Digestive and respiratory system of birds. Chicken anatomy from a to z. Midgut or small intestine

The most important functions of the intake of substances, their transformation and removal of undigested residues from the body are performed by the digestive system. Birds, being animals adapted to flight, have certain features of the internal structure. They are primarily aimed at reducing their body weight. The digestive system is no exception.

Digestive system of animals

All chordates, which include birds, have a similar structure. It begins. Then, through the pharynx, food enters the esophagus - a tube leading to the stomach. This part of the digestive system is an extension in which food stays for quite a long time. Ultimate suction nutrients occurs in and the excretion of undigested food residues is carried out by the final section of the tract. It is called the large intestine, which opens outwards as a cloaca or anus.

Features of the digestive system of birds are the presence of goiter - the expansion of the esophagus and a decrease in the length of the intestine. These structural features contribute to a more intense and reduced body weight of birds.

Can the same be said about other organ systems?

(table).

What do birds eat

The structure that the bird's digestive system has, its features and differences, are primarily due to the nature of the food. City dwellers feed on insects, seeds and the remains of human food.

The taste preferences of birds are quite diverse. Seagulls drink salt water by filtering it through their tonsils.

Poisonous is also due to the characteristics of food. She eats bugs. Their venom penetrates the skin and feathers of the bird. Although the flycatcher itself has a stable immunity to its action. A person can get burned by touching it. But very small animals die from the harmful effects of flycatcher toxins.

Birds that live in natural conditions eat tasty fruits, small vertebrates and even carrion. To do this, they have all the tools.

Beak

Birds do not have teeth. But they can easily handle both hard nuts and small seeds. After all, it is the beak that initially performs the function of the teeth. With its help, birds grind, crush or tear food. The beak consists of a hard horn-like substance that can withstand a fairly large weight and prolonged loads. For example, a woodpecker can make a hole up to 10 cm deep in the bark of trees to feast on insect larvae.

The shape and size of the beak depends on what the birds eat.

For example, predators have a large curved beak, with which they can easily grab and tear their prey. The peregrine falcon attacks even large foxes and wolves. Forest birds, extracting insects from the bark of trees, make holes in it like a chisel.

The tongue located in the oral cavity also helps to get food. It has special keratinized papillae that help keep food in the mouth.

The digestive system of a bird continues with a pharynx, with the help of which already partially processed food moves along the tract.

Esophagus and goiter

The bird's esophagus has an unusual structure. It's not just a tube leading to the stomach. It forms an extension called a goiter. It is here that the food lingers for a certain time and undergoes chemical processing with the help of saliva. And gulls and pelicans transfer food to the chicks from the feeding place to the nests in the goiter.

What is bird milk

The name of this delicious dessert is familiar to everyone since childhood. It got its name due to its resemblance to a substance that only birds can secrete.

In some birds, a nutritious foamy mass is formed in the specialized glands of the goiter. They use this valuable product for feeding chicks.

Bird's milk has nothing to do with the milk of animals. It is not liquid at all, but looks like a whipped curd mass. But it also contains many valuable organic substances and vitamins that can provide the newborn body with everything necessary.

In penguins, bird's milk is produced in the stomach, and not in the esophagus, it is the richest in fats. This substance is necessary for the development of chicks in severe northern conditions. And adult penguins use the fat layer not only to warm the body, but also as a store of food and energy. Hatching chicks for several months, males do not leave the place of laying. In this state, they are simply not able to get food and maintain viability at the expense of subcutaneous reserves.

Features of the structure of the stomach of birds

The stomach of birds also has characteristic features. It consists of two parts.

The sections of the stomach are called glandular and muscular. In the first, food is processed by gastric juice, i.e. Here, its chemical processing continues. The surface of the muscular section is covered with a film of keratinized matter. With its help, the food is ground to a mushy state.

Surely many have seen birds pecking at small pebbles. They do this not at all because they do not know about their taste. Once in the muscular section of the intestine, the stones contribute to the mechanical grinding of coarse food. Thus, the lack of teeth in birds is compensated.

Intestines

From the stomach, processed food enters the small intestine, into which the ducts of the liver and pancreas open. In this part of the digestive system, food is finally digested and absorbed into the blood.

Outwardly, the intestine opens with a cloaca. It is a hole through which undigested food residues, products of the functioning of the reproductive and excretory systems are removed.

A feature of the structure of the intestine is its small length. It depends on the nature of the food. For example, in birds that prefer plant foods, the intestines are 8 times longer than the body. And in insectivorous representatives of birds - only 4.

By the way, the bird is considered the most voracious - the champion of the smallest sizes. Guessed? Well, of course it's a hummingbird. In a day, she is able to consume pollen, the weight of which is 2 times her own weight.

And the wren brings up to 500 caterpillars and insects to chicks in one day. Here is the appetite!

And vultures are winners among the most greedy and insatiable creatures. With a large amount of food, they gorge themselves so that it is simply impossible for them to take off. The vultures solve this problem in a natural way: they wait for the body weight to decrease.

Birds digest food intensively, quickly emptying their intestines. This helps to reduce their body weight and provide the body with the right amount of energy. An ordinary sparrow is able to digest a caterpillar in 15 minutes, and grains in 3 hours. That is why birds spend most of their lives in search of food.

digestive glands

Salivary, pancreas and liver - this is the list that birds have. They secrete biologically active substances - enzymes. They speed up the digestion process by breaking down complex carbohydrates into monosaccharides, proteins into amino acids, lipids into glycerol and fatty acids. It is in this form that organic substances can be absorbed by the body.

Features of the digestive process of birds

The internal structure of birds (the table is presented in the article) indicates that all the features of their anatomical organization are aimed at adapting to flight. This also applies to the digestive system.

Instead of cheeks and lips, birds have a beak, with which food is captured and held. The oral cavity has a hard palate. It is covered by a mucous membrane, on which special cone-shaped papillae are located. With their help, food moves into the esophagus. To prevent food from entering the nasal cavity, the palatine fissure is already made by the palatine muscles.

The sections of the stomach, which perform different functions, contribute to the intensive processing of food. The intestine consists of two sections - thin and thick.

The digestive system of a bird provides all the life processes of birds. And the features of its structure determine the ability of these amazing animals to fly.

The material is taken from the site www.hystology.ru

The structure of the digestive system of birds in many respects resembles the digestive apparatus of mammals. It also consists of a digestive tube and obstetric glands - salivary, pancreas and liver.

The nature of the processing of solid feed that enters the body of birds and requires grinding in the absence of teeth determines the features of the functional morphology of the digestive system, which are covered in the Anatomy of Farm Animals course. Significant differences have the oral cavity and stomach. Other organs - small and large intestine, liver, pancreas are similar in structure to the organs of mammals.

Oral cavity birds is covered with squamous stratified epithelium. The thickness of the epithelial layer and the process of its keratinization in different parts of the oral cavity are characterized by their own characteristics. The process of keratinization proceeds intensively at the border with skin and ends with the formation of a stratum corneum. Stratified squamous epithelium is located on the main plate, built from loose connective tissue.

The excretory ducts of the following glands open into the oral cavity: maxillary, palatine, pharyngeal, submandibular (anterior and posterior), lingual, annular-arytenoid, glands of the corner of the mouth. The structure of these glands is based on a glandular lobule, consisting of mucous cells located radially around the collecting or central space (cavity). The latter passes into the excretory duct, the wall of which is built from the integumentary epithelium.

Serous secretory end sections in the composition of the salivary glands were not found. The structure of the salivary glands of birds has not been studied enough.

Esophagus. Its wall consists of mucous, muscular and adventitial membranes. Four layers are well expressed in the mucous membrane: epithelial, main and muscular plates, submucosa. The epithelial layer is represented by a flat stratified keratinized epithelium. In the process of keratinization, superficially lying cells turn into horny scales.

The lamina propria consists of loose connective tissue, which is poor in elastic fibers and lymphoid tissue. Its papillae protrude into the epithelial layer and are of considerable height. The lamina itself contains mucous glands. All terminal sections of the gland open into a collecting cavity, which is the beginning of an unbranched excretory duct. In the glandular cells of the terminal section, the nuclei are pressed with a mucous secretion to the basement membrane. In the zone of transition of the main plate of the esophagus to the stomach, there are numerous lymphoid nodules - the esophageal tonsil.

The muscularis mucosa is strongly developed. It is built from longitudinally oriented smooth muscle cells. This layer is involved in the formation of mucosal folds.

The submucosa consists of loose connective tissue, thereby creating the mobility of the mucous membrane during the formation of its inconsistent folds.

The muscular coat is represented by two layers of smooth muscle cells: inner - circular and outer - longitudinal. The circular layer is more developed.

Adventitia, as in mammals, is built from loose connective tissue. After the esophagus enters the chest cavity, the adventitia is replaced by a serous membrane.

A derivative of the wall of the esophagus is the goiter, so its wall also has three shells built from the same layers, and the layers from the same tissues. The ventral wall of the goiter is represented by a thicker epithelial layer, in which the boundary between the producing and stratum corneum passes very clearly. Mucous glands are found only in the dorsal wall of the goiter.

The stomach consists of two sections - glandular and muscular (Fig. 281). The first secretes digestive juice, the second is intended for grinding food. In the glandular stomach, the food lump is enriched with enzymes and, without lingering, enters

Rice. 281.

The mucous membrane of the glandular (BUT) and muscular (B) chicken stomach:
but- glandular sacs; b - superficial and in- deep glands; G- muscular plate; d- muscular membrane; in - glands; well- horny substance; h - connective tissue.

muscular stomach, where chemical and mechanical processing takes place.

Iron stomach. Its wall is formed from mucous, muscular and serous membranes. The epithelial layer of the mucous membrane is a single-layer cylindrical glandular epithelium, therefore, the integumentary epithelium of the stomach is an extensive glandular field that produces mucus.

The main plate is represented by loose connective tissue rich in cellular elements. It contains single-lobed (in ducks) and multi-lobed (in chickens and geese) glands. The lobules are delimited by interlobular connective tissue. Inside each lobule is a collecting, or central, cavity, covered with a single-layer glandular epithelium, passing into the superficial epithelial layer of the glandular stomach. The epithelium of the gland lobule sinks deep, forming structures similar to the gastric pits in mammals. Tubular glands located in the lobule open into these pits.

Tightly adjacent to each other, they lie radially around the collecting cavity. Tubular glands are built from one type of glandular cells. Electron microscopic studies indicate that these cells produce both hydrochloric acid and pepsinogen; therefore, the cells contain a developed granular endoplasmic reticulum, many large mitochondria with a large number of densely lying cristae, a smooth endoplasmic reticulum, vesicles and microtubules. Zymogenic granules are located in the zone of the Golgi complex. According to some authors, the synthesis of hydrochloric acid is carried out in the apical part of the glandular cell, and pepsinogen - in the basal.

The excretory ducts of the glands open on the surface of the elevations of the mucous membrane. These elevations are visible to the naked eye and are called glandular sacs. There are no other glands in the mucous membrane. A powerful layer of the muscular plate of the mucous membrane of the glandular stomach is a continuation of the muscular plate of the mucous membrane of the esophagus. Smooth muscle cells braid the glands from below, sides and top.

The submucosa consists of loose connective tissue and is only slightly developed. The muscular coat is represented by two layers of smooth muscle cells, of which the inner one is circular, the outer one is longitudinal.

The serous membrane is built, as usual, from loose connective tissue and mesothelium.

Muscular stomach. The wall of the muscular stomach has three layers: mucous, muscular and serous.

The epithelial layer of the mucous membrane is represented by a single layer of cubic epithelium. Its invaginations into the base of the mucosa are gastric dimples. They open the excretory ducts of simple tubular glands located in the main plate. The gland consists of the bottom, body and neck. The glands are built from chief cells. They are cubic in shape with an intensively developed protein-synthesizing system, that is, a granular endoplasmic reticulum. The plasmalemma on the apical surface of the cells forms many microvilli. Basal cells are the precursors of chief cells. Moving towards the neck of the gland, they become the cells of the gastric pits and the integumentary epithelium. The glands produce a secret that hardens on the surface of the stomach, forming a very hard grater-like layer - the keratinoid cover, or cuticle. It consists of vertically oriented columns formed from the secretion of the tubular glands and the matrix located between them. The latter is formed from the secret of the cells of the gastric pits and the surface epithelium. Sand, gravel, pebbles and other solid objects located in the lumen of the muscular stomach contribute to the mechanical softening of the feed. There are no enzymes in the secretion of the glands.

Digestion of food proceeds under the action of the secretion of the glandular stomach, bacteria, food enzymes.

The muscular layer of the mucous membrane is absent.

The submucosal layer is built from dense fibrous connective tissue.

The muscular coat is represented by powerful bundles of smooth muscle cells. Its strong contractions contribute to the mechanical crushing of the feed. The annular layer on the dorsal and ventral edges of the stomach forms the triangular major muscles. Intermediate muscles lie between them.

The serous membrane has a connective tissue layer and mesothelium.

Intestines. The structure of the intestinal wall is similar to the structure of mammals. The epithelial layer of the mucous membrane is a single-layer cylindrical border epithelium. It consists of border, goblet and enterochromaffin cells. The main plate, built from loose connective tissue, forms protrusions covered with a bordered epithelium. These are villi. At the base of the villi, crypts open - tubular depressions also covered with epithelium. They, like villi, increase the suction surface, glandular and stem cells are located at their base, therefore crypts are considered a zone of mitotically dividing enterocytes that replenish the epithelial layer of the villi. The connective tissue is rich in lymphoid elements, which are located diffusely and in the form of lymphoid nodules.

The muscular coat is built from two layers of smooth muscle cells. The most developed is the inner circular layer.

The serous membrane consists of loose connective tissue and mesothelium.

The cloaca is an expansion of the hindgut of the alimentary canal. The genital and urinary tracts also open into the cloaca, therefore, three sections are distinguished in it: coprodeum, urodeum and proctodeum. The first of them is the most extensive part. In structure, it resembles the hindgut.

Pancreas- lobular organ lying in the loops of the duodenum. The number of glandular lobules in farm birds of different species varies. The lobules are demarcated by interlobular connective tissue. They are built in the same way as in mammals, from exocrine and endocrine sections. The number of main excretory ducts lined, like the interlobular ducts, with a single-layer columnar epithelium, varies in different birds. Turkeys have two, chickens have three. The main excretory ducts split into interlobular ducts, and the latter into intercalary ducts. The intercalary excretory ducts are covered with a flat single-layer epithelium and pass into the secretory sections.

The endocrine part of the gland is a complex of pancreatic islets. In birds, they consist of only one type of cells - either A (dark) cells or B (light) cells, and therefore light and dark islets are distinguished. The ratio of these types of islets in chickens can change under the influence of sex and age. In young chicks, light islets predominate.

Liver. The functional morphology of the liver of birds and mammals is similar: the lobular structure is due to the blood supply to the organ; central location in the lobule of the central vein; on the periphery of the lobules are triads consisting of the interlobular bile duct, interlobular vein and interlobular artery. Hepatocytes form radially lying beams. Between them are venous sinusoids.

The digestive system of birds is somewhat more complex than that of reptiles. A feature of bird nutrition is that they eat a lot and often. Birds need to maintain a constant body temperature (they are warm-blooded) and the ability to fly, which requires a lot of energy. Therefore, they have an intensive metabolism, they need to quickly replenish energy costs. The digestive system of birds is designed in such a way as to ensure rapid digestion. The speed of digestion of food depends on its type and the species to which this or that bird belongs. Usually food is digested (from ingestion of food to the exit of residues) varies from 10 minutes (in herbivores) to several hours (in birds of prey).

Birds have no teeth. In part, they are replaced by the sharp edges of the beak. Basically, the beak is used to capture and hold food. Its shape and size depend on the food specialization of birds. The shape and size of the tongue of birds also depend on the type of food.

The salivary glands open into the mouth. Bird saliva contains enzymes that digest carbohydrates.

Many birds (especially granivorous) have a goiter in the esophagus, which is its extension. Here, food is temporarily stored, swells under the action of saliva, which it was processed in the oral cavity.

An important feature The digestive system of birds is the presence of a double stomach. The first of these is the glandular stomach. In it, food is processed by gastric juice containing digestive enzymes. The second is the muscular stomach. This is where the food gets crushed. The walls of the muscular stomach consist of powerful muscles and have folds, and in the stomach itself there are small stones that the bird swallows. We can say that the pebbles in birds act as teeth.

What is not digested in the muscular stomach (bones, wool, chitin) is compressed into lumps, which the birds burp through their mouths. Such lumps are called riddles. From them, archaeologists (scientists who study birds) can understand what birds eat.

From the muscular stomach, when its sphincter opens, food passes into the anterior part of the small intestine (duodenum), where the ducts of the liver, gallbladder and pancreas open. Under the action of their enzymes, food is finally digested and then absorbed into the blood throughout the small intestine.

A feature of the digestive system of birds is the presence of two blind processes on the border of the small and large intestines. They are most developed in herbivorous birds.

Birds have a very short large intestine. So the leftovers don't stay here. This is important to lighten the bird's weight for flight.

The large intestine passes into the cloaca, from where the excrement is quickly excreted. Birds do not have a rectum.

The digestive system in birds has significant structural and physiological features. The bird's digestive system is compact yet extremely efficient. Some small birds process an amount of food equivalent to approximately 30% of their body weight daily. Birds generally prefer high energy concentrated foods, insects and other animals, fruits and seeds. They rarely feed only on the leaves of plants, grass. For poultry, plant leaves, grass are only an addition to a concentrated diet as a source of vitamins, minerals and some water.

Structural features. Birds lack lips, teeth, cheeks. The beak-shaped jaws perform the function of capturing food. On the hard palate there are special cone-shaped papillae directed backwards and promoting the movement of food into the esophagus. Similar papillae are found on the tip and back of the tongue, in addition, there are filiform papillae on the root of the tongue. The movements of the tongue and the papilla as a whole ensure the movement of the captured portion of food into the pharynx and into the esophagus.

Small salivary glands are located on the bottom and roof of the beak cavity. Mixed saliva is a thick and viscous cloudy liquid of slightly alkaline reaction. It contains a lot of mucus, mucin and the enzyme amylase. From 3 to 20 ml of saliva is secreted per day.

Taste sticks in the thickness of the tongue provide the formation of a taste sensation.

Esophagus. Consists of two sections - upper and lower. The upper section starts from the pharynx and ends with the goiter, the lower section - from the goiter and ends at the glandular stomach. The upper esophagus is longer than the lower.

Goiter. It is an expansion of the esophagus, a abdominal muscular organ in front of the entrance to the chest cavity. There are sphincters at the place of entry and exit. The goiter is well developed in chickens, turkeys, guinea fowls, pigeons, in geese and ducks it is less developed and represents a true expansion of the esophagus.

The esophagus and goiter have a well-developed muscular wall. The inner surface of the goiter is lined with stratified squamous epithelium. In the loose connective tissue of its walls, alveolar-tubular glands are located, secreting a mucous secret that does not contain enzymes.

The lower esophagus passes into the stomach.

Stomach. It consists of two sections - the glandular stomach and the muscular stomach.

Its mucous membrane consists of single-layer glandular epithelial cells that produce a special secret, which hardens on its surface, forming a protective layer - the cuticle. The cuticle is erased and constantly replaced by a new secret. The secret also contains hydrochloric acid.

The feed is pounded, mixed, subjected to chemical transformation due to gastric juice and pancreatic juice, bile and intestinal juice periodically thrown from the intestine. The contents of the muscular stomach enters the duodenum of a well-developed small intestine. The sphincter between them closes loosely.

The muscular stomach is most developed in geese, which consume a lot of grass on grazing.

The thin section of the intestine. It has the shape of a spiral, characteristic of organs with large functionality. The small intestine is located between the air sacs. The small intestine, like that of mammals, consists of the duodenum, jejunum, and ileum. The duodenum has the appearance of a loop. There is no sharp boundary between the jejunum and ileum.

Birds have short intestines compared to mammals. The total length of the thin section in adult chickens is 140 ... 150 cm, the total length of the entire intestine is more than 170 cm, the digestive tract is 210 cm, that is, 6 times the length of the body, and in chickens it is 1: 4. The total length of the small intestine in ducks is 159 cm; in geese - 234; in turkeys - 205 cm. - 46, 165 and 23 cm, turkeys - 37, 140 and 28 cm.

Intestinal villi are thin, delicate, leaf-shaped and finger-shaped; there are more of them in the duodenum; per 1 cm 2 in chickens there are 415, ducks - 1512, geese - 2051, turkeys - 292. The height of the villi reaches 1 mm, the diameter is 100 ... 200 microns. The surface area of ​​the mucous membrane of the small intestine in chickens is about 2.0 m 2, ducks - 1.5, geese - 5.5, turkeys - 8.6 m 2.

The ducts of the pancreas and bile ducts flow into the duodenum.

Pancreas. It is well developed, has a large size and weight: in chickens 2.8 ± 0.12 g, ducks - 7.9 ± 0.30, geese - 9.1 ± 0.38 g. It has two lobes; in chickens and ducks - three ducts, in geese and turkeys - two each, which open into one papilla with the bile duct into the duodenum. The pancreas secretes pancreatic juice containing the same enzymes as in mammals, but more active.

Liver. Well developed; weight up to 40 g, but can reach up to 1 kg in geese with special fattening. The liver secretes dark or light green bile; contains alpha-amylase. Bile from the right and left lobes first enters the sinus - the expansion of the ducts, then along the sinus-vesical tract into the gallbladder. The gallbladder and sinus are connected to the duodenum by the vesico-intestinal and sinus-intestinal ducts.

Large intestine. Represented by the blind processes and the rectum, which opens into the cloaca. The ileum passes into the rectum; at the transition point, two blind processes depart. They are located at an angle of 30 ° to the intestines and have sphincters. The length of the process is 17 ... 30 cm in chickens, 20 ... 25 cm in geese. Sphincters in the beginning and end of the rectum prevent the entry of contents from the rectum into the ileum and premature entry into the cloaca. The rectum is short, poorly developed - in chickens 8 ... 11 cm long, 1 ... 1.5 cm in diameter. The rectum passes into the cloaca.

Cloaca. It is an extension of the final part of the rectum. The cloaca is divided into three sections by two transverse circular muscles: 1) the anterior, coprodium, or fecal sinus, is a true continuation of the rectum; 2) middle, urodeum, or urinary sinus, - the ureters, sperm ducts or oviduct open into it; 3) posterior, proctodium, - feces and urine are excreted through it.

The drake and gander, as well as the swan, have an organ of copulation in the cloaca.

The anus in birds has the shape of a slit, surrounded by a ring of obturator muscles.

Physiological features. Feed intake. Birds grab food with their beaks. The food eaten by birds of different species differs in properties. Accordingly, the digestive apparatus in different species of birds has its own structural and physiological features.

The captured portion of the food is not chewed, but moistened with saliva and the movements of the tongue move into the pharynx and further into the esophagus and goiter. I

Digestion in the goiter. It is characterized by a complex motor-secretory function. There are two types of contractions - peristaltic and tonic. They are difficult to combine and first ensure the supply of food to the left half of the crop, then to the right.

Goiter is characterized by a certain pattern of motor activity: 5 ... 12 consecutive contractions alternate with a pause of 10 minutes. Immediately after filling the goiter with food, its movements slow down or completely stop for 35-40 minutes. Goiter movements are provided by contractions of circular and longitudinal smooth muscles; they are regulated by vagus and sympathetic nerves.

Small components of the contents of the goiter in the first minutes pass into the lower esophagus, larger ones are delayed up to 14 hours.

The intake of food into the goiter is accompanied by the excitation of its glands. In the goiter, with the help of its own secretion and saliva, softening and swelling of the feed occur, as well as the conversion of feed nutrients due to feed enzymes, microorganisms and saliva.

Aerobic microorganisms, lactobacilli, Escherichia coli, enterococci, fungi, yeast cells live in the goiter. Mostly carbohydrates are hydrolyzed - 8 ... 13% of soluble carbohydrates of the feed, in a small amount of proteins and fats. The end products of carbohydrate conversion are lactic, acetic, propionic and butyric acids.

The main function of the goiter is capacitive.

The movement of contents from the goiter occurs due to small contractions in the area of ​​the goiter funnel. At first, one contraction appears, after 1 ... 3 minutes a second wave appears, later 2 ... 3 consecutive contractions, then a long rest.

The bulk of the contents is evacuated from the goiter in the first 3-6 hours, the smaller part - in the next 8 hours.

Digestion in the stomach. The contents of the goiter through the lower esophagus enters the glandular stomach and causes increased secretion of its juice. The secretion of gastric juice is carried out continuously. Feed intake stimulates the formation and secretion of gastric juice in chickens up to 11...13 ml/h. Gastric juice contains the enzyme pepsin; lipase is absent in it, since birds do not feed on milk.

The mechanism of excitation of the gastric glands is neuro-hormonal. Complex-reflex and gastric reflex-hormonal phases of excitation and regulation of the gastric glands have been established. The effect on the gastric glands is through the vagus and celiac nerves. A strong causative agent of the gastric glands is protein; The maximum secretion of gastric juice and the enzyme pepsin is observed when the protein content in the diet is in the range of 15...25%. A large amount of protein in chickens, ducks and geese causes overexcitation of the gastric glands and, as a result, inhibition of their secretion.

The glandular stomach also performs a motor function; the rhythm of the movement is one contraction per minute. The contents linger here for a short time, no more than an hour, and are mainly saturated with gastric juice. Then it passes into the muscular stomach.

Digestion in the muscular stomach is intensive due to the enzymes of the gastric juice of both stomachs and contractions of the muscular stomach itself. The muscular stomach of birds performs two types of contractions: phasic and tonic. They appear at the same time. Against the background of a periodic increase and decrease in muscle tone, a two-phase contraction of the stomach occurs.

The cycle of movement of the muscular stomach begins with the contraction of the upper intermediate muscle. During the period of its shortening, the reduction of the anterior main begins. At the beginning of the relaxation of the latter, successive contractions of the lower intermediate and then the posterior main muscle occur. When the intermediate muscle contracts, the contents of the cranial sac are squeezed out into the slit-like cavity between the cuticle plates of the main muscles. Subsequent contractions of the anterior main muscle displace the contents of the slit-like cavity in the posterior direction. The contraction of the lower intermediate muscle ensures the displacement of the chyme of the caudal sac into the cavity between the main muscles. The posterior main muscle propels the contents towards the cranial caecum.

The main muscles in each cycle of contractions produce counter movements, exerting a rubbing effect on the feed particles. The asymmetry of the location of the fibers in the main muscles of the stomach provides the possibility of lateral movements.

At the same time, chemical conversion of food occurs in the muscular stomach due to the enzymes of juices: gastric, as well as pancreatic, intestinal and bile, which are thrown through a loosely closed sphincter. The sphincter between the muscular stomach and the duodenum periodically opens during digestion, and the contents of the intestine with enzymes of pancreatic juice, bile, and intestinal juice flow into the stomach. Therefore, proteins, fats and carbohydrates are intensively digested in the muscular stomach. The time of gastric digestion is 3 hours.

The entrance and exit openings in the muscular stomach are located close. In this regard, contractions of the muscular stomach are accompanied by the evacuation of liquid gastric contents, and solid and larger food particles are retained in the stomach and undergo deeper transformations. The contents from the stomach enter the intestines in portions and periods.

Digestion in the intestines. Carried out abdominal and parietal digestion with a predominance of the parietal. Digestion is characterized by great intensity, since all the enzymes of the digestive juices in the intestine are highly active.

The mechanism of excitation and regulation of the secretory activity of the pancreas is reflex-hormonal.

The mechanism of formation and secretion of bile is reflex-hormonal. Hydrochloric acid is a strong causative agent.

Well-developed intestines and villi provide intensive absorption of the substances subjected to transformation. total area absorption in chickens reaches an average of 2000 cm 2. 62...63% of solids, 86...91% of protein, 62...54% of fat, 80% of BEV, 30...50% of water are absorbed in the intestine. Intestinal digestion time 3...5h. *

The intestine carries out active contractile activity: the number of peristaltic movements in 15 minutes is 6-10, anti-peristaltic contractions are less, from 0 to 3.

The evacuation of the contents occurs in periods of 30 ... 40 minutes, between which rest is about 30 minutes. More than 400 ml enters the intestines during the day, about 250 ml at night. The amount of dry matter in chyme is within 7.5...20%. In the intestinal chyme, a high activity of amylase, proteases, and lipase is observed.

The content in portions - 30 ... 56 portions per hour - enters the blind processes due to the relaxation of their sphincters. The transformation of the substances of the contents in the blind processes is carried out thanks to the enzymes supplied with the chyme, its own secret and the enzymes of the microorganisms that inhabit the blind processes. The chyme of blind sacs has amylase and protease activity. In the blind processes, 10 ... 25% of fiber, 8 ... 10% of protein, a small amount of soluble carbohydrates and lipids are split.

Digestion in the blind processes is accompanied by contractions - 10 ... 12 in 1 hour. In chickens, contractions of the nature of tonic tension are carried out with a duration of up to 80 ... 100 s.

Periodically, the sphincters open and the contents in portions enter the rectum. For 8 ... 10 contractions of the small intestine, ensuring the flow of contents into the blind processes, the latter carry out 1 contraction, ensuring the evacuation of the contents into the rectum.

Digestion time in the large intestine is 6-10 hours.

In the rectum, the formation of feces - litter - is completed. The formed litter is periodically thrown out reflexively through the cloaca.

Due to the fact that birds need to travel long distances, their internal structure is somewhat peculiar. Some individuals satisfy their natural needs in flight, including food intake. In the body of birds, several vital systems fit compactly with proper organs in them, which, if necessary, can reduce their body weight. The article will examine in detail the digestive system of birds, from the function of capturing food to its processing and excretion of waste products.

Digestive organs

In order for bird food to become fuel, it must undergo mechanical, chemical and physical processing. The digestive apparatus of birds is able to perform all the necessary functions for the normal absorption of food. The organs of the digestive system of birds include: beak, oral cavity with tongue, pharynx, esophagus, goiter, glandular stomach, muscular stomach, duodenum, liver, small intestine, gallbladder, blind processes, rectum, cloaca.

Complex apparatus

The structural features of the digestive system of birds are determined by their diet and the fact that some of them spend most of their lives in the air. This requires a lot of energy, so they eat a lot and often. Birds are warm-blooded creatures, which requires constant maintenance of body temperature. In order to replenish the expended energy in a timely manner, metabolic processes in their body occur intensively. The structure of the organs of digestion and assimilation of food ensures rapid digestion. For each individual bird species, this speed varies depending on the type of food. In connection with the above reasons, unlike reptiles, the structure of the food apparatus in birds is much more complicated. Based on this, several characteristic features of the physiology of birds can be distinguished:

• plasticity of organs;
• intensity of food digestion;
• feed passage speed;
• good digestibility and absorption of nutrients;
• some individuals have high adaptability to new food.

Short description

Before proceeding to a detailed examination of the organs, we will try to briefly describe the functioning of the digestive system of birds. The principle of its work is the breakdown of food with the help of enzymes, the absorption of the optimal amount of necessary substances into the blood and the removal of undigested waste from the body. With the help of a bird's beak, food enters the oral cavity and moves through the esophagus to the stomach, which consists of two parts. In the glandular, it is exposed to gastric juice, which ensures its further processing. In the muscle, lined with a stratum corneum, the food is ground to a homogeneous consistency. Then the crushed mass penetrates into the small intestine, where it is finally broken down and absorbed into the blood. The small intestine contains pathways for communication with the liver and pancreas. Through the cloaca, unprocessed residues from the intestine are brought out.

Beak

Birds do not have teeth, which significantly reduces the mass of the jaws and the skull itself. Instead, their upper (mandible) and lower (mandible) parts are placed in horn covers. The jaw base is represented by the intermaxillary and mandibular bones. The upper section consists of the root, the back and the cutting edge, the lower section consists of the bottom, the corner of the chin and the edge. The beak acts as lips and cheeks in birds. With its help, they extract, seize, and sometimes tear their prey. Since birds cannot chew, they swallow their food whole. The shape of the beak is very diverse, depending on the nature of the food that a particular species of individual feeds on.

Oral cavity

The oral cavity, like the beak, is divided into upper and lower sections. The upper part is occupied by a hard palate, covered with a mucous layer. It is endowed with cone-shaped papillae of various lengths. The outgrowths are directed backward and help to move the food into the esophagus. Special muscles contribute to the narrowing of the palatine fissure, thereby preventing the penetration of fluid into the nasal cavity.

The language is an auxiliary organ in obtaining food from birds. Some individuals skillfully use it when capturing and pushing food. The tongue is located at the bottom of the mouth. The hyoid bone is for him a support and a bridge to the skull. He is dressed in a keratinized membrane and has almost no ability to convey the taste sensations of food. The configuration of the tongue is usually similar to the shape of the beak and depends on the characteristic features of the lifestyle of individual individuals. In a woodpecker it is long and sticky, in birds of prey it is hard and short, in herbivores it is fleshy.

Pharynx

The pharynx runs between the oral cavity and the upper esophagus. Several paths open into it: the nasal and oral cavities, the laryngeal fissure associated with the respiratory system.

In the pharyngeal cavity, as well as in the oral cavity, several different glands are located. The development and number of these excretory organs determine the structural features of birds. The digestive system of chickens is characterized by a strong development of glands in this area. This is due to the consumption of grains and other food waste, familiar to the diet of chickens and turkeys. The following types of glands are distinguished: salivary submandibular, sublingual, ear, palatine, paired beak and maxillary. The layer of prismatic epithelium with which they are lined in birds is very high. In their shape, the glands resemble a rosette.

Esophagus

The esophagus is divided into two parts: upper and lower. The first from the pharynx reaches the goiter, the second begins at the food bag and ends with the glandular section of the stomach. The shell of the esophagus is lined with two layers of smooth muscles: longitudinal (external) and annular. Between them is located the nerve plexus, called the intermuscular or Auerbach's. When the muscles contract, the esophagus contracts and pushes food through. The digestive system of birds has glands in this area as well. The passage of food facilitates the secret produced by the sac-like organs located in the mucous layer.

Goiter

Not every bird is distinguished by the presence of a goiter. The owners of this organ are such domestic birds as pigeons, chickens, guinea fowl and turkeys. Waterfowl do not have a goiter, but their esophagus is slightly dilated. In many birds, when entering the chest cavity, the esophagus expands significantly and forms a kind of reservoir for the accumulation and processing of food. In the goiter, the feed is softened and mixed, as well as the partial breakdown of carbohydrates. There are individuals in which the esophagus looks like a tube of the same diameter along its entire length.

Seagulls, pelicans and cormorants have an interesting feeding of chicks. Cruising from the place of prey to the nest, they use their goiter as a handbag, in which they bring food. The pigeon's digestive system is also impressive. Birds feed their chicks with protein mass, which is produced by special goiter glands. This foamy substance is called bird's milk.

Stomach

In the digestive system of birds there are two stomachs: glandular, in which food is processed using chemical-enzymatic processes; and a muscular stomach that grinds food mechanically. The second stomach contains pebbles for grinding food, acting as teeth. Strongly developed muscles contribute to intensive grinding of food. Undigested remains of birds burp out in the form of compressed lumps. Sometimes they serve as material for research. With their help, experts can find out what the bird feeds on.

Individuals that tend to take vegetation and coarse foods have a well-developed muscular stomach. In those who eat more tender or animal food, the glandular stomach functions better.

Intestines

A distinctive feature of the digestive system of birds is a shortened intestine. As is the case with some other organs, this structure allows you to reduce the body weight of the bird, since food remains do not linger in it. The opening of the sphincter of the muscular stomach allows the crushed mass to pass into the duodenum, which represents the anterior part of the small intestine. It includes the channels of the liver, pancreas and gallbladder. As a result of the release of their enzymes, complete digestion of food occurs. Digestion and absorption of nutrients into the blood occurs along the entire length of the small intestine.

The pigeon has a peculiar arrangement of bile ducts. In the place where the duodenum twists into a loop, the pancreas is located with the presence of two or three ducts. This also includes the bile ducts of the liver, so pigeons do not need a gallbladder.

Between the small and large intestines are blind processes, which are developed only in birds that feed on vegetation. The rectum is the widest section of the intestine. In chickens, it is about 7 cm long and 2 cm in diameter. In agricultural individuals, blind processes perform the following functions:

• break down fiber through microflora enzymes;
• synthesize vitamins;
• convert nitrogenous substances;
• absorb water and minerals.

excretory system

As already mentioned, the structure of the body as a whole, including the digestive system of birds, is aimed at reducing their weight, due to the ability to fly. The excretory system is represented by the ureters and paired kidneys. Due to the fact that birds are deprived Bladder, metabolic products do not accumulate in their body. This greatly affects their mass. In females, the right ovary is missing.

The caudal segment of the rectum is expanded and represents a cloaca covered with a single layer of prismatic epithelium. It is divided into three parts by means of two transverse rings. The anterior section is the fecal sinus, the middle section is the sinus for opening the ureters, vas deferens and oviducts. There are no villi or glands in this area. The mucous layer of the cloaca has a wavy structure. In birds such as the swan, gander and drake, its walls are transformed into a copulation organ. The border between the rectum and the cloaca is the internal sphincter in the form of an annular muscle. The opening of the cloaca is lined with stratified epithelium. This feature of the mucous membrane is characteristic of geese. It also contains formations of lymphoid origin. The structure of the digestive system of birds ends with the anal sphincter.

Conclusion

The above information is general characteristics information in the field of biology. The digestive system of birds is actually very individual. Its differences are determined by the type of individual, type of food, origin, lifestyle, as well as the interaction of birds with environment and their habitat.