboniferous from animal-like reptiles that had a number of primitive characteristics: amphicoelous vertebrae, mobile cervical and lumbar ribs, etc.
For a long time, animal-like reptiles existed little, differing from their ancestors and retaining many of the organizational features of amphibians (this can explain the large number of skin glands in mammals)
According to modern ideas, mammals evolved from synapsid from the group cynodonts, released at the end of the Triassic period. The most advanced cynodonts already strongly resembled mammals - such as Oligokyphus from the family Tritylodontidae with its developed coat, living in the Late Triassic and Early Jurassic.
At the same time, the initial mammal divergence: Fossil remains of Cuneotherium and Haramiids were found in Late Triassic sediments. The latter are usually considered as early representatives of the subclass (or infraclass) of allotherium, which also includes polytubercles - the most diverse and numerous of the Mesozoic orders of mammals, which existed for over 100 million years. As for morganucodonts, they are extremely close in appearance and structure to the supposed ancestor of all later mammals.
In the Upper Triassic, other main lineages of mammals emerged, the known remains of which date back to a later time: a lineage including monotreme; line three conodonts(Jurassic - Cretaceous); finally, the line to which the marsupials and placentals belong, which separated from each other in the Jurassic period.
Cynodont Oligokyphus(modern reconstruction)
Morganucodon- Triassic prototype of later mammals
Origin of birds.
The origin of birds has long been the subject of lively debate. Over the foreseeable period of time, several scientific versions of the origin and kinship of birds and the emergence of flight in them have been put forward, and for more than a hundred years they were purely hypothetical.
The theory of the evolution of birds from reptiles first arose after the discovery of fossilized remains in Germany in 1860 Archeopteryx- an animal that lived about 150 million years ago in the Upper Jurassic. It had the characteristics of a typical reptile - a special structure of the pelvis and ribs, teeth, clawed paws and a long tail, like a lizard. At the same time, the fossils had well-preserved imprints of the flight wings, similar to those of modern birds. For many decades, the history of birds was viewed as an evolutionary group that developed from Archeopteryx.
It was on his study that all the first hypotheses and theories about the origin and family relationships of birds were based: wood theory("down from the trees" Marsh, 1877) and running theory(“from the ground up”, Williston, 1879) the emergence of flight in birds. The origin of the birds themselves was interpreted in accordance with these ideas - from Triassic thecodonts (archosauromorphs) under the arboreal theory, or from Jurassic running theropod dinosaurs under the terrestrial theory.
Currently, Archeopteryx is no longer considered as the common ancestor of all modern birds. However, it is probably closely related to their real ancestor. The exact position of Archeopteryx in the evolutionary tree is difficult to determine. According to cladistic analysis by Chinese paleontologists Archeopteryx may represent a parallel dead-end branch on the common trunk of dinosaurs. However, a more thorough phylogenetic analysis did not confirm the placement of Archeopteryx among Deinonychosaurs, and therefore it continues to be considered the oldest and most primitive bird (as part of the group Avialae).
However, older fossil remains have been discovered that may also be classified as a treasure. Avialae, although at the moment they are considered to be dinosaurs: Anchiornis, Xiaotingia And Aurornis.
Archeopteryx (reconstruction) and its archaeological imprint
Origin of reptiles.
The remains of the most ancient reptiles are known from Upper Carboniferous(approx. 300 million years ago)
However, the separation of reptiles should have occurred a little earlier (about 320 million years), when from primitive stegocephalians, forms were isolated that apparently had greater terrestriality
In the Middle Carboniferous, a new branch arose from similar forms - seymuriomorph, they occupy a transitional position from amphibians to mammals, while having many reptilian features
It is not yet clear when the pattern of reproduction and egg development inherent in amniotes in the air took shape, but it can be assumed that this happened in the Carboniferous during the formation of cotylosaurs. The roof of their skull was solid, the formation of the atlas and epistropheus was completed
The main ancestral group that gave rise to all the diversity of modern reptiles were cotylosaurs
Origin of chordates.
Attempts to work out the evolutionary relationships of chordates have led to the birth of several hypotheses. The current consensus is that chordates are descendants of a single common ancestor, which itself is a chordate, and its closest relatives vertebrates(lat. Vertebrata) are cephalochordates(lat. Cephalochordata).
All discovered fossils of fossil chordates were found in Early Cambrian and include two species of vertebrates classified as fish. Because chordate fossils are poorly preserved, only the method of molecular phylogenetics offers a reasonable prospect of investigating their origin. However, the use of molecular phylogenetics to study evolutionary processes is controversial.
Bilaterian animals are divided into two large taxa - protostomes and deuterostomes. Chordata are deuterostomes. It is very likely that the fossil kimberella, who lived 555 million years ago, belonged to protostomes. Ernietta, who lived 549-543 million years ago in the Ediacaran region, was already clearly a deuterostome animal. Thus, protostomes and deuterostomes must have separated before the time of the existence of these animals, that is, before the beginning of the Cambrian period.
The first known fossils of two groups closely related to chordates—echinoderms and hemichordates—are discovered from the Early and Middle Cambrian, respectively. On the other hand, fossils of other chordates are quite rare because they do not have hard body parts.
Research into the relationships of chordates began in the 90s of the 19th century. These were based on anatomical, embryological and paleontological data and resulted in different phylogenetic trees. For some time, hemichordates were considered to be the closest relatives of chordates, but this hypothesis has now been rejected. The combination of these classical methods with data from the analysis of rRNA gene sequences led to the hypothesis that tunicates are living representatives of a group basal to other deuterostomes. Regarding relationships within chordates, some scientists believe that the closest relatives of vertebrates are cephalochordates, but there is reason to consider tunicates as such.
The time of origin of chordates, based on the molecular clock method, has been estimated at 896 Ma.
Reproduction and development of reptiles
Reptiles - dioecious animals, bisexual reproduction.
The male reproductive system consists of couplestestes, which are located on the sides of the lumbar spine. Derived from each testis seminal canal, which flows into wolf channel. With the appearance of the trunk bud in wolf reptiles, the canal in males acts only as a vas deferens and is completely absent in females. The Wolff Canal opens in cloaca, forming seminal vesicle.
The female reproductive system is presented ovaries, which are suspended on the mesentery to the dorsal side of the body cavity on the sides of the spine. Oviducts(Müllerian canals) are also suspended on the mesentery. The oviducts open into the anterior part of the body cavity with slit-like openings - funnels. The lower end of the oviduct opens into the lower section cloaca on her dorsal side.
Development - fertilization internal. Development of the embryo occurs in egg with a leathery or calcareous shell, along with this there is ovoviviparity and (less often) true live birth. In reptiles, direct postembryonic development.
For many representatives it is characteristic caring for offspring, in particular, female crocodiles carry offspring from the laying site to bodies of water in the oral cavity, although in some cases they can eat the cub.
Digestive system mammals, compared to reptiles or birds, are distinguished by their greater length, greater division into sections, and also a variety of glands. Like other vertebrates, the following divisions are distinguished here: oral cavity, pharynx, esophagus, stomach And intestines.
Oral cavity
Oral cavity(cavitas oris) in mammals, unlike other vertebrates, is preceded by preoral cavity, or vestibule of the mouth(vestibulum oris). This feature arises due to the fact that lips(labia) in these animals are separated from the edges of the jaws. Thus, skin-covered cheeks(buccae), between which, on the one hand, and the jaws, on the other, a space is formed. Some representatives of the class ( rodents) this space is especially large - these are the so-called cheek pouches. Although not only mammals have lips, only they, as well as the cheeks, acquire mobility thanks to the facial (facial) muscles located here. However, not all mammals have lips - some (for example, monotreme) they are replaced by a horny beak, similar to the beak birds or turtles.
Actually, the oral cavity is delimited from below bones of the lower jaw And sublingual muscles, in front - teeth and gums, and above - bony secondary palate(palatum durum). This is also a feature of mammals (and also crocodiles). Thanks to this neoplasm, the animal receives an anatomical separation of the oral cavity from the nasal cavity; and in the physiological sense, the independence of the processes of chewing food and breathing, which can now occur simultaneously without harming each other. This hard palate transitions posteriorly into soft sky(palatum molle), separating the oral cavity from the pharynx.
The palate (and the oral cavity in general) is lined stratified squamous epithelium, on which keratinized ridges are often visible. These structures help better manipulate food and are especially developed in ungulates and carnivores. U toothless whales these ridges are especially pronounced and have turned into the so-called “whalebone” - a filtering apparatus with the help of which these giant animals extract food from the water.
The lower part of the oral cavity is occupied tongue(lingua) - derivative hypobranchial (sublingual) muscles; He was educated, in particular, genioglossus(musculus genioglossus), hypoglossal(musculus hyoglossus) and styloglossal(musculus styloglossus) muscles, as well as the own muscles of the tongue; this last group of muscles is represented by numerous fibers intersecting in three planes, the space between which is occupied by connective and adipose tissue. In some mammals that use this organ to obtain food (such as anteaters), the tongue lengthened, became sticky and acquired a special sternoglossus muscle(musculus sternoglossus), coming, as the name indicates, straight from the sternum. In addition to nutrition, the tongue of mammals also performs the function of a taste organ, and therefore is covered taste buds. The tongue of carnivores may also bear horny papillae, which help them scrape meat from bones.
Most mammals (with the exception of aquatic ones) are characterized by salivary glands(glandulae salivales), producing saliva. There are many small glands located on the surface of the tongue, lips, cheeks, soft and hard palate, as well as three pairs of large glands - parotid(glandula parotis), submandibular(glandula submandibularis) and sublingual(glandula sublingualis) - lying outside the oral cavity and opening into it from above and below through long ducts.
Teeth
Types of teeth
Original mammalian dentition
More details o Original mammalian dentition
Wolf dentition
More details o Wolf dentition
Hare dentition
More details o Dental row of a hare
Dental system mammals heterodont, i.e. teeth vary in shape, structure and functions.
There are four types of teeth:
- incisors(incisivi) - have a simple conical or chisel shape, characteristic of most mammals; their main function is biting. Herbivores acquired other devices for plucking grass; their incisors were modified or lost; ruminants (cows, rams or deer) retained one lower incisor, but completely lost the upper ones. U elephants the upper incisors became greatly elongated and formed tusks. U rodents one incisor has been preserved in each half of each jaw - but they are clearly pronounced and capable of growing throughout their lives, growing from the root part and grinding away from the upper part.
- fangs(canini) - initially long and powerful, with a deep root, conical shape and a sharp end. Their original purpose was as a weapon, and they were preserved among predators, reaching their greatest size in the extinct saber tooth tiger. However, more often they do not stand out outwardly or are even absent.
- preradical(premolares) - have a somewhat pronounced chewing surface, ruminants and other herbivores are similar in appearance to indigenous ones.
- indigenous(molares) - characterized by a complex external and internal structure, have a pronounced chewing surface and are intended for chewing. In carnivores, the last upper premolar and the first lower molar acquired sharp ridges designed for cutting bones and tendons - these are the so-called “predatory” teeth
Individual teeth, however, may be missing; then a break appears in their line - diastema(diastema).
To describe the dental system of mammals, the so-called dental formula. Teeth of each type are designated by Latin letters corresponding to the first letters of their name - I, C, P, M. The number below or above the letter indicates the location of a particular tooth, counting from the middle of the jaw. For example, I 2 is the lower second incisor, M 3 is the upper third molar. In general, the number of teeth is recorded in a row, starting from the incisors and ending with the molars, both below and above.
Initially, apparently, the mammalian dental system consisted of the following teeth on each side, both above and below: three incisors, one canine, four premolars and three molars, a total of 44. In the form of a formula, it looks like this:
3.1.4.3.
3.1.4.3.
In modern mammals, the initial set of teeth varies quite widely: in possum there are 50 of them, cats 30, at mice 16, at elephants in total 6. This difference is connected primarily with the nature of the food and the method of its extraction; the loss or, less commonly, the acquisition of individual teeth occurs in different groups. Let us show, for example, dental formulas wolf
3.1.4.2.
3.1.4.3.
which means on each side on top there are 3 incisors, 1 canine, 4 premolars and 2 molars, on the bottom - 3 incisors, 1 canine, 4 premolars and 3 molars, a total of 42;
And hare
2.0.3.3
1.0.2.3
which means on each side on top there are 2 incisors, 3 premolars and 3 molars, on the bottom - 1 incisor, 2 premolars and 3 molars, a total of 28.
Structure of teeth
Section of a mammal tooth
More details o Sectional view of a mammal tooth
In the building tooth mammals are usually distinguished as one or more roots(radix dentis), with the help of which the tooth is strengthened in the body of the bone, and protruding above the surface of the gum crown(corona dentis); distinguish between them neck(cervix dentis). Inside the tooth is located pulp(pulpa dentis), containing blood vessels and nerves. The exit from the pulp at the base of the tooth is usually narrowed, thus forming root canal(canalis radicis dentis).
The substances from which the body of the tooth is built are dentin and enamel. Dentine(dentinum) forms the thickness of the tooth. By chemical nature, more than two thirds of it are deposits calcium phosphate in a fibrous matrix. Unlike bone, cell bodies - odontoblasts - are located on the side of the pulp cavity; from them, processes extend parallel to the thickness of the dentin. Enamel(enamelum) - an exceptionally hard material covering the protruding surface of the tooth. In mammals, most of it is formed by long prisms calcium phosphate, located perpendicular to the surface. Parts of the tooth embedded in the alveoli are attached to the bones cement(cementum) - spongy bone-like material, relatively poor in cells.
Incisors And fangs mammals have a simple conical shape and are similar to the teeth of reptiles. Premolars and especially molars usually form a wide crown with various projections - tubercles; these features are often the most important systematic feature. In general terms, each hillock is assigned a name from the suffix -con and prefixes pair-, meth-, hypo-. Formations on the lower teeth are designated by the suffix -id.
Relief of the upper molars of a mammal
More details o Relief of the upper molars of a mammal
Relief of the lower molars of a mammal
More details o Relief of the lower molars of a mammal
Diagram of the original mammalian dental system
More details o Diagram of the original mammalian dental system
The upper molars initially represent a triangle in plan, the two vertices of which are located on the outer edge of the dentition and at which there are two cusps called paracone and metacone. The internal angle corresponds to a protocone, behind which there may be a fourth tubercle - the hypocone.
The lower molars initially also represent a triangle in plan, but located oppositely: on the outside there is one apex bearing the protoconid, and on the inside there are two, bearing the metaconid and paraconid. At the back, the lower teeth have a heel (talonid), lower than the main part of the tooth and bearing two more tubercles - the hypoconid and entoconid.
Mammalian teeth are characterized by occlusion- permanent relationship between the opposing teeth of the upper and lower jaws. When the jaws close, each lower tooth, which is located inside and in front of the corresponding upper tooth, enters between the adjacent upper teeth, and the protocone of the upper tooth enters the recess between the tubercles of the heel of the lower one.
This structure of molars, according to scientists, was the result of the evolution of simple conical teeth of reptiles, which, according to Cope-Osborne theory, named after its creators, went through a number of stages. The original lower tooth of reptiles had only one cusp - the protoconid. Then two more tubercles appear in front and behind - the metaconid and paraconid, which subsequently shift, thus forming a triangle. At the next stage, talonid develops at the back.
Diagram of the evolution of mammalian upper molars
More details o Diagram of the evolution of mammalian upper molars
Diagram of the evolution of mammalian lower molars
More details o Diagram of the evolution of mammalian lower molars
The evolution of the upper teeth is described amphicon theory. According to it, initially the conical tooth of reptiles again had only one vertex - the eokon. Then a new small tubercle, the protocone, formed medially from it. At the next stage, the original peak began to split in two, forming an amphicon. Then the amphicon finally bifurcates, and thus the triangle present in mammals is formed.
This is the original type of structure of mammalian teeth, characteristic of living insectivores; Their tubercles are pointed, which allows them to break the chitinous shell of invertebrates and similar food. In carnivores, the structure does not change much, with the exception of the “predatory” teeth, which acquire new sharp ridges.
View of lophodont and selenodont teeth of a mammal
More details o Species of lophodont and selenodont teeth of a mammal
View of brachiodont and hypsodont teeth of a mammal
More details o Species of brachiodont and hypsodont teeth of a mammal
In herbivores, on the contrary, the crown of the upper tooth acquires a quadrangular shape due to the appearance of a new cusp - the hypocone; the crown of the lower one, on the contrary, loses one of the five cusps and also becomes quadrangular. Subsequently, in species that feed mainly on fruits and other relatively soft foods, the cusps become low and rounded - a tooth of the so-called bunodont type is formed. In ungulates and other species that feed on relatively tough grass, the structure becomes more complex, forming teeth of the selenodont (sickle-shaped hillocks) or lophodont (hillocks connected by ridges) type. Eating grass is also different in that it causes quite strong abrasion of dental material. The original teeth with a low crown (brachyodont type) would quickly be ground down to the roots. The solution was found in the appearance of hypsodont type teeth, characteristic of, for example, horses And cows. The cusps of this type of teeth grow into long peaks connected to each other by cement, thus forming a high crown. Another solution inherent rodents, took place in maintaining the open root and growth of the tooth throughout life.
Changing teeth
The process of tooth replacement in mammals is reduced and characterized diphyodontia- the presence of two generations of teeth: dairy(dentes decidui) and permanent(dentes permanentes). Change of teeth, as a rule, occurs in all groups, except molars, which do not change. Thus, in adult mammals, the dental set consists of two (according to the time of formation) rows of teeth: the first, which includes permanent molars, and the second, which includes incisors, canines and premolars.
In some representatives of the class, however, the process of changing teeth is altered. U marsupials, for example, only the premolar teeth change. Teeth with open roots do not change at all (for example, incisors in rodents). U elephants or manatees there is a so-called “horizontal change” of teeth; in this case, the back tooth moves forward to replace the worn and fallen one. At the same time, the alveoli also move due to the destruction of one wall by osteoclast cells and the formation of a new one by osteoblast cells.
Digestive tract
Diagram of the digestive tract of a mammal
More details o Diagram of the digestive tract of a mammal
Pharynx connects the oral cavity and the esophagus; they also open into it inner nostrils leading into the nasal cavity, eustachian tubes, connecting to the middle ear cavity, and larynx, leading to the pulmonary system.
Esophagus- a muscular tube of varying lengths connecting the pharynx to the stomach.
Stomach clearly stands out from other departments; its walls contain muscle cells and glands that produce enzymes necessary for digesting food. The structure of the stomach varies among different representatives of the class and depends on the nature of the food. In carnivorous species, the stomach is single-chambered and has a fairly simple structure. In ruminant artiodactyls, which feed on plant foods, the stomach, on the contrary, is multi-chambered and formed by four sections (rumen, reticulum, book, abomasum). The stomach of cetaceans, lacking teeth, has a powerful muscular wall for grinding swallowed food.
Intestines, next to the stomach, is divided into thin, thick And straight. Its walls, like the walls of the stomach, contain smooth muscles and glands. The total length of the intestines depends on the nature of the food. The general rule is that the more plant food there is in an animal’s diet, the longer the intestines. At the border between the small and large intestines, the cecum emerges with a vermiform appendix - the appendix. In predators it is almost not noticeable; in herbivores, on the contrary, it reaches up to 25-30% of the total length.
The walls of the intestine, like the walls of the stomach, contain muscle and glandular cells. In addition, the ducts of two separate glands open into the initial part of the small intestine - liver And pancreas. The liver secretes bile into the digestive tract; pancreas - pancreatic juice enzymes
Digestion
Digestion- i.e. chemical and physical processing of food - preceded by its extraction, or food capture, by which we mean its delivery from the outside world to the oral cavity. Different representatives of mammals cope with this task in different ways, depending on the objects of their food. In any case, the oral apparatus is somehow involved in this process - in particular, lips, teeth, cheeks And language.
Mammals can feed, firstly, on invertebrates, seeds and other small particles that can be easily swallowed; and secondly, rather large objects that must first be chewed, torn, etc. Predators have ideally adapted to the second option, acquiring powerful fangs and special “predatory” teeth, and in cats, also, horny papillae on the tongue for scraping meat from bones; rodents or lagomorphs- on the contrary, sharp incisors, capable of constant growth. Herbivores that feed on tough grass cut it with sharp upper incisors - such as, for example, horses. Cows feeding on soft grass, they lack upper incisors, but have a powerful tongue and lips. Anteaters obtain food using a long sticky tongue and a specially elongated muzzle; Some people suck nectar from flowers in a similar way. the bats. Toothless whales plankton is obtained using “whalebone”, filtering it from the water. Finally, many mammals - such as rodents or primates, - in the process of capturing food, the forelimbs are intensively used, and elephants- and trunk. Some rodents can store some amount of food in their cheek pouches.
Food that enters the oral cavity is first chewed. For this purpose, the teeth of insectivores are equipped with hard cusps that can split the chitinous shell of arthropods. Carnivores, as already noted, tear meat thanks to “predatory” teeth. Rodents and especially ungulates carefully chew coarse plant food with molars with a complex chewing surface. In the latter, the horny ridges on the palate also participate in grinding food.
Secondly, the chewed food is mixed with the help of the tongue and moistened saliva secreted by the salivary glands. Saliva not only moistens food, but also helps protect against microorganisms due to the content it contains. lysozyme; in addition, in saliva bats feeding on blood, there are anticoagulants that prevent the clotting of this blood, and the saliva of some shrews poisonous. Finally, most mammals - especially herbivores - contain an enzyme in their saliva amylase, which breaks down starch.
Thirdly, the food chewed and moistened with saliva is swallowed. The muscles of the tongue and pharynx are involved in this process. The bolus of food is raised by the tongue to the palate, the soft palate and the muscles of the pharynx block the internal nostrils so that food does not enter the nasal cavity. At the same time, a temporary closure of the airways occurs; The epiglottis curves over the entrance to the trachea, preventing food from entering the pulmonary system. Breathing is thus temporarily interrupted, after which the esophageal sphincter opens, food enters it and then into the stomach.
A large proportion of the nutrients contained in food are processed in the stomach and intestines, where food is mixed with enzymes secreted by glands that break down fats, proteins and carbohydrates into simpler compounds.
Proteins are mainly broken down in the stomach by an enzyme. pepsin; At the same time, thanks to the contraction of the muscle fibers of the stomach walls, food is mixed and ground.
IN small intestine proteins are digested thanks to trypsin secreted by the pancreas. Complex carbohydrates are also broken down here, turning into glucose, and fats. Participates in the digestion of fats bile, secreted by the liver; The acids contained in it emulsify fats - separating them into tiny droplets, which are then dissolved by the enzyme lipase. Thanks to the villi lining the walls of the small intestine, simple molecules obtained during digestion are absorbed into the blood and lymph and distributed throughout the body; muscle cells in the intestinal walls contract and move food to the next sections.
Carnivorous animals do not have any major problems with the task of digesting food. Herbivores are another matter - plant foods contain a large amount of cellulose, from which the cell wall of plants is woven; The animal body does not produce enzymes capable of breaking it down. In order to still assimilate plant food, animals resort to the help of so-called symbionts - the simplest single-celled organisms that settle in various parts of their digestive system; Only these creatures secrete the necessary enzyme and break down cellulose.
In ruminant artiodactyls ( cows, rams etc.) symbionts settle in the stomach, which has a four-chamber structure, more precisely, in its first section - scar. The grass absorbed by the animal remains here for some time and undergoes fermentation, then it is regurgitated back into the mouth, thoroughly chewed a second time and swallowed, ending up in book and further in abomasum, which corresponds to the simple stomach of other mammals. In non-ruminants, the stomach is simpler, but symbionts also live in it; they are also present in other herbivores (for example, hamsters). At the same time, microorganisms not only help the animal break down cellulose, but also serve as food for themselves; In this way, the animal receives substances that are not found in plants, but are necessary for them.
Next to the small intestine colon does not take part in digestion; here only certain substances and water are absorbed. However, in the cecum, characteristic of herbivores (for example, hares And rabbits), symbiont organisms also live, and cellulose fermentation also takes place here.
In the rectum, intensive absorption of water and the formation of feces occur, which are periodically removed from the body through the anus. Hares, rabbits and some others are characterized by coprophagia - eating their own feces; the fact is that the microorganisms living in their large intestine can no longer be digested by them, as is done by ungulates whose symbionts live in the stomach. By eating their excrement, these animals again carry it into the stomach and obtain the necessary substances from it. However, the food that has passed through their digestive tract a second time forms different feces, different from those formed initially; The animal is not going to eat them.
