Features of the digestive system of cats and dogs. The pancreas and its role in digestion. dog digestion gastric intestinal

First of all, we must not forget that the dog is a predator, whose diet consists mainly of foods high in protein. The structure of the dog's body, starting with the dental formula - the number and shape of teeth, the structure of the jaw apparatus - and ending with the presence of specific enzymes, is adapted for eating and digesting food of animal origin. The dog practically does not chew food, tearing it into pieces. large pieces and swallowing, and powerful jaws allow the dog to gnaw large bones.

Unlike cats, dogs have strong molars, which indicates the ability of dogs to utilize plant foods; consequently, the dental formula of dogs suggests that dogs are omnivores, whereas cats' diets should be strictly carnivorous.

The digestive process starts at oral cavity with salivation.

Saliva is 99% water and 1% is mucus, inorganic salts and enzymes. Mucus has an effective lubricating effect and facilitates the process of swallowing, especially dry food. Unlike humans, the saliva of dogs and cats does not contain the starch-digesting enzyme, alpha-amylase, which prevents starch digestion from starting in the mouth, esophagus, and for some time in the stomach. At the same time, dog saliva contains a huge amount of a concentrated enzyme - lysozyme, which has a bactericidal effect. The dog's saliva has importance in digestion. It helps to moisturize the food, and after the process of eating food, it cleans the oral cavity.

If we compare the stomach of a dog with the stomach of a herbivore, then in a dog it is much smaller and has a single-chamber structure, and the intestines are much shorter. The dog's gastric juice has hyperacidity, which contributes to the rapid digestion of protein foods, and high content hydrochloric acid disinfects the stomach. Meat in the stomach of a dog is digested on average from 10 to 12 hours.

However, in addition to meat, which is most diet, the dog eats quite diversely. The composition of her food may include foods rich in fiber and carbohydrates.

Features of digestion of food rich in carbohydrates and fiber are different. Carbohydrate feed passes into the intestines faster, as does liquid food. Food rich in fiber is also digested faster, but stays longer in the intestines. Thus, it helps to cleanse the intestines and serves as an additional stimulus for the production of enzymes that break down protein.

The entire main process of digestion takes place in the duodenum, where the concentration of digestive enzymes is especially high. Pancreatic juice also enters here, which breaks down mainly proteins and carbohydrates and bile, which helps to digest fats. Digestion of food ends in small intestine, with the participation of intestinal juice, which also contains enzymes that finally break down food residues.
In the large intestine, water is absorbed and feces are formed.

When choosing a balanced diet for dogs, it is imperative to take into account a number of interrelated factors that cannot be considered separately. These include nutrient content, energy content, digestibility and taste qualities stern. A balanced diet is a source of all the key nutrients needed to meet the animal's needs. The role of a balanced diet is that it contributes to the maintenance of a long and healthy life of the dog and reduces their susceptibility to disease.

Understanding the mechanism of dog digestion, owners are more serious about diet and feeding, because until now the most common reasons for contacting veterinarians were violations in work. digestive system and diseases of the gastrointestinal tract.

Service Dog [Training Guide for Specialists service dog breeding] Krushinsky Leonid Viktorovich

3. Digestive system

The dog's body is built from complex organic substances - proteins, carbohydrates, fats. The most important of these is protein. In addition to these organic substances, the body also contains inorganic substances - salts and a large amount of water (from 65 to 90% of body weight). All these substances are equally necessary for the life of the organism. In the process of life, these substances are consumed, so the body needs to constantly replenish them. This replenishment comes from food. However, the food that the animal receives cannot be used by the body for replenishment until it has undergone appropriate processing, i.e. chemical decomposition into gastrointestinal tract to such a state in which it is able to be absorbed into the blood and can be absorbed by the cells of the body. This processing of food constitutes the process of digestion, which takes place in a special system of the digestive organs (Fig. 40).

Rice. 40. The layout of the internal organs of a mammal

1 - oral cavity; 2 - throat; 3 - esophagus; 4 - stomach; 5 - liver; 6 - pancreas; 7 - middle (small) intestine; 8, 9, 10 - back (large) intestine

The digestive system, if we consider it schematically, is a tube that begins with the oral cavity and ends with the anus.

Different sections of the digestive tube have an unequal width. The area starting from the oral cavity and pharynx has a narrow lumen and is called the esophagus. Then the lumen of the digestive tube expands significantly, forming the stomach, and narrows again, forming the intestines.

The wall of the digestive tube in different parts is built differently, which is associated with their various functions. In general, the wall of the digestive tube consists of: a) the inner or mucous membrane, b) the middle or muscular layer, and iv) the outer serous membrane. The mucous membrane lines the cavity of the entire digestive tube and, depending on the function in different areas, has different structure. The muscular layer consists of two layers of smooth muscle fibers - the superficial one, which has longitudinal fibers, and the inner one, consisting of circular fibers. As a result of alternating contractions of the longitudinal and circular muscle fibers, the digestive tube moves, resembling the movement of a worm, called peristalsis. The serous membrane covers the portions of the alimentary canal facing the abdominal cavity. She highlights serous fluid, which facilitates the sliding of the tube when it moves among neighboring organs or cavity walls.

The digestive system is made up of:

a) the oral cavity with the organs in it;

b) pharynx;

c) esophagus;

d) stomach;

e) small and large intestines, as well as the liver and pancreas.

Oral cavity. The oral cavity is the initial section of the alimentary canal and serves to capture, crush and wetting food. It also tastes food. The mucous membrane of the oral cavity is covered with a protective epithelium that can withstand the touch and friction of solid food. From the sides, the oral cavity is limited by the cheeks, from the front - by the lips that close the oral fissure. The lips are two skin folds surrounding the entrance to the oral cavity. In a dog, the lips are not very mobile and almost do not participate in the capture of food. A dog grasps solid food with its teeth, and liquid food with its tongue. The mucous membrane covering the dental processes of the jaw bones forms the so-called gums in the form of dense rollers. In the area of top wall oral cavity mucous membrane forms a hard palate in the form of transverse scallops. The continuation of the hard palate towards the pharynx is the soft palate, or palatine curtain. It looks like a fold separating the oral cavity from the pharynx. With special muscles palatine curtain can rise, resulting in an increase in the opening connecting the oral cavity with the pharynx.

Language. The tongue is a muscular organ consisting of striated muscles with fibers running in different directions. Due to the reduction of individual muscle groups, the tongue can produce all kinds of movements. Such mobility of the tongue allows them to capture liquid food and water (lap), mix, put under the tooth and push the food into the throat (Fig. 41).

Rice. 41. Dog tongue

1 - top of the tongue; 2 - the body of the tongue; 3 - the root of the language; a - fungiform papillae; b - roller-shaped papillae; c - foliate papillae; g - groove of the back of the tongue

The mucous membrane of the tongue from below is smooth. From above, it has a rough surface due to the presence of filiform papillae on it. These papillae are of mechanical importance. They create a rough surface that makes it easier to hold food in the mouth. The tongue is distinguished by the tip of the tongue, the middle part - the body of the tongue, and the back part - the root of the tongue. The tip of the tongue is relatively thin and can be strongly extended. The tongue is attached to the hyoid bone. On the lateral surfaces of the tongue and on its back there are small protrusions, or taste buds - filiform, mushroom-shaped and leaf-shaped. Thin nerve fibers depart from these papillae. They are transmitted to the central nervous system of irritation from flavor substances food. In this part, the tongue is the organ of taste.

Teeth. The dog uses its teeth for grasping, biting and tearing food, as well as for defense and attack. The dog has 42 teeth, of which 20 are in the upper and 22 in the lower jaw. In my own way appearance teeth are different. The shape of the tooth depends on its purpose. The front teeth are called incisors. Their purpose is to grasp food. The dog has 6 incisors in the upper and lower jaws. The most anterior pair of incisors are called hooks. Next to them on either side are the middle incisors, and along the edges are the edges. The surface of the incisors in young dogs has a three-toothed shape. Fangs are located behind the edges. The fangs are a weapon of attack and self-defense, and also serve to hold the seized food and tear it to pieces. Behind the canines are the molars. AT upper jaw 12 molars, and in the lower - 14. They are equally distributed on the right and left sides. The molars have an uneven surface, with sharp tubercles, and serve to grind solid food. In this case, the lower jaw moves in the direction from the bottom up. Teeth are divided into milk and permanent. A dog is born without teeth. Teeth begin to erupt from the third week. First, the puppy develops milk teeth, which, through certain time fall out and are replaced by permanent ones. The incisors are the first to be replaced, starting from the age of two months of the puppy. Milk teeth are whiter and smaller than permanent ones (Fig. 42).

Rice. 42. Scheme of the structure of the tooth

1 - tooth hole in the jaw; 2 - dentin; 3 - cement; 4 - enamel; 5 - dental cavity; 6 - jaw bone cavity

The teeth are fixed in special recesses of the jaw bones. These depressions are called dental sockets. The part of the tooth that enters the hole is called the root, and the part that protrudes into the oral cavity is called the crown of the tooth. Each tooth is made up of a very dense substance called dentin. Dentin is harder than normal bone and serves as the backbone of the tooth. Inside the tooth there is a cavity containing dental pulp, or pulp. It contains blood vessels and nerves. In the area of ​​the crown, the tooth is covered with an even harder tissue - enamel. During the life of a dog, the crowns of the teeth are erased and the age of the dog is determined by the degree of their wear.

Salivary glands. Simultaneously with chewing food in the oral cavity, food is moistened with saliva, which is secreted salivary glands. Three pairs of large salivary glands secrete saliva into the oral cavity - parotid, submandibular and sublingual. These glands are located at some distance from the oral cavity and communicate with the last ducts. The parotid glands secrete watery saliva, sublingual - mucous, submandibular - mixed. Saliva is a clear or slightly turbid liquid that stretches into threads. As a rule, saliva is secreted simultaneously by all salivary glands and is a mixture of secretions from these glands. There is almost no continuous salivation in a dog. Salivation occurs as a result of mechanical or chemical irritation of the oral mucosa. Irritation from the oral mucosa travels along the nerves to the salivary center, located in medulla oblongata. From the salivary center, excitation is transmitted through the secretory nerve to the cells of the salivary glands, the cells of the glands are irritated and saliva is secreted. The intensity of secretion and the nature of saliva vary depending on the food. More saliva is secreted for dry food, less for watery food. The quality of the secreted saliva also depends on the nature of the food. For substances rejected by the dog - pepper, soda, etc. - saliva is released more viscous and thick. Especially developed in the dog is the secretion of saliva in response to mental excitations. If the dog is familiar with some food substance, then at the sight (show) of it, it always reacts with salivation. Unlike other animals, dog saliva does not contain enzymes. Therefore, in the oral cavity of a dog, food is not subjected to chemical decomposition (Fig. 43).

Rice. 43. Location of the salivary glands in a dog

1 - parotid gland; 2 - its duct; 3 - a large chewing muscle; 4 - submandibular gland: 5 - its duct; 6 - sublingual long duct gland; 7 - its duct; 8 - sublingual short duct gland

Pharynx. The pharynx is a joint pathway for food and air. Air passes through the pharynx from the nasal cavity to the larynx and back when breathing. Through it, food and drink enter the esophagus from the oral cavity. The pharynx is a funnel-shaped cavity covered with a mucous membrane, facing its expanded part towards the oral and nasal cavities, and the narrowed end towards the esophagus. The pharynx communicates with the oral cavity through the pharynx, and with the nasal cavity through openings called choanae. In the upper part of the pharynx, near the choanae, openings of the auditory tubes (Eustachian) open, through which the pharynx communicates with tympanic cavity middle ear. Behind the pharynx begins the esophagus.

Swallowing is a complex muscular act, which consists of the following: chewed and collected food moves to the pharynx with the help of the tongue; when food enters the pharynx, the entrance to the larynx is closed by the epiglottis; the larynx at this moment rises towards the root of the tongue, the cavity of the pharynx and the opening of the esophagus expand to receive the food coma, which is pushed into the esophagus by compression of the pharynx. The act of swallowing is the result of irritation of the mucous membrane of the root of the tongue and pharynx. Nerve center, which controls the act of swallowing, is embedded in the brain. With the defeat of this center, as well as the nerves going to the pharynx, the act of swallowing will not occur (Fig. 44).

Rice. 44. Half-scheme of the pharynx of a dog

1 - pharyngeal cavity; 2 - esophagus; 3 - larynx

Esophagus. The esophagus is a continuation of the pharynx and is a tube consisting of an outer connective tissue membrane, a muscular layer and a mucous membrane. The mucous membrane of the esophagus forms numerous folds, and therefore the walls of the esophagus at the time of passage of the food coma can expand. The esophagus, starting from the pharynx, goes along the neck, enters chest cavity, perforates the diaphragm (the muscular septum between the thoracic and oral cavities) and ends in the stomach. Due to the contractions of the muscles of the esophagus, the peristaltic movement of its walls occurs, and with the help of these movements, food is carried through the esophagus to the stomach. Peristaltic movements of the esophagus can also occur in the opposite direction, i.e. from the stomach to the pharynx. This movement of the esophagus occurs during vomiting.

The digestive organs following the esophagus lie in the abdominal cavity, occupying most of it. The abdominal cavity is formed: from below and from the sides by the abdominal muscles, in front - by the diaphragm, from above - by the lumbar and sacral vertebrae and behind - the pelvic bones (pelvic cavity). The abdominal cavity inside is lined with a thin serous membrane - the peritoneum.

Stomach. The stomach is the first section of the digestive tube where food is digested. The stomach is an enlarged and sac-like part of the digestive tube. It lies in the anterior abdominal cavity and mostly in the left hypochondrium. Normal stomach capacity in medium-sized dogs is 2–2.5 liters. The initial part of the stomach, adjacent to the esophagus, is called the entrance to the stomach. The part of the stomach adjacent to the exit site into the duodenum is called the pylorus. middle part forms the so-called fundus of the stomach. The wall of the stomach consists of an outer layer (serosa), a muscular layer (smooth muscles) and an inner layer (mucosa) (Fig. 45).

Rice. 45. Dog stomach

1 - esophagus; 2 - small curvature; 3 - gut; 4 - large curvature

In the wall of the stomach are glands that secrete gastric juice. Gastric juice is a colorless, clear, acidic liquid containing hydrochloric acid and special substances called enzymes. Under the action of gastric juice, digestion occurs mainly of food proteins. In addition to protein digestion, gastric juice has the ability to coagulate milk, dissolve calcium salts, which is important for their further digestion. Gastric juice also has strong disinfectant properties. There is a certain pattern in the secretion of gastric juice. In the absence of food, the gastric glands are at rest, as soon as the dog begins to eat or only sees familiar food, it enters a state of food excitement. And after a few minutes, the secretion of gastric juice begins in her stomach. Even one display of food gives an impetus to the glands to begin their activity, and this indicates the participation in this process of the higher parts of the central nervous system. The separation of gastric juice occurs in two phases. The first phase of the separation of gastric juice is the result of food irritation of the taste nerves of the oral cavity (during eating) or sensory organs at a distance (the dog sees food, smells it, etc.). Academician Pavlov calls this phase "appetizing".

The second phase (coming later) is called chemical. This phase is triggered by chemical irritants food, acting already directly on the gastric mucosa.

Gastric digestion is accompanied by a number of motor phenomena in the stomach. These movements are manifested in the form of wave-like contractions of the walls of the stomach towards the outlet. In the outlet part of the stomach, contractions occur in the form of deep annular ligations. Emptying of the stomach occurs at different times depending on the type of food. So, the meat remains in it for 10-12 hours.

The act of vomiting occurs by contracting the walls of the stomach, abdominal muscles and diaphragm while relaxing the walls of the esophagus. When vomiting, the larynx and supraglottic space close in the same way as when swallowing. Vomiting is a reflex act and can be caused by irritation of the root of the tongue, pharynx, stomach, intestines, abdominal muscles and uterus. The coordinated activity of a number of muscles involved in the act of vomiting indicates the presence of a vomiting center in the central nervous system (in the medulla oblongata). In a dog, vomiting appears as a result of irritation of the mucous membrane of the stomach or intestines by toxic substances that have entered the stomach with food or as a result of strong mechanical irritation of the pharynx, and likewise the esophagus, with solid parts of food. In these cases, vomiting should be considered as defensive reaction organism.

Vomiting can be induced artificially by introducing emetics into the body. medicinal substances. The action of these drugs is reduced to irritation of the vomiting center.

Intestines. The intestine is the continuation of the alimentary tube after it leaves the stomach. It is usually divided into two sections - thin and thick. At the border of these sections, the digestive tube forms a sac-like protrusion called the caecum, which is considered the beginning of the large intestine (Fig. 46).

Rice. 46. ​​Scheme of the section of the walls of the duodenum, jejunum and rectum

A - duodenum; B - skinny and iliac; C - straight line; 1 - villi; 2 - general intestinal glands; 3 - submucosal tissue; 4 and 5 - longitudinal and circular layer of muscle tissue; 6 - bile duct; 7 - liver; 8 - pancreatic duct; 9 - pancreas

The intestinal wall consists of mucous, muscular and serous membranes. The mucosa contains small glands that secrete intestinal juice. The serous membrane covers the entire intestine from the outside, rises up to the spine, and forms folds called the mesentery. The entire intestine is suspended on the mesentery in the abdominal cavity. Blood and lymphatic vessels and nerves pass through the mesentery to the intestines. The main function of the intestine is digestion, absorption, movement of contents and the formation of feces.

The small intestine is made up of the duodenum, jejunum, and ileum. The duodenum, starting from the stomach, forms an S-shaped gyrus and then goes under the spine approximately at the middle of the height of the abdominal cavity. Having reached the pelvis, it goes forward and passes into the jejunum. The mucous membrane forms numerous villi, representing, as it were, protrusions of the mucous membrane. Blood and lymphatic vessels approach the villi, into which they enter nutrients from the intestine. In the duodenum, a small part of the food is absorbed, in the intestinal mucosa there are glands that secrete intestinal juice. in the gyrus duodenum situated big gland called the pancreas. Its structure resembles salivary gland. The pancreas secretes juice into the duodenum. Along with pancreatic juice, bile produced by the liver is secreted into the duodenum. During digestion, bile enters the duodenum through the bile duct. Bile is a viscous, thick liquid brown, has the ability to decompose fats, enhance the action of pancreatic and intestinal juices, stimulates peristalsis, and also has disinfectant properties.

The process of digestion in the duodenum is as follows. Food processed in the stomach in the form of gruel moves in separate portions into the duodenum. This movement begins shortly after food enters the stomach. When the acidic food slurry from the stomach enters the duodenum, it irritates the intestinal mucosa and causes the secretion of bile, pancreatic and intestinal juices. Under the influence of these juices, chemical decomposition (digestion) of all constituent parts food. At the same time, the food gruel moves towards the jejunum. The jejunum and ileum form numerous loops in the abdominal cavity. The jejunum is located mainly in the central part of the abdominal cavity. She received the name "skinny" because the food slurry entering it from the duodenum becomes liquid, as a result of which this intestine, in comparison with others, has a collapsed appearance. The jejunum imperceptibly passes into the ileum. The latter goes to the right iliac region (hence its name) and here it passes into a small caecum and its continuation - the colon. The terminal section of the ileum has a highly developed muscular layer and a rather narrow lumen. This contributes to a more vigorous pushing of the food slurry into the large intestine and prevents it from returning to the small intestine.

The food gruel entering the jejunum and ileum undergoes further chemical decomposition in them, as a result of which the end products of the breakdown of proteins, carbohydrates and fats capable of absorption are obtained. Water and salts are absorbed unchanged. The absorption of nutrients into the body is the main function of the jejunum and ileum. long length intestines and the presence of a huge amount of villi, increasing almost 20 times inner surface intestines, provide absorption of all necessary for the body nutrients during the movement of the food mass through the intestines. With the help of villi, nutrients are absorbed from the intestines into the blood or lymph. Once in the blood, they are carried to the liver, where they undergo complex transformations. Some of them are deposited in the liver as a reserve, the other part is carried by the blood throughout the body. The cleavage products of animal proteins are absorbed in the amount of 95–99%, and vegetable proteins- 75–80%. Fats go first to lymphatic system. Together with the lymph, they enter the blood in the form of tiny particles, are carried throughout the body and deposited in fat depots (omentum, subcutaneous tissue and etc.). Water is absorbed along with the salts dissolved in it and rather quickly (5–6 minutes after ingestion) begins to be excreted in the urine. Admission enough nutrients in the body has an impact on the behavior of the dog. Restless before eating, she becomes calm after eating food, lies down and sometimes falls asleep.

The large intestine consists of the caecum, colon and rectum. The large intestine is distinctly separated from the small intestine. On their border there are special formations in the form of valves that prevent the reverse flow of food masses into the small intestine. By lenght colon many times shorter than thin.

The caecum, representing the first section of the thick section, is located on the border of the ileum and colon and has the form of a short sac-like protrusion. It is located in the right side of the abdominal cavity.

The colon is relatively long and presents a simple, smooth, narrow loop.

The rectum is the last section of the large intestine that ends at the anus.

In the region of the anus, two ducts open into the rectum. anal glands secreting a thick mass of secretion with a specific odor.

Around the hole are laid circular muscles that form the so-called sphincter, or obturator of the rectum.

The main difference in the structure of the large and small intestines is that the mucous membrane of the large intestines has only simple general intestinal glands. These glands secrete mucus and thereby help to move the contents of the intestine.

The processes of digestion in the large intestine partly continue only due to the juices that have come from the small intestines. Little absorption of nutrients occurs in the early part of the large intestine. Water is well absorbed. In the large section, and especially in the caecum, there are favorable conditions for the vital activity of various microbes, which are present there in large quantities. Under the influence of microbes, fermentation and decay of the contents occur with the formation of gases. In the back of the thick section, feces are formed. Kal represents remnants undigested food, particles of exfoliated epithelium of the mucous membrane, coloring substances (pigments) of bile, giving color to feces, salts, lumps of mucus and microbes. The amount and composition of feces varies depending on the composition of the food. So, for example, if a dog is fed bread, feces will be excreted more than when fed meat. The amount of feces increases with excessive feeding, since in this case part of the food is not digested.

The excretion of feces is a reflex act, caused by irritation of the intestinal walls with fecal masses when it is filled. The center of the reflex is in lumbar region spinal cord.

The time it takes for food to pass through the alimentary canal different dogs various. It depends on the composition of food, individuality and a number of other reasons. It is believed that food lingers in the alimentary canal of a dog for 12-15 hours. After 2-4 hours after eating, more than 1/3 of the meat fed to her continues to remain in the stomach of the dog, after 6 hours this amount is 1/4, after 9 hours - 1/10 and after 12 hours the stomach is empty. Vegetable food causes stronger peristalsis and therefore passes through the alimentary canal faster than meat (in a dog after 4-6 hours).

The following data can be given on the digestion and absorption of nutrients in the alimentary canal.

In a dog, almost half of the accepted amount of meat is digested after 2 hours, after 4 hours - almost 3/5, after 6 hours - 7/8, and after 12 hours almost all (96.5%). Rice in a dog is digested: after an hour - 8%, after 2 hours - 25%, after 3 hours - 50%, after 4 hours - 75%, after 6 hours - 90% and after 8 hours - 98%. Absorption of meat food in a dog does not occur during the first hour. After 2 hours, 36% is absorbed, after 4 hours - 50%, after 9 hours - 75% and after 12 hours - 95%. Rice is absorbed: after 2 hours - 20%, after 3 hours - 50%, after 4 hours - 75%, after 8 hours - almost 98%.

Liver. The liver is the most big gland in the body. It lies in the abdominal cavity, directly adjacent to the diaphragm, reaching both the right and left of the last ribs. With deep incisions, the dog's liver is divided into 6–7 lobes (Fig. 47).

Rice. 47. Dog liver

1 - left lobe; 2 - right share; 3 - left middle share; 4 - recess for the esophagus; 5 - portal vein; 6- gallbladder

On the curved surface of the liver, facing the intestines, there are so-called gates of the liver - a place where blood vessels and nerves enter and exit excretory duct. On the same side of the liver, between its lobes, lies the gallbladder in the form of a small sac. It accumulates and temporarily stores bile. From the gallbladder comes the bile duct, which flows into the duodenum. In addition to the hepatic arteries, a large so-called portal vein enters the gates of the liver. It collects blood from the stomach, intestines, pancreas and spleen and carries it to the liver, where it branches into small vessels (capillaries). During the passage between the cells of the liver, the blood, as it were, is filtered and cleared of toxic substances that have entered it from the intestines. Then the blood, collecting in the hepatic veins, is carried away from the liver through the posterior vena cava and flows into the general circulation.

The liver accumulates significant reserves of carbohydrates coming from the intestines. If necessary, the body uses these reserves.

Pancreas dogs are long and narrow. It adjoins the duodenum and in its structure resembles the salivary glands. It consists of a tissue that secretes pancreatic juice, and a special tissue scattered in the form of islands throughout the gland, which releases the hormone insulin into the blood. Pancreatic juice enters the duodenum through one or two ducts.