Structure and functions of the digestive system of birds. Digestive system of poultry. Internal structure of birds. Stomach in birds

Material taken from the site www.hystology.ru

The structure of the digestive system of birds is in many ways similar to the digestive apparatus of mammals. It also consists of the digestive tube and the wall glands - salivary, pancreatic and liver.

The nature of the processing of solid food 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 course “Anatomy of Farm Animals”. The oral cavity and stomach have significant differences. Other organs - the small and large intestine, liver, pancreas - are similar in structure to the organs of mammals.

Oral cavity birds are covered with flat 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 occurs intensively at the border with the skin and ends with the formation of a horny layer. Multilayer squamous epithelium is located on the main plate, built of 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 radially located 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 terminal sections were not found in the salivary glands. The structure of the salivary glands of birds has not been studied enough.

Esophagus. Its wall consists of mucous, muscular and adventitial membranes. The mucous membrane has four distinct layers: epithelial, basal and muscular lamina, and submucosa. The epithelial layer is represented by flat stratified keratinizing epithelium. During the process of keratinization, superficial 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 plate itself contains mucous glands. All terminal sections of the gland open into the collecting cavity, which is the beginning of an unbranched excretory duct. In the glandular cells of the terminal section, the nuclei are pressed by the mucous secretion to the basement membrane. In the zone of transition of the main plate of the esophagus into the stomach there are numerous lymphoid nodules - the esophageal tonsil.

The muscular plate of the mucous membrane is highly developed. It is built from longitudinally oriented smooth muscle cells. This layer is involved in the formation of folds of the mucous membrane.

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

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

The adventitia, as in mammals, is built of loose connective tissue. After the esophagus enters the chest cavity, the adventitia is replaced by the serosa.

A derivative of the wall of the esophagus is the goiter, therefore its wall also has three membranes, built from the same layers, and the layers are from the same tissues. The ventral wall of the crop is represented by a thicker epithelial layer, in which there is a very clear boundary between the producing and stratum corneum. The mucous glands are found only in the dorsal wall of the crop. The muscular plate and muscular layer are especially strongly developed in the ventral part of the crop.

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 (A) and muscular (B) chicken stomach:
A- glandular sacs; b - superficial and V- deep glands; G- muscle plate; d- muscle membrane; c - glands; and- horny substance; h - connective tissue.

the muscular stomach, where chemical and mechanical processing occurs.

Glandular 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 covering 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 monolobed (in ducks) and multilobed (in chickens and geese) glands. The lobules are delimited by interlobular connective tissue. Inside each lobule there is a collecting, or central, cavity, covered with a single-layer glandular epithelium, which passes into the superficial epithelial layer of the glandular stomach. The epithelium of the gland lobules sinks deeper, forming structures similar to the gastric pits in mammals. The tubular glands located in the lobule open into these pits.

Closely 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, smooth endoplasmic reticulum, vesicles and microtubules. Zymogenic grains are located in the Golgi complex zone. According to some authors, the synthesis of hydrochloric acid occurs in the apical part of the glandular cell, and pepsinogen in the basal part.

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. The thick 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 entwine the glands from below, sides and above.

The submucosa consists of loose connective tissue and is poorly developed. The muscular layer 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.

Muscle stomach. The wall of the muscular stomach has three membranes: mucous, muscular and serous.

The epithelial layer of the mucous membrane is represented by single-layer cubic epithelium. Its invaginations into the base of the mucosa are gastric dimples. The excretory ducts of simple tubular glands located in the main plate open in them. The gland consists of a fundus, body and neck. The glands are built from chief cells. They are cubic in shape with an intensively developed protein synthesizing system, that is, granular endoplasmic reticulum. The plasma membrane on the apical surface of the cells forms many microvilli. The precursors of chief cells are basal cells. Moving towards the neck of the gland, they become cells of the gastric pits and integumentary epithelium. The glands produce a secretion 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 tubular glands and the matrix located between them. The latter is formed from the secretion of cells of the gastric pits and surface epithelium. Mechanical softening of the feed is facilitated by sand, gravel, pebbles and other solid objects located in the lumen of the muscular stomach. There are no enzymes in the secretions of the glands.

Digestion of food occurs under the influence of the secretion of the glandular stomach, bacteria, and food enzymes.

The muscular layer of the mucous membrane is absent.

The submucosal layer is made of dense fibrous connective tissue.

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

The serosa has a connective tissue layer and mesothelium.

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

The muscularis propria is made up of two layers of smooth muscle cells. The most developed is the inner circular layer.

The serosa consists of loose connective tissue and mesothelium.

The cloaca is an extension of the hindgut of the digestive canal. The genital and urinary tracts also open into the cloaca, so it has three divisions: coprodeum, urodeum and proctodeum. The first of these is the most extensive part. In structure it is similar to the hindgut.

Pancreas- a lobulated organ lying in the loops of the duodenum. The number of glandular lobules varies in different species of farm birds. The lobules are delimited 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 ones, with single-layer columnar epithelium, varies from bird to bird. Turkeys have two, chickens have three. The main excretory ducts split into interlobular ducts, and the latter into interlobular ducts. The intercalary excretory ducts are covered with 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 may vary under the influence of gender and age. In chickens early age light islands predominate.

Liver. The functional morphology of the liver of birds and mammals is similar: the lobulated 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 there are triads consisting of the interlobular bile duct, interlobular vein and interlobular artery. Hepatocytes form radially lying beams. Between them are venous sinusoids.

breathing bird ovulation digestion

The scientifically based use of produced compound feeds for growing and fattening poultry or for egg production guarantees the highest possible degree of utilization of feed nutrients. In this sense, special attention must be paid to the peculiarities of digestion, absorption and metabolism of substances used in agriculture bird species. From the point of view of the general course and regulation of digestive functions, there are no serious differences between individual types of poultry.

Modern methods of feeding in intensive poultry housing have shown that not only chickens, ducks, geese and turkeys, but also pigeons can digest animal protein well. On this basis, the named species poultry should be classified as omnivores.

The activity of the digestive apparatus of birds is in principle similar to that of mammals. However, there are the following morphofunctional features, which are determined by the nature of the diet and living conditions of birds:

• a) absence of teeth, presence of a beak, simple structure of the nasopharynx, absence of the epiglottis;
• b) the presence of a goiter or a corresponding dilation of the esophagus;
• c) the presence of a two-chamber stomach with glandular and muscular sections;
• d) relatively short small intestine;
• e) well-developed liver and pancreas, having 2-3 ducts each;
• f) the presence of two cecums and a cloaca into which the digestive, reproductive and urinary tracts open.

Feed intake. The bird finds food mainly through vision and tests it thanks to the well-developed tactile sensitivity of the oral mucosa. In the uncovered, keratinized parts of the beak, on the posterior palate and in the tongue, there are tactile bodies that are involved in the analysis of ingested food. The bird easily distinguishes empty grains from full ones. Taste and sense of smell in birds are much less developed than in mammals.

The bird's oral cavity is limited by the edges of the beak, formed by transforming the mandibular and intermaxillary parts of the skull. The size, shape and hardness of the beak and its horny sheaths vary from bird to bird and depend on the nature of their diet. Chicken and turkey have a sharp, short beak, while waterfowl (goose and duck) have a wide and soft beak. Ducks have notches along the edges of their beaks that are used to strain water. In geese, these formations are denser and serve to tear off grass. Chickens and turkeys eat solid food by pecking, and ducks grab solid food with their beaks, like a spoon, bite off grass, and eat mushy food by scooping it up with their beaks. Chickens, waterfowl and turkeys drink water by tilting their heads back as they swallow.

The central regulation of food intake in birds involves the same hypothalamic nuclei as in higher mammals.

Processes in the beak cavity and crop. During a short stay in the beak cavity, the food is moistened with saliva. Small glands located on the bottom and roof of the beak cavity secrete a small amount of mucin-rich saliva, which promotes better gliding of food. The act of swallowing begins with rapid movements of the tongue towards the pharynx, performed with the participation of the corresponding muscles and accompanied by a rapid movement of the head, which promotes the movement of grains accumulated in the lingual vestibule. At this time, the pharynx expands due to its partial attachment to the area bordering the spinal column. These processes cause an increase in pressure in the pharyngeal cavity. In the area of ​​the esophagus, after exceeding a certain threshold of irritation, peristalsis begins. Small glands located in the upper part of the esophagus secrete additional amounts of mucin into passing portions of food. After this, the food, under the influence of peristaltic contractions of the esophageal wall, slips into the crop.

In geese and ducks, instead of a crop, there is an expansion in the upper part of the esophagus. In chickens, the crop is an expansion of the middle part of the esophagus, which consists of the left and right crop sacs.

The inner surface of the goiter is lined with stratified squamous epithelium; The alveolar tubular glands, located in their own connective tissue layer of the mucosa, secrete mucus that does not contain enzymes. Digestion in the crop occurs due to the enzymes of food and bacteria and, to a small extent, due to the amylolytic enzymes of the salivary glands, which are poorly developed in birds. In 1 g of crop contents there are 108 cells, mainly aerobic microorganisms and lactobacilli. There are also fungi and yeast cells.

Microflora carries out proteolysis, lipolysis and especially amylolysis of feed. Fiber in the crop is practically not broken down; part of the starch is hydrolyzed to maltose and glucose. The latter (like free sugars in the feed) is fermented to form lactic acid, but not large quantity VFA and alcohol (maximum formation at 4-5 hours after feeding). In total, 15-20% of incoming carbohydrates are digested in the crop. Fermentation products can be absorbed into the blood and used as energy sources.

Proteolytic and lipolytic processes in the crop are of less importance: when feeding with a grain mixture, the mobilization of these components is hardly possible at all, and when feeding with soft feed, the food is in the crop for a short time - 1-3 hours (corn and wheat grains are retained in the crop for up to 16-- 18 hours). Apparently, with free access to feed, when the crop is regularly emptied, microbial proteolysis and lipolysis do not exceed 7-10%. Removing the crop reduces feed intake at one time and disrupts the normal rhythm of feed entering the stomach.

Impulses coming from an empty stomach cause contraction of the goiter. Filling the stomach with food inhibits the reduction of the crop, and the movement of food from it temporarily stops. Motility of the crop begins 35-40 minutes after ingestion of food. It manifests itself in the form of periodic series of contractions (10-12 per 1 hour) lasting 20-30 seconds each, with a force of 8-12 mm Hg. Art.

The vagus nerves stimulate the motility of the goiter; after cutting these nerves, the goiter does not shrink.

During the period of feeding the chicks, male and female pigeons develop a special liquid in their crops. milky. It serves to feed the chicks and contains fats, proteins, minerals and enzymes. All these substances are formed from degenerating and exfoliating cells of the mucous epithelium of the goiter.

Digestion in the stomach. From the crop, the feed mass flows through the lower (recrotal) segment of the esophagus into the glandular stomach-- ampoule-shaped expansion of the digestive tube with thickened walls (Fig. 2). In its mucous membrane there are superficial glands such as crypts, in the submucosal layer there are complex alveolar glands corresponding to the glands of the fundic part of the stomach of mammals: they produce gastric juice and hydrochloric acid. The total acidity of the juice ranges from 0.2 to 0.5% HC1, in adult birds it is mainly free, in young birds up to 20-30 days old it is bound (pH value of pure gastric juice is 1.4-2.0). All proteolytic enzymes are, according to modern data, varieties of pepsin with different optimum pH (from 1.0 to 3.5-4.0). Data on the presence of lipase and chymosin (rennin) in gastric juice are not convincing.

The feed mass from the crop passes through the glandular stomach in transit, almost without stopping; it acts as an irritant that causes juice secretion. The juice flows along with the food into the gizzard, where the main process of gastric digestion occurs. Since under normal conditions, with free access to food, the stomach of birds is never empty, juice secretion occurs continuously from the first days of life, changing in waves throughout the day.

According to the literature, birds have all three phases of gastric juice secretion complex reflex, gastric and intestinal. This is confirmed by experiments with imaginary feeding of birds, transection of the vagus nerves, and parenteral administration of gastrin and histamine. On average, from 6 to 16 ml of juice per 1 kg of live weight per hour is released. This indicator, as well as the total excretion of pepsin in juice, is higher in birds than in mammals.

The gastric juice of chickens and turkeys has the greatest digestive power, the least - of geese; duck juice occupies an intermediate position.

Muscle stomach-- a disc-shaped organ connected by a short isthmus to the glandular stomach. It is based on two pairs of powerful smooth muscles - main and intermediate. The cavity has a bag-like, slit-like shape, the entrance to and exit from the stomach are close together. The inside of the stomach is covered with hard cuticle, formed by the hardened secretion of the glands located underneath. The cuticle is constantly renewed.

In many birds of prey, the muscular stomach serves as a continuation of the glandular stomach and, therefore, it is considered a modification of the pyloric part.

In the muscular stomach, food is mechanically processed (ground) and proteins are hydrolyzed under the influence of proteinases from the glandular stomach juice. During 2-4 hours of stay in the muscular stomach, 35-50% of the protein supplied with food is broken down mainly into polypeptides (pH of the contents 2.5-3.5). Some carbohydrates and lipids (10-15%) are also digested here. This may be due to the action of enzymes in pancreatic juice thrown into the stomach from the duodenum.

Motor function of the stomach consists of regular movements of the glandular stomach and synchronous rotational-tonic contractions of the muscular stomach, followed by movements of the duodenum. The frequency of contractions is 2--4 per 1 minute after feeding and 1--2 per 5 minutes at rest. In this case, the pressure in the cavity of the muscular stomach increases to 100-160 mm Hg. Art. in chickens and up to 250 mm Hg. Art. in geese, this ensures crushing, grinding (with the help of gravel, glass, etc.) and compaction of the contents. The regulation of gastric motility in birds is, in principle, similar to mammals, although the influence of the vagus nerves prevails; when they are cut, the motility and secretory activity of the stomach are inhibited.

Digestion in the small intestine. If the function of the crop, glandular and muscular stomachs contribute, first of all, to the mechanical and digestive processes themselves, then in the relatively short small intestine of the bird absorption processes occur. Morphologically and functionally, the small intestine is divided into the duodenum, small intestine and ileum. In the mucous membrane there are Lieberkühn's crypts, into which the ducts of the intestinal glands themselves open. The surface of the mucous membrane is equipped with long villi. The superficial layer of villi, facing the lumen, consists of densely located columnar epithelial cells.

The duration of stay of chyme in the small intestine is 1-2 hours.

The contents of the stomach pass into the duodenum in separate small portions (in ducks) or as a continuous mass (in geese). The length of the intestines in birds is relatively small, only 3-7 times the length of their body (and in mammals 15-30 times). Thus, in chickens, the total length of the intestine ranges from 1.2 to 2.6 m. In this regard, food passes through the gastrointestinal tract quickly (in chickens on average within 24 hours).

Birds have a well-developed pancreas; there are several pancreatic (usually 3) and several bile (usually 2) ducts, opening as a common papilla into the ascending limb of the duodenum. Pancreatic juice and bile are secreted continuously. Adult chickens secrete an average of 25 ml of pancreatic juice and approximately the same amount of bile per 1 kg of weight per hour. This is higher than that of other animals (10-15). The same enzymes found in pancreatic juice as in mammals, except lactase. Lipase hydrolyzes mainly triglycerides containing unsaturated fatty acid, promotes the formation of chylomicrons. Amylase was found in bile; The main one among cholic acids is chenodeoxycholic acid.

The main phases of movements of the small intestine in poultry consist of peristalsis, antiperistalsis and the resting stage. Peristaltic waves, resulting from contractions of the annular muscles, quickly spread to individual areas of the intestine. After the peristaltic wave, the ring muscles do not relax, but an antiperistaltic wave immediately appears in the opposite direction. The movements of the stomach and duodenum are especially closely coordinated with each other. Peristaltic waves, starting in the glandular stomach, regularly spread through the intermediate muscles to the duodenum. The peristalsis of the duodenum, starting directly from the pylorus, is replaced, as in the underlying parts of the small intestine, by an antiperistaltic wave. These movements of the small intestine, characteristic of poultry, ensure intense mixing and shaking of the contents, as well as close contact with the surface of the long villi. The regulation of motility of the small intestine is carried out by nerve plexuses embedded in its wall, as well as through sympathetic and parasympathetic nerve fibers.

The pH value in the gastrointestinal tract of poultry ranges from slightly acidic to slightly alkaline.

The biochemical processes of digestion in the cecum largely depend on both enzymes coming from the small intestine and microflora enzymes. Along with the enzymatic breakdown of carbohydrates, proteins and fats under the influence of residual amounts of enzymes of the small intestine, processes of proteolysis and breakdown of cellulose with the participation of microorganisms occur in the cecum. The role of digestion in the cecum in terms of the use of fiber is small, since only a small proportion of the food mass passing through the entire digestive tract ends up here.

Due to the rapid passage of feed through digestive tract, intensive digestion in the small intestine and the insignificant participation of the bacterial microflora of the cecum in the digestion of crude fiber, it is more economically profitable to feed poultry feed poor in crude fiber.

Absorption in birds is essentially the same as in mammals. The mucous membrane of the small intestine has villi arranged in zigzag, spirally twisting rows. This arrangement of the villi causes a peculiar movement of the contents and an increase in the suction surface. The absorption process in birds is intensive in the cecum and even in the cloaca.

The large intestine ends in an expanded section - the cloaca. Two ureters and excretory openings of the genital organs - sperm ducts or oviducts - open into its cavity. Feces are formed in the cloaca. In birds it is semi-liquid (74% water) and is excreted along with urine. A white film of urea crystals forms on the surface of the stool. Bowel movement occurs in the same way as in mammals.

Duration of stay of feed in individual areas gastrointestinal tract and the speed of their movement through the entire digestive canal depends on various factors and, first of all, on the properties of the food. The duration of stay of wheat in the crop of chickens is (depending on the quantity) 3-14 hours, corn 25 hours, barley and millet 20, and barley derti - 16 hours. Emptying of the cecum in chickens begins no earlier than 48 hours and ends only 120 hours after ingestion of food. It is noted that at low ambient temperatures, the movement of contents accelerates, and with vitamin deficiencies it slows down almost 2 times.

The introduction of intensive forms of keeping poultry creates conditions that are significantly different from the natural ones to which the bird adapted in the process of its evolutionary development. Therefore, knowledge on the peculiarities of the manifestation of the life processes of birds in conditions of industrial rearing is absolutely necessary in order to have a more favorable effect not only on their behavior, but also on productivity.

Birds' evaluation of food, i.e. the preference given to a certain food over another is a product of optical and tactile perception. This preference depends on the type of food expected and the time the bird has to eat it. Turkeys and chickens, when eating mealy feeds, require significantly more time to become satiated than when eating grains or pellets (turkeys, for example, need 16 minutes to saturate with pellets, 136 minutes with mealy feeds).

The optimal particle size of poultry feed is determined primarily by the size of the beak and the width of the esophagus. For chickens and geese, these parameters are satisfied by wheat grains, for pigeons - hemp, and for ducks - corn. The bird usually consumes granular feed of the appropriate size immediately; In the absence of feed with particles of the required size, preference is given to smaller particles. The bird must be accustomed to eating large grains, for which it usually needs to starve. If the bird overcomes the initial hostility, then subsequently it always chooses the largest grains from the food first. Only with the onset of saturation does she begin to eat more small grains, which are easier for her to swallow.

The state of the environment also plays a big role. As the ambient temperature rises, the palatability of feed quickly decreases. If at the same time the body temperature rises above 42 0 C, the chickens stop pecking at food, get worried and excitedly run from place to place. It is of interest to observe the rate of food consumption at in different ways distribution in caged chicken conditions. Cage batteries with a chain feeder in most cases turn on automatically at certain intervals. Chickens get so used to these intervals that a few minutes before turning on the feeder they stick their heads out of the cage and rarely take the food in the feeder. As soon as the chain starts moving, all the chickens begin to peck at the same time, although before the chain was turned on, there was the same food in the feeder. Something similar happens when distributing feed with straddle loaders. Chickens begin to peck food mainly after the loader passes, even in cases when an empty cart passes, which does not supply any feed to the feeders.

The rate of feed intake also depends on whether the bird has free access to feed or whether this access is limited by time. Changing the form of feed (loose mixture, granules, grains) also caused its increased consumption if the bird got used to the new type of diet. So, when a bird that has been constantly receiving granulated food is replaced with granules with a loose mixture, the palatability of the latter decreases and increases again only after getting used to it (after a few days).

When placing feeders and drinkers in the poultry house, it is necessary to remember the tendency of birds to form groups, for which it is necessary to provide areas of about 12-15 m 2 in size. In order not to force chickens to leave their area, a feeder, a drinker and nests for laying eggs are placed in it. The distance between these points should not exceed 3-5 m.

Birds depend largely on proper nutrition. Unfortunately, at home, our feathered friends quite often eat incorrectly, and this happens not because we love them little, but because of a lack of knowledge about the peculiarities of the digestive system of birds. Let's try to understand its structure and physiology.

In general terms, the digestive system is a hollow tube from the beak to the cloaca. The system accepts food, secretes juice with enzymes that break down food, absorbs the resulting substances and removes undigested residues. The principle of the structure of the digestive system and its functions are the same in all birds, however, there are differences in details associated with the diet and behavior of a particular group of birds.

The organs of the avian digestive system include:

· beak;

· oral cavity;

· esophagus;

goiter (not in all species);

· glandular stomach;

· muscular stomach;

· liver;

· pancreas;

· intestines;

· cloaca.

Let's look at it in order:

Beak

Everyone has modern birds no teeth. Birds got rid of teeth in the process of evolution, since teeth weigh down the head, thereby making flight more difficult. The beak and oral cavity of birds are intended exclusively for obtaining food, as well as transporting it into the esophagus and further into the stomach.

Parrots have features in the structure of their beaks, which we will dwell on a little (Fig. 2). The beak is a stratum corneum or cornea that covers the bony formation of the jaws, both externally and internally. inside beak. The inside of the beak is made of bone. The upper part of the beak - the beak - consists of three bones: the premaxillary, jaw and nasal. The lower part - the mandible - consists of a larger number of small bones. Parrots have a special tendon ligament between the beak bones and the skull. The upper part of the beak in parrots is not fused with the skull, like in other birds, which allows the upper beak to be moved. A movable upper jaw and highly developed muscles that move it are distinctive features of the structure of a parrot's beak.

Rice. 2. Parrot skull

A parrot's beak constantly grows and wears out from work. Growth rates depend on the type of parrot. The cornea grows at the base of the beak and moves forward, replacing those layers that are worn away. Thus, any damage to the cornea of ​​the beak, scratches and small cracks eventually move to the tip of the beak and disappear. Deep cracks and damage to the skin at the base of the beak are dangerous to the health of all birds; in case of such injuries, you should immediately consult a doctor. A complete change of the stratum corneum occurs in approximately six months. The change of the cornea of ​​the mandible occurs a little faster. A complete change of the horny sheath in budgerigars occurs within a few months. Most parrots, including parrots, have special grooves on the inside of the beak that resemble a grater, which are used for grinding food. Depending on the type of parrot, the horny membrane of the beak has a different color. In some species, the mandible and mandible differ in color.

A parrot's beak is very sensitive. At the end of the beak there are special receptors that allow you to recognize cold, heat, the shape of an object, and also feel touch. The beak of parrots is very strong, and at the same time precise and neat. The strength of the beak depends on the size and structure of the bird. For example, it can crack even very hard nuts with its beak, but it can also peck seeds from strawberries. It is interesting to watch how a macaw feeds chicks that are smaller than its beak and does it surprisingly carefully.

It is precisely because of the constant growth of the beak that parrots need unlimited access to devices for grinding down the beak (mineral stones, sepia, special perches, branches of trees and shrubs). For the natural grinding of the beak, the parrot also needs vertical, diagonal perches, ladders, along which the parrot climbs with the help of its beak. A parrot's diet should consist not only of soft food, but also of hard grain. If the parrot does not have the opportunity to grind down its beak, then it inevitably overgrows (Fig. 3), and the bird loses the ability to normally capture food, which leads to a fairly rapid exhaustion of the parrot.

Oral cavity

The digestion process begins when food enters the mouth. The oral cavity is lined with stratified ectodermal epithelium. Most birds have salivary glands that secrete saliva, which moistens the food and begins to digest it. Processing food with saliva greatly facilitates its movement through the esophagus. The salivary glands are poorly developed in all parrots and only slightly moisten food. The tongue is located at the bottom of the oral cavity. Its skeletal part is formed by the sublingual apparatus. In birds, the tongue is pointed at the front and lacks muscles in its thickness. The shape and functions of the tongue, like the beak, depend on the bird’s lifestyle. The tongue can be used to hold food, manipulate it in the mouth, feel and taste. The tongue is distinguished by the strong development of the stratum corneum on its surface. Budgerigars have a fleshy tongue. There are taste buds on the palate and pharynx, and there are a small number of them on the tongue. Parrots have a subtle sense of taste. Despite the fact that the beak of parrots is hard and horny, the sense of touch is highly developed in the mouth of parrots. A well-feeling, dexterous tongue allows birds to turn the seeds into the best position in order to bite through them and get the grain.

Goiter

Behind the tongue lies the laryngeal fissure, behind which the oral cavity imperceptibly passes into the intestinal tube, i.e., the esophagus, which lies under the skin of the neck and serves to carry food. The walls of the esophagus do not secrete any digestive juices; it is intended solely for transporting food to the stomach. Swallowed food ends up in a special lower extension of the esophagus, the goiter, for several hours (Fig. 4). The walls of the crop, in turn, can contract, pushing softened food further into the stomach. Not all birds have it, except parrots, for example, pigeons, chickens, daytime raptors, canaries, and finches have a goiter. Birds need a gradual but constant intake of food into the stomach, so the goiter gives them the opportunity to first eat a lot of food at once, and then ensures that it enters the stomach in small portions. Sometimes food passes into the glandular stomach without being retained in the crop. This happens, for example, when a bird is forced to starve for some time.

Stomach

Birds swallow unchewed food and its processing begins directly in the stomach. From the esophagus, food enters the glandular stomach. Its walls secrete strong acid and some enzymes in abundance, which trigger the process of digestion of food, which soon passes into the second stomach. The glandular stomach is not clearly demarcated from the esophagus flowing into it and differs only in thicker walls and an abundance of glands that secrete digestive enzymes. The second part of the stomach is the muscular stomach (Fig. 4). It is a very powerful organ with a tough, rough lining inside (the cuticle) that crushes the seeds into a paste. The cuticle is a hardened secretion of the digestive glands of the stomach. Food richly moistened with digestive enzymes is ground in the muscular stomach due to rhythmic contractions of its walls. Grinding of food is facilitated by pebbles (gastroliths) swallowed by granivorous birds, which accumulate in the stomach cavity and play the role of millstones. The retention of pebbles in the stomach is helped by the cuticle, which has a slight fold, which allows the pebbles to perform their function. In the absence of stones in the gizzard of birds, the cuticle wears off and this, in turn, leads to the development of a disease (cuticulitis). With this disease, birds exhibit food selectivity. It turns out that the muscular stomach of birds performs the same function as the teeth of mammals when chewing food. That is why birds need to add pebbles and shell rock to the feeder. At the same time, it is not recommended to give the bird minerals with dyes and odors, and the size of the mineral particles should be equal to the size of the grain mixture that the bird eats. Parrots do not need gastroliths.

In species that eat seeds and other solid foods, the muscle walls of this section are especially thick. On the contrary, in birds that consume delicate food, nectar or fruit pulp, there is virtually no muscular stomach; for example, in tropical American tanagers it is only a small protrusion on the wall of the glandular stomach. In many birds of prey, flat round pellets are formed in the muscular stomach from indigestible parts of food, in particular bones, feathers, hair and hard parts of insects, which are periodically regurgitated.

Small intestine

Behind the muscular stomach is the duodenum (Fig. 5). It receives digestive juices from the pancreas and bile from the gallbladder. Digestive juices consist of enzymes that can convert starch into sugar and break down proteins and fats into fatty acids. Bile, in turn, promotes the dissolution of fatty acids.

Interior features of the bird. Their relationship to productivity and feeding practices

Digestive system in birds it begins with the oropharyngeal cavity. The beak consists of a mandible and a mandible, covered with a horny sheath - rhamphotheca. The pharynx passes directly into the esophagus (oesophagus), which is a tube with easily extensible walls.

In chickens and turkeys, in the lower third of the neck, the esophagus has a spherical expansion - goiter (ingluvies). The crop is a temporary location for food reserves. Under the epithelial layer lining both the esophagus and the crop are glands that secrete mucus. This mucus does not contain any amylolytic enzyme. However, amylolytic processes occur in the crop under the influence of amylolytic enzymes in saliva coming from the oral cavity along with food. In the crop, the food softens and is partially digested.

The stomach of birds is represented by two sections: glandular (proventrieulus) and muscular (ventriculus). The glandular stomach is a relatively short, thick-walled tube located between the final segment of the esophagus and the muscular stomach. Under the mucous membrane of the glandular stomach there are complex tubular glands that open into the stomach cavity in the form of pores on the surface of papillary elevations. The glands secrete pepsinogen and hydrochloric acid.

Chicken digestive system (diagram)

1 – oropharynx; 2 – esophagus; 3 – goiter; 4 – glandular stomach; 5 – muscular stomach; 6 - duodenum; 7 – pancreas;

8 – gallbladder; 9 – liver; 10 - small intestine; 11 – ileum; 12 – blind processes of the intestine; 13 – rectum; 14 – cloaca

From the outside, the muscular stomach is a disc-shaped organ formed by two pairs of muscles: main (anterior and posterior) and intermediate (upper and lower).

The intermediate muscles are located asymmetrically, which creates conditions not only for squeezing, but also for grinding of food located in the stomach cavity. The inside of the muscular stomach is lined with cuticle - a dense chitin-like film. It is especially developed in granivorous birds and plays important role when grinding feed. As the cuticle wears out, it grows from the inside due to the secretion of glands located in the mucous membrane. Powerful contractions of the muscular stomach cause the feed to be crushed. The grinding of feed is facilitated by pebbles swallowed by the bird: the most suitable are quartzite pebbles 2.5-3 mm in diameter for chickens and up to 10 mm for adult chickens.

The length of the intestines in chickens is 180 cm and exceeds the body length by 6 times.

The intestines in birds are divided into duodenum, small intestine, rectum, cecum and cloaca.

The duodenum (duodenum), starting from the pyloric opening of the muscular stomach, forms a simple long loop in which the pancreas is located. The length of the duodenum in chickens is about 30 cm.

The pancreas opens into a duct into the duodenum. Pancreatic juice contains proteolytic enzymes (trypsin and erepsin), an amylolytic enzyme (amylase) and a lipolytic enzyme (lipase or steapsin). Trypsin in pancreatic juice is in the inactive form of trypsinogen, which is activated in the intestine under the influence of the intestinal enzyme enterokinase. Trypsin and erepsin break down proteins, albumoses and peptones into amino acids. Digestion in the intestines of birds is ensured almost exclusively by pancreatic juice.

The bile ducts of the liver also open into the duodenum. The liver (hepar) reaches 1/25 of the bird's body weight. Bile, produced in the liver, helps emulsify fats, preparing them for the action of a lipolytic enzyme, activating this enzyme. Bile acids form easily soluble compounds with the products of fat breakdown, which are well absorbed through the intestinal wall.

The small intestine, conventionally divided into jejunum and ileum, reaches a length of 150 cm in chickens. At the border of the small and rectal intestines, paired cecums open, having a length of 15-25 cm in chickens. The absorption of feed nutrients occurs in the small intestine. Part of the chyme containing small particles of food enters the cecum, where fiber is digested and water is absorbed.

The rectum is short, its length in chickens is 6-7 cm. The cloaca is the final, significantly expanded part of the intestine. The ureters open into the middle section of the cloaca, as well as the vas deferens in males and the oviduct in females. When defecating in birds, except ostriches, feces are excreted along with urine.

Anatomical indices are used to characterize the development of the alimentary tract.

Due to the fact that birds need to travel long distances, their internal structure is somewhat unique. Some individuals satisfy their natural needs during flight, including eating. In the body of birds, several vital systems are compactly packed with the appropriate organs in them, allowing, if necessary, to 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

For bird food to become fuel, it must undergo mechanical, chemical and physical processing. The digestive apparatus of birds is capable of performing 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, crop, glandular stomach, muscular stomach, duodenum, liver, small intestine, gallbladder, caeca, 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 promptly replenish expended energy, metabolic processes in their bodies occur intensively. The structure of the digestive and assimilation organs ensures rapid digestion. For each individual bird species, this speed varies depending on the type of food. Due to the above reasons, unlike reptiles, the structure of the feeding apparatus in birds is much more complex. Based on this, several characteristic features physiology of birds:

• plasticity of organs;
• intensity of food digestion;
• speed of feed passage;
• 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 operation is to break down feed with the help of enzymes, absorb the optimal amount of necessary substances into the blood and remove undigested waste from the body. With the help of the bird's beak, food enters the oral cavity and moves through the esophagus into the stomach, which consists of two parts. In the glandular one, it is exposed to gastric juice, which ensures its further processing. In the muscular layer, lined with a keratinized layer, the feed is ground to a uniform consistency. Then the crushed mass penetrates 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 intestines are removed to the outside.

Beak

Birds do not have teeth, which significantly reduces the mass of the jaws and the skull itself. Instead, their upper (upper beak) and lower (underbeak) parts are placed in horny sheaths. The jaw base is represented by the premaxillary and mandibular bones. The upper section consists of the root, back and cutting edge, the lower section consists of the bottom, corner of the chin and edge. The beak acts as the lips and cheeks of birds. With its help, they hunt, capture, and sometimes tear apart their prey. Since birds cannot chew, they swallow their food whole. The shape of the beak can be 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 the hard palate, covered with a mucous layer. It is endowed with cone-shaped papillae of varying lengths. The outgrowths are directed backward and help move food into the esophagus. Special muscles help narrow the palatine fissure, thereby preventing fluid from entering the nasal cavity.

The tongue is an auxiliary organ for obtaining food in birds. Some individuals skillfully use it when capturing and pushing food. The tongue is located in the lower part of the mouth. The hyoid bone is a support for it and a bridge to the skull. It is dressed in a keratinized shell 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 characteristics of the lifestyle of individual individuals. In woodpeckers it is long and sticky, in birds of prey it is hard and short, in herbivores it is fleshy.

Pharynx

The pharynx passes between the oral cavity and the upper esophagus. Several paths open into it: the nasal and oral cavities, the slit of the larynx, connected to the respiratory system.

The pharyngeal cavity, like the oral cavity, contains several different glands. The development and number of these excretory organs determine the structural characteristics of birds. The digestive system of chickens is characterized by the strong development of glands in this area. This is due to the consumption of grains and other food wastes that are common to chickens and turkeys. The following types of glands are distinguished: salivary submandibular, sublingual, auricular, palatine, paired beak and maxillary. The layer of prismatic epithelium with which they are lined in birds is very high. The shape of the glands resembles a rosette.

Esophagus

The esophagus is divided into two parts: upper and lower. The first reaches from the pharynx to the crop, the second begins at the food pouch and ends with the glandular section of the stomach. The lining of the esophagus is lined with two layers of smooth muscles: longitudinal (external) and annular. Between them is a nerve plexus called the intermuscular or Auerbachian. 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 is facilitated by a secretion produced by sac-like organs located in the mucous layer.

Goiter

Not every bird has 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, upon entering the chest cavity, the esophagus expands significantly and forms a kind of reservoir for accumulating and processing food. In the crop, softening and mixing of feed occurs, as well as partial breakdown of carbohydrates. There are individuals whose esophagus looks like a tube of the same diameter along its entire length.

Gulls, pelicans and cormorants have an interesting feeding process for their chicks. Traveling from the place of prey to the nest, they use their crop as a purse, 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 glands of the crop. This foamy substance is commonly called bird's milk.

Stomach

The digestive system of birds has two stomachs: the glandular stomach, in which food is processed using chemical-enzymatic processes; and the muscular stomach, which grinds food mechanically. The second stomach contains pebbles for grinding food, acting as teeth. Intensive grinding of food is facilitated by highly developed muscles. Birds regurgitate undigested remains 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 accept vegetation and roughage products have a well-developed muscular stomach. Those who eat more delicate or animal foods have a better functioning glandular stomach.

Intestines

A distinctive feature of the bird's digestive system is its shortened intestine. As is the case with some other organs, this structure makes it possible to reduce the body weight of the bird, since food remains are not retained in it. The opening of the sphincter of the gizzard 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 gall bladder. As a result of the release of their enzymes, food is completely digested. Digestion and absorption of nutrients into the blood occurs along the entire length of the small intestine.

The pigeon's bile ducts are arranged in a unique way. At the place where the duodenum twists into a loop, the pancreas is located with two or three ducts. This also includes the bile ducts of the liver, so pigeons do not need a gall bladder.

Between the small and large intestines there are blind processes, which are developed only in birds that feed on vegetation. The rectum is the widest part of the intestine. In chickens it is about 7 cm in length and 2 cm in diameter. In agricultural individuals, the 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, in connection with the ability to fly. The excretory system consists of the ureters and paired kidneys. Due to the fact that birds do not have a bladder, metabolic products do not accumulate in their bodies. This significantly affects their weight. In females, the right ovary is missing.

The caudal segment of the rectum is expanded and represents a cloaca, covered with one layer of prismatic epithelium. It is divided into three parts by 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 an organ of copulation. The border between the rectum and the cloaca is the internal sphincter in the form of a ring-shaped muscle. The cloaca opening 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 the environment and their habitat.