1. List the departments digestive system.
Sections of the digestive system: oral cavity, pharynx, esophagus, stomach, small and large intestines, anus and a number of large digestive glands: liver, pancreas, salivary glands.
2. What substances begin to break down in oral cavity? In what chemical environment are the enzymes of the salivary glands active? Name the end product of this breakdown in the oral cavity.
Saliva has a slightly alkaline reaction (pH = 6.5-7.5) and consists of 98-99% water and 1-2% mucus, organic and inorganic substances and digestive enzymes. Salivary enzymes: amylase and maltase (begin the breakdown of carbohydrates in the oral cavity) and lipase (begin the breakdown of fats). Complete breakdown of substances in the oral cavity does not occur due to the short duration of food in the oral cavity. With longer exposure to enzymes, starch is broken down into maltose, and maltose into glucose.
3. Tell us about the structure of the tooth.
A tooth consists of a root hidden in the bone cell of the jaw and a visible part - the crown and neck. Inside the root there is a canal that expands into the tooth cavity and is filled with pulp containing blood vessels and nerves. The tooth is built from a dense substance similar to bone - dentin, covered with cement in the root area, and very dense enamel in the crown area, which protects the tooth from abrasion and the penetration of bacteria.
4. At what age do baby teeth change to permanent ones?
The eruption of permanent teeth, except wisdom teeth, begins at 6-7 years and ends by 10-12 years; The eruption of wisdom teeth can sometimes end by the age of 20-30, rarely later.
5. How many teeth does a person have? Find out what a dental formula is and how it is written. Using the drawing, make a dental formula for a person.
In total, a person has 32 teeth: on each jaw there are 4 incisors, 2 canines, 4 small molars (premolars) and 6 large molars (molars).
Dental formula - written in the form of special notations short description dental system of mammals and other heterodont tetrapods. All teeth are divided into 4 sectors (counterclockwise). The teeth are numbered from 1 to 8. Since there are only 32 bone formations, each number will be used to designate the four teeth of the same name in the upper and lower jaws. To do this, both dental rows are conventionally divided in half along the line between the central incisors, so that on each side of this line there are: central incisor - 1; lateral incisor – 2; fang – 3; first premolar – 4; second premolar – 5; first molar – 6; second molar – 7; third molar – 8.
6. Many of us are familiar with toothache. What exactly hurts in the tooth? What causes tooth decay? Why is he dangerous?
Toothache occurs as a result of irritation of sensitive receptors in the dental pulp. Most common cause toothache is caries. Unclean teeth become covered with food debris, bacteria, and saliva components. This mucus is called plaque. Bacteria, feeding on sugars from food debris, release acid, which first destroys enamel and then dentin. As a result, a cavity forms in the tooth and strong pain. If the carious process is not stopped, the damage will affect both the tooth canal and even bone tissue jaw, which may lead to the need to remove a carious tooth. If caries appears on baby teeth, then bacteria can get on the buds of permanent teeth, and then they will also become infected.
7. What is saliva? What function does it perform?
Saliva is the secretion of the salivary glands, secreted into the oral cavity and consisting of water, mucus, organic and inorganic substances and digestive enzymes. Functions of saliva: saliva wets food during chewing, facilitating the formation of a bolus for swallowing food; Digestive enzymes begin to break down carbohydrates and fats; lysozyme contained in saliva has a disinfecting effect, destroying the membranes of bacterial cells.
8. What role does language play?
When chewing, it directs food to the teeth, mixes it and moves it into the pharynx for swallowing. The tongue is also an organ of taste and is involved in the formation of speech sounds.
9. What is the mechanism of movement of a bolus of food along the esophagus?
Chewed, moistened with saliva, a slippery lump of food enters the pharynx, and then into the esophagus. Food is pushed through the esophagus thanks to peristalsis - wave-like contractions of its walls. In this case, the muscles located in the wall of the esophagus contract, pushing the bolus of food into the stomach. This process takes 6–8 seconds.
The pharynx is where air and food enter the body. This potentially creates a danger that lumps of food can enter the respiratory system - the larynx, nasopharynx. However, this does not happen, since during swallowing food the cartilage - the epiglottis closes the entrance to the larynx, and the uvula of the soft palate rises and separates the nasopharynx from the oropharynx. These processes occur reflexively. If you talk while eating, the epiglottis may take an intermediate position, which can cause a bolus of food to enter the respiratory tract.
11. Why is it so important to chew your food thoroughly?
The more thoroughly the food is crushed in the mouth, the better prepared it is for processing by enzymes and, therefore, the more actively and quickly it breaks down into its component parts. And vice versa, the larger the pieces of food that enter the stomach, the more time it takes for digestive juices to soak and process them. And excessive work of the glands of the digestive system causes disruption of their function, which entails various diseases digestive organs, for example, gastritis. Also, excessive stomach fullness puts pressure on the diaphragm and disrupts the functioning of the heart.
Large unchewed pieces first enter the esophagus. They can easily injure him.
A person who eats quickly becomes full more slowly. This is due to the fact that when chewing, histamine begins to be produced, which, reaching the brain, gives it a signal of saturation. However, this happens only twenty minutes after the meal has started. If a person eats slowly, they will eat less food during those twenty minutes and feel full from fewer calories.
The digestive system consists of the digestive tube and a number of large glands. The digestive tube, the length of which in an adult can reach 7-8 m, forms extensions (oral cavity, stomach) and many bends and loops.
The digestive system begins with the oral cavity, where food is crushed and moistened with saliva.
The entrance to the oral cavity is limited by the lips; they are covered with very thin skin, rich in blood vessels and nerve endings. Lips are involved in capturing food and determining its quality.
Having bitten off a piece of food, we chew it with the help of teeth located in the recesses of the upper and lower jaws. The lower jaw moves due to contractions of the masticatory muscles. These are very strong muscles, they can develop a force of up to 400 kg.
Teeth. Human teeth grow in two shifts; first dairy, then permanent. The replacement of baby teeth with permanent ones begins at the age of 6-7 years, and by the age of 15 it generally ends. The last teeth to grow are the wisdom teeth (third molar). Sometimes they appear by the age of 25-30, or they may not appear at all.
In total, a person has 32 teeth: on each jaw there are 4 incisors, 2 canines, 4 small molars and 6 large molars.
A tooth is a complex organ; it consists of a root hidden in the bone cell of the jaw and a visible part - the crown and neck.
The tooth is built from a dense substance similar to bone - dentin, covered with cement in the root area, and very dense enamel in the crown area, which protects the tooth from abrasion and the penetration of bacteria.
Salivary glands. Small salivary glands are located in the oral mucosa. The ducts of three pairs of large salivary glands also open here: parotid, sublingual, submandibular. These glands secrete saliva - more than 1 liter per day.
Saliva moistens food and washes away harmful or foreign substances from the mucous membrane. Saliva contains up to 99.4% water and has a slightly acidic or slightly alkaline reaction. It contains enzymes and substances that make it sticky and kill bacteria. Under the action of enzymes, the starch contained in food begins to break down into simpler molecules - to glucose.
Once in the mouth, food irritates numerous receptors (temperature, taste, tactile), and we feel its taste, temperature, and movement. Irritation of the receptors also causes reflexes of chewing and salivation. These reflexes are unconditional.
At the same time, throughout life, a person develops conditioned salivary reflexes in response to the smell of food, its appearance and other stimuli.
Language. Important role the tongue plays in the oral cavity. When chewing, it directs food to the teeth, mixes it and moves it into the pharynx for swallowing. In addition, the tongue, like the lips, is involved in determining the quality of food.
Pharynx and esophagus. Chewed, moistened with saliva, a slippery lump of food enters the pharynx and then into the esophagus. Food is pushed through the esophagus thanks to peristalsis - wave-like contractions of its walls. In this case, the muscles located in the wall of the esophagus contract, pushing the bolus of food into the stomach. This process takes 6-8 seconds.
The pharynx is where air and food enter the body. It would seem that there is a danger that lumps of food can get into the respiratory organs - into the larynx, nasopharynx. However, this does not happen, since during swallowing food the cartilage - the epiglottis closes the entrance to the larynx, and the uvula of the soft palate rises and separates the nasopharynx from the oropharynx. These processes occur reflexively. Still, you shouldn’t talk or laugh while chewing and swallowing food.
- Until recently, it was believed that chewing gum leads to depletion of the salivary glands. However, it turned out that with prolonged chewing of gum, the salivary glands begin to produce saliva with a reduced content of enzymes, so depletion does not occur.
Test your knowledge
- How does the digestive system work?
- Tell us about the structure of the tooth.
- At what age do primary teeth replace permanent ones?
- What is the significance of tooth enamel?
- What is dentin?
- How many molars does a person have?
- What happens to food in the mouth?
- What is saliva? What function does it perform?
- What role does language play?
- What is the mechanism by which a bolus of food moves through the esophagus?
Think
- Why is it not recommended to talk while eating?
- Why is it so important to chew your food thoroughly?
In the oral cavity, food is subjected to mechanical and chemical processing. The teeth grind food, and saliva is a digestive juice: under the influence of its enzymes, starch begins to break down.
Our body needs food as a source of “spare parts”, as well as a source of energy. Both of them need to be squeezed to the maximum from food. The human food system works as an efficient bioreactor. In addition, we have voluntary helpers in this matter - bacteria, of which there are much more than cells in our body
The digestive tract of most animals is long and tortuous - the limited volume of the body must accommodate as long a “corridor” as possible, in which all possible benefits will be extracted from the food. And the less nutritious the food, the longer the intestines should be, so in predators it is significantly shorter than in herbivores. The human digestive system is universal and is not tailored to a specific type of food.
Oral cavity: crusher and sterilizer
Whatever the animal eats, the food must first be crushed (to increase the absorption surface). Then nutrients can be extracted not only from the surface of pieces of food, but also from its entire volume. Grinding devices are different. In mollusks, for example, they resemble graters, and in mammals they consist of a whole arsenal of teeth, suitable both for tearing and gnawing pieces of food, and for crushing and grinding it.
Even at the entrance to the digestive system, food must be disinfected as best as possible. This is done by the enzyme lysozyme, which is part of saliva. It destroys the cell walls of bacteria to reduce the risk of infection.
A few chewing movements - and at the same moment individual food molecules hit the taste buds (which are located not only on the tongue, but also on the soft palate), and they immediately send a signal to the digestive system (via the brain): combat readiness! The stomach and intestines immediately begin to actively secrete digestive enzymes, and peristalsis—the movement of muscles that move food through the intestines—increases.
Meanwhile, in the oral cavity, the breakdown of the least pliable substances of food - carbohydrates - begins. This digestion process is the longest, so it is better to start it immediately at the entrance. Basically, cell carbohydrates are stored in the form of complex polymers - chains of sugars. These chains are arranged differently in organisms of different kingdoms. Those in which plants store sugars are called starch, and those formed in animals and fungi are called glycogen. Sugars (especially glucose) are one of the body's most popular energy currencies, so it is important to get as much of them from food as possible. This is done by the enzymes amylase and maltase, which are part of saliva. Amylase breaks down starch and glycogen into disaccharides, and maltase divides the resulting maltose into two glucose molecules. Only a small portion of all carbohydrates in food are broken down in the mouth, a long process that continues for almost the entire time the food spends in the digestive system.
Stomach: Pool of acid
The crushed food goes down the esophagus into the stomach. In fact, it is a well-protected super-acid reactor necessary for the breakdown of the next important component of food - proteins. Proteins consist of amino acids, which the body constantly needs as building material. As part of the protein, amino acids are connected into chains, which are also intricately arranged. It is easiest to unwind them (denature the protein) in an acidic environment. It is meat (which, as a rule, consists mainly of proteins, except for water) that is often marinated in acidic conditions, for example in vinegar, so that its amino acid chains begin to unravel even before being eaten and the meat is digested better. But we don’t get kebab pre-treated with vinegar every day, so in the stomach the food will end up in a solution of hydrochloric acid (about 0.5%). The saturation of the solution fluctuates all the time, but in general it is a rather aggressive environment, so the walls of the stomach are covered with a thick layer of mucus so that it does not begin to digest itself. And the exit from it is firmly closed with a special valve so that hydrochloric acid does not enter the next, more vulnerable parts of the digestive system. Since our stomach is well protected, we can eat other acids, such as citric or phosphoric. The first is included in juice and is often used as a preservative, and the second is in Coca-Cola and other sodas.
The acidic environment of the stomach serves as an additional filter against bacteria swallowed with food; not all of them are able to survive in such conditions. Among the pleasant inhabitants of the stomach are the notorious lactobacilli, the increased content of which is proudly reported on the packaging of some yoghurts. Lactobacilli are good because they occupy a niche that could be populated instead by harmful microbes, such as ulcer-causing bacteria. Helicobacter pylori. But the harmful microbes are met by symbiont bacteria and in a language they understand they are told: it’s busy here.
So, the hydrochloric acid solution “unwound” the proteins, and the enzyme pepsin immediately began cutting them into amino acids. Ideally, food should supply enough amino acids to build all the proteins in the body. The easiest way is to collect all necessary set amino acids by consuming animal meat, since its composition most closely resembles human tissue. But amino acids are also found in other organisms, such as plants and fungi. You can also create a complete diet from them, but it is worth considering that the amino acid ratios of these organisms are not similar to ours. Therefore, a vegetarian diet must be carefully planned, collecting a set of necessary substances, like a mosaic.
The set of amino acids is almost ready (but not yet completely), and complex carbohydrates have begun to break down in the oral cavity. At this stage, you can already begin to absorb the elementary components of food into the blood. Therefore, behind the dense valve of the stomach begins a long intestine, the entire surface of which is ready to absorb nutrients.
Intestines: bile flows and long-time tenants
After the stomach, food enters duodenum- to the beginning of the small intestine. The gallbladder ducts open into it. Bile is needed to deal with the last of the unprocessed components of food - lipids. Lipids form fat droplets that are insoluble in water. To make them easier to absorb, it is enough to divide large drops into smaller ones, which is what the components of bile do. Small drops of fat are broken down into elementary molecular components by the lipase enzyme. The body uses lipids both as building materials (cell membranes are made of them) and as a form of energy storage. The energy value of lipids is much higher than that of the same mass of proteins or carbohydrates, so lipids are best suited for storing reserves.
Other enzymes - trypsin and chymotrypsin, secreted into the duodenum - continue to break down proteins into amino acids. The familiar amylase found in saliva still processes the complex carbohydrates starch and glycogen. The muscles around the intestines periodically contract, pushing food through the intestines, from which nutrients are gradually removed. Food does not just move along the intestinal corridor - it is met there by a wide variety of microflora (according to various estimates, up to 1500 species, and human cells, by the way, are only 220 species). The microflora consists mainly of bacteria, but there are also a few representatives of fungi and protozoa. We share food with these microscopic cohabitants for a reason - they perform many useful functions. In fact, they digest what we ourselves were unable to digest, and, on the contrary, they also share with us: bacteria secrete additional digestive enzymes, and also synthesize vitamins and hormones that stimulate the deposition of excess nutrients in the form of fat reserves. Like the lactobacilli of the stomach, intestinal microflora takes up space where someone less pleasant could live instead. Getting into the baby's intestines with mother's milk, beneficial microbes equip it so that only certain species that do not cause harm to humans can live there.
Even if all the nutrients have been removed from food to the maximum, there is still something valuable left in it - water. It is carefully squeezed out of the leftover food while moving through the last part of the digestive tract - the large intestine.
Blood and lymph: useful acquisitions
Everything that is broken down into component blocks (amino acids, glucose, glycerol, soluble salts of fatty acids) in the mouth, stomach and small intestine is absorbed through special villi into the blood and lymph and distributed throughout the body through internal “transport arteries”. New cells will be built from amino acids to replace dead ones; glucose will serve as fuel for human cells, penetrating into them with the help of the enzyme insulin (if it is poorly produced, the cells weaken and die of hunger); human fat will be built from glycerol and fatty acids: it will save us from the cold, help us absorb vitamins, and become another building material, and will also turn into a long-term energy store (the body resorts to it in the absence of glucose). In addition, vitamins and minerals (potassium, calcium, magnesium, sodium, phosphorus and others) come to us with food - in very minute quantities, but we cannot do without them.
Exit: light at the end of the tunnel
As a result, on average, only about a third (in the case of highly digestible food, up to zero) of the mass of food eaten remains, which is excreted from the body in the form of feces. More than half of its dry matter is made up of unlucky gut bacteria. Feces also contain a lot of cellulose (aka fiber), the most stubborn of complex carbohydrates. Mammals do not have their own enzymes that break down cellulose, which is why humans cannot eat, for example, paper or wood, although they have a certain energy value. Therefore, everyone who wants to eat exclusively plants, which contain a lot of cellulose, has to contain in the digestive tract entire farms of special bacteria capable of digesting this complex carbohydrate. The complex stomachs of ruminants are best suited for breaking down cellulose. They are designed for long and complex fermentation of food, which the animal helps by additionally chewing the regurgitated mass. Nevertheless, cellulose is also useful for us: firstly, it stimulates peristalsis, and secondly, it takes up space in the stomach. Our body evaluates satiety by different parameters, including stretching of the stomach walls.
Not only undigested food remains are released with feces, but also substances that need to be actively disposed of, for example bilirubin, a toxic breakdown product of hemoglobin. It is released into the intestines with bile and leaves the body along with everything that the digestive system has not absorbed.
Thus, the food we eat supplies us with materials to renew the body and energy to search for new joys in life. Not the least of which are favorite and new dishes.
Illustrations: Andrey Dorokhin
Food stays in the mouth for only 15 seconds and during this period of time the digestion process begins. Despite the fact that saliva does not contain such aggressive components as gastric juice, it breaks down polysaccharides. Digestion in the oral cavity is an important step towards the digestion of food. Let's consider its meaning in more detail.
Composition and functions of saliva
Not only mechanical but also chemical processing of food occurs in the mouth. And all this thanks to such a biological fluid as saliva. It contains enzymes that begin to grind and digest food.
The mouth contains the submandibular, parotid and sublingual salivary glands. These are the three largest glands. Besides them, there are others, smaller ones. They are located on top of the tongue, palate and cheeks.
During the day, a person produces up to two liters of saliva from all glands; the largest amount is released during the process of eating food.
Saliva is 99% water and has a pH of 6.8-7.4, and contains:
- anions (chlorides, bicarbonates, sulfates and phosphates);
- cations (sodium, potassium and calcium);
- trace elements (iron, copper and nickel);
- proteins, in particular mucin - a substance that glues food particles together;
- enzymes (amylase, maltase, transferase, protease and others).
It is enzymes such as amylase and maltase that are involved in the breakdown of food in the mouth. Amylase breaks down polysaccharides, and maltase breaks down maltose, converting it into glucose.
A protein substance in saliva – lysozyme – has an antibacterial effect.
Digestion in the oral cavity is the first step towards the digestion of food; even complete breakdown of carbohydrates does not occur in the mouth. But despite this, without it the gastrointestinal tract would not function normally and the breakdown of food would not occur.
Saliva is an integral part of digestion in the mouth. It performs the following functions:
- Digestive. Participates in the breakdown of food.
- Excretory. In addition to the above components, saliva may contain salt, lead, urea, medications and other substances that enter the body.
- Protective. Due to the content of lysozyme it produces a bactericidal effect. Also, the high content of immunoglobulins provides protection against pathogens that can affect the state of the microflora. Saliva protects the oral mucosa from drying out.
- Trophic. Due to the content of microelements in the composition, it promotes the formation of tooth enamel.
Let's look at how digestion occurs in the mouth and what the role of saliva is in this process.
How does digestion happen?
As mentioned above, digestion in the oral cavity is initial stage gastrointestinal digestion. After all, the oral cavity is the initial section of the esophagus; food enters it and is transformed for further digestion and breakdown into useful material.
After eating food, the receptors that are located on the mucous membrane of the mouth and tongue are irritated. Thanks to them, a person recognizes taste. Bitter, salty, sweet or bitter foods lead to irritation of the receptors and the production of large amounts of saliva.
The volume of saliva produced when eating food depends on the degree of dryness and chemical composition. The coarser the food, the more saliva is produced by the salivary glands.
It is worth noting that in addition to saliva, the organs of the oral cavity also take part in cavity digestion:
- Language. This is a mobile muscular organ that helps move food in the mouth and promote it for chewing and further digestion in the gastrointestinal tract;
- Teeth. They help to carry out the main task of the oral cavity - mechanical grinding of food. There are 32 teeth in the adult mouth.
When food enters the oral cavity, cavity digestion begins. The food is moistened with saliva and its decomposition into certain substances begins. In addition to chemical processing, food is simultaneously subjected to mechanical processing, which involves the tongue and teeth.
Salivary enzymes come into action. Amylase breaks down complex carbohydrates and thereby helps to easily digest heavy foods in the gastrointestinal tract. Since food is in the mouth for a short amount of time, only carbohydrates have time to be broken down. After the food bolus passes into the stomach, salivary enzymes still continue to act. Even in the gastrointestinal tract, cavity digestion continues until gastric juice comes into action.
Food stays in the mouth for no more than 30 seconds and during this time it is subjected to sufficient chemical and mechanical processing. Crushed and moistened with saliva, it is formed into one lump. The food is ready to be swallowed and further digested.
The final stage of digestion
It is swallowing and the movement of food through the esophagus that is the final stage of digestion in the oral cavity. Consider this process in detail.
Swallowing is a complex reflex process in which food moves from the mouth to the stomach.
The swallowing process consists of three stages: oral, pharyngeal and esophageal.
At the first stage, the act of swallowing is involuntary. After processing, the food bolus is in volume from 5 to 15 cm3. Thanks to chewing movements, in which the tongue and teeth are involved, the lump moves to the root of the tongue, after which swallowing becomes involuntary and is based only on physiological reflexes.
During involuntary swallowing at the first stage, food does not enter the respiratory tract, because the entrance to the nasal cavity is blocked by the soft palate, while the tongue moves the food lump into the pharynx.
During the pharyngeal stage, food is on its way to the stomach. The esophageal sphincter opens and it enters directly into the esophagus.
The final esophageal stage. It is characterized by food entering the stomach for digestion. Food passing through the esophagus causes irritation of the mechanoreceptors, and this in turn affects the contraction of the esophageal muscles. The food bolus moves towards the stomach. Food enters the stomach when the muscle tone of the organ decreases. After the act of eating is completed and the person feels full, the muscle tone of the stomach increases, which prevents the contents from flowing back into the esophagus.
In a second, the food bolus moves 3 cm down the esophagus. In addition to reflexes, the passage of a food bolus through the esophagus is affected by the following:
- pressure difference between different parts of the gastrointestinal tract;
- contraction of the muscle tissue of the esophagus;
- low muscle tone;
- weight and density of the food bolus. Rough food passes more slowly than liquid food.
The spinal cord sends impulses that trigger the act of swallowing. As food passes from the mouth into the esophagus, the breathing process slows down, causing heart contractions to increase and breathing to stop.
For digestion, the chemical and mechanical processing of food in the mouth is of great importance. After all, it is in the mouth after eating food that a powerful reflex reaction is triggered, which occurs due to irritation of the receptors of the oral mucosa. Nerve impulses sent by neutral nervous system, activate the activity of all gastrointestinal organs, in particular affecting the stomach, pancreas, intestines, liver, as well as the smooth muscles of the digestive tract.
Digestion is a complex process. It starts in the mouth and ends in the intestines. At each stage, food is exposed to chemical effects due to the content of enzymes in biological fluids.