Sequence of digestive processes. Types of digestion. Breakdown and absorption of substances

Eating is a process for which every person leaves all his affairs and worries several times a day, because nutrition supplies his body with energy, strength and all the substances necessary for normal life. It is also important that food provides it with material for plastic processes, so that body tissues can grow and repair, and destroyed cells are replaced with new ones. After the body has received everything it needs from food, it turns into waste, which is eliminated from the body naturally.

The coordinated operation of such a complex mechanism is possible thanks to the digestive system, which digests food (its physical and chemical processing), absorbs digestion products (they are absorbed into the lymph and blood through the mucous membrane) and removes undigested residues.

Thus, the digestive system performs several important functions:

• Motor-mechanical (food is crushed, moved and excreted)
• Secretory (enzymes, digestive juices, saliva and bile are produced)
• Absorbent (proteins, fats, carbohydrates, vitamins, minerals and water are absorbed)
• Excretory (undigested food residues, excess of a number of ions, heavy metal salts are eliminated)

A little about the development of the digestive organs

The digestive system begins to develop in the first stages of development of the human embryo. After 7-8 days of development of the fertilized egg, the primary gut is formed from the endoderm (inner germ layer). On the 12th day, it is divided into two parts: the yolk sac (extra-embryonic part) and the future digestive tract - the gastrointestinal tract (intra-embryonic part).

Initially, the primary gut is not connected to the oropharyngeal and cloacal membranes. The first melts after 3 weeks of intrauterine development, and the second - after 3 months. If for some reason the membrane melting process is disrupted, anomalies appear in development.

After 4 weeks of embryo development, sections of the digestive tract begin to form:

• The pharynx, esophagus, stomach, segment of the duodenum (the liver and pancreas begin to form) are derivatives of the foregut
• Distal part, jejunum and ileum - derivatives of the midgut
• Sections of the large intestine - derivatives of the hindgut

The basis of the pancreas is made up of outgrowths of the foregut. Simultaneously with the glandular parenchyma, pancreatic islands are formed, consisting of epithelial strands. 8 weeks later, the hormone glucagon is immunochemically detected in alpha cells, and at week 12, the hormone insulin is detected in beta cells. Between the 18th and 20th weeks of gestation (pregnancy, the duration of which is determined by the number of complete weeks of gestation that have passed from the 1st day of the last menstruation to the moment of cutting the umbilical cord of the newborn), the activity of alpha and beta cells increases.

After the baby is born, the gastrointestinal tract continues to grow and develop. The formation of the gastrointestinal tract ends around the age of three.

Digestive organs and their functions

Along with studying the digestive organs and their functions, we will also analyze the path taken by food from the moment it enters the oral cavity.

The main function of converting food into substances necessary for the human body, as has already become clear, is performed by the gastrointestinal tract. It’s called a tract for a reason, because... is a nature-designed path for food, and its length is about 8 meters! The gastrointestinal tract is filled with all sorts of “regulatory devices”, with the help of which food, making stops, gradually goes its way.

The beginning of the digestive tract is the oral cavity, in which solid food is moistened with saliva and ground by the teeth. Saliva is secreted into it by three pairs of large and many small glands. During the process of eating, the secretion of saliva increases many times. In general, the glands secrete approximately 1 liter of saliva in 24 hours.

Saliva is required to moisten food lumps so that they can move further more easily, and also supplies an important enzyme - amylase or ptyalin, with the help of which carbohydrates begin to break down already in the oral cavity. In addition, saliva removes from the cavity any substances that irritate the mucous membrane (they enter the cavity by accident and are not food).

Lumps of food, chewed by teeth and moistened with saliva, when a person makes swallowing movements, pass through the mouth into the pharynx, bypass it and then go into the esophagus.

The esophagus can be described as a narrow (about 2-2.5 cm in diameter and about 25 cm in length) vertical tube that connects the pharynx and stomach. Despite the fact that the esophagus is not actively involved in food processing, its structure is similar to that of the underlying sections of the digestive system - the stomach and intestines: each of these organs has walls consisting of three layers.

What are these layers?

• The inner layer is formed by the mucous membrane. It contains different glands that differ in their characteristics in all parts of the gastrointestinal tract. Digestive juices are secreted from the glands, thanks to which food products can be broken down. They also secrete mucus, which is necessary to protect the inner surface of the digestive canal from the effects of spicy, rough and other irritating foods.
• The middle layer lies under the mucous membrane. It is a muscular sheath composed of longitudinal and circular muscles. The contractions of these muscles allow the food lumps to be tightly grasped, and then, using wave-like movements (these movements are called peristalsis), to push them further. Note that the muscles of the digestive canal are muscles of the smooth muscle group, and their contraction occurs involuntarily, unlike the muscles of the limbs, torso and face. For this reason, a person cannot relax or contract them at will. You can intentionally contract only the rectum with striated, not smooth, muscles.
• The outer layer is called the serosa. It has a shiny and smooth surface, and is composed mainly of dense connective tissue. A wide connective tissue plate called the mesentery originates from the outer layer of the stomach and intestines along its entire length. With its help, the digestive organs are connected to the posterior wall of the abdominal cavity. The mesentery contains lymphatic and blood vessels - they supply lymph and blood to the digestive organs and nerves that are responsible for their movements and secretion.

These are the main characteristics of the three layers of the walls of the digestive tract. Of course, each department has its own differences, but the general principle is the same for everyone, starting with the esophagus and ending with the rectum.

After passing through the esophagus, which takes about 6 seconds, the food enters the stomach.

The stomach is a so-called pouch, which has an elongated shape and an oblique location in the upper region of the abdominal cavity. The main part of the stomach is located to the left of the central section of the torso. It begins at the left dome of the diaphragm (the muscular septum separating the abdominal and thoracic cavities). The entrance to the stomach is where it connects to the esophagus. Just like the exit (pylorus), it is distinguished by the circular obturator muscles - sphincter. Thanks to the contractions, the sphincter separates the gastric cavity from the duodenum, which is located behind it, as well as from the esophagus.

To put it figuratively, the stomach seems to “know” that food will soon enter it. And he begins to prepare for her new intake even before the moment when the food enters his mouth. Remember that moment when you see some tasty dish and your mouth begins to water. Along with these “drools” that occur in the mouth, digestive juice begins to be released in the stomach (this is exactly what happens before a person begins to eat directly). By the way, this juice was called by Academician I.P. Pavlov igniting or appetizing juice, and the scientist assigned it a large role in the process of subsequent digestion. Appetizing juice serves as a catalyst for more complex chemical processes that take a major part in the digestion of food entering the stomach.

Note that if the appearance of the food does not evoke appetizing juice, if the eater is absolutely indifferent to the food in front of him, this can create certain obstacles to successful digestion, which means that the food will enter the stomach, which is not sufficiently prepared for its digestion. This is why it is customary to attach such great importance to the beautiful table setting and appetizing appearance of the dishes. Know that in the central nervous system (CNS) of a person, conditioned reflex connections are formed between the smell and type of food and the work of the gastric glands. These connections help determine a person’s attitude towards food even at a distance, i.e. in some cases he experiences pleasure, and in others - no feelings or even disgust.

It would not be superfluous to note one more side of this conditioned reflex process: in the case when the ignition juice has already been caused for some reason, i.e. If you are already salivating, it is not recommended to delay eating. Otherwise, the connection between the activities of the gastrointestinal tract areas is disrupted, and the stomach begins to work “idle”. If such violations are frequent, the likelihood of certain ailments, such as stomach ulcers or catarrh, will increase.

When food enters the oral cavity, the intensity of secretion from the glands of the gastric mucosa increases; Innate reflexes in the work of the above-mentioned glands come into force. The reflex is transmitted along the sensitive endings of the taste nerves of the pharynx and tongue to the medulla oblongata, and then sent to the nerve plexuses embedded in the layers of the walls of the stomach. Interestingly, digestive juices are released only when only edible foods enter the oral cavity.

It turns out that by the time the crushed food moistened with saliva ends up in the stomach, it is already absolutely ready for work, representing like a machine for digesting food. Lumps of food, entering the stomach and automatically irritating its walls with the chemical elements present in them, contribute to an even more active secretion of digestive juices, affecting individual elements of food.

The digestive juice of the stomach contains hydrochloric acid and pepsin, a special enzyme. Together they break down proteins into albumoses and peptones. The juice also contains chymosin, a rennet enzyme that curdles dairy products, and lipase, an enzyme necessary for the initial breakdown of fats. Among other things, mucus is secreted from some glands, which protects the inner walls of the stomach from the overly irritating effects of food. Hydrochloric acid, which helps digest proteins, performs a similar protective function - it neutralizes toxic substances that enter the stomach along with food.

Almost no food breakdown products enter the blood vessels from the stomach. For the most part, alcohol and substances containing alcohol, for example, dissolved in alcohol, are absorbed in the stomach.

The “metamorphoses” of food in the stomach are so great that in cases where digestion is somehow disrupted, all parts of the gastrointestinal tract suffer. Based on this, you must always adhere to. This can be called the main condition for protecting the stomach from any kind of disorders.

Food stays in the stomach for approximately 4-5 hours, after which it is redirected to another part of the gastrointestinal tract - the duodenum. It passes into it in small parts and gradually.

As soon as a new portion of food has entered the intestine, the pyloric muscle contraction occurs, and the next portion will not leave the stomach until the hydrochloric acid, which ends up in the duodenum along with the already received lump of food, is neutralized by alkalis contained in the intestinal juices.

The duodenum was called the duodenum by ancient scientists, the reason for which was its length - about 26-30 cm, which can be compared with the width of 12 fingers located side by side. The shape of this intestine resembles a horseshoe, and the pancreas is located in its bend.

Digestive juice is secreted from the pancreas, flowing into the cavity of the duodenum through a separate channel. The bile produced by the liver also enters here. Together with the enzyme lipase (found in pancreatic juice), bile breaks down fats.

The pancreatic juice also contains the enzyme trypsin - it helps the body digest proteins, as well as the enzyme amylase - it promotes the breakdown of carbohydrates to the intermediate stage of disaccharides. As a result, the duodenum serves as a place where all the organic components of food (proteins, fats and carbohydrates) are actively affected by a variety of enzymes.

Turning into food gruel in the duodenum (called chyme), food continues on its way and enters the small intestine. The presented segment of the gastrointestinal tract is the longest - approximately 6 meters in length and 2-3 cm in diameter. Enzymes finally break down complex substances into simpler organic elements along this path. And already these elements become the beginning of a new process - they are absorbed into the blood and lymphatic vessels of the mesentery.

In the small intestine, the food taken by a person is finally transformed into substances that are absorbed into the lymph and blood, and then used by the cells of the body for their own purposes. The small intestine has loops that are in constant motion. This peristalsis ensures complete mixing and movement of food masses to the large intestine. This process is quite long: for example, ordinary mixed food included in the human diet passes through the small intestine in 6-7 hours.

Even if you look closely at the mucous membrane of the small intestine without a microscope, you can see small hairs - villi, approximately 1 mm high - all over its surface. One square millimeter of mucous membrane contains 20-40 villi.

When food passes through the small intestines, the villi constantly (and each of the villi has its own rhythm) contract by about ½ of its size, and then stretch upward again. Thanks to the combination of these movements, a suction action appears - it is this that allows broken down food products to pass from the intestines into the blood.

A large number of villi help to increase the absorption surface of the small intestine. Its area is 4-4.5 square meters. m (and this is almost 2.5 times more than the outer surface of the body!).

But not all substances are absorbed in the small intestine. The remains are sent to the large intestine, about 1 m long and about 5-6 cm in diameter. The large intestine is separated from the small intestine by a valve - the bauhinium valve, which from time to time allows parts of the chyme to pass through to the initial section of the large intestine. The large intestine is called the cecum. On its lower surface there is a process resembling a worm - this is the well-known appendix.

The large intestine is distinguished by its U-shape and raised upper corners. It consists of several segments, including the cecum, ascending, transverse colon, descending and sigmoid colon (the latter is curved like the Greek letter sigma).

The large intestine is home to many bacteria that produce fermentation processes. These processes help break down fiber, which is abundantly found in foods of plant origin. And along with its absorption, water is also absorbed, which enters the large intestine with chyme. This is where feces begin to form.

The large intestines are not as active as the small intestines. For this reason, chyme stays in them much longer - up to 12 hours. During this time, food goes through the final stages of digestion and dehydration.

The entire volume of food entering the body (as well as water) undergoes a lot of various changes. As a result, it is significantly reduced in the large intestine, and from several kilograms of food only 150 to 350 grams remain. These remains are subject to defecation, which occurs due to contraction of the striated muscles of the rectum, abdominal muscles and perineum. The process of defecation completes the path of food passing through the gastrointestinal tract.

A healthy body spends from 21 to 23 hours to completely digest food. If any deviations are noticed, they should under no circumstances be ignored, because they indicate that there are problems in some parts of the digestive canal or even in individual organs. In case of any violation, it is necessary to contact a specialist - this will not allow the disease to become chronic and lead to complications.

Speaking about the digestive organs, we should say not only about the main, but also about the auxiliary organs. We have already talked about one of them (the pancreas), so it remains to mention the liver and gall bladder.

The liver is one of the vital unpaired organs. It is located in the abdominal cavity under the right dome of the diaphragm and performs a huge number of different physiological functions.

Liver cells form hepatic beams that receive blood from the arterial and portal veins. From the beams, the blood flows to the inferior vena cava, where the paths through which bile is drained into the gallbladder and duodenum begin. And bile, as we already know, takes an active part in digestion, as do pancreatic enzymes.

The gallbladder is a sac-like reservoir located on the lower surface of the liver where bile produced by the body is collected. The reservoir has an elongated shape with two ends - wide and narrow. The length of the bubble reaches 8-14 cm, and the width - 3-5 cm. Its volume is approximately 40-70 cubic meters. cm.

The bladder has a bile duct that connects to the hepatic duct at the porta hepatis. The fusion of the two ducts forms the common bile duct, which unites with the pancreatic duct and opens into the duodenum through the sphincter of Oddi.

The importance of the gallbladder and the function of bile cannot be underestimated, because they perform a number of important operations. They are involved in the digestion of fats, create an alkaline environment, activate digestive enzymes, stimulate intestinal motility and remove toxins from the body.

In general, the gastrointestinal tract is a real conveyor belt for the continuous movement of food. His work is subject to strict consistency. Each stage affects food in a specific way, so that it supplies the body with the energy it needs to function properly. And another important characteristic of the gastrointestinal tract is that it adapts quite easily to different types of food.

However, the gastrointestinal tract is “needed” not only for processing food and removing unusable residues. In fact, its functions are much wider, because... As a result of metabolism (metabolism), unnecessary products appear in all cells of the body, which must be removed, otherwise their poisons can poison a person.

A large proportion of toxic metabolic products enters the intestines through blood vessels. There these substances break down and are excreted along with feces during bowel movements. It follows that the gastrointestinal tract helps the body get rid of many toxic substances that appear in it during life.

The clear and harmonious operation of all systems of the digestive canal is the result of regulation, for which the nervous system is largely responsible. Some processes, for example, the act of swallowing food, the act of chewing it, or the act of defecation, are controlled by the human consciousness. But others, such as the release of enzymes, the breakdown and absorption of substances, contractions of the intestines and stomach, etc., occur on their own, without conscious effort. The autonomic nervous system is responsible for this. In addition, these processes are associated with the central nervous system, and in particular with the cerebral cortex. So any person (joy, fear, stress, excitement, etc.) immediately affects the activity of the digestive system. But this is a conversation on a slightly different topic. We are summing up the first lesson.

In the second lesson, we will talk in detail about what food consists of, tell you why the human body requires certain substances, and also provide a table of the content of useful elements in foods.

Test your knowledge

If you want to test your knowledge on the topic of this lesson, you can take a short test consisting of several questions. For each question, only 1 option can be correct. After you select one of the options, the system automatically moves on to the next question. The points you receive are affected by the correctness of your answers and the time spent on completion. Please note that the questions are different each time and the options are mixed.

The concept of physiology can be interpreted as the science of the patterns of operation and regulation of a biological system in conditions of health and the presence of diseases. Physiology studies, among other things, the vital activity of individual systems and processes; in a particular case, this is, i.e. vital activity of the digestive process, patterns of its work and regulation.

The very concept of digestion means a complex of physical, chemical and physiological processes, as a result of which the food received in the process is broken down into simple chemical compounds - monomers. Passing through the wall of the gastrointestinal tract, they enter the bloodstream and are absorbed by the body.

Digestive system and oral digestion process

A group of organs is involved in the digestion process, which is divided into two large sections: the digestive glands (salivary glands, liver glands and pancreas) and the gastrointestinal tract. Digestive enzymes are divided into three main groups: proteases, lipases, and amylases.

Among the functions of the digestive tract are: promotion of food, absorption and removal of undigested food debris from the body.

The process begins. During chewing, food received during the process is crushed and moistened with saliva, which is produced by three pairs of large glands (sublingual, submandibular and parotid) and microscopic glands located in the mouth. Saliva contains enzymes amylase and maltase, which break down nutrients.

Thus, the process of digestion in the mouth consists of physically breaking up food, chemically attacking it, and moistening it with saliva to make it easier to swallow and continue the digestion process.

Digestion in the stomach

The process begins with food, crushed and moistened with saliva, passing through the esophagus and entering the organ. Over the course of several hours, the food bolus experiences mechanical (muscle contraction as it moves into the intestines) and chemical effects (stomach juice) inside the organ.

Gastric juice consists of enzymes, hydrochloric acid and mucus. The main role belongs to hydrochloric acid, which activates enzymes, promotes fragmentary breakdown, and has a bactericidal effect, destroying a lot of bacteria. The enzyme pepsin in the gastric juice is the main one, breaking down proteins. The action of mucus is aimed at preventing mechanical and chemical damage to the organ membrane.

What composition and amount of gastric juice will depend on the chemical composition and nature of the food. The sight and smell of food promotes the release of necessary digestive juices.

As the digestion process progresses, food gradually and portionwise moves into the duodenum.

Digestion in the small intestine

The process begins in the cavity of the duodenum, where the bolus is affected by pancreatic juice, bile and intestinal juice, since it contains the common bile duct and the main pancreatic duct. Inside this organ, proteins are digested into monomers (simple compounds), which are absorbed by the body. Learn more about the three components of chemical action in the small intestine.

The composition of pancreatic juice includes the enzyme trypsin, which breaks down proteins, which converts fats into fatty acids and glycerol, the enzyme lipase, as well as amylase and maltase, which break down starch into monosaccharides.

Bile is synthesized by the liver and accumulates in the gallbladder, from where it enters the duodenum. It activates the enzyme lipase, participates in the absorption of fatty acids, increases the synthesis of pancreatic juice, and activates intestinal motility.

Intestinal juice is produced by special glands in the inner lining of the small intestine. It contains more than 20 enzymes.

There are two types of digestion in the intestines and this is its peculiarity:

• cavitary - carried out by enzymes in the organ cavity;
• contact or membrane - performed by enzymes that are located on the mucous membrane of the inner surface of the small intestine.

Thus, nutrients in the small intestine are actually completely digested, and the final products - monomers - are absorbed into the blood. Upon completion of the digestion process, digested food remains pass from the small intestine to the large intestine.

Digestion in the large intestine

The process of enzymatic processing of food in the large intestine is quite minor. However, in addition to enzymes, the process involves obligate microorganisms (bifidobacteria, E. coli, streptococci, lactic acid bacteria).

Bifidobacteria and lactobacilli are extremely important for the body: they have a beneficial effect on intestinal function, participate in the breakdown, ensure the quality of protein and mineral metabolism, increase the body's resistance, and have an antimutagenic and anticarcinogenic effect.

Intermediate products of carbohydrates, fats and proteins are broken down here into monomers. Microorganisms of the colon produce (groups B, PP, K, E, D, biotin, pantothenic and folic acids), a number of enzymes, amino acids and other substances.

The final stage of the digestion process is the formation of feces, which are 1/3 of bacteria, and also contain epithelium, insoluble salts, pigments, mucus, fiber, etc.

Nutrient Absorption

Let's take a closer look at the process. It represents the final goal of the digestion process, when food components are transported from the digestive tract into the internal environment of the body - blood and lymph. Absorption occurs in all parts of the gastrointestinal tract.

Absorption in the mouth is practically not carried out due to the short period (15 - 20 s) of food remaining in the organ cavity, but not without exceptions. In the stomach, the absorption process partially involves glucose, a number of amino acids, dissolved alcohol, and alcohol. Absorption in the small intestine is most extensive, largely due to the structure of the small intestine, which is well adapted to absorption function. Absorption in the large intestine concerns water, salts, vitamins and monomers (fatty acids, monosaccharides, glycerol, amino acids, etc.).

The central nervous system coordinates all processes of nutrient absorption. Humoral regulation is also involved in this.

The process of protein absorption occurs in the form of amino acids and water solutions - 90% in the small intestine, 10% in the large intestine. Absorption of carbohydrates occurs in the form of various monosaccharides (galactose, fructose, glucose) at different rates. Sodium salts play a certain role in this. Fats are absorbed in the form of glycerol and fatty acids in the small intestine into the lymph. Water and mineral salts begin to be absorbed in the stomach, but this process occurs more intensively in the intestines.

Thus, it covers the process of digestion of nutrients in the mouth, stomach, small and large intestines, as well as the process of absorption.

To maintain his life, a person must eat food. Food products contain all the substances necessary for life: water, mineral salts and organic compounds. Proteins, fats and carbohydrates are synthesized by plants from inorganic substances using solar energy. Animals build their bodies from nutrients of plant or animal origin.

Nutrients that enter the body with food are building materials and at the same time a source of energy. During the breakdown and oxidation of proteins, fats and carbohydrates, a different but constant amount of energy is released for each substance, characterizing their energy value.

Digestion

Once in the body, food products undergo mechanical changes - they are crushed, moistened, split into simpler compounds, dissolved in water and absorbed. The set of processes as a result of which nutrients from the environment pass into the blood is called digestion.

Plays a huge role in the digestion process enzymes- biologically active protein substances that catalyze (accelerate) chemical reactions. During digestion processes, they catalyze reactions of hydrolytic breakdown of nutrients, but do not themselves change.

Main properties of enzymes:

• specificity of action - each enzyme breaks down nutrients only of a certain group (proteins, fats or carbohydrates) and does not break down others;
• act only in a certain chemical environment - some in alkaline, others in acidic;
• enzymes are most active at body temperature, and at a temperature of 70–100ºС they are destroyed;
• a small amount of enzyme can break down a large mass of organic matter.

Digestive organs

The alimentary canal is a tube that runs throughout the body. The canal wall consists of three layers: outer, middle and inner.

Outer layer(serous membrane) is formed by connective tissue that separates the digestive tube from surrounding tissues and organs.

Middle layer(muscular membrane) in the upper parts of the digestive tube (oral cavity, pharynx, upper part of the esophagus) is represented by striated muscle tissue, and in the lower parts - smooth muscle tissue. Most often, the muscles are located in two layers - circular and longitudinal. Thanks to the contraction of the muscular membrane, food moves through the digestive canal.

Inner layer(mucosa) is lined with epithelium. It contains numerous glands that secrete mucus and digestive juices. In addition to small glands, there are large glands (salivary, liver, pancreas) lying outside the digestive canal and communicating with them through their ducts. The following sections are distinguished in the digestive canal: oral cavity, pharynx, esophagus, stomach, small and large intestines.

Digestion in the mouth

Oral cavity- the initial section of the digestive tract. It is bounded above by the hard and soft palate, below by the diaphragm of the mouth, and in front and on the sides by the teeth and gums.

The ducts of three pairs of salivary glands open into the oral cavity: parotid, sublingual and submandibular. In addition to these, there is a mass of small mucous salivary glands scattered throughout the oral cavity. The secretion of the salivary glands - saliva - moistens food and participates in its chemical changes. Saliva contains only two enzymes - amylase (ptialin) and maltase, which digest carbohydrates. But since food does not remain in the oral cavity for long, the breakdown of carbohydrates does not have time to complete. Saliva also contains mucin (a mucous substance) and lysozyme, which has bactericidal properties. The composition and quantity of saliva may vary depending on the physical properties of the food. During the day, a person secretes from 600 to 150 ml of saliva.

In the oral cavity, an adult has 32 teeth, 16 in each jaw. They grab food, bite it off and chew it.

Teeth They consist of a special substance called dentin, which is a modification of bone tissue and has greater strength. The outside of the teeth is covered with enamel. Inside the tooth there is a cavity filled with loose connective tissue containing nerves and blood vessels.

Most of the oral cavity is occupied tongue, which is a muscular organ covered with mucous membrane. It is distinguished by the top, root, body and back, on which taste buds are located. The tongue is the organ of taste and speech. With its help, food is mixed during chewing and pushed through when swallowing.

Food prepared in the oral cavity is swallowed. Swallowing is a complex movement that involves the muscles of the tongue and pharynx. During swallowing, the soft palate rises and blocks the food from entering the nasal cavity. At this time, the epiglottis closes the entrance to the larynx. The food bolus gets into throat- upper part of the digestive canal. It is a tube, the inner surface of which is lined with mucous membrane. Through the pharynx, food enters the esophagus.

Esophagus- a tube about 25 cm long, which is a direct continuation of the pharynx. No food changes occur in the esophagus, since digestive juices are not secreted in it. It serves to carry food into the stomach. The movement of the food bolus through the pharynx and esophagus occurs as a result of contraction of the muscles of these sections.

Digestion in the stomach

Stomach- the most expanded section of the digestive tube with a capacity of up to three liters. The size and shape of the stomach changes depending on the amount of food taken and the degree of contraction of its walls. At the point where the esophagus flows into the stomach and where the stomach passes into the small intestine, there are sphincters (squeezers) that regulate the movement of food.

The mucous membrane of the stomach forms longitudinal folds and contains a large number of glands (up to 30 million). The glands consist of three types of cells: main (producing enzymes of gastric juice), parietal (secreting hydrochloric acid) and accessory (secreting mucus).

Contractions of the stomach walls mix food with juice, which promotes better digestion. Several enzymes are involved in the digestion of food in the stomach. The main one is pepsin. It breaks down complex proteins into simpler ones, which are further processed in the intestines. Pepsin acts only in an acidic environment, which is created by hydrochloric acid in gastric juice. Hydrochloric acid plays a major role in the disinfection of stomach contents. Other gastric juice enzymes (chymosin and lipase) are able to digest milk protein and fats. Chymosin curdles milk, so it stays in the stomach longer and undergoes digestion. Lipase, present in small quantities in the stomach, breaks down only the emulsified milk fat. The action of this enzyme in the stomach of an adult is weakly expressed. There are no enzymes that act on carbohydrates in gastric juice. however, a significant portion of the food's starch continues to be digested in the stomach by salivary amylase. The mucus secreted by the glands of the stomach plays an important role in protecting the mucous membrane from mechanical and chemical damage and from the digestive action of pepsin. The glands of the stomach secrete juice only during digestion. In this case, the nature of juice secretion depends on the chemical composition of the food consumed. After 3-4 hours of processing in the stomach, the food gruel enters the small intestine in small portions.

Small intestine

Small intestine It is the longest part of the digestive tube, reaching 6–7 meters in an adult. It consists of the duodenum, jejunum and ileum.

The excretory ducts of two large digestive glands - the pancreas and liver - open into the initial section of the small intestine - the duodenum. Here the most intensive digestion of food gruel occurs, which is exposed to the action of three digestive juices: pancreatic, bile and intestinal.

Pancreas located behind the stomach. It distinguishes between the apex, body and tail. The apex of the gland is surrounded in a horseshoe shape by the duodenum, and the tail is adjacent to the spleen.

Gland cells produce pancreatic juice (pancreatic). It contains enzymes that act on proteins, fats and carbohydrates. The enzyme trypsin breaks down proteins into amino acids, but is active only in the presence of the intestinal enzyme enterokinase. Lipase breaks down fats into glycerol and fatty acids. Its activity increases sharply under the influence of bile produced in the liver and entering the duodenum. Under the influence of amylase and maltose in pancreatic juice, most food carbohydrates are broken down into glucose. All pancreatic juice enzymes are active only in an alkaline environment.

In the small intestine, food gruel undergoes not only chemical, but also mechanical processing. Thanks to the pendulum-like movements of the intestine (alternate lengthening and shortening), it mixes with digestive juices and liquefies. Peristaltic movements of the intestines cause contents to move towards the large intestine.

Liver- the largest digestive gland in our body (up to 1.5 kg). It lies under the diaphragm, occupying the right hypochondrium. The gallbladder is located on the lower surface of the liver. The liver consists of glandular cells that form lobules. Between the lobules there are layers of connective tissue in which nerves, lymphatic and blood vessels and small bile ducts pass.

Bile, produced by the liver, plays a large role in the digestion process. It does not break down nutrients, but prepares fats for digestion and absorption. Under its action, fats break up into small drops suspended in liquid, i.e. turn into an emulsion. In this form they are easier to digest. In addition, bile actively influences absorption processes in the small intestine, enhances intestinal motility and the secretion of pancreatic juice. Despite the fact that bile is produced continuously in the liver, it enters the intestines only when eating. Between periods of digestion, bile is collected in the gallbladder. Through the portal vein, venous blood flows into the liver from the entire digestive canal, pancreas and spleen. Toxic substances that enter the blood from the gastrointestinal tract are neutralized here and then excreted in the urine. In this way, the liver carries out its protective (barrier) function. The liver is involved in the synthesis of a number of important substances for the body, such as glycogen, vitamin A, and influences the process of hematopoiesis, the metabolism of proteins, fats, and carbohydrates.

Nutrient Absorption

In order for the amino acids, simple sugars, fatty acids and glycerol resulting from the breakdown to be used by the body, they must be absorbed. These substances are practically not absorbed in the oral cavity and esophagus. Water, glucose and salts are absorbed in the stomach in small quantities; in the large intestines - water and some salts. The main processes of nutrient absorption occur in the small intestine, which is quite well adapted to carry out this function. The mucous membrane of the small intestine plays an active role in the absorption process. It has a large number of villi and microvilli, which increase the absorption surface of the intestine. The walls of the villi contain smooth muscle fibers, and inside them there are blood and lymphatic vessels.

Villi take part in the absorption of nutrients. By contracting, they promote the outflow of blood and lymph, rich in nutrients. When the villi relax, fluid from the intestinal cavity again enters their vessels. The products of the breakdown of proteins and carbohydrates are absorbed directly into the blood, and the bulk of digested fats are absorbed into the lymph.

Colon

Colon has a length of up to 1.5 meters. Its diameter is 2–3 times larger than the thin one. It contains undigested food residues, mainly plant foods, the fiber of which is not destroyed by enzymes of the digestive tract. There are a lot of different bacteria in the large intestine, some of which play an important role in the body. Cellulose bacteria break down fiber and thereby improve the absorption of plant foods. There are bacteria that synthesize vitamin K, which is necessary for the normal functioning of the blood coagulation system. Thanks to this, a person does not need to take vitamin K from the external environment. In addition to the bacterial breakdown of fiber in the large intestine, a large amount of water is absorbed, which enters there along with liquid food and digestive juices, which ends with the absorption of nutrients and the formation of feces. The latter pass into the rectum, and from there they are discharged out through the anus. The opening and closing of the anal sphincter occurs reflexively. This reflex is under the control of the cerebral cortex and can be voluntarily delayed for some time.

The entire process of digestion with animal and mixed food in humans lasts about 1–2 days, of which more than half of the time is spent moving food through the large intestines. Feces accumulate in the rectum, and as a result of irritation of the sensory nerves of its mucous membrane, defecation occurs (emptying the colon).

The digestion process is a series of stages, each of which takes place in a certain part of the digestive tract under the influence of certain digestive juices secreted by the digestive glands and acting on certain nutrients.

Oral cavity- the beginning of the breakdown of carbohydrates under the action of salivary enzymes produced by the salivary glands.

Stomach- breakdown of proteins and fats under the influence of gastric juice, continuation of the breakdown of carbohydrates inside the bolus of food under the influence of saliva.

Small intestine- completion of the breakdown of proteins, polypeptides, fats and carbohydrates under the action of enzymes of pancreatic and intestinal juices and bile. As a result of biochemical processes, complex organic substances are transformed into low-molecular substances, which, when absorbed into the blood and lymph, become a source of energy and plastic materials for the body.

Digestion- a set of processes that ensure physical change and chemical breakdown of nutrients into simple constituent water-soluble compounds that can be easily absorbed into the blood and participate in the vital functions of the human body. Digestion takes place in a special human digestive apparatus.

It consists of the following organs: the oral cavity (oral opening, tongue, teeth, muscles of mastication, salivary glands, glands of the oral mucosa), pharynx, esophagus, stomach, duodenum, pancreas, liver, small intestine, large intestine, rectum (Fig. 2.1). The esophagus, stomach, intestines consist of three membranes: the inner - mucous membrane, in which they are located

Rice. 2.1. Diagram of the digestive apparatus:

/ - oral cavity; 2 - salivary glands; 3 - pharynx; 4 - esophagus; 5 - stomach; 6 - pancreas; 7 - small intestines; 8- large intestines; 9 - rectum; 10 - duodenum; // - gallbladder; 12 - liver

glands that secrete mucus, and in a number of organs, digestive juices; middle - muscle, which ensures the movement of food by contraction; outer - serous, playing the role of a covering layer.

In humans during the day stands out about 7 l digestive juices, which include: iodine, which thins food gruel, mucus, which promotes better movement of food, salts and enzyme catalysts of biochemical processes that break down food substances into simple compounds. Depending on the action of nate or other substances, enzymes are divided into proteases, breaking down proteins (proteins), amylase, breaking down carbohydrates (amylose), and lipases, breaking down fats (lipids). Each enzyme is active only in a certain environment (acidic, alkaline, or neutral). As a result of breakdown, amino acids are obtained from proteins, glycerol and fatty acids from fats, and mainly glucose from carbohydrates. Water, mineral salts, and vitamins contained in food do not undergo changes during the digestion process.

Digestion in the mouth and esophagus. Oral cavity - This is the initial section of the digestive apparatus. With the help of teeth, tongue and cheek muscles, food undergoes initial mechanical processing, and with the help of saliva - chemical processing.

Saliva is a slightly alkaline digestive juice produced by three pairs of salivary glands (parotid, sublingual, submandibular) and entering the oral cavity through ducts. In addition, saliva is secreted by the salivary glands of the lips, cheeks and tongue. In just a day, about 1 liter of saliva of different consistencies is produced: thick saliva is secreted for the digestion of liquid food, liquid saliva for dry food. Saliva contains enzymes: amylase, or ptyalin, which partially breaks down starch into maltose, an enzyme babypaza, which breaks down maltose into glucose, and an enzyme lysozyme, having an antimicrobial effect.

Food remains in the oral cavity for a relatively short time (10...25 s). Digestion in the mouth consists mainly of the formation of a bolus of food prepared for swallowing. The chemical effect of saliva on food substances in the oral cavity is negligible due to the short residence of food. Its action continues in the stomach until the bolus of food is completely saturated with acidic gastric juice. However, processing food in the mouth is of great importance for the further progress of the digestive process, since the act of eating is a powerful reflex stimulator of the activity of all digestive organs. The bolus of food, with the help of coordinated movements of the tongue and cheeks, moves towards the pharynx, where the act of swallowing occurs. From the mouth, food enters the esophagus.

Esophagus- a muscular tube 25...30 cm long, through which, due to muscle contraction, the food bolus moves to the stomach in 1...9 s, depending on the consistency of the food.

Digestion in the stomach. Stomach - the widest part of the digestive tract - is a hollow organ consisting of an inlet, a bottom, a body and an outlet. The inlet and outlet openings are closed with a muscle roller (spike). The volume of an adult's stomach is about 2 liters, but can increase to 5 liters. The inner mucous membrane of the stomach is folded, which increases its surface area. The thickness of the mucous membrane contains up to 25 million glands that produce gastric juice and mucus.

Gastric juice is a colorless acidic liquid containing 0.4...0.5% hydrochloric acid, which activates enzymes gastric juice and has a bactericidal effect on microbes that enter V stomach with food. Contains gastric juice enzymes include: pepsin, chymosin (rennet enzyme), lipase. Enzyme pepsin breaks down food proteins into more simple substances(peptones and albumoses), which undergo further digestion in the small intestine. Chymosin found in the gastric juice of infants, coagulating milk protein in their ventricles. Lipase gastric juice breaks down only emulsified fats (milk, mayonnaise) into glycerol and fatty acids.

The human body secretes 1.5...2.5 liters of gastric juice per day, depending on the amount and composition of food. Food in the stomach is digested from 3 to 10 hours, depending on the composition, volume, consistency and method of its processing. Fatty and dense foods stay in the stomach longer than liquid foods containing carbohydrates. Due to the contraction of the muscular lining of the stomach, the food is crushed, turning into a homogeneous mass.

The mechanism of gastric juice secretion is a complex process consisting of two phases. The first phase of gastric secretion is a conditioned and unconditioned reflex process, depending on the appearance, smell and conditions of food intake. The great Russian scientist-physiologist I.P. Pavlov called this gastric juice “appetizing” or “ignition”, on which the further course of digestion depends. The second phase of gastric secretion is associated with chemical pathogens of food and is called neurochemical. The mechanism of gastric juice secretion also depends on the action of specific hormones of the digestive organs. Partial absorption occurs in the stomach V blood water and mineral salts.

After digestion in the stomach, the food gruel enters the initial section of the small intestine in small portions - duodenum, where the food mass is exposed to

The active effects of the digestive juices of the pancreas, liver and the mucous membrane of the intestine itself.

The role of the pancreas in the digestive process. Pancreas- digestive organ, consists of cells that form lobules that have output ducts connecting V common duct. That's why duct digestive juice from the pancreas enters into the duodenum intestine (up to 0.8 l per day).

Digestive juice of the pancreas is a colorless transparent liquid alkaline reactions. It contains enzymes: trypsin, chymotrypsin, lipase, amylase, maltase. Trypsin And chymotrypsin break down proteins, peptones, albumoses coming from the stomach into polypeptides. Lipase With the help of bile, it breaks down food fats into glycerol and fatty acids. Amylase And maltase break down starch into glucose. In addition, the pancreas has special cells (islets of Langerhans) that produce the hormone insulin, which enters the blood. This hormone regulates carbohydrate metabolism, facilitating the absorption of sugar by the body's cells. In the absence of insulin, diabetes mellitus occurs.

The role of the liver in the digestive process. Liver - a large gland weighing up to 1.5...2 kg, consisting of cells that produce bile up to 1 liter per day. Bile is a liquid from light yellow to dark green in color, slightly alkaline, activates the enzyme lipase of pancreatic and intestinal juice, emulsifies fats, promotes the absorption of fatty acids, enhances intestinal movement (peristalsis), suppresses putrefactive processes in the intestines.

Bile from the hepatic ducts enters gallbladder - thin-walled pear-shaped bag with a volume of 60 ml. During the digestion process, bile flows from the gallbladder through the duct into the duodenum.

In addition to the digestion process, the liver is involved in metabolism, hematopoiesis, retention and neutralization of toxic substances that enter the blood during the digestion process.

Digestion in the small intestine. Length small intestine is 5...6 m. The digestion process is completed in it thanks to pancreatic juice, bile and intestinal juice secreted by the glands of the intestinal mucosa (up to 2 liters per day).

Intestinal juice is a cloudy liquid of an alkaline reaction, which contains mucus and enzymes: polypeptidases And dipeptidases, splitting (hydrolyzing) polypeptides into amino acids; lipase, breaking down fats into glycerol and fatty acids; amylase And maltase, digest starch and maltose to glucose; sucrase, fissionable

sucrose to glucose and fructose; lactase, breaking down lactose into glucose and galactose.

The main causative agent of the secret activity of the intestines are chemicals contained in food, bile and pancreatic juice.

In the small intestine, food gruel (chyme) moves, mixes, and is distributed in a thin layer along the wall, where the final process of digestion occurs - the absorption of the products of the breakdown of nutrients, as well as vitamins, minerals, and water into the blood. Here, aqueous solutions of nutrients formed during the digestion process penetrate through the mucous membrane of the gastrointestinal tract into the blood and lymphatic vessels.

The walls of the small intestine contain special suction organs - villi, which there are 18...40 pcs. by 1 mm 2 (Fig. 2.2). Nutritious substances are absorbed through the superficial layer of villi. Amino acids, glucose, water, minerals, vitamins, soluble in water, enter the blood. Glycerol and fatty acids in the walls villi form droplets of fat, characteristic the human body, which penetrate the lymph, A then V blood. Next, the blood flows through the portal vein to the liver, where, having been cleared of toxic digestive substances, it supplies all tissues and organs with nutrients.

The role of the large intestine in the digestive process. IN colon up to 1 m long, undigested food remains arrive. A small number of glands of the large intestine secrete inactive digestive juice, which partially continues the digestion of nutrients. The large intestines contain a large number of bacteria that cause fermentation of

Rice. 2.2. Scheme of the structure of the villi:

/ - villi; 2 - layer of cells through which absorption occurs; 3 - the beginning of the lymphatic vessel in the villus; 4 - blood vessels in the villi; 5 - intestinal glands; 6 - lymphatic vessel in the intestinal wall; 7- blood vessels in the intestinal wall; 8 - part of the muscle layer in the intestinal wall

loss of carbohydrates, rotting of protein residues and partial breakdown of fiber. In this case, a number of toxic substances harmful to the body are formed (indole, skatole, phenol, cresol), which are absorbed into the blood and then neutralized V liver.

Composition of colon bacteria depends on the composition of the incoming food. Thus, dairy-vegetable foods create favorable conditions for the development of lactic acid bacteria, and foods rich in protein promote the development of putrefactive microbes. In the large intestines, the bulk of water is absorbed into the blood, as a result of which the intestinal contents become denser and move towards the outlet. Removing feces from body carried out through rectum and is called defecation.

Nutrition is a complex process through which substances necessary for the body are supplied, digested and absorbed. Over the past ten years, a special science devoted to nutrition—nutritiology—has been actively developing. In this article we will look at the process of digestion in the human body, how long it lasts and how to manage without a gallbladder.

The structure of the digestive system

It is represented by a set of organs that ensure the absorption of nutrients by the body, which are a source of energy for it, necessary for cell renewal and growth.

The digestive system consists of: the mouth, pharynx, small intestine, colon and rectum.

Digestion in the human oral cavity

The process of digestion in the mouth involves grinding food. In this process, energetic processing of food with saliva occurs, interaction between microorganisms and enzymes. After treatment with saliva, some of the substances dissolve and their taste appears. The physiological process of digestion in the oral cavity involves the breakdown of starch into sugars by the amylase enzyme contained in saliva.

Let's follow the action of amylase using an example: while chewing bread for a minute, you can feel a sweet taste. The breakdown of proteins and fats does not occur in the mouth. On average, the digestion process in the human body takes approximately 15-20 seconds.

Digestive department - stomach

The stomach is the widest part of the digestive tract, has the ability to expand in size, and can accommodate huge amounts of food. As a result of the rhythmic contraction of the muscles of its walls, the process of digestion in the human body begins with thorough mixing of food with gastric juice, which has an acidic environment.

Once a lump of food enters the stomach, it remains there for 3-5 hours, during which time it is subjected to mechanical and chemical treatment. Digestion in the stomach begins with exposure of food to gastric juice and the hydrochloric acid that is present in it, as well as pepsin.

As a result of digestion in the human stomach, proteins are digested with the help of enzymes into low molecular weight peptides and amino acids. The digestion of carbohydrates, which begins in the mouth, stops in the stomach, which is explained by the loss of amylases’ activity in an acidic environment.

Digestion in the stomach cavity

The process of digestion in the human body occurs under the influence of gastric juice containing lipase, which is capable of breaking down fats. In this case, great importance is given to the hydrochloric acid of gastric juice. Under the influence of hydrochloric acid, the activity of enzymes increases, denaturation and swelling of proteins is caused, and a bactericidal effect is exerted.

The physiology of digestion in the stomach is that food enriched with carbohydrates, which remains in the stomach for about two hours, undergoes an evacuation process faster than food containing proteins or fats, which lingers in the stomach for 8-10 hours.

Food that is mixed with gastric juice and partially digested, being in a liquid or semi-liquid consistency, passes into the small intestine in small portions at simultaneous intervals. In which department does the digestion process still take place in the human body?

Digestive department - small intestine

Digestion in the small intestine, into which the bolus of food enters from the stomach, has the most important place, from the point of view of the biochemistry of the absorption of substances.

In this section, the intestinal juice consists of an alkaline environment due to the arrival of bile, pancreatic juice and secretions of the intestinal walls into the small intestine. The digestive process in the small intestine does not go quickly for everyone. This is facilitated by the presence of an insufficient amount of the lactase enzyme, which hydrolyzes milk sugar, which is associated with the indigestibility of whole milk. During the digestion process, more than 20 enzymes are consumed in this part of the human body, for example, peptidases, nucleases, amylase, lactase, sucrose, etc.

The activity of this process in the small intestine depends on the three intersecting sections of which it consists - the duodenum, jejunum and ileum. Bile formed in the liver enters the duodenum. Here food is digested thanks to the pancreatic juice and bile that act on it. This colorless liquid contains enzymes that promote the breakdown of proteins and polypeptides: trypsin, chymotrypsin, elastase, carboxypeptidase and aminopeptidase.

Role of the liver

An important role in the process of digestion in the human body (we will briefly mention this) is played by the liver, in which bile is formed. The peculiarity of the digestive process in the small intestine is due to the assistance of bile in emulsifying fats, absorbing triglycerides, activating lipase, also helps stimulate peristalsis, inactivate pepsin in the duodenum, has a bactericidal and bacteriostatic effect, increases hydrolysis and absorption of proteins and carbohydrates.

Bile does not contain digestive enzymes, but is important in the dissolution and absorption of fats and fat-soluble vitamins. If bile is not produced enough or is secreted into the intestines, then the processes of digestion and absorption of fats are disrupted, as well as an increase in their excretion in their original form with feces.

What happens in the absence of a gallbladder?

The person is left without the so-called small sac, in which bile was previously deposited “in reserve.”

Bile is needed in the duodenum only if there is food in it. And this is not a constant process, only during the period after eating. After some time, the duodenum is emptied. Accordingly, the need for bile disappears.

However, the work of the liver does not stop there; it continues to produce bile. It is for this purpose that nature created the gallbladder, so that the bile secreted in the intervals between meals does not deteriorate and is stored until the need for it arises.

And here the question arises about the absence of this “bile storage”. As it turns out, a person can do without a gallbladder. If the operation is performed on time and other diseases associated with the digestive organs are not provoked, then the absence of a gallbladder in the body is easily tolerated. The timing of the digestion process in the human body is of interest to many.

After surgery, bile can only be stored in the bile ducts. After bile is produced by liver cells, it is released into the ducts, from where it is easily and continuously sent to the duodenum. Moreover, this does not depend on whether the food is taken or not. It follows that after the gallbladder has been removed, food must be taken frequently and in small portions for the first time. This is explained by the fact that there is not enough bile to process large portions of bile. After all, there is no longer a place for its accumulation, but it enters the intestine continuously, albeit in small quantities.

It often takes time for the body to learn to function without a gallbladder and to find the necessary place to store bile. This is how the digestion process works in the human body without a gallbladder.

Digestive department - large intestine

The remains of undigested food move into the large intestine and remain there for approximately 10 to 15 hours. Here the following digestive processes take place in the intestines: absorption of water and microbial metabolization of nutrients.

In digestion, food plays a huge role, which includes indigestible biochemical components: fiber, hemicellulose, lignin, gums, resins, waxes.

The structure of food affects the speed of absorption in the small intestine and the time of movement through the gastrointestinal tract.

Some of the dietary fiber that is not broken down by enzymes belonging to the gastrointestinal tract is destroyed by microflora.

The large intestine is the place of formation of feces, which includes: undigested food debris, mucus, dead cells of the mucous membrane and microbes that continuously multiply in the intestines and which cause the processes of fermentation and gas formation. How long does the digestion process in the human body last? This is a common question.

Breakdown and absorption of substances

The absorption process occurs throughout the entire digestive tract, which is covered with hairs. On 1 square millimeter of mucous membrane there are about 30-40 villi.

In order for the process of absorption of substances that dissolve in fats, or rather fat-soluble vitamins, to occur, fats and bile must be present in the intestines.

Absorption of water-soluble products such as amino acids, monosaccharides, mineral ions occurs with the participation of blood capillaries.

In a healthy person, the entire digestion process takes from 24 to 36 hours.

This is how long the digestion process in the human body lasts.