Light-optical microphotography of the junction of the esophagus into the stomach Artery Muscular lamina of the mucosa Submucosa of the esophagus Vein Adipocytes Submucosa of the stomach Muscle membrane Cardiac glands of the esophagus Lamina propria of the esophageal mucosa Zone of transition of the esophagus into the stomach Single-layer prismatic. epithelium of the stomach Gastric pits Cardiac glands of the stomach Multilayered neocorns. esophageal epithelium

Features of the relief of the mucous membrane of the small intestine. The arrows show the displacement of the cells of the epithelial layer Villi Epithelium Lamina propria Muscular lamina Exfoliation of epitheliocytes from the upper edge of the villus into the intestinal lumen Crypts (Lieberkühn's glands)

Electron micrograph of the epithelial lining of the small intestine. Goblet cell surrounded by columnar epitheliocytes with a striated border Granular endoplasmic reticulum Microvilli Goblet cell Golgi complex Columnar epitheliocyte with a border Granules of mucous secretion Columnar epitheliocyte with a striated border

Semi-schematic reproduction of the relief of the mucous membrane of the large intestine Lymph nodule with a germinal center Muscular lamina of the mucosa Goblet cells lamina propria of the mucosa Crypts (Lieberkün's glands) Mucosa Epithelium with a striated border Blood vessels Submucosa

Scheme of topographic zones and features of the micromorphology of the rectum External hemorrhoid plexus Circular layer of the muscular membrane Pectinate line External anal sphincter Anal gland Zone of epithelium changes Internal hemorrhoid plexus Longitudinal layer of the muscular membrane Internal anal sphincter Muscle of the pelvic floor Pillars of Morgagni Anal canal Skin of the anus Submucosa Fibroelastic septum

Liver functions: 1. detoxification 2. protective 3. takes part in: a) protein metabolism - blood protein synthesis b) carbohydrate metabolism - glycogen synthesis c) fat metabolism - bile production d) vitamin metabolism - accumulation of vitamins A, D, E, K e) metabolism of cholesterol, iron 4. hematopoietic organ (in the embryonic period!) 5. endocrine-hormone somatomedin

Structure The structural and functional unit of the liver, according to classical concepts, is the hepatic lobule. The liver lobules are shaped like hexagonal prisms. In the center of the lobule is the hepatic vein, along the periphery there are triads (interlobular arteries, veins, bile ducts), which are located in poorly developed connective tissue. Hepatic lobules are built of hepatic beams that run in a radial direction from the periphery to the center of the lobule. Hepatic beams consist of two rows of hepatocytes. Sinusoidal hemocapillaries pass between the beams, bile capillaries inside the beam.

Features of the blood supply to the liver. 1) receives blood from two vessels: a) hepatic artery - blood rich in oxygen, b) portal vein - blood rich in substances that are absorbed in the intestine; 2) paralobular veins form sphincters; 3) intralobular sinusoidal capillaries lined with endothelium between which there are stellate macrophages (Kupffer cells), blood is mixed and flows slowly; 4) central vein - non-muscular type; 5) the blood that comes out of the liver differs in chemical composition from the blood that comes to the gates of the liver.

bile ducts. Bile is formed in the biliary poles of hepatocytes, then enters the bile capillaries (go inside the hepatic beams), then into the cholangiols, the interlobular bile ducts, the right and left hepatic ducts, the common hepatic duct, the cystic duct, the common bile duct.

Pancreas. Functions: 1. Exocrine - pancreatic juice is produced (enzymes trypsin, lipase, amylase, etc.) - which cause the breakdown of proteins, fats and carbohydrates. 2. Endocrine - produces hormones that regulate carbohydrate, protein and fat metabolism.

The structure of the exocrine part This is a complex, alveolar, branched, merocrine gland with a protein secret. The structural and functional unit of the exocrine part of the pancreas is the pancreatic acinus, which consists of a terminal secretory section and an intercalary duct. The secretory section consists of 8-12 large pancreatocytes (acinocytes) having a conical shape. Their basal pole contains a highly developed granular endoplasmic reticulum and stains basophilically - this is a homogeneous zone. The apical pole contains zymogen granules (enzymes in an inactive form) that stain oxyphilically - this is the zymogen zone. In the center of the acinus there are centroacinous cells - cells of the intercalary section. Excretory ducts: intercalary interacinous intralobular interlobular common excretory duct.

Endocrine part The structural part is represented by pancreatic islets of Langerhans, which have a round or oval shape. Outside, the islets are covered with a connective tissue capsule, which contains sinusoidal capillaries. Islets are located between the acini, more in the caudal part of the gland.

P / p Insulocytes Excreted hormones Influence 1. B-cells (70-75%) insulin Decrease in blood glucose 2. A-cells (20-25%) glucagon Increase in blood glucose 3. D-cells (5-10 %) somatostatin Inhibits the secretion of insulin and glucagon, as well as pancreatic juice 4.F-cells Pancreatic polypeptide Stimulates the secretion of gastric and pancreatic juice

Lesson on the topic: The importance of digestion. Digestive system: digestive tract, digestive glands.

The purpose of the lesson: Explain the importance of nutrition and digestion. To ensure the assimilation of knowledge about the structure and functions of the digestive tract and digestive glands.

Tasks:

Educational:

Development of knowledge about the structure and functions of the digestive system;

Development of skills to analyze, establish relationships between structure and function; improve the ability to highlight the main thing;

Provide hygiene education to students.

Developing:

To teach how to apply the acquired knowledge about the process of digestion in everyday life;
-development of logical thinking;
- continue the formation of skills to compare objects, work with drawings and diagrams;

To teach to analyze and systematize information, to process it creatively.

Educational:
-development of interest in knowledge, motivation and culture of mental work;
-development of a culture of communication and reflective qualities of a person,
-creation of conditions for emotionally pleasant intellectual activity of students, with high cognitive activity of students
-show the importance of biological knowledge;
- to carry out hygienic education of students.

Lesson type: learning new material, repeating and consolidating what has been learned.

Forms of organization of educational activities : oasking at the blackboard, frontal survey, conversation, working with slides of a computer presentation, watching a video, differentiated homework.

Lesson plan:

Organizational moment.2 min

Homework survey. 12 min.

Problem task. 3 min.

Learning new material. 18 min.

Fixing the material. 3 min.

Summarizing. Homework. 2 minutes.

Lesson outline.

I. Hello guys! Let's smile, clap our hands, positively tune in to the lesson.

II. In the last lesson, we started to study a large section. Today we will continue to study it.

Homework survey.

Several students work with cards. (Attachment 1).

Participants answer the following questions at the board:

What is the importance of nutrients in the body?

What substances should be in our food?

What organic compounds does the body get from food?

What are the functions of proteins, and what organic compounds do they break down into?

What are the functions of fats, and what organic compounds do they break down into?

What are the functions of carbohydrates, and what organic compounds do they break down into?

What is the role of water in the body?

III. We have considered the importance of nutrients to find out what topic today

Let's get back to history...

… Even in ancient India, the “rice test” was used. At the trial, to decide the question of guilt or innocence, the defendant was offered to eat dry rice. If he eats it, then he is not guilty, if not, then he is guilty.

What do you think this test was based on? Knowing about which organ systems helped to find out the truth?

Students: Oh, the digestive organs.

That's right, today in the lesson we will learn aboutthe teaching of digestion. digestive system: digestive tract, digestive glands. We will return to the rice problem a little later.

Students write down the topic of the lesson.

Who can say what is the purpose of our lesson?

Students guess.

Summarizing the answers formulation of the goal.

The purpose of our lesson: to learn about the importance of digestion, about the structure and functions of the digestive tract and digestive glands.

Did everyone have breakfast today? Why do we eat? what digestive organs do you know?

Student responses.

How food is converted into energy and building materials, we will now consider.

IV. Digestion- a process that ensures the process of splitting complex organic substances and their entry into the blood and lymph.

The role of the digestive organs is to make nutrients available to the cells of our body.

Students draw diagrams in their notebooks.

Functions of the digestive system

Mechanical Chemical Intake, grinding of food Suction Breakdown of food

under the influence of enzymes

Composition of the digestive system

alimentary canal digestive glands

oral cavity salivary glands

Throat Liver

Esophagus Pancreas

Stomach Intestinal glands

Small intestine

Colon

The composition of the walls of the alimentary canal

Outdoor Medium Indoor

(connective tissue) (muscle tissue) (epithelial tissue)

Digestive canal. View video.

The oral cavity is closed from the outside by the muscles of the cheeks and lips. Inside are the jaws, gums, teeth, pharynx, palate, tongue. The space between the cheeks, lips and oral cavity is called the vestibule. At the bottom is the tongue - it mixes food and pushes it down the throat. The ducts of the salivary glands open into the oral cavity. (Slide number 7).

Pharynx - formed by striated muscle tissue, located in front of the cervical vertebrae. It is divided into 2 sections, one connected to the larynx, the other to the esophagus. (Slide number 9).

The esophagus is a hollow muscular organ 25 cm long. The mucous membrane is formed by stratified epithelium. (Slide number 10).

The stomach is a hollow muscular organ located in the upper part of the abdominal cavity, just below the diaphragm. At the junction with the esophagus and duodenum there are circular muscles (sphincters). The place of transition to the 12th duodenum is the pylorus. (Slide No. 11).

The small intestine is about 5 m long. It is divided into: duodenum (25-30 cm), jejunum, ileum. The walls consist of 2 muscle layers - longitudinal and transverse, their rhythmic contraction is called intestinal peristalsis. This is where the digestion process ends. Numerous villi absorb nutrients. (Slide number 12).

The large intestine is 1.3 m long. It absorbs water and breaks down fiber.

Includes:

1. The cecum, a process departs from it - the appendix.

2. Colon (ascending, transverse, descending, sigmoid).

Liver(1.5 kg., bile, ducts flow into the duodenum, barrier role, glucose storage, activates digestive enzymes). slide number 19.

pancreasiron (pancreatic juice, ducts flow into the duodenum, insulin) Slide No. 16

Intestinalglands (enzymes that can break down food in the islands secrete mucus). slide number 18.

mucosal glandsstomach (Odorless transparent viscous secretion, pepsin proteins, NSIbactericidal activity). Slide number 16.

V. Today in the lesson we got acquainted with the structure of the digestive tract and digestive glands.

Oral survey of students.

Name the organs of the digestive tract?

Name the digestive glands?

Briefly describe the properties of enzymes?

What are the main groups of enzymes you know.

VI. Summary of the lesson: So, our lesson is coming to an end. What did you know before the lesson? What did you learn in today's lesson?

Student responses.

Homework §41 §43 §44. Complete the table with 196 - 197.

You've worked hard today, let's clap our hands for that. Goodbye!

The digestive system is designed to provide the body with nutrients that are an energy substrate for all body cells.

Plan of the structure of the digestive system

Alimentary canal (alimentary tube)

Liver

Pancreas

Salivary glands.

Digestion is the process of gradual, gradual mechanical and chemical breakdown of food components, followed by their absorption, occurring in various parts of the gastrointestinal tract.

There are 3 sections in the digestive system:

Initial department

middle department

Caudal department

The initial section of the gastrointestinal tract includes:

Oral organs

Salivary glands

Throat

Esophagus

It is carried out: mechanical processing of food and carrying it into the middle section of the gastrointestinal tract.

The middle gastrointestinal tract includes:

Stomach

Small intestine

Colon

Liver

pancreas

It is carried out: chemical (enzymatic) processing of food with subsequent absorption of split products, the formation of feces.

The posterior (caudal) gastrointestinal tract includes:

Lower third (3-4 cm) of the rectum

Carried out: excretion of unprocessed products of the body.

The wall of the alimentary canal has a layered structure and consists of 4 shells:

Mucous

Submucosal

muscular

External (adventitial and serous)

The mucous membrane (tunica mucosa) is constantly moistened by the secretion of the mucous glands. It is covered with epithelial tissue, which, depending on the type of epithelium, is divided into 2 types:

The mucous membrane of the skin type is covered with stratified squamous and non-keratinizing epithelium.

The mucous membrane of the intestinal type is covered with a single-layer, cylindrical epithelium.

The mucous membrane has a different relief (surface irregularities).

The mucous membrane of the gums and palate is almost smooth, and the intestines are uneven and may contain:

gastric dimples

Intestinal crypts

Outgrowths (folds or intestinal villi). increase the functioning surface of the mucous membrane.

Submucosal membrane (tunic sub mucosa) (located outwards from the mucous membrane) Consists of connective tissue, which contains blood and lymphatic vessels, nerves, nerve endings and nerve plexus (Mesner's plexus) as well as various glands: 1) own glands in the esophagus

Duodenal glands in the duodenum.

Some organs of the gastrointestinal tract are devoid of a mucous membrane, such as the back of the tongue, the mucous membrane, which fuses tightly with the deeper muscular layer and loses its mobility.

Submucosal function:

Trophic function (nutrition)

Participation in the formation of the relief of the mucous membrane

Ensuring the mobility of the mucous membrane.

Muscular membrane (tunica muskulyaris) (located to the outside of the submucosa)

Consists of 2 layers of muscle cells:

Internal circular

Outer longitudinal

The third layer appears in the stomach in the organ of the middle section, is the most internal in terms of the location of the fibers - oblique.

Muscle tissue in different parts of the gastrointestinal tract has a different structure and origin, for example, in the caudal and initial sections, it is formed mainly by striated, skeletal, voluntary (we can control its work), but in the organs of the middle section it is formed only by smooth muscle tissue.

Functions of the muscular membrane: 1) participates in the formation of pendulum and peristaltic movements of the wall of the alimentary canal, which leads to the advancement of the food bolus from the initial ate to the posterior section.

Outer shell:

In the organs of the initial section - adventitious, represented by a loose tissue containing blood vessels, nerves and nerve plexuses

In the organs of the middle section - serous. in addition to the connective tissue component contains 1 layer of flat cells called mesothelium

The mesothelium produces serous fluid and facilitates the friction of neighboring organs of the middle gastrointestinal tract.

Oral cavity (cavitas oris):

mouth vestibule

Oral cavity.

mouth vestibule it is limited from the external environment, in front by the lips, from the sides by the cheeks, and from the inside by the teeth and gums. The vestibule of the mouth, through the lips forming the oral opening, communicates with the external environment, and through the gaps between the teeth it communicates with the oral cavity proper. Lip structure is based on orbicular muscle of the mouth (Musculus orbicularis oris).

It is customary to distinguish several parts of the lips:

Skin part (outer part) covered with skin

The inner part (mucous part) is covered with a mucous membrane

The intermediate part of the lips. Lined with stratified squamous keratinized epithelium, does not contain hair follicles and mucous glands. Red color acquires due to the capillaries, which are located superficially.

Oral cavity. The boundaries of the oral cavity: in front of the teeth and gums, on the sides of the cheeks, on top of the hard and soft palate, behind the pharynx, below the diaphragm of the bottom.

Hard palate - forms the upper wall of the oral cavity. Formed by bone tissue. Covered with mucous membrane. It consists of horizontal plates of paired palatine bones and palatine processes of the maxillary bones.

The soft palate (adjacent to the back of the hard palate) is distinguished by:

Uvula (uvula)

Sky curtain.

The palatine curtain is a paired fold, which is divided into two parts: 1) Anterior (palatine-lingual curtain) or arch

Back (palato-pharyngeal curtain) or arch.

Between the two arches is a paired organ of the immune system, the palatine tonsil. The palatine curtain and uvula form a pharynx, which is the boundary between the oral cavity and the oral part of the pharynx.

The oral cavity is formed by the diaphragm of the mouth. The diaphragm of the mouth is formed by a pair of mandibular-hyoid muscles fused along the midline, covered from the surface with a mucous membrane rich in numerous blood vessels.

The tongue (lingua) (located on the diaphragm of the mouth) is divided into sections:

tongue root

Top of the tongue

body of tongue (between apex and root)

The language is also distinguished:

Two side surfaces

Back of the tongue (top)

Ventral surface (bottom)

The tongue belongs to the organs of a layered type of structure. The basis of the tongue is striated muscle tissue (muscular membrane), above which (in the back area) is the mucous membrane, and below the muscular membrane is the submucosa and to the outside of it is the mucous membrane.

The muscular basis of the tongue is formed by two groups of muscles:

outdoor

Own muscles of the tongue

The concept of dental formula. The dental formula is a graphic representation of the number of different types of teeth in the upper and lower jaws, the dental form of the milk bite has the following form. 2 incisors, 1 canine, no small short teeth, 2 large short teeth. tooth.numerator(upper jaw) denominator(lower jaw) on both sides.

Permanent bite: 2 incisors, 1 canine, 2 small. short teeth and 3 large short teeth

Salivary glands. The ducts of 3 pairs of large salivary glands and numerous ducts of small salivary glands open into the human oral cavity, minor glands- these are lingual palatine buccal, pharyngeal - located in the thickness of the mucous membrane, in the submucosa, as well as in the muscular membrane of the organs of the oral cavity. The name depends on where they are located. Large salivary glands: parotid, submandibular and sublingual. All of them are paired located behind the alimentary canal.

The parotid salivary gland (parotis looked) -20-30 grams, covered with a connective tissue capsule and located on the lateral surface of the face anteriorly and slightly lower than the auricle, behind it goes into the back of the jaw fossa, and in front partially covers the masticatory muscle, the gland produces exclusively protein secretion , which, along the common duct of the gland (Warton's duct), is secreted in the vestibule of the mouth on its lateral wall against the second upper molar, under the lower jaw gland (looked submanidibularis) -13-16 grams, covered with a dense capsule and located posterior to the body of the lower jaws in the submandibular triangle. It is located superficially and is covered with skin and a connective tissue capsule, has a common duct (Wharton's duct), which removes a mixed secret (protein-mucous) with a predominance of the protein component to the top of the sublingual fossa on the side of the frenulum of the tongue. The sublingual salivary gland (glance sublingualis) has a mass of about 5 grams, is covered with a ton of connective tissue capsule and is located on the diaphragm of the mouth, has 1 main sublingual duct and several additional ducts, the main sublingual duct (revinus) opens along with the Wharton duct, at the top of the sublingual mass , on the side of the frenulum of the tongue. It secretes a mixed mucus-protein secret with a predominance of the mucous component, it moisturizes the mucous membrane and helps to form articulate speech, has a bactericidal effect and chemically breaks down food.

The pharynx is a funnel-shaped tubular organ with a length of 11-12 cm (up to 15 cm). The upper part of the pharynx is expanded and attached to the base of the skull, the lower part of the pharynx is narrowed and passes into the esophagus at the level of the 6th cervical vertebra.

Pharynx

1. Nasopharynx - communicates with the nasal cavity through the juans,

Oropharynx - communicates with the oral cavity through the pharynx

The hypopharynx communicates with the larynx through an opening called the entrance to the larynx.

The mucous membrane of the nasopharynx is lined with ciliated epithelium. Roto and laryngopharynx-nonkeratinizing epithelium.

On the side walls of the nasal part of the pharynx there are paired openings of the auditory or Eustachian tubes, which communicate the nasal part of the pharynx with the ear cavity (with the tympanic cavity) and contribute to pressure equalization. On the side of each of the openings of the estachian tubes there is an accumulation of lymphoid tissue, called the tubal tonsil, on the border of the upper and posterior walls of the pharynx there is an unpaired pharyngeal tonsil. The pharyngeal tonsil, tubal tonsils, palatine tonsils, lingual tonsil form the Pirogov-Waldeyer lymphoepithelial ring, located in the region of the respiratory tract and digestive tract.

The wall of the pharynx has a layered structure and includes the mucous membrane, an analogue of the submucosa, the pharyngeal-basilar fascia, which is involved in attaching the pharynx to the bones of the base of the skull, and the muscular membrane, consisting of the muscles of the constrictors (narrowing) of the pharynx, there are 3 constrictors upper middle and lower. In their posterior part, the constrictors exchange fibers to form a longitudinal suture of the pharynx. The muscles that lift the pharynx - during the act of swallowing, the longitudinal muscles raise the pharynx to the top and the circular ones - contribute to the promotion of food.

The esophagus (Aesaphagus) is a tube 30 centimeters long, between 6-7 cervical vertebrae to 11-12 thoracic vertebrae, where the esophagus passes into the stomach, a section of the digestive tract that connects the pharynx to the stomach. Takes part in swallowing food, peristaltic contractions of the P.'s muscles ensure the promotion of food into the stomach.

The length of the P. of an adult is 23-30 cm, the wall thickness is 4-6 mm. The esophagus is divided into cervical, thoracic and abdominal parts. The cervical part, 5-6 cm long, begins at the level of the VII cervical vertebra behind the cricoid cartilage of the larynx, is located between the trachea and the spine; to the right and left of it are the lobes of the thyroid gland. The thoracic part, 17-19 cm long, passes through the posterior mediastinum, first between the trachea and the spine, then between the heart and the thoracic part of the aorta. The abdominal part of P., located between the diaphragm and the cardial part of the stomach (at the level of the XI-XII thoracic vertebrae), has a length of 2-4 cm. There are three narrowings in the esophagus. The upper constriction (most pronounced) corresponds to the area of ​​transition of the pharynx into the esophagus, the middle one is located in the zone of P.'s attachment to the posterior surface of the left bronchus, the lower one - at the point where P. passes through the diaphragm. Along the P., in addition to the trachea, heart and aorta, bronchi, the common carotid artery, the thoracic duct, the sympathetic border trunk, the lungs and pleura, the diaphragm, the superior and inferior vena cava are located at a close distance from it.

The wall of the esophagus consists of a mucous membrane, submucosa, muscular and connective tissue (adventitial, in the abdominal part of the serous) membranes (Fig. 2). The mucous membrane is covered with stratified squamous epithelium and is separated from the submucosa by a layer of muscle tissue - the muscularis mucosa. P.'s glands, which produce mucus, are scattered in the mucous membrane. In the submucosa, among the loose connective tissue, there are small glands, lymph nodes, blood vessels and nerves. The muscular layer consists of two layers; circular (internal) and longitudinal (external), between which there is a layer of loose connective tissue. In the area of ​​P.'s transition to the stomach, muscle fibers form a sphincter.

The blood supply of the cervical part of P. is carried out mainly due to the lower thyroid arteries, the chest - due to the branches of the thoracic part of the aorta; abdominal - left gastric and left lower phrenic arteries.

The outflow of venous blood from the P.'s capillary bed occurs in the submucosal venous plexus, which connects to the superficial and deep veins of the P. From the cervical part of the P., venous blood enters the inferior thyroid vein, from the thoracic - into the unpaired and semi-azygous veins, from the abdominal part of the P. outflow blood is carried into the left gastric vein. The presence of porto-caval anastomoses leads to the expansion of P.'s veins with portal hypertension.

The outflow of lymph occurs in the regional lymph nodes: from the cervical part of the P. to the deep lymph nodes located along the internal jugular vein and trachea, from the chest to the prevertebral and posterior mediastinal lymph nodes, from the abdominal part of the P. to the left gastric lymph nodes.

P. is innervated by the vagus nerves and branches of the sympathetic trunks, which together form the thoracic aortic plexus.

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Plan

Introduction

1. The structure of the digestive system

Oral cavity

Small intestine

2. Functions of the gastrointestinal tract

Digestion in the mouth, chewing

Functions of saliva

swallowing

Digestion in the stomach

Principles of regulation of digestion processes

The passage of chyme from the stomach to the intestines.

Digestion in the small intestine

Digestion in the large intestine

Bibliography

Introduction

In the process of vital activity of the body, nutrients are continuously consumed, which perform a plastic and energy function.

The body has a constant need for nutrients, which include: amino acids, monosaccharides, glycine and fatty acids. The source of nutrients is a variety of foods, consisting of complex proteins, fats and carbohydrates, which, during digestion, turn into simpler substances that can be absorbed. The process of splitting complex food substances under the action of enzymes into simple chemical compounds that are absorbed, transported to cells and used by them is called digestion. The sequential chain of processes leading to the breakdown of nutrients into absorbable monomers is called the digestive conveyor. The digestive conveyor is a complex chemical conveyor with a pronounced continuity of food processing processes in all departments. Digestion is the main component of a functional nutrition system.

1. The structure of the digestive system

The digestive system includes organs that carry out mechanical and chemical processing of food products, the absorption of nutrients and water into the blood or lymph, the formation and removal of undigested food residues. The digestive system consists of the alimentary canal and digestive glands, details of which are shown in Figure 1.

Digestive system

Consider schematically the passage of food through the digestive tract. Food first enters the oral cavity, which is limited by the jaws: upper (fixed) and lower (movable).

Oral cavity

In the jaws there are teeth - organs that serve for biting and grinding (chewing) food. An adult contains 28-32 teeth.

An adult tooth consists of a soft part - the pulp, penetrated by blood vessels and nerve endings. The pulp is surrounded by dentin, a bone-like substance. Dentin forms the basis of the tooth - it consists of most of the crown (the part of the tooth protruding above the gum), the neck (the part of the tooth located on the gum line) and the root (the part of the tooth located deep in the jaw). The crown of the tooth is covered with tooth enamel, the hardest substance of the human body, which serves to protect the tooth from external influences (increased wear, pathogenic microbes, excessively cold or hot food, etc. factors).

Teeth according to their purpose are divided into: incisors, canines and molars. The first two types of teeth serve for biting off food and have a sharp surface, and the last one is for chewing it and for this it has a wide chewing surface. An adult has 4 canines and an incisor, and the rest of the teeth are molars.

In the oral cavity, in the process of chewing food, it is not only crushed, but also mixed with saliva, turns into a food lump. This mixing in the oral cavity is carried out with the help of the tongue and the muscles of the cheeks.

The mucous membrane of the oral cavity contains sensitive nerve endings - receptors, with the help of which it perceives taste, temperature, texture and other qualities of food. Excitation from the receptors is transmitted to the centers of the medulla oblongata. As a result, according to the laws of the reflex, the salivary, gastric and pancreas glands begin to work sequentially, then the above-described act of chewing and swallowing occurs. Swallowing is an act characterized by pushing food into the throat with the help of the tongue and then, as a result of contraction of the muscles of the larynx, into the esophagus.

Pharynx

The pharynx is a funnel-shaped canal lined with a mucous membrane. The upper wall of the pharynx is fused with the base of the skull, on the border between the VI and VII cervical vertebrae of the pharynx, narrowing, passes into the esophagus. Food enters from the oral cavity through the pharynx into the esophagus; in addition, air passes through it, coming from the nasal cavity and from the mouth to the larynx. (In the pharynx, the digestive and respiratory tracts cross.)

Esophagus

The esophagus is a cylindrical muscular tube located between the pharynx and the stomach, 22-30 cm long. The esophagus is lined with a mucous membrane, its submucosa contains numerous glands of its own, the secret of which moisturizes food during its passage through the esophagus to the stomach. The promotion of the food bolus through the esophagus occurs due to wave-like contractions of its wall - the contraction of individual sections alternates with their relaxation.

Stomach

From the esophagus, food enters the stomach. The stomach is a retort-like, extensible organ that is part of the digestive tract and is located between the esophagus and the duodenum. It connects to the esophagus through the cardial opening, and to the duodenum through the pyloric opening. The stomach is covered from the inside with a mucous membrane, which contains glands that produce mucus, enzymes and hydrochloric acid. The stomach is a reservoir for the absorbed food, which is mixed in it and partially digested under the influence of gastric juice. Produced by the gastric glands located in the gastric mucosa, gastric juice contains hydrochloric acid and the enzyme pepsin; these substances take part in the chemical processing that enters the stomach of food in the process of its digestion. Proteins are broken down here under the influence of gastric juice. This - along with the mixing action exerted on the food by the muscular layers of the stomach - turns it into a partially digested semi-liquid mass (chyme), which then enters the duodenum. The mixing of chyme with gastric juice and its subsequent expulsion into the small intestine is carried out by contracting the muscles of the walls of the stomach.

Small intestine

The small intestine occupies most of the abdominal cavity and is located there, in the form of loops. Its length reaches 4.5 m. The small intestine, in turn, is divided into the duodenum, jejunum and ileum. It is here that most of the processes of digestion of food and the absorption of its contents take place. The area of ​​the inner surface of the small intestine increases due to the presence of a large number of finger-like outgrowths on it, which are called villi. Next to the stomach is the 12th duodenum, which is isolated in the small intestine, since the cystic duct of the gallbladder and the pancreatic duct flow into it.

The duodenum is the first of the three sections of the small intestine. It starts from the pylorus of the stomach and reaches the jejunum. The duodenum receives bile from the gallbladder (through the common bile duct) and pancreatic juice from the pancreas. In the walls of the duodenum there are a large number of glands that secrete a mucus-rich alkaline secret that protects the duodenum from the effects of acidic chyme from the stomach.

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The jejunum is part of the small intestine. The jejunum makes up approximately two-fifths of the entire small intestine. It connects the duodenum and ileum.

The small intestine contains many glands that secrete intestinal juice. Here the main digestion of food and absorption of nutrients into the lymph and blood takes place. The movement of chyme in the small intestine occurs due to longitudinal and transverse contractions of the muscles of its wall.

From the small intestine, food enters the large intestine 1.5 m long, which begins with a sac-like protrusion - the caecum, from which a 15 cm process (appendix) departs. It is believed that it performs some protective functions. The colon is the main part of the large intestine, which consists of four sections: the ascending, transverse, descending and sigmoid colon.

The large intestine primarily absorbs water, electrolytes, and fiber, and ends in the rectum, which collects undigested food. The rectum is the final part of the large intestine (about 12 cm long), which starts from the sigmoid colon and ends with the anus. During the act of defecation, feces pass through the rectum. Further, this undigested food through the anus (anus) is excreted from the body.

2. Functions of the gastrointestinal tract

The motor or motor function is carried out by the muscles of the digestive apparatus and includes the processes of chewing in the oral cavity, swallowing, moving food through the digestive tract and removing undigested residues from the body.

The secretory function is the production of digestive juices by glandular cells: saliva, gastric juice, pancreatic juice, intestinal juice, bile. These juices contain enzymes that break down proteins, fats and carbohydrates into simple chemical compounds. Mineral salts, vitamins, water enter the bloodstream unchanged.

The endocrine function is associated with the formation in the digestive tract of certain hormones that affect the digestive process. These hormones include: gastrin, secretin, cholecystokinin-pancreozymin, motilin and many other hormones that affect the motor and secretory functions of the gastrointestinal tract.

The excretory function of the digestive tract is expressed in the fact that the digestive glands secrete metabolic products into the cavity of the gastrointestinal tract, for example, ammonia, urea, salts of heavy metals, medicinal substances, which are then removed from the body.

suction function. Absorption is the penetration of various substances through the wall of the gastrointestinal tract into the blood and lymph. The products of hydrolytic breakdown of food - monosaccharides, fatty acids and glycerol, amino acids, etc. are mainly absorbed. Depending on the localization of the digestion process, it is divided into intracellular and extracellular.

Intracellular digestion is the hydrolysis of nutrients that enter the cell as a result of phagocytosis (the protective function of the body, expressed in the capture and digestion of foreign particles by special cells - phagocytes) or pinocytosis (the absorption of water and substances dissolved in it by cells). In the human body, intracellular digestion takes place in leukocytes.

Extracellular digestion is divided into distant (cavity) and contact (parietal, membrane).

Distant (cavitary) digestion is characterized by the fact that enzymes in the composition of digestive secrets hydrolyze nutrients in the cavities of the gastrointestinal tract. It is called distant because the process of digestion itself is carried out at a considerable distance from the place where enzymes are formed.

Contact (parietal, membrane) digestion is carried out by enzymes fixed on the cell membrane. The structures on which enzymes are fixed are represented in the small intestine by a glycocalyx - a network-like formation of membrane processes - microvilli. Initially, hydrolysis of nutrients begins in the lumen of the small intestine under the influence of pancreatic enzymes. The resulting oligomers are then hydrolyzed by pancreatic enzymes. Directly at the membrane, the hydrolysis of the resulting dimers is produced by intestinal enzymes fixed on it. These enzymes are synthesized in enterocytes and transferred to the membranes of their microvilli.

The presence of folds, villi, microvilli in the mucous membrane of the small intestine increases the inner surface of the intestine by 300-500 times, which ensures hydrolysis and absorption on the huge surface of the small intestine.

Digestion in the mouth, chewing

Digestion in the oral cavity is the first link in a complex chain of processes of enzymatic breakdown of nutrients to monomers. Digestive functions of the oral cavity include approbation of food for edibility, mechanical processing of food and its partial chemical processing.

Motor function in the oral cavity begins with the act of chewing. Chewing is a physiological act that ensures the grinding of nutrients, wetting them with saliva and the formation of a food lump. Chewing ensures the quality of mechanical processing of food in the oral cavity. It affects the process of digestion in other parts of the digestive tract, changing their secretory and motor functions.

One of the methods for studying the functional state of the chewing apparatus is masticography - recording the movements of the lower jaw during chewing. On the record, which is called a masticogram, a chewing period can be distinguished, consisting of 5 phases:

1 phase - rest phase;

Phase 2 - the introduction of food into the oral cavity;

Phase 3 - approximate chewing or initial chewing function, it corresponds to the process of approbation of the mechanical properties of food and its initial crushing;

4 phase - the main or true phase of chewing, it is characterized by the correct alternation of chewing waves, the amplitude and duration of which is determined by the size of the portion of food and its consistency;

Phase 5 - the formation of a food bolus has the form of a wavy curve with a gradual decrease in the amplitude of the waves.

Chewing is a self-regulatory process based on the functional chewing system. A useful adaptive result of this functional system is a food bolus formed during chewing and prepared for swallowing. The functional chewing system is formed for each chewing period.

When food enters the oral cavity, irritation of the mucosal receptors occurs.

Excitation from these receptors through the sensory fibers of the lingual (a branch of the trigeminal nerve), glossopharyngeal, tympanic string (a branch of the facial nerve) and the upper laryngeal nerve (a branch of the vagus nerve) enters the sensory nuclei of these nerves of the medulla oblongata (the nucleus of the salitary tract and the nucleus of the trigeminal nerve). Further, the excitation along a specific path reaches the specific nuclei of the visual hillocks, where the excitation switches, after which it enters the cortical section of the oral analyzer. Here, based on the analysis and synthesis of incoming excitations, a decision is made about the edibility of substances entering the oral cavity.

Inedible food is rejected (spit out), which is one of the important protective functions of the oral cavity. Edible food remains in the mouth and chewing continues. In this case, excitation from the mechanoreceptors of the periodontium, the supporting apparatus of the tooth, joins the flow of information from the receptors.

Voluntary contraction of the masticatory muscles is provided by the participation of the cerebral cortex. Saliva takes an obligatory part in the act of chewing and the formation of a food bolus. Saliva is a mixture of the secrets of three pairs of large salivary glands and many small glands located in the oral mucosa. Epithelial cells, food particles, mucus, salivary bodies (leukocytes, lymphocytes), microorganisms are added to the secretion secreted from the excretory ducts of the salivary glands. Such saliva, mixed with various inclusions, is called oral fluid. The composition of the oral fluid varies depending on the nature of the food, the state of the body, and also under the influence of environmental factors.

The secret of the salivary glands contains about 99% water and 1% dry residue, which includes anions of chlorides, phosphates, sulfates, bicarbonates, iodites, bromides, fluorides. Saliva contains sodium, potassium, calcium, magnesium cations, as well as trace elements (iron, copper, nickel, etc.).

Organic matter is represented mainly by proteins. In saliva there are proteins of various origins, including the protein mucous substance mucin. Saliva contains nitrogen-containing components: urea, ammonia, etc.

Functions of saliva

The digestive function of saliva is expressed in the fact that it wets the food bolus and prepares it for digestion and swallowing, and saliva mucin glues a portion of food into an independent lump. Over 50 enzymes have been found in saliva.

Despite the fact that food is in the oral cavity for a short time - about 15 s, digestion in the oral cavity is of great importance for the implementation of further food splitting processes, since saliva, by dissolving food substances, contributes to the formation of taste sensations and affects appetite.

In the oral cavity, under the influence of saliva enzymes, the chemical processing of food begins. The saliva enzyme amylase breaks down polysaccharides (starch, glycogen) to maltose, and the second enzyme, maltase, breaks down maltose to glucose.

The protective function of saliva is expressed as follows:

saliva protects the oral mucosa from drying out, which is especially important for a person who uses speech as a means of communication;

the protein substance of saliva mucin is able to neutralize acids and alkalis;

saliva contains an enzyme-like protein substance lysozyme, which has a bacteriostatic effect and takes part in the processes of regeneration of the epithelium of the oral mucosa;

nuclease enzymes contained in saliva are involved in the degradation of viral nucleic acids and thus protect the body from viral infection;

blood coagulation enzymes were found in saliva, the activity of which determines the processes of inflammation and regeneration of the oral mucosa;

substances that prevent blood clotting (antithrombin plates and antithrombins) were found in saliva;

saliva contains a large amount of immunoglobulins, which protects the body from pathogens.

Trophic function of saliva. Saliva is a biological medium that comes into contact with tooth enamel and is its main source of calcium, phosphorus, zinc and other trace elements, which is an important factor for the development and preservation of teeth. excretory function of saliva. The composition of saliva can release metabolic products - urea, uric acid, some medicinal substances, as well as salts of lead, mercury, etc., which are excreted from the body after spitting, due to which the body is freed from harmful waste products.

Salivation is carried out by a reflex mechanism. There are conditioned reflex and unconditioned reflex salivation.

Conditioned salivation is caused by the sight, smell of food, sound stimuli associated with cooking, as well as talking and remembering food. At the same time, visual, auditory, olfactory receptors are excited. Nerve impulses from them enter the cortical section of the corresponding brain analyzer, and then to the cortical representation of the center of salivation. From it, excitation goes to the department of the center of salivation, the commands of which go to the salivary glands.

Unconditionally reflex salivation occurs when food enters the oral cavity. Food irritates the mucosal receptors. Nerve impulses are transmitted to the center of salivation, which is located in the reticular formation of the medulla oblongata and consists of the upper and lower salivary nuclei.

Excitatory impulses for the process of salivation pass through the fibers of the parasympathetic and sympathetic divisions of the autonomic nervous system.

Irritation of the parasympathetic fibers that excite the salivary glands leads to the separation of a large amount of liquid saliva, which contains many salts and few organic substances.

Irritation of sympathetic fibers causes the separation of a small amount of thick, viscous saliva, which contains few salts and many organic substances.

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Of great importance in the regulation of salivation are humoral factors, which include hormones of the pituitary, adrenal, thyroid and pancreas, as well as metabolic products.

The separation of saliva occurs in strict accordance with the quality and quantity of nutrients taken. For example, when taking water, saliva almost does not separate. And vice versa: with dry food, saliva is more abundant, its consistency is more liquid. When harmful substances enter the oral cavity (for example: too bitter or sour food enters the mouth), a large amount of liquid saliva is separated, which washes the oral cavity from these harmful substances, etc. Such an adaptive nature of salivation is ensured by the central mechanisms of regulation of the activity of the salivary glands , and these mechanisms are triggered by information coming from the receptors of the oral cavity.

The secretion of saliva is a continuous process. In an adult, about one liter of saliva is secreted per day.

swallowing

After the food bolus has formed, swallowing occurs. This is a reflex process in which three phases are distinguished:

oral (voluntary and involuntary);

pharyngeal (fast involuntary);

esophageal (slow involuntary).

The swallowing cycle lasts about 1 s. With coordinated contractions of the muscles of the tongue and cheeks, the food bolus moves to the root of the tongue, which leads to irritation of the receptors of the soft palate, the root of the tongue and the posterior pharyngeal wall. Excitation from these receptors through the glossopharyngeal nerves enters the swallowing center located in the medulla oblongata, from which impulses go to the muscles of the oral cavity, larynx, pharynx and esophagus as part of the trigeminal, hypoglossal, glossopharyngeal and vagus nerves. The contraction of the muscles that lift the soft palate closes the entrance to the nasal cavity, and the elevation of the larynx closes the entrance to the respiratory tract. During the act of swallowing, contractions of the esophagus occur, which have the character of a wave that occurs in the upper part and spreads towards the stomach. The motility of the esophagus is mainly regulated by the fibers of the vagus and sympathetic nerves and the nerve formations of the esophagus.

The swallowing center is located next to the respiratory center of the medulla oblongata and interacts with it (when swallowing, the breath is held). From the pharynx, the food bolus enters the esophagus, and then into the stomach.

Digestion in the stomach

The digestive functions of the stomach are:

deposition of chyme (preservation for processing the contents of the stomach);

mechanical and chemical processing of incoming food;

evacuation of chyme into the intestine.

The excretory function of the stomach is to excrete metabolic products, drugs, salts of heavy metals.

motor function of the stomach. The motor function of the stomach is carried out by contraction of smooth muscles located in the wall of the stomach. The motor function of the stomach ensures the deposition of ingested food in the stomach, mixing it with gastric juice, moving the contents of the stomach to the exit into the intestine, and finally, portionwise evacuation of the gastric contents into the duodenum.

There are two main types of movement in the stomach - peristaltic and tonic.

Peristaltic movements are carried out by contraction of the circular muscles of the stomach. These movements begin at the greater curvature in the area adjacent to the esophagus, where the cardiac pacemaker is located. A peristaltic wave traveling through the body of the stomach moves a small amount of chyme into the pyloric part, which is adjacent to the mucous membrane and is most exposed to the digestive action of gastric juice. Most of the peristaltic waves are damped in the pyloric region of the stomach. Some of them spread through the pyloric region with increasing amplitude (suggesting the presence of a second pacemaker localized in the pyloric region of the stomach), which leads to pronounced peristaltic contractions of this region, an increase in pressure, and part of the contents of the stomach passes into the duodenum.

The second type of stomach contraction is tonic contractions. They arise due to changes in muscle tone, which leads to a decrease in the volume of the stomach and an increase in pressure in it. Tonic contractions contribute to the mixing of the contents of the stomach and soaking it with gastric juice, which greatly facilitates the enzymatic digestion of food slurry.

The intestinal phase of gastric secretion begins from the moment chyme enters the duodenum. Chyme irritates the receptors of the intestinal mucosa and reflexively changes the intensity of gastric secretion. In addition, local hormones (secretin, cholecystokinin-pancreozymin), the production of which is stimulated by the acidic gastric chyme entering the duodenum, have an effect on gastric juice secretion in this phase.

Principles of regulation of digestion processes

The activity of the digestive system is regulated by nervous and humoral mechanisms.

Juice secretion of the digestive glands is carried out conditioned-reflex and unconditioned-reflex. Such influences are especially pronounced in the upper part of the digestive tract. As you move away from it, the participation of reflexes in the regulation of digestive functions decreases and the importance of humoral mechanisms increases. In the small and large intestines, the role of local regulatory mechanisms is especially great - local mechanical and chemical irritation increases the activity of the intestine at the site of the stimulus. Consequently, there is an uneven distribution of nervous, humoral and local regulatory mechanisms in the digestive tract. Local mechanical and chemical stimuli affect by peripheral reflexes and through the hormones of the digestive tract. Chemical stimulators of nerve endings in the gastrointestinal tract are: acids, alkalis, products of hydrolysis of nutrients. Entering the blood, these substances are brought by its current to the digestive glands and excite them.

Particularly great role in the humoral regulation of the activity of the digestive organs of hormones formed in the endocrine cells of the mucous membrane of the stomach, duodenum, jejunum, in the pancreas.

The main hormones and the effects to which their action leads: Gastrin - increased secretion of the stomach and pancreas, hypertrophy of the gastric mucosa, increased motility of the stomach, small intestine and gallbladder.

Secretin - an increase in the secretion of bicarbonates by the pancreas, inhibition of the secretion of hydrochloric acid in the stomach.

CCK-PZ (cholecystokinin-pancreozymin) - increased contraction of the gallbladder and bile secretion, secretion of pancreatic enzymes, inhibition of the secretion of hydrochloric acid in the stomach, increased secretion of pepsin in it, increased motility of the small intestine.

MOTILIN - increased motility of the stomach and small intestine, increased secretion of pepsin by the stomach.

Villikinin - increased motility of the villi of the small intestine, etc.

From this we can conclude that the hormones of the gastrointestinal tract play an important role. They affect the functions of the entire gastrointestinal tract, namely: motility, the secretion of water, electrolytes and enzymes, the absorption of water, electrolytes and nutrients, the functional activity of the endocrine cells of the gastrointestinal tract. In addition, they affect metabolism, the endocrine and cardiovascular systems, and the central nervous system. Some hormones are found in various brain structures.

Stimulate gastric secretion: the hormone gastrin is formed in the gastric mucosa; histamine - found in nutrients and is formed in the gastric mucosa; products of protein digestion; extractives of meat and vegetables; secretin - formed in the intestinal mucosa (inhibits the secretion of hydrochloric acid, but enhances the secretion of pepsinogens) cholecystokinin-pancreozymin enhances the secretion of pepsins (inhibits the secretion of hydrochloric acid) and other substances.

Inhibit gastric secretion: fat hydrolysis products and other substances.

The passage of chyme from the stomach to the intestines.

The rate of evacuation of the contents of the stomach into the intestine is influenced by many factors:

Consistency of food - the contents of the stomach pass into the intestine when its consistency becomes liquid or semi-liquid. Liquids begin to pass into the intestine immediately after they enter the stomach.

The nature of food - carbohydrate food is evacuated faster than protein, fatty food lingers in the stomach for 8-10 hours.

The degree of filling of the stomach and duodenum.

Motor function of the stomach and duodenum.

Hormones: secretin, cholecystokinin-pancreozymin - inhibit the motility of the stomach and the rate of evacuation of its contents.

Enterogastric reflex - is expressed in the inhibition of the motor activity of the stomach when the chyme enters the duodenum.

Digestion in the small intestine

Contractions of the small intestine are carried out as a result of coordinated movements of the longitudinal (outer) and transverse (inner) layers of smooth muscle cells. On a functional basis, reductions are divided into two groups:

1) local - provide rubbing and mixing of the contents of the small intestine;

There are several types of abbreviations:

pendulum,

rhythm segmentation,

peristaltic,

tonic.

Pendulum contractions are due to the sequential contraction of the annular and longitudinal muscles of the intestine. Successive changes in the length and diameter of the intestine lead to the movement of the food gruel in one direction or the other (like a pendulum). Pendulum-like contractions promote mixing of chyme with digestive juices.

Rhythmic segmentation is provided by the contraction of the annular muscles, resulting in the resulting transverse interceptions divide the intestine into small segments. Rhythmic segmentation contributes to rubbing the chyme and mixing it with digestive juices. Peristaltic contractions are due to the simultaneous contraction of the longitudinal and annular muscle layers. In this case, there is a contraction of the annular muscles of the upper segment of the intestine and pushing the chyme into the simultaneously expanded, due to the contraction of the longitudinal muscles, the lower section of the intestine. Thus, peristaltic contractions ensure the movement of chyme through the intestine.

Tonic contractions have a low speed and may not even spread at all, but only narrow the intestinal lumen over a small extent.

The small intestine, and primarily its initial section, the duodenum, is the main digestive section of the entire gastrointestinal tract. It is in the small intestine that nutrients are converted into those compounds that can be absorbed from the intestine into the blood and lymph. Digestion in the small intestine occurs in its cavity - cavitary digestion, and then continues in the zone of the intestinal epithelium with the help of enzymes fixed on its microvilli and folds - parietal digestion. Folds, villi and microvilli of the small intestine increase the inner surface of the intestine by 300-500 times.

In the hydrolysis of nutrients in the duodenum, the role of the pancreas is especially great. Pancreatic juice is rich in enzymes that break down proteins, fats and carbohydrates.

Pancreatic amylase converts carbohydrates into monosugars. Pancreatic lipase is very active due to the emulsifying effect of bile on fats. Ribonuclease in pancreatic juice breaks down ribonucleic acid into nucleotides.

Intestinal juice is secreted by the glands of the entire mucous membrane of the small intestine. More than 20 different enzymes have been found in the intestinal juice, the main of which are: enterokinase, peptidases, alkaline phosphatase, nuclease, lipase, phospholipase, amylase, lactase, sucrase. Under natural conditions, these enzymes carry out parietal digestion.

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The motor activity of the small intestine is regulated by nervous and humoral mechanisms. The act of eating briefly inhibits, and then enhances the motility of the small intestine. The motor activity of the small intestine largely depends on the physical and chemical properties of the chyme: roughage and fats increase its activity.

Humoral substances have an effect directly on the muscle cells of the intestine, and through receptors - on the neurons of the nervous system. Strengthen the motility of the small intestine: histamine, gastrin, motilin, alkalis, acids, salts, etc.

The initial secretion of the pancreas is caused by conditioned reflex signals (view, smell of food, etc.). Inhibition of pancreatic secretion is observed during sleep, during pain reactions, during strenuous physical and mental work.

The leading role in the humoral regulation of pancreatic secretion belongs to hormones. The hormone secretin causes the secretion of a large amount of pancreatic juice rich in bicarbonates, but poor in enzymes. The hormone cholecystokinin-pancreozymin also enhances the secretion of the pancreas, and the secreted juice is rich in enzymes. Increase the secretion of the pancreas: gastrin, serotonin, insulin. Inhibit the separation of pancreatic juice: glucagon, calcitonin, GIP, PP.

The secretion of the intestinal glands increases during meals, with local mechanical and chemical irritation of the intestine and under the influence of certain intestinal hormones.

Chemical stimulants of the secretion of the small intestine are the products of digestion of proteins, fats, etc.

Digestion in the large intestine

The motor activity of the large intestine ensures the accumulation of intestinal contents, the absorption of a number of substances from it, mainly water, the formation of feces and their removal from the intestine. There are the following types of contractions of the colon:

tonic,

pendulum,

rhythm segmentation,

peristaltic contractions,

anti-peristaltic contractions (contribute to the absorption of water and the formation of feces),

The regulation of the motor activity of the large intestine is carried out by the autonomic nervous system, moreover, sympathetic nerve fibers inhibit motility, and parasympathetic ones increase it. The motility of the colon is inhibited by: serotonin, adrenaline, glucagon, as well as irritation of the mechanoreceptors of the rectum. Of great importance in stimulating the motility of the colon are local mechanical and chemical irritations.

The secretory activity of the colon is weakly expressed. The glands of the mucous membrane of the large intestine secrete a small amount of juice, rich in mucous substances, but poor in enzymes. Small amounts of the following enzymes are found in the colonic juice:

cathepsin,

peptidases,

amylase and nucleases.

Of great importance in the life of the body and the functions of the digestive tract is the microflora of the colon. The normal microflora of the gastrointestinal tract is a necessary condition for the life of the body. There is little microflora in the stomach, much more in the small intestine and especially in the large intestine.

The value of the intestinal microflora lies in the fact that it is involved in the final decomposition of the remnants of undigested food. The microflora is involved in the decomposition of enzymes and other biologically active substances. Normal microflora suppresses pathogenic microorganisms and prevents infection of the organism. Bacterial enzymes break down fiber fibers that are not digested in the small intestine. The intestinal flora synthesizes vitamin K and B vitamins, as well as other substances needed by the body. With the participation of the intestinal microflora in the body, the exchange of proteins, bile and fatty acids and cholesterol occurs.

Juice secretion in the large intestine is due to local mechanisms, with its mechanical irritation, secretion increases by 8-10 times. Absorption is understood as a set of processes that ensure the transfer of various substances into the blood and lymph from the digestive tract.

Distinguish between the transport of macro- and micromolecules. The transport of macromolecules and their aggregates is carried out using phagocytosis and pinocytosis. A certain amount of substances can be transported through the intercellular spaces. Due to these mechanisms, a small amount of proteins (antibodies, enzymes, etc.) and some bacteria penetrate into the internal environment from the intestinal cavity.

From the gastrointestinal tract, mainly micromolecules are transported: nutrient monomers and ions. This transport is divided into:

active transport;

passive transport;

facilitated diffusion.

Active transport of substances is the transfer of substances through membranes with the expenditure of energy and with the participation of special transport systems: mobile carriers and transport membrane channels.

Passive transport is carried out without energy consumption and includes: diffusion, filtration. The driving force behind the diffusion of solute particles is the presence of a change in their concentration.

Filtration is understood as the process of transferring a solution through a porous membrane under the action of hydrostatic pressure.

Facilitated diffusion, like simple diffusion, is carried out without the expenditure of energy to change the concentration of the solute. However, facilitated diffusion is a faster process and is carried out with the participation of a carrier.

Absorption of vital substances in various parts of the digestive tract.

Absorption occurs throughout the digestive tract, but its intensity in different departments is different. In the oral cavity, absorption is practically absent due to the short stay of substances in it and the absence of monomeric (simple) hydrolysis products. However, the oral mucosa is permeable to sodium, potassium, certain amino acids, alcohol, and certain medicinal substances.

In the stomach, the intensity of absorption is also low. Water and mineral salts dissolved in it are absorbed here, in addition, weak solutions of alcohol, glucose and small amounts of amino acids are absorbed in the stomach.

In the duodenum, the intensity of absorption is greater than in the stomach, but even here it is relatively small. The main process of absorption occurs in the small intestine. The motility of the small intestine is of great importance in the processes of absorption, since it not only promotes the hydrolysis of substances (by changing the parietal layer of chyme), but also the absorption of its products. In the process of absorption in the small intestine, contractions of the villi are of particular importance. Villus contraction stimulators are the hydrolysis products of nutrients (peptides, amino acids, glucose, food extractives), as well as some components of the secretions of the digestive glands, for example, bile acids. Humoral factors also increase villi movements, such as the hormone villikinin, which is produced in the duodenal mucosa and in the jejunum.

Absorption in the colon under normal conditions is negligible. Here, water is mainly absorbed and stool is formed. In small quantities, glucose, amino acids, and other easily absorbed substances can be absorbed in the large intestine. On this basis, nutritional enemas are used, i.e., the introduction of easily digestible nutrients into the rectum.

Proteins after hydrolysis to amino acids are absorbed in the intestine. Absorption of various amino acids in different parts of the small intestine occurs at different rates. The absorption of amino acids from the intestinal cavity is carried out actively with the participation of the carrier and with the expenditure of energy. Then the amino acids are transported by the mechanism of facilitated diffusion into the intercellular fluid. The amino acids absorbed into the blood enter the liver through the portal vein system, where they undergo various transformations. A significant part of the amino acids is used for protein synthesis. Amino acids carried by the bloodstream throughout the body serve as the starting material for the construction of various tissue proteins, hormones, enzymes, hemoglobin and other substances of a protein nature. Some of the amino acids are used as an energy source.

The intensity of absorption of amino acids depends on age (it is more intense at a young age), on the level of protein metabolism in the body, on the content of free amino acids in the blood, and on nervous and humoral influences.

Carbohydrates are absorbed mainly in the small intestine in the form of monosaccharides. Hexoses (glucose, galactose, etc.) are absorbed most rapidly, pentoses are absorbed more slowly. The absorption of glucose and galactose is the result of their active transport through the membranes of the intestinal walls. The transport of glucose and other monosaccharides is activated by the transport of sodium ions across membranes.

The absorption of different monosaccharides in different parts of the small intestine occurs at different rates and depends on the hydrolysis of sugars, the concentration of monomers formed, and on the characteristics of the transport systems of intestinal epitheliocytes.

Various factors, especially endocrine glands, are involved in the regulation of carbohydrate absorption in the small intestine. Glucose absorption is enhanced by adrenal, pituitary, thyroid and pancreatic hormones. The monosaccharides absorbed in the intestines enter the liver. Here, a significant part of them is retained and converted into glycogen. Part of the glucose enters the general circulation and is carried throughout the body and used as an energy source. Some of the glucose is converted into triglycerides and deposited in fat depots (fat storage organs - liver, subcutaneous fat layer, etc.). Under the action of pancreatic lipase in the cavity of the small intestine, diglycerides are formed from complex fats, and then monoglycerides and fatty acids. Intestinal lipase completes lipid hydrolysis. Monoglycerides and fatty acids with the participation of bile salts pass into intestinal epitheliocytes through membranes using active transport. In intestinal epitheliocytes, complex fats are broken down. From triglycerides, cholesterol, phospholipids and globulins, chylomicrons are formed - the smallest fatty particles enclosed in a lipoprotein shell. Chylomicrons leave the epitheliocytes through the membranes, pass into the connective tissue spaces of the villi, from there they, with the help of contractions of the villus, pass into its central lymphatic vessel, thus, the main amount of fat is absorbed into the lymph. Under normal conditions, a small amount of fat enters the bloodstream.

Parasympathetic influences increase, and sympathetic influences slow down the absorption of fats. The hormones of the adrenal cortex, thyroid gland and pituitary gland, as well as the hormones of the duodenum - secretin and cholecystokinin - pancreozymin, enhance the absorption of fats.

Fats absorbed into the lymph and blood enter the general circulation. The main amount of lipids is deposited in fat depots, from which fats are used for energy purposes.

The gastrointestinal tract takes an active part in the water-salt metabolism of the body. Water enters the gastrointestinal tract in the composition of food and liquids, the secrets of the digestive glands. The main amount of water is absorbed into the blood, a small amount - into the lymph. Absorption of water begins in the stomach, but it occurs most intensively in the small intestine. Actively absorbed solutes by epitheliocytes “pull” water along with them. The decisive role in the transfer of water belongs to sodium and chlorine ions. Therefore, all factors affecting the transport of these ions also affect the absorption of water. Water absorption is associated with the transport of sugars and amino acids. Exclusion of bile from digestion slows down the absorption of water from the small intestine. Inhibition of the central nervous system (for example, during sleep) slows down the absorption of water.

Sodium is intensively absorbed in the small intestine. Sodium ions are transferred from the cavity of the small intestine into the blood through intestinal epithelial cells and through intercellular channels. The entry of sodium ions into the epitheliocyte occurs passively (without energy expenditure) due to the difference in concentrations. From epitheliocytes, sodium ions are actively transported through membranes into the intercellular fluid, blood and lymph.

In the small intestine, the transfer of sodium and chlorine ions occurs simultaneously and according to the same principles, in the large intestine, the absorbed sodium ions are exchanged for potassium ions. With a decrease in the sodium content in the body, its absorption in the intestine increases sharply. The absorption of sodium ions is enhanced by the hormones of the pituitary and adrenal glands, and they are inhibited by gastrin, secretin and cholecystokinin-pancreozymin.

The absorption of potassium ions occurs mainly in the small intestine. The absorption of chloride ions occurs in the stomach, and most actively in the ileum.

Of the divalent cations absorbed in the intestines, calcium, magnesium, zinc, copper and iron ions are of the greatest importance. Calcium is absorbed along the entire length of the gastrointestinal tract, but its most intensive absorption occurs in the duodenum and the initial section of the small intestine. Magnesium, zinc and iron ions are absorbed in the same part of the intestine. Absorption of copper occurs mainly in the stomach. Bile stimulates calcium absorption.

Water-soluble vitamins can be absorbed by diffusion (vitamin C, riboflavin). Vitamin B2 is absorbed in the ileum. The absorption of fat-soluble vitamins (A, D, E, K) is closely related to the absorption of fats.

Bibliography

Great Medical Encyclopedia Vasilenko V. Kh., Galperin E. I. et al., Moscow, "Soviet Encyclopedia", 1974.

Disease of the digestive system Daihovsky Ya. I., Moscow, "Medgiz", 1961.

Diseases of the liver and biliary tract Tareev E. M., Moscow, Medgiz, 1961.

Treatment of diseases of the digestive system Gazhev B. N., Vinogradova T. A., St. Petersburg, MiM-Express, 1996.

Reference book of the paramedic Bazhanov N. N., Volkov B. P. et al., Moscow, "Medicine", 1993.